[Federal Register Volume 90, Number 11 (Friday, January 17, 2025)]
[Rules and Regulations]
[Pages 6218-6295]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-31367]
[[Page 6217]]
Vol. 90
Friday,
No. 11
January 17, 2025
Part III
Department of Transportation
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National Highway Traffic Safety Administration
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49 CFR Part 571
Federal Motor Vehicle Safety Standards; Fuel System Integrity of
Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity;
Incorporation by Reference; Final Rule
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules
and Regulations
[[Page 6218]]
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DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
[Docket No. NHTSA-2024-0090]
RIN 2127-AM40
Federal Motor Vehicle Safety Standards; Fuel System Integrity of
Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity;
Incorporation by Reference
AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).
ACTION: Final rule.
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SUMMARY: This final rule establishes two new Federal Motor Vehicle
Safety Standards (FMVSS) specifying performance requirements for all
motor vehicles that use hydrogen as a fuel source. The final rule is
based on Global Technical Regulation (GTR) No. 13, Hydrogen and Fuel
Cell Vehicles. FMVSS No. 307, ``Fuel system integrity of hydrogen
vehicles,'' specifies requirements for the integrity of the fuel system
in hydrogen vehicles during normal vehicle operations and after
crashes. FMVSS No. 308, ``Compressed hydrogen storage system
integrity,'' specifies requirements for the compressed hydrogen storage
system to ensure the safe storage of hydrogen onboard vehicles. These
two standards will reduce deaths and injuries from fires due to
hydrogen fuel leakages and/or explosion of the hydrogen storage system.
DATES:
Effective date: This final rule is effective July 16, 2025.
IBR date: The incorporation by reference of certain publications
listed in the rule is approved by the Director of the Federal Register
as of July 16, 2025.
Compliance Dates: The compliance date is September 1, 2028.
Petitions for reconsideration: Petitions for reconsideration of
this final rule must be received no later than March 3, 2025.
ADDRESSES: Petitions for reconsideration of this final rule must refer
to the docket and notice number set forth above and be submitted to the
Administrator, National Highway Traffic Safety Administration, 1200 New
Jersey Avenue SE, West Building, Washington, DC 20590. All petitions
received will be posted without change to http://www.regulations.gov,
including any personal information provided.
Privacy Act: DOT will post any petition for reconsideration, and
any other submission, without edit, to http://www.regulations.gov, as
described in the system of records notice, DOT/ALL-14 FDMS, accessible
through https://www.transportation.gov/individuals/privacy/privacy-act-system-records-notices. Anyone is able to search the electronic form of
all submissions to any of our dockets by the name of the individual
submitting the submission (or signing the comment, if submitted on
behalf of an association, business, labor union, etc.). You may review
DOT's complete Privacy Act Statement in the Federal Register published
on April 11, 2000 (Volume 65, Number 70; Pages 19477-78).
FOR FURTHER INFORMATION CONTACT: For technical issues, Ian MacIntire,
General Engineer, Special Vehicles & Systems Division within the
Division of Rulemaking, at (202) 493-0248 or [email protected]. For
legal issues, Paul Connet, Attorney-Advisor, NHTSA Office of Chief
Counsel, at (202) 366-5547 or [email protected] or Evita St. Andre,
Attorney-Advisor, NHTSA Office of Chief Counsel, at (617) 494-2767 or
[email protected]. The mailing address of these officials is:
National Highway Traffic Safety Administration, 1200 New Jersey Avenue
SE, Washington, DC 20590.
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Executive Summary
II. Background
III. Summary of Comments
IV. Response to Comments on Proposed Requirements
V. Other Changes to the Regulatory Text
VI. Rulemaking Analyses and Notices
I. Executive Summary
Vehicle manufacturers have continued to seek out renewable and
clean fuel sources as alternatives to gasoline and diesel. Compressed
hydrogen has emerged as a promising potential alternative because
hydrogen is an abundant element in the atmosphere and does not produce
tailpipe greenhouse gas emissions when used as a motor fuel. However,
hydrogen must be compressed to high pressures to be an efficient motor
fuel and is also highly flammable, similar to other motor fuels. NHTSA
has already set regulations ensuring the safe containment of other
motor vehicle fuels such as gasoline in FMVSS No. 301, ``Fuel system
integrity,'' and compressed natural gas (CNG) in FMVSS No. 304,
``Compressed natural gas fuel container integrity,'' and the fuel
integrity systems of those fuels in FMVSS No. 301 and FMVSS No. 303,
``Fuel system integrity of compressed natural gas vehicles,''
respectively. No such standards currently exist in the United States
covering vehicles that operate on hydrogen. Accordingly, this document
establishes two new FMVSS to address safety concerns relating to the
storage and use of hydrogen in motor vehicles, and to align the safety
regulations of hydrogen vehicles with those of vehicles that operate
using other fuel sources.
NHTSA published the Notice of Proposed Rulemaking (NPRM) on April
17, 2024, seeking comments on the proposed standards.\1\ This final
rule responds to and addresses the comments to the NPRM, reflecting
input from stakeholders on various concerns and recommendations. The
rule was developed in concert with efforts to harmonize hydrogen
vehicle standards with international partners through the GTR process
and harmonizes the FMVSS with GTR No. 13, Hydrogen and Fuel Cell
Vehicles.\2\
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\1\ See 89 FR 27502 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
\2\ A copy of GTR No. 13 as updated by the Phase 2 amendments is
available at: https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf
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The two new FMVSS established by this document are: FMVSS No. 307,
``Fuel system integrity of hydrogen vehicles,'' and FMVSS No. 308,
``Compressed hydrogen storage system integrity.'' FMVSS No. 307
regulates the integrity of the fuel system in hydrogen vehicles during
normal vehicle operations and after crashes. To this end, it includes
performance requirements for the hydrogen fuel system to mitigate
hazards associated with hydrogen leakage and discharge from the fuel
system, as well as post-crash restrictions on hydrogen leakage,
concentration in enclosed spaces, container displacement, and fire.
FMVSS No. 308 regulates the compressed hydrogen storage system (CHSS)
itself and primarily includes performance requirements that ensure the
CHSS is unlikely to leak or burst during use, as well as requirements
intended to ensure that hydrogen is safely expelled from the container
when it is exposed to a fire. FMVSS No. 308 also specifies performance
requirements for different closure devices in the CHSS.
FMVSS No. 308 applies to all motor vehicles that use compressed
hydrogen gas as a fuel source to propel the vehicle, regardless of the
vehicle's gross
[[Page 6219]]
vehicle weight rating (GVWR), except vehicles that are only equipped
with cryo-compressed hydrogen storage systems or solid-state hydrogen
storage systems to propel the vehicle. Portions of FMVSS No. 307 also
apply to all motor vehicles that use compressed hydrogen gas as a fuel
source to propel the vehicle, regardless of the vehicle's GVWR.
However, while FMVSS No. 307's fuel system integrity requirements
during normal vehicle operations apply to both light vehicles (vehicles
with a GVWR of 4,536 kg or less) and to heavy vehicles (vehicles with a
GVWR greater than 4,536 kg), FMVSS No. 307's post-crash fuel system
integrity requirements apply only to compressed hydrogen-fueled light
vehicles and to all
II. Background
A. Overview of GTR No. 13
1. The GTR Process
The United States is a contracting party to the the Agreement
concerning the Establishing of Global Technical Regulations for Wheeled
Vehicles, Equipment and Parts which can be fitted and/or be used on
Wheeled Vehicles (``1998 Agreement''). This agreement entered into
force in 2000 and is administered by the United Nations Economic
Commission for Europe's (UN ECE's) World Forum for the Harmonization of
Vehicle Regulations (WP.29). The purpose of this agreement is to
establish Global Technical Regulations (GTRs).
At its 160th session in June 2013, UN ECE WP.29 formally adopted
the proposal to establish GTR No. 13. NHTSA chaired the development of
GTR No. 13 and voted in favor of establishing GTR No. 13. The Phase 2
updates to GTR No. 13 were adopted at the 190th Session of WP.29 on
June 21, 2023.\3\
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\3\ See https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf.
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As a Contracting Party Member to the 1998 Global Agreement that
voted in favor of GTR No. 13 and the Phase 2 updates to GTR No. 13,
NHTSA is obligated to initiate the process used in the U.S. to adopt
Phase 2 GTR No. 13 as an agency regulation. This process was initiated
by the NPRM published on April 17, 2024. NHTSA is not obligated to
adopt the GTR, in whole or in part, after initiating this process.
Additionally, NHTSA may adopt a modified version of the GTR to ensure
that it meets relevant requirements. In deciding whether to adopt a GTR
as an FMVSS, NHTSA follows the requirements for NHTSA rulemaking,
including the Administrative Procedure Act, the National Traffic and
Motor Vehicle Safety Act (Vehicle Safety Act), Presidential Executive
Orders, and DOT and NHTSA policies, procedures, and regulations. Among
other things, FMVSS issued under the Vehicle Safety Act ``shall be
practicable, meet the need for motor vehicle safety, and be stated in
objective terms.''
2. GTR No. 13 and Phase 2 Updates
GTR No. 13 specifies safety-related performance requirements and
test procedures with the purpose of minimizing human harm that may
occur as a result of fire, burst, or explosion related to the hydrogen
fuel system of vehicles. The regulation consists of system performance
requirements for CHSS, CHSS closure devices, and the vehicle fuel
delivery system. GTR No. 13 does not specify the type of crash tests
for post-crash safety evaluation and instead permits Contracting
Parties to use their domestic regulated crash tests.
The Phase 2 updates of GTR No. 13 accomplished several goals,
including: broadening of the scope and application of GTR No. 13 to
cover heavy/commercial vehicles; harmonizing, clarifying, and expanding
the requirements for thermally-activated pressure relief device (TPRD)
discharge direction in case of controlled release of hydrogen;
strengthening test procedures for containers with pressures below 70
MPa, including comprehensive fire exposure tests; and extending the
requirements to 25 years to more accurately capture the expected useful
life of vehicles.
B. April 2024 NPRM
The April 2024 NPRM \4\ proposed to establish two new FMVSS for
hydrogen vehicles that are based on GTR No. 13, Phase 2. The proposed
FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles,'' is
designed to set performance requirements to ensure the integrity of the
hydrogen fuel system during normal vehicle operations and after
crashes. These requirements aimed to mitigate safety risks associated
with hydrogen fuel leakages, fires, and explosions, ensuring that
hydrogen would not pose risks to vehicle occupants or those nearby. The
standard addressed the hazards posed by the flammability of hydrogen
and its tendency to leak under high pressure, particularly in crash
scenarios.
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\4\ See 89 FR 27502 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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FMVSS No. 307 prescribes a series of performance standards aimed at
ensuring the safety of hydrogen vehicle fuel systems during both normal
operations and post-crash scenarios. The NPRM proposed five key
performance requirements for hydrogen fueling receptacles to prevent
leakage, incorrect fueling, and contamination from dirt or water. These
included reverse flow prevention, clear labeling, positive locking,
protection against contamination, and secure placement to avoid crash-
related deformations. An over-pressure protection device requirement
was proposed to protect downstream components from excessive pressure.
The proposal also included requirements for hydrogen discharge
mechanisms, specifying that vent lines must be protected from dirt and
water and that hydrogen gas discharge must be directed safely away from
critical components like the wheels, doors, and emergency exits.
The NPRM also proposed requirements in FMVSS No. 307 to protect
against flammable conditions. These included a visual warning system
that would alert the driver if hydrogen concentrations reached
dangerous levels (above 3% in enclosed or semi-enclosed spaces), and an
automatic shut-off valve closure if hazardous hydrogen concentrations
were detected. The proposed standard further specified that hydrogen
concentrations in the exhaust system must not exceed set thresholds
during normal vehicle operation.
In post-crash scenarios, the proposal set limits on fuel leakage
and specified crash tests to ensure that the hydrogen containers
remained intact and that any post-crash hydrogen leakage remained
within manageable limits. The proposal allowed a hydrogen leak rate not
to exceed 118 normal liters per minute for a duration of 60 minutes
after impact.
The NPRM also proposed establishing FMVSS No. 308, ``Compressed
Hydrogen Storage System Integrity,'' focused on ensuring the safety and
durability of the CHSS used in hydrogen vehicles. The proposed standard
outlined performance requirements for the CHSS to prevent leaks,
bursts, and other failures during normal vehicle use and under extreme
conditions, such as exposure to fire. The proposal included tests and
performance criteria to evaluate the CHSS's resistance to various
stress factors that could occur over the vehicle's lifetime. The CHSS,
which includes components such as the hydrogen container, check valve,
shut-off valve, and TPRD, was required to meet several durability and
safety benchmarks throughout its operational lifespan.
The proposal established specific requirements for hydrogen
containers,
[[Page 6220]]
which are the primary components of the CHSS. Testing procedures for
these containers included hydraulic pressure tests to evaluate burst
thresholds, pressure cycling tests to simulate long-term use in
service, and tests applying a series of external stress factors such as
impact, chemical exposure, high and low temperatures, high pressure
hold, and over-pressure along with pressure cycling to assess the
container's durability against leak or burst during its lifetime.
The proposed FMVSS No. 308 also included an on-road performance
test for the entire CHSS to ensure the CHSS contains hydrogen without
leak or burst. This test uses on-road operating conditions including
fueling and defueling the container at different ambient conditions
with hydrogen gas at low and high temperatures, a static high-pressure
hold, and an overpressure, designed to replicate the stress factors the
system could encounter during a vehicle's operational life.
Fire exposure testing was another critical aspect in the proposed
FMVSS No. 308, evaluating whether the CHSS could prevent dangerous
hydrogen release or explosion in a vehicle fire scenario. The proposed
fire test includes a localized and engulfing stage, which were
developed based on real vehicle fire data. The NPRM also proposed
requirements for the CHSS's closure devices (check valves, shut-off
valves, and TPRDs). Additionally, the NPRM proposed labeling
requirements in FMVSS No. 308 for hydrogen containers.
Together, the two proposed standards, FMVSS No. 307 and FMVSS No.
308, aimed to align U.S. regulations with GTR No. 13 and address the
specific safety challenges posed by hydrogen as a vehicle fuel source.
C. How the Final Rule Differs From the NPRM
The final rule largely mirrors the proposed standards, with some
minor changes to the requirements and test procedures based on the
public comments and feedback received. Details of the reasoning behind
each of the changes is provided in relevant sections of the notice.
FMVSS No. 307, established by this final rule, differs from the
proposed FMVSS No. 307 in the following ways:
Revises the definition for enclosed or semi-enclosed
spaces to be more specific and avoid ambiguity.
Removes the requirement for an overpressure protection
device.
Removes the requirement that the fueling receptacle
``shall not be mounted to or within the impact energy-absorbing
elements of the vehicle.''
Removes the requirements for specific TPRD discharge
angles.
Eliminates the option to use an electronic leak detector
in section S6.6, leaving leak detection liquid as the only applicable
test method.
Revises the regulatory text in instances where the NPRM
stated that the vehicle is set to the ``on'' or ``run'' position (and
preventing the vehicle from idling) to instead state that the
propulsion system shall be operational.
FMVSS No. 308, established by this final rule, differs from the
proposed FMVSS No. 308 in the following ways:
Excludes cryo-compressed and solid-state hydrogen storage
systems from the requirements in FMVSS No. 308.
Requires manufacturers to provide the median initial burst
pressure for a container (BPO) within fifteen business days
instead of five.
Removes the requirement to include BPO on the
container label.
Removes the requirement for container burst pressure
variability to be within 10 percent of BPO.
Changes the requirement that the manufacturer specify the
primary constituent of the container to specifying whether the primary
constituent of the container is glass fiber composite.
Increases the timeframe from 5 business days to 15
business days for manufacturers to submit vehicle-specific information
for testing purposes.
Revises the cycling rate for the baseline initial pressure
cycle test to be no more than ten cycles per minute.
Removes the minimum time of three minutes to sustain a
visible leak before the baseline initial pressure cycle test can end
successfully due to ``leak before burst.''
Removes the proof pressure test from both the test for
performance durability and the test for expected on-road performance.
Permits the option to conduct the closure tests with an
inert gas such as helium instead of hydrogen gas.
For both standards, various editorial and clerical updates were
made to improve clarity and consistency throughout the document.
III. Summary of Comments
The NPRM preceding this final rule included requests for comment on
several topics. From April 17, 2024, to July 17, 2024, the agency
received 31 comments on the NPRM, four of which were requests to extend
the NPRM comment period.\5\ The comments were generally supportive of
the proposed rule, particularly regarding harmonization with
international regulations. Many commenters suggested modifications to
the proposed requirements, including details of various test
procedures. Of the 26 unique comments, the majority (21 comments) were
submitted by vehicle and component manufacturers and industry
associations. Comments were also submitted by standards testing
laboratories (1 comment), and other stakeholders (4 comments).
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\5\ In response to the comments to extend the comment period,
NHTSA extended the comment period for the NPRM by 30 days. The
original comment period for the NPRM was scheduled to end on June
17, 2024. The extended comment period ended on July 17, 2024.
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The vehicle and component manufacturers that provided comments were
Ballard Power Systems (``Ballard''), Daimler Truck North America
(``DTNA''), Ford Motor Company (``Ford''), Glickenhaus Zero and
Scuderia Cameron Glickenhaus LLC (collectively, ``Glickenhaus''),
Hexagon Agility, Inc. (``Agility''), Hyundai America Technical Center,
Inc. (``HATCI''), Hyundai Motor Group (``Hyundai''), Luxfer Gas
Cylinders, New Flyer of America (``NFA''), Nikola Corporation
(``Nikola''), Noble Gas Systems (``NGS''), Hyzon Motors Inc. (Hyzon),
H2MOF, Inc. (``H2MOF''), Quantum Fuel Systems, LLC (``Quantum''),
Verne, Inc. (``Verne''), Westport Fuel Systems Canada, Inc. (``WFS''),
and Air Products and Chemicals, Inc. (``Air Products'').
The industry associations that provided comments were the Alliance
for Automotive Innovation (``Auto Innovators''), The Vehicle Suppliers
Association (``MEMA''), the Transport Project (``TTP''), and the Truck
and Engine Manufacturers Association (``EMA''). Some manufacturers
stated support for the comments submitted by an industry association.
The testing laboratory that provided comments was TesTneT Canada,
Inc. (``TesTneT''). The other stakeholders that provided comments were
Faurecia Hydrogen Solutions (``FORVIA''), Consumer Reports, Newhouse
Technology, LLC (``Newhouse''), and an anonymous commenter.
IV. Response to Comments on Proposed Requirements
A. Deviation From GTR No. 13
Several commenters submitted repeated comments for many sections of
the proposed FMVSS Nos. 307 and 308 asking that the agency follow GTR
No.
[[Page 6221]]
13 exactly, often without further explanation or justification. Several
commenters also stated that the agency should completely harmonize with
various industry standards.
Commenters seem to misunderstand the requirements of the 1998
Agreement and NHTSA's obligation under the Agreement. As noted earlier,
under the 1998 Agreement, NHTSA must propose a GTR on which it has
voted in the affirmative. NHTSA is committed to harmonizing to the
extent practical, but NHTSA is not required to finalize the text of a
GTR when it has justification to deviate from that text. The 1998
Agreement, by design, does not include mutual recognition \6\ because
the 1998 Agreement spans different regulatory regimes (i.e., type
approval and self-certification), and it acknowledges the domestic
rulemaking and substantive legal requirements in the United States.
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\6\ Mutual recognition occurs when two or more countries or
other institutions recognize one another's decisions or policies,
for example in the field of conformity assessment, professional
qualifications or in relation to criminal matters.
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The FMVSS are designed to be a unique set of regulations tailored
specifically for the United States' regulatory approach to vehicle
safety. FMVSS must adhere strictly to principles of objectivity and
verifiability, as these are foundational to the self-certification
process required in the U.S. automotive market. Some other standards,
like industry standards and regulations from other countries, may
include some degree of subjectivity or flexibility in their criteria
due to their broader focus and the differing regulatory frameworks
across countries.
NHTSA aimed to harmonize FMVSS Nos. 307 and 308 with GTR No. 13 and
the related industry standards to the maximum extent possible. However,
it was not always feasible or appropriate to match the regulations word
for word. FMVSS must remain objective, ensuring that every requirement
is clear, measurable, and enforceable. FMVSS must also have clear,
unambiguous test procedures with minimal discretion given to test
facilities. This requirement ensures the integrity of the self-
certification system and protects consumers and manufacturers alike.
Ignoring these fundamental requirements for FMVSS would undermine the
effectiveness of FMVSS and could potentially compromise vehicle safety
in the U.S.
B. FMVSS No. 308, ``Compressed Hydrogen Storage System Integrity''
1. FMVSS No. 308 as a Vehicle-Level Standard
Background
Consistent with GTR No. 13, NHTSA proposed that FMVSS No. 308 be a
vehicle-level standard, rather than an equipment standard. Some
performance requirements and test procedures for the CHSS in FMVSS No.
308 are specific to the vehicle design and to its gross vehicle weight
rating. NHTSA sought comment on whether FMVSS No. 308 should remain a
vehicle standard.
Comments Received
Auto Innovators expressed concern about NHTSA's proposal to
structure FMVSS No. 308 as a vehicle-level standard, arguing that the
development and quality assurance of CHSS require specialized
knowledge. Since many vehicle manufacturers source CHSS from
independent suppliers, Auto Innovators suggested that compliance
responsibility should lie with the CHSS supplier. It further stated
that it is unclear how vehicle manufacturers could practically
implement testing, given that CHSS design is more applicable to
suppliers. It also emphasized the importance of including replacement
parts in FMVSS No. 308 to maintain consistency and ensure integrity
during repairs.
DTNA supported the proposal to maintain FMVSS No. 308 as a vehicle-
level standard. It agreed that the performance requirements should
apply only to originally equipped CHSS and stated that further research
is needed before addressing replacement CHSS. It also concurred that
the CHSS performance should be evaluated based on vehicle design and
gross vehicle weight rating.
EMA recommended revising FMVSS No. 308 to apply as an equipment
standard that would also include replacement containers. It proposed
that both motor vehicles using compressed hydrogen gas and containers
designed to store it should be subject to the standard.
Glickenhaus advocated for FMVSS No. 308 to focus on tank-level
testing rather than vehicle-level certification, arguing that CHSS
components should be certified by the component manufacturer. It
pointed out that NHTSA has a precedent in other FMVSS standards for
differentiating requirements based on vehicle weight and size, and
suggested that FMVSS No. 308 could follow a similar approach. This
approach, according to Glickenhaus, would reduce costs by allowing
tanks to be certified for use across multiple vehicle platforms without
re-certification for each vehicle.
H2MOF proposed that FMVSS No. 308 remain a component standard with
applicability for hydrogen storage systems ranging from 10 MPa to 70
MPa.
Nikola stated that FMVSS No. 308 should remain a separate standard
but questioned why replacement parts should not be required to meet the
standard and suggested using separate markings to indicate which
vehicle types a particular component is suitable for.
Newhouse suggested that FMVSS No. 308 should be an equipment
standard focusing on the fuel container and directly integral
components, such as the valve and TPRD. It recommended that FMVSS No.
307 cover system issues, including the connection of fuel containers
with tubing.
FORVIA agreed with not extending FMVSS No. 308 to replacement
parts, stating it would provide replacement parts equivalent to the
original ones.
Luxfer Gas Cylinders referenced compliance with FMVSS No. 304,
where CNG fuel containers were purchased directly from manufacturers,
and questioned whether NHTSA intended to purchase hydrogen vehicles to
obtain CHSS for testing. It also asked if NHTSA plans to test both
containers and TPRDs from container manufacturers or vehicle providers.
It stated that FMVSS No. 308 would be more appropriate as a component-
level standard since it focuses on performance tests for CHSS rather
than the vehicle as a whole.
Agency Response
NHTSA is maintaining FMVSS No. 308 as a vehicle-level standard, as
proposed. Several requirements in FMVSS No. 308 are specific to the
vehicle design and to the gross vehicle weight rating of the vehicle in
which a CHSS is installed.\7\ It is not possible to fully evaluate the
performance of a CHSS without knowledge of the vehicle in which it is
installed.
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\7\ For example, as discussed below, the number of pressure
cycles to which the container is subjected during the baseline
initial pressure cycle test is dependent on the vehicle GVWR, with a
different number of cycles required for light and heavy vehicles.
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While CHSSs may be sourced from specialized equipment suppliers,
vehicle manufacturers must ensure that the CHSS installed on their
vehicles meet all applicable FMVSS requirements to certify that the
entire vehicle is compliant. Vehicle manufacturers may consider working
[[Page 6222]]
closely with CHSS suppliers regarding system design to ensure all
requirements are met for a particular vehicle.
Following the lead of GTR No. 13, FMVSS No. 308 establishes
standards intended to ensure the safety and integrity of the CHSS
throughout the lifetime of a vehicle. NHTSA recognizes that some
containers and parts may still need to be replaced due to damage
incurred through extraordinary events or due to defects, but in
general, the agency expects the demand for replacement CHSS parts to be
minimal. Given the likely low demand for replacement containers by
ordinary consumers, the limited current market penetration of hydrogen
vehicles, and the fact that any recalls will be serviced by
manufacturers, we expect the market for aftermarket products to be
negligible, and that replacement parts will be supplied predominantly
through OEMs, therefore obviating the safety need to set an equipment-
level standard. However, NHTSA will monitor the deployment of hydrogen
vehicles and how consumers are replacing parts of the fuel system and
update the standard as necessary.
While NHTSA recognizes that some manufacturers would prefer that
FMVSS No. 308 be an equipment standard, thus potentially shifting the
burden of certification onto other entities like suppliers, NHTSA
remains invested in ensuring that the end product it regulates--the
vehicle--is as safe as possible. The safety of the end product is most
important to protecting consumers and the public. Because a compliant
CHSS is essential to certifying the safety of the end product, NHTSA
maintains the vehicle-level standard. Additionally, NHTSA expects that
manufacturers will maintain proper record-keeping practices, including
detailed hardware bills of materials, to ensure traceability to
originating suppliers.
Regarding the procurement of CHSS or subcomponents for compliance
testing, NHTSA will have the option of purchasing complete vehicles or
the relevant replacement parts from the vehicle or sub-component
manufacturer. This flexibility will enable NHTSA to obtain the needed
vehicle and components to conduct compliance testing efficiently.
Additionally, final-stage vehicle manufacturers will not
necessarily be required to conduct CHSS testing themselves. Vehicle
manufacturers must take reasonable care in certifying that their
vehicles meet FMVSS No. 308, but they are not required to follow any
set testing procedure and may, if they find it reasonable, work with
CHSS suppliers to ensure compliance with FMVSS No. 308. This approach
allows vehicle manufacturers to use their discretion in determining
which party is best suited to conduct specific tests. This arrangement
is often formalized through contractual obligations, with CHSS
suppliers guaranteeing the functionality of their systems and agreeing
to supply replacement parts exclusively through the vehicle
manufacturer, ensuring consistency and regulatory compliance.
2. FMVSS No 307 and 308 as Separate Standards
Background
NHTSA sought comment on whether FMVSS Nos. 307 and 308 should be
combined into a single standard in the final rule.
Comment Received
Luxfer Gas Cylinders commented that it would be better to keep
FMVSS Nos. 307 and 308 separate. EMA also supported maintaining
separate standards, recommending that FMVSS No. 308 be applicable to
vehicles using hydrogen as a motor fuel, as well as to hydrogen
containers designed for on-board storage, similar to FMVSS No. 304 for
CNG containers. Glickenhaus agreed that FMVSS Nos. 307 and 308 should
remain distinct. H2MOF similarly stated that the two standards should
not be combined. Nikola argued that FMVSS No. 308 should remain its own
standard, pointing out that component-specific testing is common in
FMVSS regulations, citing examples such as FMVSS Nos. 106, 108, and
304. Nikola further suggested that FMVSS No. 307 should cover vehicle-
level requirements, while FMVSS No. 308 should address component-
specific requirements. Hyundai supported the separation of the
standards, stating that it is logical to distinguish between fuel
system integrity and hydrogen storage system requirements, drawing a
parallel with FMVSS Nos. 303 and 304 for CNG vehicles. FORVIA, while
generally neutral, expressed a preference for combining the standards,
suggesting that doing so could simplify future amendments and create a
more consistent alignment with GTR No. 13.
Agency Response
NHTSA is keeping FMVSS No. 307 and FMVSS No. 308 as separate
standards, as proposed. This separation will make future management of
the standards more efficient and is consistent with FMVSS No. 303,
``Fuel system integrity of compressed natural gas vehicles,'' and FMVSS
No. 304. All commenters on this matter supported requirements in
separate standards, as proposed. Regarding H2MOF's comment, NHTSA does
not believe that combining FMVSS No. 307 and 308 into a single standard
will improve consistency with GTR No. 13. Consistency relates to the
specifics of the requirements themselves, and is not based on whether
those requirements are in a single standard or in two standards.
3. Change of Design Table
Background
Some international standards include what is known as a ``change of
design table.'' This type of table is used in type-approval regulatory
systems to specify what qualification testing must be redone for a
given change in an approved system's design. GTR No. 13 does not
contain a change of design table because GTRs are neutral toward the
different national certification systems used and change of design
tables are only relevant in type-approval systems.
Comments Received
Quantum Fuel Systems, LLC commented that the proposed standard
omits the deviation table, also known as a change of design table, that
is included in Economic Commission for Europe Regulation No. 134, (UN
ECE R134).\8\ Quantum Fuel Systems, LLC stated that the only difference
between GTR No. 13 and UN ECE 134 is that UN ECE 134 also includes a
deviation table. Quantum Fuel Systems, LLC provided a copy of the
change of design table in UN ECE R134. Quantum Fuel Systems, LLC stated
it would like the change of design table to be added to the FMVSS Nos.
307 and 308 standards.
---------------------------------------------------------------------------
\8\ See Economic Commission for Europe Regulation No. 134,
Uniform provisions concerning the approval of motor vehicles and
their components with regard to the safety related performance of
hydrogen-fuelled vehicles. https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2015/R134e.pdf.
---------------------------------------------------------------------------
Agency Response
NHTSA is not including a change of design table in FMVSS Nos. 307
and 308. Change of design tables are not relevant to FMVSS because
FMVSS are self-certification standards. Manufacturers themselves are
responsible for determining if any design changes require re-
certification of the overall design or system.
[[Page 6223]]
4. Compressed Hydrogen Storage System
a. Container Definition
Background
GTR No. 13 defines a container as ``the pressure-bearing component
on the vehicle that stores the primary volume of hydrogen fuel in a
single chamber or in multiple permanently interconnected chambers.''
NHTSA proposed a similar definition with the following modifications:
Replace ``the vehicle'' with ``a compressed hydrogen
storage system'' to clarify that the container is a subcomponent of a
CHSS, and therefore a container cannot exist on its own without the
other components of the CHSS.
Remove the word ``primary'' because this word introduces
ambiguity regarding secondary or tertiary volumes of stored hydrogen.
Add the word ``continuous'' to clarify that a container
does not have any valves or other obstructions that may separate its
different chambers.
Thus, NHTSA proposed that ``container means pressure-bearing
component of a compressed hydrogen storage system that stores a
continuous volume of hydrogen fuel in a single chamber or in multiple
permanently interconnected chambers.'' NHTSA sought comment on the
proposed definition for the container.
Comments Received
Commenters provided a range of opinions on NHTSA's proposed
definition of ``container'' in FMVSS No. 308. Auto Innovators suggested
that NHTSA should harmonize with the definition in GTR No. 13, stating
that it is well understood and provides sufficient clarity without
necessitating a new definition. Similarly, DTNA raised concerns that
removing the word ``primary'' could introduce ambiguity, particularly
in relation to whether plumbing and piping systems might be considered
part of the container and thus subject to the same testing requirements
as the container itself. It requested clarification that such systems
are not part of the container.
Glickenhaus and H2MOF expressed support for the proposed
definition, with Glickenhaus backing the entire proposal and H2MOF
agreeing with the characterization of a container as consisting of a
single chamber or multiple interconnected chambers. However, Agility
voiced concerns about the practicality of certain performance tests,
specifically with live lines, and requested clarification on how
multiple-chamber containers would be tested.
Several commenters, including Nikola, WFS, TesTneT, and FORVIA,
advocated for retaining the definition from GTR No. 13. WFS suggested
that if changes are necessary, only the modification to replace ``the
vehicle'' with ``a compressed hydrogen storage system'' should be
adopted, while the term ``primary'' should remain to prevent confusion
between containers and the CHSS. FORVIA also opposed adding the term
``continuous,'' noting that it could mislead interpretations of
interconnected chambers. It suggested that further clarification could
be provided through additional notes, especially regarding the
definition of ``permanently interconnected.''
HATCI supported NHTSA's proposed definitions for the container,
closure devices, shut-off valves, and container attachments, stating
agreement with the rationale provided.
Agency Response
NHTSA is maintaining the definition of container as proposed. It is
important to indicate in the definition that a container is a component
of a CHSS, rather than simply a component of a vehicle. This language
makes clear that a container cannot exist outside a CHSS. In other
words, there can be no ``independent'' containers that are not part of
a CHSS. This clarification is important because the CHSS includes the
critical safety functions of shut-off valve, check valve, and TPRD, as
discussed below. A container without these functions is unsafe and is
not permitted by the standard. All containers must exist as a component
of a CHSS, and a vehicle may not have containers that are not part of a
CHSS.
It is also important to remove the word ``primary'' from the
definition of container. Including the word ``primary'' could introduce
ambiguity about secondary or tertiary volumes of stored hydrogen, or
secondary or tertiary containers on the vehicle. All containers onboard
a vehicle that supply hydrogen to propel the vehicle need to be
regulated by the standard, and including the word primary in the
definition could imply that only the ``first'' or ``primary'' container
is covered by the regulation, while other ``secondary'' containers and
their respective CHSS are unregulated. This is not NHTSA's intent, and
therefore the word ``primary'' has been removed.
Additionally, it is important to include the word ``continuous'' in
the definition. This word is used to determine the specific volume that
constitutes a container's single or multiple permanently interconnected
chambers. The continuous volume that constitutes the container
continues until it is ``interrupted'' or ``broken'' by a shut-off
valve. Any continuous volume up to the shut-off valve is considered
part of the container. For example, if there are lines \9\ between a
cylindrical chamber and the shut off valve, then those lines are
considered part of the continuous volume that constitutes the container
with hydrogen stored at high pressure. A conformable container design
consisting of multiple small high-pressure cylinders interconnected by
high-pressure piping that are all enclosed in a casing, and that
collectively have one set of closure devices (i.e. shut-off valve,
TPRD, check valve), would be considered as one container by this
definition. Such conformable containers are in development for vehicle
application in the near future.
---------------------------------------------------------------------------
\9\ In this context, ``lines'' refers to any plumbing, piping,
and/or connections where hydrogen fuel may be present.
---------------------------------------------------------------------------
Similarly, if two conventional high-pressure containers share a
single shut-off valve through piping or lines, such lines present the
same safety risks as the container itself, due to the large quantity of
stored high-pressure hydrogen that could be uncontrollably released in
the event of a failure of those lines to contain the hydrogen.
Therefore, those lines would be required to undergo durability testing
along with the remainder of the container. However, if the lines are
attached to the cylindrical chamber with high pressure hydrogen after
the shut-off valve, then they would not be considered part of the
continuous volume that constitutes the container. These lines after the
shut-off valve do not present the same safety risk of uncontrolled
release of high-pressure hydrogen, due to the shut-off valve's ability
to close and isolate the stored hydrogen.
Including the word continuous is also important to clarify that a
container does not have any valves or other obstructions that may
separate its different chambers, in the case of a container with
multiple permanently interconnected chambers. There cannot be a shut-
off valve or other obstruction between any of the chambers of a
container that is composed of multiple permanently interconnected
chambers (such as the example provided earlier of a conformable
container). Containers composed of multiple chambers forming a
continuous volume are tested as a single unit, whereas if there are
valves or other obstructions that separate the chambers and ``break''
the continuous volume, the chambers are considered separate containers
and are evaluated
[[Page 6224]]
separately. For example, in the case of three permanently
interconnected chambers joined together by piping before a single shut-
off valve, all three chambers and the piping together would be
considered ``the container.'' Alternatively, if each of the three
chambers had its own shut-off valve prior to the piping connections,
then each of the three chambers would be a separate container.
Finally, NHTSA does not intend to apply the definition of container
to fuel lines outside a CHSS after the shut-off valve, or to low
pressure fuel system components downstream of the shut-off valve that
may contain residual hydrogen. These lines are covered by other
requirements such as the fuel system leakage requirement in FMVSS No.
307, discussed below, which specifies that the fuel system shall not
leak, as evaluated by FMVSS No. 307 S6.6, Test for fuel system leakage.
b. Container Attachments Definition
Background
NHTSA proposed defining ``container attachments'' as ``non-pressure
bearing parts attached to the container that provide additional support
and/or protection to the container and that may be removed only with
the use of tools for the specific purpose of maintenance and/or
inspection.'' GTR No. 13 defined container attachments as ``non-
pressure bearing parts attached to the container that provide
additional support and/or protection to the container and that may be
only temporarily removed for maintenance and/or inspection only with
the use of tools.'' NHTSA's definition is similar to that in GTR No. 13
with some exceptions.
GTR No. 13 uses the phrase ``only temporarily removed for
maintenance and/or inspection'' in the definition of container
attachment. In the NPRM proposed definition, the words ``only
temporarily'' and ``for maintenance and/or inspection,'' were removed
because anything that can be removed temporarily can also be removed
permanently. Additionally, from a regulatory perspective, it is not
possible to control and monitor the purpose of removing the container
attachments and so the phrase ``for maintenance and/or inspection'' was
removed.
Comments Received
Several commenters, including Nikola, Auto Innovators, TesTneT,
NGS, and FORVIA, suggested that the definition should remain aligned
with GTR No. 13 to maintain consistency. Nikola expressed concern that
changes could lead to unintended consequences, while Auto Innovators
acknowledged NHTSA's rationale for removing the term ``temporary'' but
stated that the amendment was unnecessary and recommended harmonization
with GTR No. 13. TesTneT also noted that the proposed change was
insignificant, and NGS recommended keeping the GTR No. 13 definition
but adding a safety mark to parts critical to the system's function.
EMA proposed adding ``repair'' to the definition and emphasized the
need for consistency between FMVSS Nos. 307 and 308. It pointed out a
discrepancy in the wording of the definitions between the two standards
and suggested it be addressed. FORVIA opposed permitting permanent
removal of container attachments, stating that it could pose safety
risks, and emphasized the need for allowing only temporary removal for
repairs.
In contrast, H2MOF and HATCI supported NHTSA's proposed definition,
with H2MOF agreeing directly and HATCI expressing support for the
definitions of container attachments as well as other related
components.
Agency Response
NHTSA is maintaining the definition of container attachments as
proposed. The agency does not anticipate unintended consequences from
removing the word ``temporary'' from the definition. By removing the
word ``temporary,'' NHTSA is avoiding having to determine whether an
attachment was designed to be removed permanently or temporarily. As
stated in the NPRM, anything that can be removed temporarily can also
be removed permanently, so a distinction between temporary removal and
permanent removal is not meaningful.
It is also not necessary to add the word ``repair'' to the
definition or keep the phrase ``for maintenance and/or inspection,''
because any attachments that can be removed for maintenance,
inspection, or repair can also be removed for other reasons and FMVSS
No. 308 cannot enforce the purpose of removing the attachments.
In response to the comment from EMA regarding discrepancy in the
definition of container attachment in FMVSS Nos. 307 and 308, NHTSA
acknowledges that the omission of ``and/'' from the definition in FMVSS
No. 307 was a clerical omission and the definition has been corrected
in this final rule.
c. Closure Devices Definition
Background
GTR No. 13 refers to closure devices as ``primary'' closure
devices. This language creates ambiguity about potential secondary or
tertiary closure devices. As a result, NHTSA proposed to define the
term ``closure devices'' as ``the check valve(s), shut-off valve(s) and
thermally-activated pressure relief device(s) that control the flow of
hydrogen into and/or out of a CHSS'' and does not use the word
``primary.''
Comments Received
Commenters provided mixed feedback on NHTSA's proposal to remove
the word ``primary'' from the definition of closure devices. HATCI
supported NHTSA's proposed definitions and agreed with the rationale
provided. On the other hand, Auto Innovators opposed the removal,
stating that ``primary'' is necessary to distinguish between primary,
secondary, and tertiary closure devices, which may be outside the
regulation's scope. It recommended harmonizing with GTR No. 13, which
it argued provides sufficient clarity by defining primary closure
devices as those directly attached to the chamber or manifold.
Glickenhaus also disagreed with the proposed change, noting that its
design approach includes redundant safety measures for critical
components. It questioned whether secondary shut-off valves would be
considered part of the CHSS if the term ``primary'' was removed.
H2MOF commented that ``primary'' should remain, as additional
devices like pressure-activated pressure relief devices may be required
in some cases. It also suggested adding a clarification that CHSS test
units do not need closure devices, as most tests are performed
hydraulically. Nikola agreed that the definition should retain
``primary'' to differentiate between main shut-off valves and secondary
valves like manual isolation valves, which are outside the document's
scope.
DTNA noted its concern for removal of the word ``primary'' from the
definition of ``closure devices.'' It stated that ``volumes of hydrogen
that are located between other valves, often along the piping, could be
considered part of the CHSS.'' WFS similarly recommended keeping the
word ``primary,'' as its removal would create more ambiguity regarding
the distinction between the CHSS and the broader fuel system. TesTneT
and FORVIA also opposed the change, with FORVIA asserting that the
differentiation between primary and
[[Page 6225]]
secondary closure devices is essential, as GTR No. 13 only covers
primary devices. It stated that removing ``primary'' would create
uncertainty about whether secondary closures are included.
Agency Response
NHTSA is keeping the proposed definition of closure devices.
NHTSA's intention is to subject all TPRDs, check-valves, and shut-off
valves that directly control flow of hydrogen into and/or out of the
CHSS to the requirements of FMVSS No. 308 S5.1.5. Therefore, there is
no need to identify closure devices as ``primary.'' Whether a closure
device directly controls the flow into and/or out of the CHSS will be
dispositive. Redundant, back-up, or downstream devices are not intended
to be subject to the requirements of FMVSS No. 308 S.5.1.5.
There will be no confusion about ``other'' closure devices because
the proposed definition specifically identifies only ``the check
valve(s), shut-off valve(s) and thermally-activated pressure relief
device(s) that control the flow of hydrogen into and/or out of a
CHSS,'' and the CHSS is defined as ``a system that stores compressed
hydrogen fuel for a hydrogen-fueled vehicle, composed of a container,
container attachments (if any), and all closure devices required to
isolate the stored hydrogen from the remainder of the fuel system and
the environment.'' Any other device types, as well as any devices that
do not directly control flow into and/or out of a CHSS, are not closure
devices under this definition, or are not part of the CHSS and
therefore are not subject to the requirements of FMVSS No. 308 S5.1.5.
For example, a valve that is not providing the CHSS with one or all of
its required functions of check valve, shut-off valve, and TPRD is not
considered a closure device and would not be tested under the standard.
Similarly, a valve located ``downstream'' from the CHSS shut-off valve
is not considered a closure device since it would not be controlling
flow into or out of the CHSS. Likewise, a ``manual isolation valve'' is
not a shut-off valve because it is not automatically activated, and so
would not be considered a closure device per the final rule.
d. Shut-Off Valve Definition
Background
GTR No. 13 defines a shut-off valve as ``a valve between the
container and the vehicle fuel system that must default to the `closed'
position when not connected to a power source.'' NHTSA proposed adding
the words ``electrically activated'' to the definition, so that a shut-
off valve would be ``an electrically activated valve between the
container and the vehicle fuel system that must default to the `closed'
position when not connected to a power source.''
Comments Received
Commenters expressed a strong preference for maintaining alignment
with the definition of a shut-off valve as outlined in GTR No. 13.
Nikola commented that the existing GTR No. 13 definition should be
retained, arguing that other activation methods, such as pneumatic, are
possible and that the proposed change to ``electrically activated''
would be overly prescriptive. Auto Innovators recommended harmonizing
the definitions of shut-off valves in FMVSS Nos. 307 and 308 with the
definition in GTR No. 13, noting that the definitions in these FMVSS
standards are currently inconsistent. Similarly, DTNA requested the
removal of ``electrically activated'' from the definition, suggesting
that the term is not design-neutral and could limit future innovations.
DTNA further proposed using the term ``automatically activated'' as a
more inclusive option. EMA supported consistency with GTR No. 13 and
recommended that NHTSA harmonize the definition of shut-off valves
across FMVSS Nos. 307 and 308, offering an alternative definition that
would omit ``electrically activated.''
Several commenters, including H2MOF and TesTneT, opposed adding
``electrically activated,'' with H2MOF stating that shut-off valves can
also be pneumatically activated. WFS suggested that while leaving the
definition as written in GTR No. 13 would suffice, there would be no
harm in adding ``electrically activated'' if NHTSA felt it improved
clarity. NGS and FORVIA also raised concerns about restricting future
innovations, such as pneumatic systems, if the definition were limited
to electrically activated valves. Both commenters advocated for
retaining the GTR No. 13 wording to avoid stifling potential
advancements in valve technology.
Agency Response
NHTSA agrees with the commenters and has removed the words
``electrically activated,'' consistent with the definition in GTR No.
13. This change avoids the possibility of being design restrictive by
specifying ``electrically activated.'' NHTSA notes, however, that the
definition indicates that the valve must default to the ``closed''
position when not connected to a power source, which directly implies
the valve must utilize electrical actuation of some kind.
NHTSA made an editorial modification to the definition of ``shut-
off valve'' by replacing the words ``when not connected to a power
source'' with ``unpowered.'' This was an editorial change for
conciseness. However, NHTSA omitted this update from the definition for
shut-off valve in FMVSS No. 307, and only applied it in FMVSS No. 308.
In the final rule, both definitions have been revised to reflect this
update.
e. CHSS Definition
Background
NHTSA proposed a definition of the CHSS that matches the definition
in GTR No. 13, with the exception of the removal of the word
``primary'' before ``closure devices,'' as discussed above.
Comments Received
Luxfer Gas Cylinders commented that the proposed definition of CHSS
is appropriate but noted that most of the hydraulic performance tests
in FMVSS No. 308 cannot be conducted with the check valve, shut-off
valve, and TPRD attached to the container. NFA suggested that NHTSA
should consider including Figure-3, the Typical CHSS diagram from the
NPRM, in the standard to help clarify the definition.
Agency Response
NHTSA is maintaining the definition of CHSS as proposed. The
regulatory text clearly specifies where the CHSS or its subcomponents,
such as the container, must meet the various requirements. For example,
FMVSS No. 308 S5.1.2 specifies that the test for performance durability
is conducted only with the container, and in some cases, container
attachments. As Luxfer Gas Cylinders points out, it is not possible to
conduct hydraulic tests with the closure devices attached to the
container.
NHTSA is not including a figure in the definition because the
definition is already clear, and the referenced figure only shows a
generic CHSS that may not be representative of all CHSS types that meet
the definition.
f. Cryo-Compressed Hydrogen Systems
Background
Cryo-compressed hydrogen (CcH2) storage systems store compressed
hydrogen gas at very low temperatures and high pressures. NHTSA
proposed that FMVSS No. 307 and 308 would apply to ``each motor vehicle
that uses compressed hydrogen gas as a fuel source.''
[[Page 6226]]
Comments Received
Verne, Inc. commented that many of the performance requirements in
GTR No. 13 and FMVSS Nos. 307 and 308 are relevant for ensuring the
safety of some aspects of cryo-compressed hydrogen storage systems.
These aspects include crash safety, fire resistance, external vehicle
hazards, and performance durability. However, Verne stated that these
regulations do not adequately address the specific design, components,
and service conditions of CcH2 systems. It further noted that CcH2
technology, which operates at a nominal working pressure (NWP) of 35
MPa and temperatures below -200 [deg]C, is not sufficiently covered by
existing global or local regulations, codes, and standards.
Verne requested clarification from NHTSA on whether CcH2 storage
systems and hydrogen-powered vehicles using such systems fall under the
scope of FMVSS Nos. 307 and 308 as a type of CHSS. Verne also stated
that while CcH2 is not explicitly out of scope in GTR No. 13, there is
a note in GTR No. 13 Part I Section C.3 that could suggest it should
not be included. It emphasized that CcH2 systems meet the definition of
CHSS, including key components like a container, TPRD, shut-off valve,
and check valve.
Verne listed several ways in which CcH2 systems differ from
conventional gaseous CHSS, such as the inclusion of additional devices
like multiple pressure relief devices, insulation, and an all-metal
vacuum jacket. It also highlighted that due to the pressure dynamics
after fueling, the target and maximum fueling pressure should be set
lower than 43.75 MPa, suggesting a target of 35 MPa and operational
relief at 40 MPa. Furthermore, Verne noted that CcH2 systems are
designed to operate at temperatures far below the typical range for
gaseous hydrogen systems, with expected operational temperatures
between -253 [deg]C and +85 [deg]C.
Verne requested an exemption from FMVSS No. 308 S5.1.3, Test for
expected on-road performance, for CcH2 systems, stating that test
primarily assesses the performance of non-metallic liners in Type 4
containers and non-metallic sealing interfaces. Verne stated that since
CcH2 systems rely on metal-to-metal sealing designs to perform at
cryogenic temperatures, they do not face the same vulnerabilities as
systems using non-metallics. Verne also stated that the temperature
conditions in the on-road performance test do not accurately reflect
the normal or extreme operational conditions of CcH2 systems. It stated
that the current requirements would make the test impossible to execute
due to the lower setpoints of the PRDs in CcH2 systems. Finally, Verne
stated that the test for on-road performance, as currently written, is
costly and provides little safety assurance for CcH2 systems,
recommending that it be revised to better suit the technology.
Agency Response
Verne, Inc. has highlighted significant differences between CcH2
and conventional CHSS,\10\ including very low operational temperatures,
the use of metal-to-metal sealing at cryogenic temperatures, and the
presence of PRDs in the storage system. CcH2 systems operate under
significantly different conditions than conventional CHSS, including
lower temperatures and altered pressure dynamics. These technological
distinctions would pose challenges for applying FMVSS No. 308 to CcH2
systems given that the current testing protocols do not adequately
address these differences.\11\
---------------------------------------------------------------------------
\10\ By ``conventional CHSS,'' we mean a CHSS that stores
hydrogen in gaseous form at high pressures, typically 35 to 70 MPa
\11\ There are varied CcH2 system designs under development and
there are no standardized testing protocols that address safety
issues unique to each of these CcH2 systems. CcH2 storage system
manufacturers conduct Failure Modes Effects Analysis (FMEA) to
identify potential failure modes, analyze the causes of these
failures, and assess their potential effects on the system's safety
and functionality, including hydrogen leaks, pressure surges,
thermal issues, and component malfunctions. The manufacturers take
steps to ensure their CcH2 system designs prevent occurrence of
these failures and mitigate the safety effects of any failure mode.
---------------------------------------------------------------------------
GTR No. 13, on which FMSS No. 308 is based, was developed to
consider conventional CHSS and does not yet provide sufficient guidance
for CcH2 systems. GTR No. 13 acknowledges the potential inclusion of
additional storage technologies, such as cryo-compressed systems, in
future revisions of the GTR and as the development of these systems
progresses. However, it is likely that more research and safety
standard development will be required to address the technological
distinctions between CcH2 systems and conventional CHSS before GTR No.
13 can be expanded to include these systems.
As such, applying the specific performance requirements of FMVSS
No. 308 to vehicles utilizing CcH2 systems is not feasible. Therefore,
NHTSA will not apply the requirements of FMVSS No. 308 to vehicles
using CcH2 storage systems at this time. However, while CcH2 systems
are unique hydrogen storage systems and distinct from conventional
CHSSs, most of the vehicle fuel delivery system (piping, pressure
regulators, filters, flow control valves, and heat exchangers) and the
fuel cell system used to power and propel a vehicle with CcH2 storage
systems are similar to those in hydrogen powered vehicles with
conventional CHSSs. Additionally, the safety aspects associated with
the hydrogen fuel delivery system and the fuel cell system in vehicles
with CcH2 storage systems would be similar to that in vehicles with
conventional CHSSs. Therefore, NHTSA will still require that vehicles
utilizing CcH2, like all vehicles that use hydrogen fuel, meet the
vehicle safety requirements outlined in FMVSS No. 307. These include
provisions for in-use fuel system integrity and post-crash fuel system
integrity, ensuring that vehicles using CcH2 technology maintain
overall vehicle safety. Additionally, while NHTSA is exempting CcH2
systems from the requirements of FMVSS No. 308 at this time, NHTSA will
continue to monitor developments in cryogenic storage technologies and
associated safety standards to inform future regulatory actions.
g. Solid State Hydrogen Systems
Background
Solid-state hydrogen storage systems use advanced materials
designed for the storage of hydrogen within solid structures. These
materials are composed of porous frameworks onto which hydrogen can
adsorb. These frameworks feature expansive internal surface areas that
allow the capture and storage of hydrogen molecules within porous
networks. These systems can store hydrogen at high densities due to
their structural versatility and their ability to reversibly absorb and
release hydrogen.
Comments Received
H2MOF commented that its solid-state hydrogen storage systems use
adsorbent materials to store hydrogen safely and efficiently. H2MOF
stated this method helps reduce costs associated with hydrogen storage,
transportation, and use by avoiding the expenses of gas compression and
cryogenic liquefaction. H2MOF stated its system involves hydrogen
adsorption materials housed within a metallic pressure vessel, which
typically operates at 5 MPa, and is enclosed in an insulated outer
shell. H2MOF requested that low-pressure solid-state storage solutions
operating below 10 MPa be exempted from the requirements of the NPRM,
which H2MOF stated are designed for non-metallic high-pressure
[[Page 6227]]
vessels functioning at 35 MPa and 70 MPa.
Agency Response
Similar to the case of CcH2 systems discussed in the previous
section, H2MOF has highlighted significant differences between its low-
pressure solid-state storage systems and conventional CHSS. These
distinctions include the use of adsorbent materials within metallic
pressure vessels, lower operational pressures, and the avoidance of
high-pressure compression fueling typically seen in traditional CHSS.
As with CcH2 systems, these technological differences present
challenges for applying the proposed FMVSS No. 308, which was developed
for conventional high-pressure gaseous CHSS and does not consider the
unique characteristics of solid-state hydrogen storage systems. As with
CcH2 systems, NHTSA recognizes the need for more research and standards
development to address the specific safety characteristics of solid-
state hydrogen storage systems.
Therefore, NHTSA has determined that it is not feasible to apply
the performance requirements of FMVSS No. 308 to vehicles using solid-
state hydrogen storage systems. However, similar to vehicles with CcH2
storage systems and for the same reasoning, vehicles that use solid-
state hydrogen storage technology must still comply with the overall
vehicle safety requirements specified in FMVSS No. 307, including in-
use fuel system integrity and post-crash fuel system integrity.\12\
While NHTSA is exempting solid-state hydrogen storage systems from the
requirements of FMVSS No. 308 at this time, NHTSA will continue to
monitor advancements in solid-state hydrogen storage technology and
consider future regulatory updates as these systems and associated
safety standards further develop.
---------------------------------------------------------------------------
\12\ The vehicle fuel delivery system and the fuel cell system
in vehicles using solid-state hydrogen storage systems are similar
to hydrogen powered vehicles with conventional CHSSs.
---------------------------------------------------------------------------
5. General Requirements for the CHSS
a. Maximum CHSS Working Pressure of 70 MPa
Background
Consistent with GTR No. 13, NHTSA proposed requiring that CHSS have
a NWP of 70 MPa or less. This is because working pressures above 70 MPa
for motor vehicle applications are currently considered impractical and
may pose a safety risk given current known technologies. The energy
density of hydrogen does not increase significantly when pressurized
above 70 MPa, so there is no significant improvement in hydrogen
storage efficiency at pressures above 70 MPa. Pressures above 70 MPa,
however, may present a greater safety hazard. NHTSA sought comment on
this requirement, and specifically asked commenters to identify any
technologies that can safely store hydrogen at pressures above 70 MPa.
Comments Received
Nikola stated that CHSS are identified by NWP and maximum filling
pressure, with pressures above 70 MPa offering diminishing returns.
Nikola also commented that current industry does not have containers
that operate above this threshold. Auto Innovators generally agreed
with NHTSA's rationale but requested a plan for adapting to future
technological developments. It recommended aligning with GTR No. 13,
which sets 70 MPa as the highest NWP, and expressed that it would be
inappropriate to specify anything higher. Luxfer Gas Cylinders
commented that 70 MPa is the appropriate limit due to the absence of
filling infrastructure for pressures above this level.
Glickenhaus raised concerns about unintended consequences from
limiting the NWP of CHSS to 70 MPa. It pointed out that limiting
pressures could hinder future research, comparing this to past
limitations when 35 MPa was the industry standard. Glickenhaus
commented that today's 70 MPa containers were made possible by
technological advances, and a similar restriction in the past might
have hindered progress. It also stated that high temperature conditions
could reduce the effectiveness of refueling at a fueling station with
70 MPa containers, leading to slower refills and greater energy
consumption due to the thermodynamics relating pressure, volume,
temperature, and amount of gas.
H2MOF supported the proposal to limit NWP to 70 MPa and requested
that FMVSS Nos. 307 and 308 apply to containers ranging from 10 MPa to
70 MPa NWP. WFS agreed with NHTSA's proposal, noting that it aligns
with GTR No. 13 and the practical limit for on-board storage. While
hydrogen can be safely stored above 70 MPa at fueling stations, it
commented that 70 MPa is the practical upper limit for on-board
storage.
TesTneT referenced the GTR No. 13 requirement that all new
compressed hydrogen storage systems produced for on-road vehicle
service have an NWP of 70 MPa or less. TesTneT also noted that there is
no increased risk with higher storage pressures, and stated that
greater container wall thickness at higher pressures provides more
resistance to damage and fire effects. TesTneT noted that the safety
issues at pressures higher than 70 MPa involves the ability to seal
connections within valves and regulators. It mentioned that it
currently use 95 MPa and 100 MPa containers for storing hydrogen at a
fueling station. FORVIA agreed with the proposal and commented that
introducing additional pressure levels would not benefit
interoperability between vehicles and fueling stations, further
supporting the 70 MPa limit.
Agency Response
NHTSA is adopting its proposal to limit the NWP of CHSS to 70 MPa
or less. Most commenters agreed with the proposal, noting that NWP
above 70 MPa offer diminishing returns and that current fueling
infrastructure is not compatible with CHSS with NWP greater than 70
MPa. NHTSA has determined that limiting the NWP of CHSS to 70 MPa or
less is critical due to safety concerns at higher pressures.
TesTneT noted that it uses 95 MPa and 100 MPa NWP containers to
store hydrogen at a fueling station and that the thicker walls of these
containers make them inherently safer against damage and fire. NHTSA
notes that TesTneT's example of containers with NWP greater than 70 MPa
are stationary storage containers. While containers with thicker walls
are more resistant to damage and fire, they are significantly heavier
and likely not practical for use in hydrogen vehicles.
The requirements in this final rule do not fully address the safety
risks associated with storage pressures above 70 MPa. Higher pressures
present a greater risk of severe leaks and/or rupture, and the
consequences of such failures at increased pressures are more severe
due to the larger quantity of energy that could be released. TPRD
releases may also be unsafe due to the quantity of hydrogen that must
be released at pressures above 70 MPa. Additionally, the test for
performance durability of containers in this final rule may not be
sufficient to address stress rupture risk for containers with NWP
greater than 70 MPa. NHTSA is concerned that a container with NWP
greater than 70 MPa may comply with the performance durability
requirements and yet have a significant risk of catastrophic stress
rupture. As a result, additional safety considerations are necessary
for pressures exceeding 70 MPa, and the safety of such systems is not
yet known.
[[Page 6228]]
Therefore, consistent with GTR No. 13, NHTSA is maintaining the
requirement that all CHSS must have an NWP of 70 MPa or less.\13\
---------------------------------------------------------------------------
\13\ Storing hydrogen above 70 MPa is also impractical given
current technology. As pressure increases beyond 70 MPa, hydrogen
becomes increasingly difficult to compress. This difficulty leads to
diminishing returns in terms of hydrogen storage density, where only
a small increase in stored hydrogen results from a
disproportionately higher input of compression energy. Storing
hydrogen at higher pressures also requires containers with thicker
walls to manage the increased stress from extreme pressurization.
These thicker containers add considerable weight, which is
impractical for vehicle use where minimizing weight is critical.
---------------------------------------------------------------------------
Glickenhaus stated that limiting the NWP of CHSS to 70 MPa could
have unintended consequences by hindering technological advances in
hydrogen storage. While Auto Innovators generally agreed with the
proposal to limit NWP of CHSS to 70 MPa, it requested a plan for
adopting future technological developments. NHTSA agrees with the
commenters that technological advances are likely to continue in this
space and the agency will monitor such advancement and continue
research work on CHSS and hydrogen fuel system integrity. NHTSA
coordinates closely with the U.S. Department of Energy (USDOE) and the
Pipeline and Hazardous Materials Safety Administration (PHMSA) on
research, technical advancements, and standards development for
hydrogen vehicles, and plans to update the standards in the future, as
needed. Additionally, for vehicles using CHSS with NWP greater than 70
MPa, NHTSA has provisions for exemptions for alternative fuel vehicles
that vehicle manufacturers may use.\14\
---------------------------------------------------------------------------
\14\ See Part 555--Temporary Exemption from Motor Vehicle Safety
and Bumper Standards, https://www.ecfr.gov/current/title-49/part-555.
---------------------------------------------------------------------------
Glickenhaus commented that fueling stations with 70 MPa tanks would
take longer and more energy to refuel hydrogen powered vehicle tanks in
extremely hot weather. NHTSA notes that the NPRM and final rule apply
to hydrogen storage systems in vehicles used for vehicle propulsion and
not the tanks used in fueling stations. Generally, the tanks in fueling
stations are at about 100 MPa (similar to those noted by TesTneT). This
final rule does not apply to hydrogen tanks in fueling stations.
Limiting CHSS NWP to 70 MPa does not mean 70 MPa is the maximum
pressure that can occur inside a CHSS. Under hot conditions or during
fueling, a fully fueled CHSS may experience pressures of 125 percent
NWP (87.5 MPa for a 70 MPa CHSS). Limiting CHSS NWP to 70 MPa does not
limit the maximum allowable working pressure of the container to 70
MPa, nor does it limit manufacturers' ability to design containers that
can withstand severe over-pressurization events as tested in subsequent
tests.
Finally, H2MOF requested that low-pressure solid-state storage
systems typically operating at pressure below 10 MPa be exempted from
the requirements of the NPRM, which H2MOF stated are designed for non-
metallic high-pressure vessels functioning at 35 MPa and 70 MPa. NHTSA
notes that it is not limiting applicability of the standard to vehicles
with CHSS pressures above 10 MPa. Instead, NHTSA is excluding low-
pressure sold-state hydrogen storage systems from FMVSS No. 308
requirements, as explained earlier in this notice.
b. Mounting Closure Devices On or Within Each Container
Background
GTR No. 13 provided contracting parties with the discretion to
require that the closure devices be mounted directly on or within each
hydrogen fuel container. The relevant safety concern is that the high-
pressure lines required to connect remotely located closure devices
with the container could be susceptible to damage or leak. However, as
discussed above, the definition of a container is sufficiently broad
that it includes lines that are part of the continuous volume of stored
hydrogen (as determined by the location of the shut-off valve or any
other obstruction that ``breaks'' or ``interrupts'' the container's
continuous volume). Thus, any lines that form part of the container's
continuous volume are themselves part of the container and will be
included in the container performance testing discussed below. If a
container (which includes any lines that are part of the container's
continuous volume) can successfully complete the performance testing in
FMVSS No. 308, then the risk of failure of the lines has been
addressed. As a result, NHTSA tentatively concluded that it is not
necessary to specify that closure devices be mounted directly on or
within each container. NHTSA sought comment on requiring closure
devices to be mounted directly on or within each container.
Comments Received
Commenters generally supported NHTSA's proposal not to require
closure devices to be mounted directly on or within each container,
with most agreeing that this approach provides necessary flexibility
for system design. Auto Innovators noted that discussions within the
GTR No. 13 Phase 2 Informal Working Group suggested mounting the
closure device directly on a chamber for single-chamber systems or on
one of the chambers for multi-chamber systems, but also highlighted the
benefits of allowing manufacturers discretion, particularly for non-
traditional designs like conformable tanks. H2MOF, HATCI, and WFS also
supported leaving the location of closure devices to manufacturer
discretion, stating that this flexibility enhances design options. WFS
and TesTneT pointed out that allowing remote TPRDs, which have been
safely used in the CNG industry, could enhance system safety in fire
protection. However, Nikola disagreed with NHTSA's approach, stating
that ``CNG is not the same as hydrogen'' and that allowing this could
lead to unintended issues. Luxfer Gas Cylinders and NGS agreed with
NHTSA's proposal, with NGS emphasizing the importance of not limiting
manufacturers' ability to design systems tailored to their specific
applications.
Agency Response
NHTSA will not require closure devices to be mounted on or within
each container. As discussed above, the definition of ``container'' in
the final rule is sufficiently broad to include any lines that may form
part of the container's continuous volume of pressurized hydrogen up to
the closure device.\15\ Therefore, these lines must be included in the
applicable performance testing as part of the container itself. If a
container, including all portions of the container's continuous volume,
can successfully complete the performance testing in FMVSS No. 308,
then the risk of failure of the lines has been sufficiently addressed.
---------------------------------------------------------------------------
\15\ In this context, ``lines'' refers to any pluming, piping,
and/or connections where hydrogen fuel may be present.
---------------------------------------------------------------------------
c. Requiring Check Valve Functionality as Part of the CHSS
Background
During fueling, hydrogen enters the CHSS after passing through a
check valve. The check valve prevents back-flow of hydrogen into the
fueling supply line or even out of the fueling receptacle to the
atmosphere. NHTSA proposed that the CHSS be required to include the
functionality of a check valve. However, NHTSA is aware of CNG vehicles
that do not include check valves as part of their CNG storage system.
NHTSA sought comment on whether the check valves should be required as
part of the CHSS.
[[Page 6229]]
Comments Received
Commenters expressed mixed opinions on whether check valves should
be required as part of the CHSS. Some, including Nikola, EMA, HATCI,
and FORVIA, supported requiring check valves, citing the higher
pressure of hydrogen and the role of check valves in ensuring safety,
especially for multi-container systems. FORVIA stated that not
including a check valve would leave the fueling line vulnerable to
hydrogen leakage.
Others, such as Agility, Glickenhaus, H2MOF, and TesTneT, opposed
making check valves a mandatory component of the CHSS. Agility stated
that system-level protections are appropriate and requested
clarification whether a single check valve near the fuel receptacle is
adequate. Glickenhaus argued that a remotely located check valve could
offer advantages. H2MOF pointed to the safety record of millions of CNG
vehicles without check valves in its storage systems and suggested the
requirement would be too design restrictive. TesTneT noted that check
valve functionality could be integrated into other components, making a
separate check valve unnecessary.
WFS commented that the key issue is not having a dedicated check
valve but ensuring ``check valve functionality,'' which could be
incorporated into other system components, as outlined in GTR No. 13.
Agency Response
Consistent with GTR No. 13, NHTSA is requiring that the CHSS
include a check valve or the function of a check-valve. A check valve
means ``a valve that prevents reverse flow.'' Therefore, each CHSS must
have hydrogen flow control functionality equivalent to a valve that
prevents reverse flow. This requirement is not design restrictive
because manufacturers have the option to design systems that provide
the required functionality without the need for a traditional check
valve. For example, the functions of check valve and shut-off valve may
be combined into a single device, or multiple containers may share a
single check valve. Additionally, it may be possible for a vehicle to
use a single check valve located at the fueling receptacle to provide
check valve functionality to multiple CHSS. In such a design, each CHSS
onboard the vehicle would derive the function of check valve from the
single check valve located at the fueling receptacle.
6. Specification of BPO on the Container Label
Background
Several of the performance tests in FMVSS No. 308 use a
manufacturer-supplied value known as BPO. A container's
BPO is a design parameter specified by the manufacturer that
represents the median burst pressure for a batch of containers. To
facilitate compliance testing, NHTSA proposed that manufacturers
specify the BPO associated with each container on the
container label.
Comments Received
Several commenters addressed the proposal to include the
manufacturer-specified median burst pressure (BPO) on
container labels. Nikola stated that BPO is not useful to
and could confuse end users, suggesting that if BPO is not
available for compliance testing, NHTSA should assume a value of 2.25
times NWP. Luxfer Gas Cylinders argued that requiring BPO on
labels is unnecessary, as the burst pressure is a quality control
measure, and the median burst pressure of a batch is irrelevant to
manufacturers or end users. Auto Innovators disagreed with the
assertion that BPO varies significantly between batches,
stated that BPO is based on manufacturer testing, and
recommended consistency with GTR No. 13. Auto Innovators opposed
including BPO on labels, citing potential confusion for end
users and lack of safety benefits, and noted that BPO can be
provided to NHTSA during testing without needing to be on the label.
EMA echoed concerns about potential customer confusion and recommended
alignment with GTR No. 13, suggesting that BPO could be
provided by the manufacturer upon request.
Glickenhaus supported a labeling requirement for burst pressure but
raised concerns that NHTSA's proposed definition of BPO
could restrict manufacturers' ability to maintain higher safety
margins. It proposed an alternative definition of BPO based
on the minimum burst pressure from the design and manufacturing process
to allow for increased safety margins. H2MOF and HATCI both stated the
requirement was impractical and unnecessary, with HATCI stressing that
BPO is primarily a design parameter and market strategy
issue, often considered confidential. Agility and TesTneT also opposed
the requirement, with Agility calling it impracticable and TesTneT
suggesting that compliance testing should focus on meeting minimum
standards rather than a manufacturer-specified value.
Other commenters, including NGS and Newhouse, requested aligning
with GTR No. 13, with Newhouse noting that BPO information
can be found through part numbers if needed. FORVIA expressed strong
opposition to including BPO on labels, citing concerns over
confidentiality and potential misinterpretation by consumers and
requested alignment with GTR No. 13. Several commenters, including Auto
Innovators and Luxfer Gas Cylinders, reiterated concerns that labeling
BPO would create confusion and add unnecessary burdens
without any clear safety benefit, recommending harmonization with GTR
No. 13 instead.
Agency Response
After consideration of the comments, NHTSA will not require
BPO to be listed on the container label. NHTSA agrees this
requirement could cause confusion for consumers regarding slight
differences in BPO that may exist between vehicles. Such
differences will have no impact on safety or performance. NHTSA also
acknowledges that listing BPO on the container label could
create confusion about the highest rated pressure for a given vehicle.
Since BPO will typically be a multiple of NWP, but have the
same pressure units, it could be dangerous for a user to mistake
BPO for NWP.
Nevertheless, NHTSA still needs to know the value of BPO
to conduct compliance testing on a given vehicle. Instead of requiring
BPO on the container label, NHTSA will obtain BPO
directly from the vehicle manufacturer. The method for obtaining
BPO from the manufacturer will match that for obtaining the
primary constituent of the container, discussed below.
Some comments appear to reflect a misunderstanding of the role of
BPO within the proposed regulation. The BPO is a
manufacturer-specified parameter that represents the median burst
pressure for a batch of containers. Manufacturers are free to
incorporate additional safety factors into their designs if they wish.
The use of BPO in the requirements does not restrict this
ability. As discussed in the NPRM, the use of BPO during the
residual strength burst test ensures that containers at the end of
their service life would still be safe even if they were to remain in
service.\16\ Specifically, the burst pressure after testing must be at
least 80% of the container's BPO. This
[[Page 6230]]
requirement controls the degradation rate of the container over time,
preventing a high degradation rate that could lead to dangerous bursts
if the container were to remains in use beyond its intended life. This
standard is comparable to safety standards for other vehicle components
like seatbelt webbing.
---------------------------------------------------------------------------
\16\ See 89 FR 27518 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------
Additionally, the concerns raised about the ambiguity of the
BPO definition are misplaced, as the regulation does not
provide a prescriptive definition but rather relies on the
manufacturer's expertise in determining BPO. There is no
requirement to calculate a mean burst pressure by bursting every tank
in a batch. Manufacturers may use standard industry practices based on
their design, materials, manufacturing processes, and testing to
determine BPO.
7. Tests for Baseline Metrics
a. Required Number of Containers Tested
Background
GTR No. 13 requires three new containers to be tested during the
baseline initial burst test and the baseline pressure cycle test. As
NHTSA explained in the proposal, this requirement originates from the
type-approval certification process commonly found in other nations and
that NHTSA did not believe that three new containers needed to be
tested under the U.S. self-certification system where NHTSA buys and
tests vehicles and equipment at the point of sale. Therefore, NHTSA
proposed basing the results of testing of any container for the
baseline initial pressure cycle test. NHTSA sought comment on this
decision.
Comments Received
FORVIA and TesTneT agreed with the proposal, stating that only one
container needs to be pressure cycled to demonstrate compliance with
the cycle life requirements. TesTneT likened this approach to batch
testing, where only one container is required to be tested, rather than
three.
DTNA expressed concern that testing only one container for baseline
metrics might not provide sufficient information on the burst behavior
of all containers in vehicles equipped with multiple containers. DTNA
acknowledged that NHTSA purchases vehicles and equipment from the
public market to monitor FMVSS compliance, but proposed that for
vehicles with multiple containers, at least two should be subjected to
the baseline initial pressure cycle test.
Luxfer Gas Cylinders commented that testing any one container is
reasonable, noting that all cylinders must pass the minimum required
cycle tests and that testing three containers does not represent a
significant statistical sample.
Nikola disagreed with the proposal, suggesting that NHTSA obtain
containers directly from tank manufacturers, similar to how testing is
conducted under FMVSS No. 304 compliance.
H2MOF supported NHTSA's proposal to test one container for the
baseline initial pressure cycle test and recommended allowing a retest
if there is an assignable cause of any non-compliance.
Agency Response
NHTSA is maintaining its decision that it is not required to test
three containers for the baseline initial burst test, as specified by
GTR No. 13. Under the U.S. self-certification system, NHTSA purchases
vehicles and equipment for testing randomly at the point of sale, and
the selected container must meet all applicable safety requirements.
This approach ensures that manufacturers are incentivized to ensure all
vehicles consistently comply with safety standards, knowing that any
one of their containers could be tested. Removing the requirement to
test three containers, the test burden is potentially reduced without
compromising safety, and allowing NHTSA to potentially test more
containers with the same operating budget. Manufacturers must still
ensure that each vehicle meets the standard.
Additionally, concerns about variability among containers are
addressed through the random selection process, which provides an
effective representation of real-world conditions. While some
commenters raised concerns about vehicles with multiple containers,
NHTSA has the flexibility to conduct repeat tests, as well as
additional tests on any of the various container types if needed. This
allows NHTSA to respond to specific cases where there may be a safety
concern without mandating the testing of three containers in every
instance, which maintains an efficient means of ensuring safety.
b. Baseline Initial Burst Pressure Test
(1) Need for the Baseline Initial Burst Test
Background
Consistent with GTR No. 13, NHTSA proposed the baseline initial
burst pressure test in addition to the test for performance durability,
which includes a 1000 hour high-temperature (85 [deg]C) static pressure
test designed to evaluate the container's resistance to stress rupture,
in combination with other lifetime stress factors. Given that the high-
temperature static pressure test evaluates stress rupture risk, and the
test for performance durability represents an overall worst-case
lifetime of multiple stress factors, NHTSA sought comment on whether
the baseline initial burst pressure test even needs to be included in
the standard's requirements.
Comments Received
Nikola commented that the baseline initial burst pressure test is
necessary to ensure that the container meets its initial strength
integrity requirements, which can then be compared to the final burst
pressure. Agility expressed concern that the high-temperature static
pressure test does not sufficiently evaluate reliability against stress
rupture, stating that testing one million cylinders would be required
to demonstrate the same reliability. EMA recommended that the baseline
initial burst pressure test is unnecessary, proposing the removal of
S5.1.1.1 from the standard. H2MOF stated that the residual burst
pressure after the performance durability test is a better indicator of
design fitness than an initial burst pressure test. Auto Innovators
suggested aligning with GTR No. 13, which uses the initial baseline
burst pressure for comparison with residual values.
TesTneT clarified that the high-temperature static pressure test,
originally called the ``accelerated stress rupture test,'' was
developed to assess combined effects on the container but not the
individual stress rupture characteristics of fiber strands. TesTneT
stated that the baseline initial burst pressure test is necessary for
container design and manufacturing control. Newhouse commented that
both tests should be conducted, as they assess different factors.
FORVIA recommended including the baseline initial burst pressure test
for harmonization with GTR No. 13, while also questioning whether NHTSA
must perform all tests during field surveillance or if it has
discretion in test selection. Auto Innovators reiterated its support
for harmonizing with GTR No. 13.
Agency Response
NHTSA is maintaining the proposed baseline initial burst pressure
test. Several commenters provided sufficient explanation of why the
baseline initial pressure test is different from the test for
performance durability. On the other
[[Page 6231]]
hand, the commenters proposing the removal of the baseline initial
burst pressure test did not provide sufficient justification why the
baseline initial burst pressure test is not needed. The initial burst
pressure test evaluates the container's start-of-life integrity,
whereas the test for performance durability examines different aspects
of material performance and stresses, such as resistance to physical
damage, chemical exposure, and extreme environmental temperatures, and
the container's subsequent end-of-life integrity. Therefore, both
testing requirements should be included in the standard, as proposed.
NHTSA notes, however, that the results of the baseline initial burst
pressure test are not referenced in subsequent tests as a comparison or
``baseline.'' Instead, subsequent tests reference the BPO
value discussed above. Regarding field surveillance, NHTSA may conduct
any of the tests in the FMVSS as part of field surveillance.
(2) Burst Pressure Within 10 Percent of BPO
Background
As proposed, the baseline initial burst pressure test would have
verified that the initial burst pressure is within 10 percent of the
manufacturer specified BPO. The requirement that the
container tested must have a burst pressure within 10
percent of BPO was based on the need to control variability
in container production. If a manufacturing process produces containers
with highly variable initial burst pressures, there is a possibility of
a container with a dangerously low burst pressure. NHTSA sought comment
on the safety need for specifying a limit on burst pressure variability
in a batch and whether the 10 percent limit is appropriate. Commenters
were asked to provide supporting data if they believed another limit
was appropriate.
Comments Received
Commenters provided mixed opinions regarding the proposal for a
10 percent limit on burst pressure variability, with some
supporting the limit and others suggesting it is unnecessary or
impractical. Nikola commented that the 10 percent limit is
achievable and accepted by manufacturers. Agility stated that limiting
maximum burst pressure does not necessarily improve safety and
suggested that variability in carbon fiber strength would take up most
of the proposed limit, making it impractical. Agility also recommended
omitting the requirement, stating that the existing minimum burst
requirement already addresses safety concerns. HATCI and Auto
Innovators both noted that burst pressure variability could be managed
through a manufacturer's quality management system, with Auto
Innovators supporting alignment with GTR No. 13 and affirming the
appropriateness of the 10 percent limit. Luxfer Gas
Cylinders stated that specifying a limit is unnecessary, as
manufacturers already ensure no cylinder bursts below the minimum
level, typically by setting burst pressures significantly higher than
required. TesTneT also supported the 10 percent limit,
noting that burst testing in accordance with GTR No. 13 had not
revealed any issues with the limit.
In contrast, Quantum suggested that the 10 percent requirement is
unrealistic due to the influence of factors such as carbon fiber
performance, recommending a more lenient limit of 20 percent. NGS and
H2MOF commented that managing batch variation should be left to the
manufacturer as long as the minimum burst pressure is met. Newhouse
questioned the practicality of the 10 percent limit, noting
that variability is inherent in the production process and that meeting
the minimum burst pressure is a more meaningful safety measure. MEMA
and FORVIA both supported maintaining alignment with GTR No. 13, with
FORVIA emphasizing that the 10 percent variability allowance accounts
for reasonable manufacturing differences while maintaining safety
margins. FORVIA also discouraged adding new batch-related requirements,
suggesting that automotive production often relies on other control
methods, such as sampling in continuous production.
Agency Response
NHTSA is removing the requirement that the burst pressure of the
container be within 10 percent of the BPO. FMVSS are
designed to set minimum safety performance standards for vehicles,
rather than control variability in manufacturing processes. This
approach ensures that every vehicle meets a baseline level of safety,
regardless of specific manufacturing methods or variability in
production. The responsibility for managing variability and ensuring
consistent quality within manufacturing processes falls to the
manufacturers themselves. They must ensure that their production
processes consistently produce vehicles that meet or exceed the FMVSS
requirements.
When NHTSA tests a vehicle component to ensure it meets the FMVSS,
the component is expected to meet or exceed the specified performance
criteria every time it is tested, regardless of variability in the
manufacturing process. NHTSA's approach to testing typically involves
randomly selecting a single test article for evaluation. If this single
component fails to meet the standard, it indicates that the entire
batch, or potentially the entire production process, may be flawed.
Per the requirements of the Safety Act, manufacturers are required
to ensure that every unit produced meets the FMVSS requirements. This
requirement compels manufacturers to control the variability within
their production processes. If a manufacturer allows too much
variability, there is a risk that the vehicle may not meet the
standards, which could result in non-compliance. The prospect of non-
compliance drives manufacturers to maintain high levels of consistency
and quality control, ensuring that every component or vehicle produced
is likely to pass NHTSA's testing, no matter which one is chosen for
evaluation. This method of testing essentially requires control of
variability indirectly, as manufacturers must ensure that all of their
products, not just a select few, comply with FMVSS requirements.
(3) BPmin of 200% NWP
Background
For the reasons discussed in the NPRM, NHTSA believes that the
minimum burst pressure, BPmin, of 200 percent NWP, as set
forth in GTR No. 13 Phase 2, meets the need for safety.\17\ The
proposed BPmin of 200 percent NWP facilitates hydrogen
vehicle development without unnecessary overdesign of components. NHTSA
sought comment on the proposed BPmin of 200 percent NWP
instead of the 225 percent NWP specified in GTR No. 13 Phase 1.
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\17\ See 89 FR 27511 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed. This section's discussion applies to containers
that do not contain glass fiber composite as a primary constituent.
Containers with glass fiber composite as a primary constituent are
discussed in the following section.
---------------------------------------------------------------------------
Comments Received
Several commenters supported NHTSA's proposal to set the
BPmin at 200 percent of NWP as aligned with GTR No. 13 Phase
2. Luxfer Gas Cylinders commented that the 200 percent of NWP for
BPmin is ``acceptable.'' Auto Innovators expressed support
for both the harmonization with GTR No. 13 and the
[[Page 6232]]
BPmin of 200 percent, noting that it reflects the consensus
of the Informal Working Group from GTR No. 13 Phase 2. Nikola also
agreed with the proposed 200 percent BPmin.
Agility commented that while 200 percent NWP may be adequate for
high-strength carbon fiber, it may not be sufficient for other
materials or thin-walled cylinders. Agility suggested requiring 225
percent for NWP values of 35 MPa or lower, as permitted by GTR No. 13.
HATCI expressed support for both the proposed BPmin and the
harmonization with GTR No. 13.
Glickenhaus disagreed with reducing the burst pressure for carbon
fiber containers from 225 percent to 200 percent NWP, stating that the
proposed 200 percent is too low and could create safety risks,
particularly when considering variability in actual burst pressures.
Glickenhaus provided an example involving a theoretical container with
an NWP of 100 bar. Based on the example where a container with a
baseline initial burst pressure of 200 percent NWP had an end-of-life
burst pressure of only 160 percent NWP, it recommended retaining a 225
percent BPmin.
H2MOF supported the proposal, stating that a BPmin of
200 percent would avoid unnecessary overdesign. TesTneT also supported
the 200 percent NWP BPmin, stating it is safe as proposed.
NGS agreed with the 200 percent BPmin for carbon fiber but
requested that other fibers be allowed if sufficient data proves their
durability.
Newhouse commented that 200 percent NWP should be adequate for
carbon fiber reinforced containers, but it suggested establishing a
minimum NWP of 350 bar for this standard. For containers with lower
NWP, Newhouse recommended retaining a BPmin of 225 percent
due to concerns about reduced damage tolerance and safety. Newhouse
further noted that stress rupture is not adequately addressed by
specifying a burst ratio and recommended using stress ratios to ensure
safety for different container types, especially Type 2 and Type 3
containers.
FORVIA expressed agreement with the 200 percent BPmin,
stating that GTR No. 13 Phase 2 has demonstrated that this value is
sufficient based on performance data.
Agency Response
NHTSA is maintaining the proposed BPmin of 200 percent
NWP for containers that do not contain glass-fiber as the primary
constituent. The counterexample given by a commenter in which a
container with a BPO of 200 percent NWP underwent the test
for performance durability and finished with an end-of-life burst
pressure of 160 percent NWP is not valid. The residual pressure test at
the end of the test for performance durability requires a four-minute
hold period at 180 percent of NWP. Therefore, a container with an end-
of-life burst pressure of 160 percent would fail to meet the
performance requirements of the standard and thereby be prohibited from
entering service. There is no option to meet some but not all the
requirements of the test for performance durability.
NHTSA is not currently considering requirements related to strain
gauges to further address stress rupture, nor is it considering
prohibitions on metal liners as that would likely be design
restrictive. Regarding the concerns about the durability of thin-walled
containers, the durability of all containers is rigorously evaluated
with the test for performance durability. The baseline initial burst
pressure test is not intended to address container durability
throughout its lifetime.
Regarding allowing the use of other fiber types, NHTSA is not
restricting designs to any particular fiber type nor excluding any
particular fiber type. Manufacturers are free to design products using
any material they choose. The requirements are designed to apply to
containers regardless of material type. The only material-specific
consideration for containers is for those containers that have glass
fiber composite as a primary constituent, as discussed in the next
section.
Lastly, burst ratios such as BPmin are a well-
established safety metrics that ensure containers' structural
integrity, even if differences exist between burst ratio and stress
ratio for some container types. The proposed requirement for
BPmin of at least 200 percent NWP along with the 1,000 hour
high temperature pressure hold test in the sequential test for
performance durability are in accordance with the requirements in GTR
No. 13 Phase 2 and likely sufficient to mitigate the risks associated
with stress rupture in most containers. Further research would be
needed to fully understand the relationship between burst ratios,
stress ratios, and risk of stress rupture. For now, this final rule
adopts the proposed requirement for an initial baseline burst pressure
of at least 200 percent NWP.
(4) Primary Constituent
Background
NHTSA sought comment on how NHTSA could determine if a container
has glass fiber as a primary constituent and on appropriate criteria to
determine the primary constituent of a container.
In the case of containers constructed of both glass and carbon
fibers, NHTSA proposed to apply the requirements according to the
primary constituent of the container as specified by the manufacturer.
NHTSA proposed that the manufacturer shall specify upon request, in
writing, and within five business days, the primary constituent of the
container. NHTSA proposed that if the manufacturer fails to specify
upon request, in writing, and within five business days, the primary
constituent of a container, the burst pressure of the container must
not be less than 350 percent of NWP.
Comments Received
Luxfer Gas Cylinders commented that a higher minimum burst pressure
is typically required for containers with glass-fiber composites and
suggested that NHTSA request information from manufacturers regarding
the container's composite overwrap and stress analysis to assess the
load share of glass fiber in hybrid designs. Nikola had no objections
to the 350 percent NWP requirement and stated that NHTSA could either
ask the manufacturer for details or cut a container to determine its
composition. Agility expressed concern over the definition of ``primary
constituent'' and suggested that other materials might also be
inappropriate at 200 percent NWP burst. It recommended that
manufacturers be asked to provide the load share of glass fiber, which
could then be used to adjust the minimum burst pressure.
HATCI supported confirming the primary constituent with
manufacturers but opposed the proposed five-day response time,
recommending that NHTSA use its existing information request authority
without specifying a timeline in the regulation. Luxfer Gas Cylinders
added that the five-day period was too short, suggesting a revision to
at least 14 business days due to potential delays in identifying the
appropriate contact at the container manufacturer. EMA requested a ten-
day response period and recommended that the required burst pressure be
based on the material specified by the manufacturer rather than
defaulting to 350 percent NWP. Glickenhaus suggested that the primary
container composition be included in labeling requirements to ensure
transparency throughout the container's lifecycle, eliminating the need
for inquiries to manufacturers. It also proposed that container
manufacturers be required to register with NHTSA, similar to other
safety-critical component
[[Page 6233]]
manufacturers, and submit relevant data such as burst pressures and NWP
ratings.
TesTneT downplayed concerns about glass-fiber-reinforced containers
in hydrogen service, noting that such designs are rare and impractical
for hydrogen applications. It also pointed out the lack of a test
method for determining the primary constituent, suggesting that asking
the manufacturer is the only feasible approach. NGS supported the
requirement for manufacturers to provide primary constituent details
but argued that the response time should be extended to 30 days.
Newhouse highlighted the complexity of determining the primary
constituent in hybrid designs, noting that analysis is required to
assess load-sharing between fibers, and simply specifying a burst ratio
does not ensure safety. Newhouse provided an alternative approach which
provides specific guidelines for hybrid constructions based on fiber
load sharing.
MEMA questioned the implementation and enforcement of the response
time requirements, suggesting that the information could be provided as
part of the self-certification process without the need for a specified
deadline. FORVIA disagreed with changing requirements based on
potential delays in mailing and proposed that NHTSA conduct field
surveillance testing. If a burst test raises suspicions of glass fiber
being a primary constituent, further investigation could be conducted.
Auto Innovators expressed support for harmonization with GTR No. 13 and
agreed with the 350 percent NWP burst pressure requirement for glass-
fiber-reinforced containers. H2MOF also supported the higher burst
pressure requirement, citing its success in CNG containers over the
past two decades. It suggested that the test agency could verify the
container's composition after conducting a burst test.
Agency Response
NHTSA is maintaining the requirement that container with glass
fiber composite as a primary constituent shall have a BPmin
of 350 percent of NWP. However, commenters did not provide a specific
method for determining the primary constituent of a container. Since
NHTSA has no way of determining the load sharing properties of a
container's individual fibers, nor a way to determine whether that load
sharing is fundamental to the strength of the container, whether or not
glass fiber composite is the container's primary constituent must be
determined by and specified by the manufacturer.
NHTSA will not require the primary constituent to be listed on the
label. Similar to BPO, listing the primary constituent on
the container label could potentially confuse consumers. Additionally,
NHTSA does not need to know the specifics of the container's primary
constituent other than whether the primary constituent is glass fiber
composite. Therefore, NHTSA will require that the manufacturer specify
upon request, and in writing, whether the primary constituent of the
container is glass fiber composite or not. Based on the comments,
however, the timeline for responding to the request has been increased
to 15 business days instead of five business days.\18\ NHTSA is
removing the option that if the manufacturer fails to respond to the
request, then the container minimum burst pressure must not be less
than 350 percent of NWP. This option is not appropriate for containers
other than those with glass fiber composite as a primary constituent,
and therefore, the only option is for the manufacturer to specify
whether the container's primary constituent is glass fiber composite.
FMVSS No. 308 S5.1.1.1 has been updated to reflect this change.
S6.2.2.2(e), which contained a similar five business day response
timeline, has also been updated to 15 business days.
---------------------------------------------------------------------------
\18\ The increase from five days to 15 days is intended to give
manufacturers additional time to respond to NHTSA's request.
---------------------------------------------------------------------------
Furthermore, NHTSA will not obtain a copy of the stress analysis
for the container to determine the load sharing from glass fiber in a
mixed fiber overwrap. The stress analysis for the container is outside
the scope of the proposed regulation. NHTSA will simply obtain the
primary constituent from the manufacturer, and then conduct the tests
as specified depending on whether the container includes glass fiber
composite as a primary constituent.
(5) Pressurization Rates Above 0.35 MPa/sec
Background
GTR No. 13 states that if the pressurization rate exceeds 0.35 MPa/
s at pressures higher than 150 percent NWP, then either the container
must be placed in series between the pressure source and the pressure
measurement device, or the time at the pressure above a target burst
pressure must exceed 5 seconds. The first option of placing the
container in series between the pressure source and the pressure sensor
ensures that the container will experience the pressure before the
sensor, so there is no chance that the pressure sensor could read a
pressure level that is not being experienced by the container. However,
NHTSA did not propose the second option that the time at the pressure
above the target burst pressure exceeds 5 seconds because it is unclear
and difficult to enforce. It is not clear what pressure the ``target
burst pressure'' is referring to since during the test, pressure will
be increasing continuously.
Comments Received
Nikola stated that it do not want any changes to the procedure
outlined in GTR No. 13. Luxfer Gas Cylinders commented that while the
procedure is effective for cycle tests, it may not be feasible for
burst testing due to the risk of damaging the pressure measurement
device when placed after the container. It suggested either placing the
container in series between the pressure source and the measurement
device or including a five-second hold at the minimum burst pressure to
ensure the container experiences the correct pressure. TesTneT agreed
with NHTSA's approach of situating the container between the pressure
source and the sensor but noted that this setup is not always practical
or necessary. It mentioned that it has performed many burst tests with
the sensor positioned before the container and have not encountered any
issues, as the slow pressurization rate effectively eliminates pressure
drop concerns. It also stated that holding the pressure for five
seconds at the target burst pressure is clear and enforceable.
Glickenhaus supported NHTSA's decision not to adopt the second
option from GTR No. 13, agreeing that the sensor should be placed in
series between the pressure source and the container to maintain clear
and objective testing. H2MOF recommended including the second method,
noting that various industry standards specify a five-second hold at
the target burst pressure. Newhouse commented that the five-second hold
allows time for the pressure to equalize inside the container, ensuring
accurate readings in cases where flow restrictions may be present.
FORVIA stated that the ``target burst pressure'' should be understood
as the minimum burst pressure. It suggested keeping the pressurization
rate below 0.35 MPa/s at pressures exceeding 150 percent NWP or placing
the container in series between the pressure source and the sensor,
maintaining the wording of GTR No. 13.
Auto Innovators stated that is not practical for all designs to
have
[[Page 6234]]
containers placed in series between pressure source and pressure
measurement device. It requested an alternative method be provided. It
also stated that the pressure pulsations are small to moderate compared
to the absolute pressure level.
Agency Response
Consistent with GTR No. 13, NHTSA proposed that ``If the rate
exceeds 0.35 MPa per second at pressures higher than 1.50 times NWP,
then the container is placed in series between the pressure source and
the pressure measurement device.'' GTR No. 13 also provides the
alternative option that ``the time at the pressure above a target burst
pressure exceeds five seconds.'' As discussed in the NPRM, NHTSA did
not select this latter option because it is unclear.\19\ A five-second
hold period may be feasible for manufacturers that are ``targeting'' a
particular burst pressure. In such a case, manufacturers can simply
pressurize the container to the ``target'' pressure and hold for five
seconds. NHTSA, however, will need to determine an unknown burst
pressure for the container. Since there is no ``target'' burst pressure
stated in the test procedure, the pressure inside the container is
increased continuously until the container bursts. It is not possible
to hold for five seconds at each and every pressure level that occurs
during a burst test. The commenters did not provide any explanation
regarding how, with continuously increasing pressure, any single
specific pressure could be considered to have been held for five
seconds. Instead, NHTSA has selected to use only the option to put the
container in series between the pressure source and the measurement
device. This way the container can be pressurized continuously until it
bursts, and the container's burst pressure can be determined without
prior knowledge of a target burst pressure.
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\19\ See 89 FR 27511 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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Additionally, a configuration where the container is placed in
series between the pressure source and the pressure measurement device
can be achieved regardless of container design and does not necessitate
alternative methods for different container designs. For example, a
pressurization setup that includes a T-fitting, through which the
container connects to both the pressure source and to a line leading to
the pressure measurement device, in which the line leading to the
pressure measurement device is equal in length to or longer than the
connection from the container to the T-fitting, would meet the
requirement for the container to be placed in series between the
pressure source and the pressure measurement device. This configuration
ensures that the container experiences all pressure increases as or
before the sensor records them, accurately reflecting the container's
pressurization level. Furthermore, the maximum allowable pressurization
rate of 1.4 MPa/s for pressures exceeding 150 NWP provides adequate
time for the pressure measurement device to capture accurate pressure
readings during pressurization without premature or unrepresentative
measurements.
c. Number of Cycles for the Baseline Initial Pressure Cycle Test for
Containers on Light and Heavy Vehicles
Background
NHTSA proposed 7,500 as the number of cycles in the baseline
initial pressure cycle test for which the container does not leak nor
burst for light vehicles. To ensure the container leaks before bursting
after reaching the maximum service life, the container is pressure
cycled beyond the 7,500 cycles (representing maximum service life)
until either a container leak occurs without burst or the container
does not leak nor burst for up to a maximum of 22,000 hydraulic
pressure cycles. In accordance with GTR No. 13 Phase 2, NHTSA proposed
that heavy vehicle containers to neither leak nor burst for 11,000
hydraulic pressure cycles, and also to leak without burst (or neither
leak nor burst) beyond the 11,000 hydraulic pressure cycles up to a
maximum of 22,000 pressure cycles. As discussed in the NPRM, these
number of cycles are based on a service life for light and heavy
vehicles of 25 years.\20\ This service life, number of hydraulic
pressure cycles representing the maximum service life for which the
container is required to not leak nor burst, and the number of pressure
cycles beyond that representing maximum service life of the container
for which the container is required to leak without burst or not leak
nor burst at all are summarized in Table 1 for light and heavy
vehicles.
---------------------------------------------------------------------------
\20\ See 89 FR 27513 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
Table 1--Service Life and Number of Cycles in the Baseline Hydraulic Pressure Cycle Test for Light and Heavy
Vehicles
----------------------------------------------------------------------------------------------------------------
Number of cycles
representing maximum Numbe of cycles for
Service life service life for which the container
Vehicle type (years) which the container leaks without burst,
does not leak nor or does not leak nor
burst burst
----------------------------------------------------------------------------------------------------------------
Light.............................................. 25 7,500 7,501-22,000
Heavy.............................................. 25 11,000 11,001-22,000
----------------------------------------------------------------------------------------------------------------
NHTSA sought comment on the proposed number of cycles in Table 1.
NHTSA also sought any additional data available related to vehicle
life, lifetime miles travelled, and number of lifetime fuel cycles.
Comments Received
Several commenters provided feedback on the proposed number of
pressure cycles in Table 1 of the NPRM. Nikola expressed agreement with
the approach outlined, while Luxfer Gas Cylinders also stated that the
cycle values were appropriate. Auto Innovators supported the approach
and suggested that it would be more straightforward to define the
number of cycles beyond the maximum service life as double the number
of cycles for which the container does not leak nor burst. It stated
that specifying 15,000 cycles for light vehicles and 22,000 cycles for
heavy vehicles would be sufficient.
H2MOF, however, recommended a significantly lower cycle count,
suggesting that 1,500 cycles as recommended by the USDOE would be more
appropriate. It calculated that at
[[Page 6235]]
300 miles per fill, this would result in 450,000 miles of service.
TesTneT commented that while light vehicles may experience fewer fill
cycles than heavy vehicles, factors such as partial fill cycles should
be considered. It stated that the industry is not particularly
concerned with fatigue cracking, as no fuel cylinder in CNG or hydrogen
service has experienced this issue. Additionally, it noted that there
is little cost or weight savings in reducing the cycle numbers and
suggested aligning with GTR No. 13 cycle numbers.
FORVIA commented that the proposed numbers were conservative but
reasonable. It indicated that these cycle numbers would cover all
vehicle service life expectations and that containers could handle
these cycles without issue. Therefore, it supported keeping the table
as it is.
Agency Response
NHTSA is maintaining the number of cycles of the baseline initial
pressure cycle test as proposed in the NPRM and listed in Table-1
above. NHTSA is not lowering the number of cycles for which the light
vehicle container leaks without burst, or does not leak nor burst, to
15,000. Because the potential harm from a potential burst would be
catastrophic, the number 22,000 was selected to both exceed extreme on-
road vehicle lifetime range and promote global harmonization with GTR
No. 13, as requested by commenters, and therefore there is no need to
lower this number of cycles. As discussed in the NPRM, 22,000 cycles
simulate over 6 million miles of driving, which is well beyond extreme
vehicle lifetimes. The use of 22,000 cycles ensures that containers
leak before bursting in all extreme cases.\21\
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\21\ See 89 FR 27512 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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The comment regarding a 1,500-cycle recommendation from USDOE
appears to be referring to technical performance targets for CHSS
published by USDOE.\22\ However, performance targets are not the same
as safety standards. Performance targets are goals for how a system
performs under optimal conditions, whereas safety standards are
designed to protect users by minimizing risks and preventing harm in
hazardous or sub-optimal conditions. Therefore, NHTSA is not lowering
the number of cycles for the baseline initial pressure cycle test to
1,500.
---------------------------------------------------------------------------
\22\ See https://www.energy.gov/eere/fuelcells/doe-technical-targets-onboard-hydrogen-storage-light-duty-vehicles.
---------------------------------------------------------------------------
d. Details of the Baseline Initial Cycle Test for Containers on Light
and Heavy Vehicles
(1) Leak Before Burst and Sustaining a Visible Leak for 3 Minutes
Background
A burst may be preceded by an instantaneous moment of leakage,
especially if observed in slow motion. Therefore, NHTSA proposed a
minimum time of 3 minutes to sustain a visible leak before the test can
end successfully due to ``leak before burst.'' NHTSA sought comment on
this additional requirement.
Comments Received
Luxfer Gas Cylinders commented that NHTSA's proposed wording
regarding the number of hydraulic pressure cycles is unclear. It noted
that the phrasing ``neither leak nor burst'' contradicts itself by
allowing leakage after 11,000 cycles but also stating neither leakage
nor bursting should occur. It suggested the wording should be revised
to state: ``The cylinder shall be allowed to leak, but not burst,
beyond the 11,000 cycles up to a maximum of 22,000 pressure cycles.''
Luxfer also expressed concerns about the 3-minute sustained leak
requirement, stating that most pressure equipment is designed to shut
off when detecting pressure loss, making it difficult to hold a leak
under pressure for three minutes. It proposed alternative wording to
state that containers should fail by leakage but not rupture.
H2MOF raised concerns about the proposed 3-minute hold requirement
for a visible leak, stating that if the pressure vessel leaks, the pump
may not be able to maintain pressure, potentially causing the test to
abort.
Nikola disagreed with NHTSA's proposal, commenting that leak-
before-burst is not currently a requirement and that the term implies
the container should leak and never burst at the end of its life.
FORVIA also disagreed with the 3-minute sustained leak requirement
and recommended keeping the test procedure harmonized with GTR No. 13.
It questioned the justification for the 3-minute requirement and noted
that the behavior described, where a burst is preceded by leakage, is
extremely improbable. It suggested that pressure should be allowed to
drop below a certain level instead of imposing a time-based
requirement, as this behavior is unknown in its experience.
TesTneT commented that the 3-minute sustained leak requirement
changes the test from a leak-before-burst test to a stress rupture
test. Based on its 35 years of experience performing leak-before-burst
testing, it stated it has never encountered an issue distinguishing
between a leak and a burst. TesTneT also referred to NHTSA's mention of
observing leaks in slow motion and suggested that it is unnecessary to
observe the location of failure during testing. It recommended
maintaining the current wording in GTR No. 13 without any changes.
Agency Response
The requirements regarding the number of cycles for which a
container shall not leak nor burst, and thereafter shall not burst are
clarified in the proposed FMVSS No. 308 S5.1.1.2. The proposed S5.1.1.2
clearly specifies the number of cycles for which a container shall not
leak nor burst and thereafter the number of cycles for which the
container shall not burst. The number of cycles specified is dependent
on the GVWR of the vehicle under test.
Based on the comments, however, NHTSA is removing the statement
about sustaining a visible leak for three minutes before the test can
end successfully due to ``leak before burst.'' Instead, the final rule
simply states that if a leak occurs while conducting the test as
specified in S5.1.1.2(a)(2) or S5.1.1.2(b)(2), the test is stopped and
not considered a failure. Test labs will not observe the baseline
initial pressure cycling test in slow motion and therefore it will be
clear to the test lab whether the test has resulted in leakage or in a
burst.
NHTSA also made a clerical correction to S6.2.2.2(e) to remove the
word ``container,'' such that S6.2.2.2(e) reads ``The manufacturer may
specify a hydraulic cycling profile within the specifications of
S6.2.2.2(c).''
(2) Effect of the Cycling Profile
Background
NHTSA proposed a maximum hydraulic pressure cycle rate of five to
ten cycles/minute for the baseline initial pressure cycle test. This
rate was selected to allow for efficient compliance testing. Actual
fueling cycles for hydrogen vehicles occur more slowly. Therefore, the
container manufacturer may specify a hydraulic pressure cycle profile
that will prevent premature failure of the container due to test
conditions outside of the container design envelope. NHTSA sought
comment on cycling profiles and whether the pressure cycling profile
[[Page 6236]]
will significantly affect the test result. NHTSA sought comment on more
specifics of what manufacturers should be allowed to specify regarding
an appropriate pressure cycling profile for testing their system.
Comments Received
Luxfer Gas Cylinders stated that the maximum cycle rate of 10
cycles per minute specified in GTR No. 13 is rarely approached in
testing, noting that Luxfer uses 4 cycles per minute for larger
containers. Auto Innovators commented that cycle rates and profiles do
affect container performance, and manufacturers should be allowed to
specify these parameters, as unrealistic testing conditions could lead
to failures not representative of actual service. It suggested that
NHTSA consider aligning with GTR No. 13 Phase 2, which specifies a
maximum of 10 cycles per minute. It also stated that the pressure
cycling profile has not been seen to significantly affect test results
and that manufacturers generally cycle as quickly as is safe and
practical.
H2MOF agreed with NHTSA that the cycling profile can impact test
results depending on materials and design margins, emphasizing the
importance of the number of cycles and pressure limits. It supported
allowing manufacturers to specify pressurization and depressurization
rates, as well as hold times.
TesTneT, drawing on over 35 years of experience, disagreed with the
idea that cycling profiles affect test results, stating that no
evidence supports this concern and criticizing the Powertech report
referenced by NHTSA. It also noted that GTR No. 13 allows manufacturers
to specify any cycle profile as long as it stays within the 10 cycles
per minute limit.
Nikola commented that the defueling or unloading phase of the
pressure cycle can impact container life, supporting the idea that
manufacturers should be allowed to specify an appropriate profile.
HATCI recommended that NHTSA fully harmonize with the GTR No. 13 Phase
2 requirement where the container is cycled less than or equal to 10
cycles per minute.
Agency Response
NHTSA is maintaining the maximum hydraulic pressure cycle rate of
10 cycles/minute for the baseline initial pressure cycle test,
consistent with GTR No. 13. However, NHTSA will remove the lower
cycling limit of 5 cycles per minute. As a result, the cycling rate may
be any rate up to 10 cycles per minute. This change will accommodate
larger containers which may take longer to cycle.
While some commenters stated that the cycling profile is
inconsequential, others stated the profile can have an effect for some
container designs. NHTSA acknowledges that the cycling profile may
affect the test result for some containers. As a result, NHTSA will
maintain the specification that manufacturers may specify a pressure
cycling profile for testing their system. The manufacturer's
specifications will need to be within the above cycling rate range and
the other conditions specified in FMVSS No. 308 S6.2.2.2(c). At NHTSA's
option, NHTSA will cycle the container within 10 percent of the
manufacturer's specified cycling profile.
8. Test for Performance Durability
Background
The test for performance durability addresses impact (drop during
installation and/or road wear), static high pressure from long-term
parking, over-pressurization from fueling and fueling station
malfunction and environmental exposures (chemicals and temperature/
humidity). These stresses are compounded in a series is because a
container may experience all of these stresses during its service life,
and the safety need for a hydrogen system remains an issue for the
vehicle's entire service life.
Comments Received
Luxfer Gas Cylinders commented that the verification tests for
performance durability, on-road performance, and service-terminating
performance in fire can be expensive, with costs exceeding $500,000,
and potentially reaching $1,000,000 for larger containers. It asked
whether NHTSA was aware of the high cost associated with conducting the
proposed test program.
Quantum stated that completing the entire hydraulic and pneumatic
test sequences with the on-tank-valves (OTV) installed would
significantly increase the time required for testing. It explained that
the small orifice size of OTVs restricts hydrogen or hydraulic fluid
flow, thus extending the duration of each test sequence. Additionally,
Quantum noted that other components of the CHSS, such as the TPRD,
check valve, and shut-off valve, are tested separately from the
container for cycle life. Since these valves are designed for gas use
rather than continuous liquid flow, Quantum recommended removing the
requirement for the OTV to be installed during testing.
Agency Response
NHTSA is aware of the test burden of the proposed tests. FMVSS
establish minimum safety requirements and the FMVSS test procedures
establish how the agency would verify compliance. However,
manufacturers are not required to conduct the exact test in the FMVSS
to certify their vehicles. The Safety Act requires manufacturers to
certify that their vehicles meet all applicable FMVSS, and specifies
that manufacturers may not certify compliance if, in exercising
reasonable care, the manufacturer has reason to know the certificate is
false or misleading. Manufacturers may use different types of tests or
even simulations to certify their vehicles if they exercise reasonable
care in doing so. In other words, manufacturers must ensure that their
vehicles will meet the requirements of FMVSS No. 308 when NHTSA tests
the vehicles in accordance with the test procedures specified in the
standard, but manufacturers may use different test procedures and
evaluation methods to do so.
Regarding Quantum's comment regarding testing with OTVs, the NPRM
clearly specifies that only the container is subject to the
requirements of the test for performance durability. The ``container,''
as defined the regulation, does not include closure devices. On the
other hand, the test for expected on-road performance is conducted
using hydrogen gas, and with the entire CHSS. The test for expected on-
road performance therefore includes closure devices as part of the
CHSS.
a. Proof Pressure Test
Background
GTR No. 13 states that a container that has undergone a proof
pressure test in manufacture is exempt from this test. However, NHTSA
may not know whether a container has undergone the proof pressure test.
As a result, NHTSA proposed that all containers will be subjected to
the proof pressure test as part of the test for performance durability.
In the event that a proof pressure test is conducted during manufacture
and as part of the tests for performance durability, the container
would experience two proof pressure tests. NHTSA sought comment on
conducting the proof pressure test on all containers.
Comments Received
Nikola opposed NHTSA's proposal to add the proof pressure test,
stating that all onboard vehicle containers already undergo 100 percent
proof pressure tests by manufacturers. Luxfer Gas Cylinders
[[Page 6237]]
supported the decision to require all containers to undergo the proof
pressure test as part of the test for performance durability. Auto
Innovators disagreed, arguing that this would add unnecessary burden
without additional safety benefits, as proof pressure testing is
already required before service. It requested harmonization with GTR
No. 13 Phase 2, which exempts containers that have already undergone
proof testing during manufacturing.
Air Products suggested reviewing the proposed 30- to 35-second hold
time, as it is significantly shorter than the 10-minute hold period
specified in other industry standards. DTNA supported NHTSA's proposal
for consistency, stating that all containers should undergo the proof
pressure test regardless of prior testing during manufacturing. H2MOF
opposed duplicating the test, stating that the additional high-stress
cycle would negatively impact container performance during durability
testing, as containers are already factory proof tested according to
industry standards. HATCI also opposed the requirement, recommending
the adoption of GTR No. 13 Phase 2, which exempts containers that have
undergone proof pressure testing in manufacture.
TesTneT commented that proof pressure testing is conducted on all
designs during production, not merely to confirm the container's
resistance to over-pressurization, but to ensure consistency in
manufacturing through measurements of elastic and permanent expansion.
It suggested that if a design is damaged by a proof pressure test, it
would become apparent during pressure cycle testing, thus rendering
additional proof pressure testing unnecessary.
MEMA disagreed with the assumption that it is unknown whether a
container has undergone proof testing during manufacturing, stating
that some manufacturers conduct this test as part of the fabrication
process, which is required under GTR No. 13. MEMA suggested adding
language to FMVSS No. 308 allowing an exemption for containers that
have already undergone proof pressure testing.
FORVIA acknowledged concerns about dual testing but suggested that
NHTSA incorporate language from GTR No. 13 Phase 2, which allows for
exemptions for duplicative proof tests, ensuring that all containers
comply with FMVSS requirements. It further argued that if a second test
is deemed not to significantly stress the container, the first test
should also be considered adequate, as repeated pressurizations are
unlikely to make a significant difference.
Agency Response
Based on the comments received, NHTSA is removing the proof
pressure test. Commenters emphasized that 100 percent of all containers
already undergo a proof pressure test during manufacturing, as part of
standard production practices, and that requiring an additional proof
pressure test would be redundant and burdensome without offering any
additional safety benefits. Several commenters also raised concerns
that subjecting a container to multiple proof pressure tests could
introduce unnecessary stress and possibly affect the container's
performance in subsequent tests.
After considering these comments, NHTSA agrees that a second proof
pressure test would not provide additional safety benefits and could
possibly impose undue stress on the container. As a result, the proof
pressure test has been removed from the test for performance durability
and the test for expected on-road performance, discussed below.
b. Drop Test
(1) Damage That Prevents Further Testing
Background
It is possible that the container could experience damage from the
drop test that prevents continuing with the remainder of the tests for
performance durability. This damage would prevent NHTSA from completing
the evaluation of a container. To address this possibility, NHTSA
proposed that if any damage to the container following the drop test
prevents further testing of the container, the container is considered
to have failed the tests for performance durability and no further
testing is conducted.
Comments Received
HATCI commented that the inability to conduct subsequent tests
after damage from the drop test should not automatically result in a
failed test for performance durability. It suggested that additional
containers should be used for further testing in such cases. As an
example, it noted that deformation of an aluminum nozzle opening or
valve connection after a drop test could prevent further testing, but
this deformation does not necessarily indicate a lack of durability.
MEMA agreed with the single drop event specified in FMVSS No. 308
S5.1.2.2 but raised concerns about the potential for confusion
regarding the damage criteria. It suggested that NHTSA clarify the
wording to specify ``irrecoverable damage'' or ``damage that cannot be
readily repaired'' to account for conditions where minor repairs, such
as fixing damaged threads on a shut-off valve, could allow testing to
continue.
Agency Response
NHTSA is maintaining the test requirements as proposed. Damage that
prevents the continuation of testing under S6.2.3.4 must be considered
a failure of the test for performance durability because the required
test sequence cannot be completed in its entirety. NHTSA will not
repair containers that are damaged during the drop test.
(2) Including Container Attachments for the Drop Test
Background
The drop test is a test in which container attachments may improve
performance by protecting the container when it impacts the ground.
Consistent with GTR No. 13, the drop test is conducted on the container
with any associated container attachments. NHTSA sought comment on
including container attachments for the drop test.
Comments Received
EMA stated that its members lack experience with dropping
containers with attachments and are unsure of what qualifies as a
``container attachment'' for heavy vehicles, which often use multiple
hydrogen containers. EMA commented that including attachments could
make it difficult to ensure consistent impact locations during the test
and recommended aligning FMVSS No. 308 with UN ECE R134, dropping the
container without attachments unless the manufacturer opts to include
impact-mitigating attachments. It suggested requiring the manufacturer
to specify whether container attachments should be included for the
test.
H2MOF supported conducting the drop test with container
attachments, as it reflects real-life scenarios. Auto Innovators
opposed including attachments unless they are permanently fixed to the
container, arguing that removable attachments should be excluded to
maintain flexibility and focus on container robustness. It noted that
this approach aligns with GTR No. 13's intent to demonstrate container
durability before installation.
Nikola commented that attachments should be included only if they
are present during shipping; if added during vehicle assembly, they
should be excluded. Luxfer Gas Cylinders opposed dropping containers
with attachments,
[[Page 6238]]
stating that the attachments are more likely to break than the
container itself, and including them would complicate the test by
introducing additional variables. It also noted that conducting the
test with valves and PRDs attached would be impractical. TesTneT
commented that if attachments are part of the container when it leaves
production, they should remain for the drop test, as the test addresses
potential handling damage before installation. FORVIA supported
including container attachments in the drop test, referencing that
their inclusion was a key factor in the development of GTR No. 13.
Agency Response
``Container attachments'' means non-pressure bearing parts attached
to the container that provide additional support and/or protection to
the container and that may be removed only with the use of tools for
the specific purpose of maintenance or inspection. Container
attachments do not refer to the structures that physically attach the
container(s) to the vehicle. NHTSA will not rely on the manufacturer to
specify container attachment configurations as this adds unnecessary
complexity. NHTSA will simply purchase vehicles or replacement
containers at the point of sale and conduct the drop test with any
included, pre-installed container attachment that meet the definition
for container attachments. Given that manufacturers are required to
ensure that the vehicle is compliant at the time it is delivered to a
dealer or distributor, manufacturers should take reasonable care to
ensure they are not damaging or installing damaged containers into
vehicles. If a container is sold at the point of sale without pre-
installed container attachments, it will be tested as such.
(3) Center of Gravity
Background
In the case of a non-cylindrical or asymmetric container, the
horizontal and vertical axes may not be clear. The proposed rule
provided that in such cases, to conduct the drop test, the container
will be oriented using its center of gravity and the center of any of
its shut-off valve interface locations. The two points will be aligned
horizontally (i.e., perpendicular to gravity), vertically (i.e.,
parallel to gravity) or at a 45[deg] angle relative to vertical. The
center of gravity of an asymmetric container may not be easily
identifiable, so NHTSA sought comment on the appropriateness of using
the center of gravity as a reference point for this compliance test and
how to properly determine the center of gravity for a highly asymmetric
container.
Comments Received
Auto Innovators supported NHTSA's proposal to align with GTR No.
13, stating that for asymmetric containers, orientation is typically
determined when mounted in a vehicle. It added that technical
information on the center of gravity could be provided to NHTSA if
needed, noting that identifying the center of gravity, even for
asymmetric shapes, is not particularly difficult. It advocated for
maintaining the same specifications as GTR No. 13 Phase 2, which it
found to be adequate.
DTNA agreed that using the center of gravity as a reference for the
drop test was appropriate, as it ensures reproducibility in test
results. It emphasized that determining the center of gravity
accurately is critical for valid test outcomes. DTNA recommended that
manufacturers provide this data to NHTSA prior to testing, allowing the
agency to verify the information and request clarification if
necessary. It highlighted that the accuracy of this reference point is
essential, especially given the NPRM's proposal that failure of the
drop test would result in failing the entire performance durability
testing process.
H2MOF proposed that the center of gravity for a highly asymmetric
container be determined using the container's geometric CAD file.
Nikola suggested maintaining the current center of gravity definition
as outlined in GTR No. 13.
TesTneT supported using the center of gravity as a reference,
noting that it is a physical characteristic shared by all container
designs, including asymmetric ones. It added that orientation for such
containers could be determined when installed on a vehicle, and the
center of gravity could be established in consultation with the
manufacturer.
FORVIA stated that keeping the test procedure harmonized with GTR
No. 13 was appropriate. It noted that identifying the center of gravity
experimentally is not overly difficult, and it believed that fully
asymmetric containers are unlikely to be prevalent in the market.
Instead, it anticipated new rectangular designs with centers of gravity
near their geometric centers, providing a good basis for testing.
Agency Response
The center of gravity is not defined in GTR No. 13, nor is a method
provided for determine the center of gravity for an asymmetric
container. NHTSA will not have access to CAD files for the container.
Therefore, in the case of an asymmetric container, NHTSA will obtain
the center of gravity from the manufacturer, similar to how it obtains
the primary constituent and BPO. The manufacturer shall
specify, in writing, and within 15 business days, the center of gravity
of the container. In the drop test, t container will be oriented using
its center of gravity and the center of any of its shut-off valve
interface locations. These two points will be aligned horizontally
(i.e., perpendicular to gravity), vertically (i.e., parallel to
gravity) or at a 45[deg] angle relative to vertical, as specified.
c. Surface Damage Test
Background
NHTSA proposed the surface damage test based on GTR No. 13 Phase 2.
The surface damage test applies cuts and impacts to the surface of the
container. The surface damage test consists of two linear cuts and five
pendulum impacts.
Comments Received
MEMA commented on the surface damage test proposed by NHTSA,
stating that there were differences between the proposed requirements
and those in GTR No. 13. It stated that in Section 6.2.3.3(a), for non-
metallic containers, NHTSA's proposal includes two longitudinal saw
cuts, which is consistent with GTR No. 13. However, it stated that
NHTSA proposed different lengths and depths for the cuts without
explaining why the differences are necessary or how they might improve
test results.
MEMA further stated that NHTSA's proposal specifies the first cut
as being 0.75 millimeters to 1.25 millimeters deep and 200 millimeters
to 205 millimeters long, while the second cut, only required for
containers affixed to the vehicle by compressing its composite surface
(i.e., clamped), would be 1.25 millimeters to 1.75 millimeters deep and
25 millimeters to 28 millimeters long. MEMA stated that GTR No. 13
requires two cuts regardless of how the container is affixed, with the
first cut being at least 1.25 millimeters deep and 25 millimeters long
toward the valve end, and the second cut being at least 0.75
millimeters deep and 200 millimeters long toward the opposite end.
MEMA stated that its members believe that the GTR No. 13
requirements provide a better minimum threshold and requested that
NHTSA harmonize FMVSS No. 308 with GTR No. 13 on this matter. It also
expressed concern that additional surface damage test requirements, as
part of the already lengthy pressure cycling test, would
[[Page 6239]]
increase the complexity, duration, and cost of the process without
delivering more representative or improved results. MEMA proposed that
FMVSS No. 308 S6.2.3.3. be revised to align with GTR No. 13.
Agency Response
The commenter appears to be referencing the original version of GTR
No. 13. GTR No. 13 has undergone a comprehensive Phase 2 revision that
was adopted at the 190th Session of WP.29 on June 21, 2023.\23\ Phase 2
accomplished several goals, including strengthening test procedures for
containers with pressures below 70 MPa. The U.S. voted in favor of
adopting Phase 2 and the changes made to GTR No. 13 by Phase 2 are
reflected in NHTSA's proposal for FMVSS Nos. 307 and 308 and in this
final rule. GTR No. 13 Phase 2 states in section 6.2.3.3(a): ``Surface
flaw generation: A saw cut at least 0.75 mm deep and 200 mm long is
made on the surface specified above. If the container is to be affixed
to the vehicle by compressing its composite surface, then a second cut
at least 1.25 mm deep and 25 mm long is applied at the end of the
container which is opposite to the location of the first cut.''
Regarding the difference in lengths of the proposed FMVSS No. 308
S6.2.3.3(a), these differences are simply due to tolerances added to
FMVSS No. 308, as discussed below.
---------------------------------------------------------------------------
\23\ A copy of GTR No. 13 as updated by the Phase 2 amendments
is available at https://unece.org/transport/documents/2023/07/standards/un-global-technical-regulation-no-13-amendment-1.
---------------------------------------------------------------------------
(1) Including Container Attachments
Background
The surface damage test is a test in which container attachments
may improve performance by shielding the container from the impacts.
For containers with container attachments, GTR No. 13 specifies that if
the container surface is accessible, then the test is conducted on the
container surface. Determining whether the container surface is
accessible is subjective because ``accessible'' is not defined in the
GTR and could have many potential meanings. Therefore, NHTSA did not
propose a specification involving the accessibility of the container
surface. Instead, NHTSA proposed that if the container attachments can
be removed using a process specified by the manufacturer, they will be
removed and not included for the surface damage test nor for the
remaining portions of the test for performance durability. Container
attachments that cannot be removed are included for the test. NHTSA
sought comment on including container attachments for the surface
damage test.
Comments Received
HATCI expressed agreement with NHTSA's proposal to remove container
attachments, when possible, and to exclude them from the surface damage
test. Auto Innovators recommended harmonizing with GTR No. 13,
supporting the removal of attachments if specified by the manufacturer,
and including non-removable attachments, as doing so ensures the test
is conducted on the container's pressure-bearing chamber. H2MOF agreed
that non-removable container attachments should be included in the
test.
Luxfer Gas Cylinders commented that containers can be used in
various vehicle systems with different attachments, making it
impractical to test each type of attachment. It supported testing
containers without attachments if they can be removed, adding that the
drop test and the four-minute hold at 180 percent NWP are the primary
design drivers, and it is unnecessary to include attachments in any
tests. TesTneT stated that pendulum impacts do not affect the integrity
of composite containers and were originally intended to test protective
coatings. It recommended including attachments in the test if these
attachments are designed to protect the container surface from road
conditions. FORVIA requested keeping non-removable attachments in the
surface damage test, noting that these attachments were introduced in
GTR No. 13 due to the surface damage test.
Agency Response
NHTSA is maintaining the surface damage test as proposed. If the
container attachments can be removed using a process specified by the
manufacturer, they will be removed and not included for the surface
damage test nor for the remaining portions of the test for performance
durability. Testing the container without its container attachments is
representative of a situation in which installation personnel remove
the container attachments and fail to re-install them before the
container enters service. Additionally, since the goal of a surface
damage test is to test the surface, it makes sense to remove the
container attachments that are capable of being removed. While NHTSA
has chosen to keep container attachments on for other tests (e.g. the
drop test, if the container attachment is pre-installed and meets the
definition of container attachment), the surface damage test is
different enough to warrant a deviation from that practice. Container
attachments that cannot be removed are included for the test.
If different vehicles require different configurations of container
attachments, each configuration would be subject the requirements
separately. If some of the configurations have removable container
attachments, those container attachments would be removed. If some
configurations have non-removable container attachments, those
container attachments would remain in place during the surface damage
test.
(2) Exempting All-Metal Containers
Background
GTR No. 13 exempts all-metal containers from the linear cuts.
NHTSA's proposal included this exemption, but NHTSA sought comment on
whether another objective and practicable procedure exists for
evaluating surface abrasions that could apply to all containers, such
as, for example, the application of a defined cutting force to the
container surface.
Comments Received
TesTneT commented that its experience with CNG cylinders has shown
that steel cylinders are resistant to abrasion damage of the magnitude
proposed for composite containers. It noted that developing a
performance test to simulate defect dimensions as outlined in GTR No.
13 would be complicated, involving variables such as the shape, angle,
and force of impact. Since surface abrasions do not cause failure in
thinner-walled CNG cylinders, it suggested such abrasions would not
pose a problem for hydrogen containers. Nikola and H2MOF both agreed
with the exemption for all-metal containers from the linear cuts.
Auto Innovators supported the proposed exemption for metal
containers and stated that requiring a test for a defined cutting force
would add unnecessary regulatory burden. It emphasized that container
manufacturers should provide sufficient technical information for
compliance purposes. Verne, Inc. recommended extending the exemption to
all-metal container attachments as well, noting that metal is resistant
to scratches and cuts, and flaw cut depths may exceed the wall
thickness of metal attachments.
Luxfer Gas Cylinders raised the concern that containers could
experience cuts during service, such as from poorly fitted brackets. It
suggested that metal containers with walls thin enough to be penetrated
by cuts would be unsuitable for high-pressure vehicle
[[Page 6240]]
fuel systems and recommended a more clearly defined test instead of a
blanket exemption. FORVIA requested that the test procedure remain
harmonized with GTR No. 13, noting that GTR No. 13 sets minimum
requirements. It asked for clear justification if flaws in metallic
containers are considered a concern and suggested discussing this issue
in GTR No. 13 phase 3.
Agency Response
NHTSA is maintaining the exemption from the linear cuts for all-
metal containers. The commenters did not provide sufficient information
regarding how to conduct an alternative test with a defined cutting
force applied to the metal container surface. Moreover, as stated by
the commenters, metal containers are resistant to abrasions so this
form of surface damage is not expected to be a significant safety
concern. NHTSA is not extending the exemption to all-metal container
attachments, however. Doing so would add complexity to the testing
process where some container attachments would be treated differently
from others. Furthermore, container attachments may be in place to
protect the containers from abrasions and other surface damage, so the
container attachments themselves should be able to tolerate surface
damage.
The global community also considered this issue in developing GTR
13 and found that an exemption for-all metal containers was appropriate
based on challenges with an adequate test procedure. Accordingly, both
harmonization and practical challenges favor exempting all-metal
containers from the linear cuts at this time. However, NHTSA has robust
enforcement authority to address defects that pose an unreasonable risk
to safety, including in all-metal containers. NHTSA will continue to
monitor the state of the industry and will revise the standard in a
future rulemaking as necessary.
(3) Applying Impacts on the Opposite Side vs. a Different Chamber
Background
In accordance with GTR No. 13, NHTSA specified the pendulum impacts
``on the side opposite from the saw cuts.'' For containers with
multiple permanently interconnected chambers, GTR No. 13 specifies
applying the pendulum impacts to a different chamber to that where the
saw cuts were made. However, the agency did not propose this
distinction for pendulum impact location for containers with multiple
permanently interconnected chambers because NHTSA was concerned that it
may be less stringent than when impacts are to the same chamber where
the cuts were applied. NHTSA sought comment on whether applying the
impacts to the opposite side of the same chamber that received the saw
cuts may be more stringent than applying the impacts to a separate
chamber, and whether including the specification as written in GTR No.
13 would reduce stringency for containers with multiple permanently
interconnected chambers relative to containers with a single chamber.
Comments Received
H2MOF supported the approach in GTR No. 13, stating that the
likelihood of both saw cuts and pendulum impacts affecting the same
chamber is extremely low. HATCI supported NHTSA's proposal to harmonize
with the GTR No. 13 surface damage test but recommended also adopting
the GTR No. 13 requirement to apply the pendulum impact to a different
chamber when multiple chambers are present. While acknowledging NHTSA's
concerns, HATCI recommended harmonization with GTR No. 13 Phase 2
specifications.
Auto Innovators supported adopting the GTR No. 13 requirements and
commented that applying impacts to the same chamber does not make the
test more stringent than performing the impacts on separate chambers.
TesTneT stated that pendulum impacts are designed to puncture
protective coatings or resin gel coats but do not affect the structural
integrity of the composite reinforcement. It argued that there is no
reason to deviate from GTR No. 13 since stringency is not an issue.
MEMA members also supported the procedure outlined in GTR No. 13
and did not see the need for modifications. MEMA encouraged NHTSA to
fully align with GTR No. 13 for the pendulum impact portion of the
surface damage test. FORVIA echoed the recommendation to align with GTR
No. 13 Phase 2, stating that different specifications based on chamber
type could introduce confusion in testing. It added that there is no
evidence suggesting changes in the surface cut and pendulum impact
locations would impact safety and recommended following the industry
standard until further research is conducted. FORVIA also commented
that combining surface flaws with pendulum impacts and chemical
exposure in testing is unnecessary since such damage combinations are
highly improbable during service life.
Agency Response
Based on the comments received, in the case of a container with
multiple permanently interconnected chambers, NHTSA will specify the
impacts on the surface of a different chamber. NHTSA is convinced that
applying the impacts to a different chamber is equivalently stringent
to applying the impacts on the opposite side of a single chamber. NHTSA
agrees that the pendulum impacts were not intended to be compounded in
close proximity with the surface cuts as would occur if both types of
damage were applied to a single small chamber of a multi-chamber
container. FMVSS No. 308 S6.2.3.3(b) has been updated to reflect this
change.
d. Chemical Exposure and Ambient Pressure Cycling Test
Background
The chemical exposure test is a test in which container attachments
may improve performance by shielding the container from the chemical
exposures. The proposed rule provided that container attachments will
be included in the chemical exposure test unless they were removed
prior to the surface damage test. NHTSA sought comment on including
container attachments for the chemical exposure test.
Comments Received
Auto Innovators supported harmonizing these requirements with GTR
No. 13, commenting that if attachments can be removed, they should be
removed before testing, but if they cannot be removed, they should be
included in the test. Auto Innovators added that if chemicals can reach
the surface of removable attachments, then the surface should also be
exposed to chemicals. EMA recommended modifying FMVSS No. 308, S6.2.3.4
to state that each of the five areas preconditioned by pendulum impact
should be exposed to a different solution. H2MOF agreed that container
attachments may be present during the chemical exposure test, as they
are present during regular service. TesTneT commented that any
attachments included in a vehicle installation should also be included
in the chemical exposure test, as these attachments might protect the
container surface from road conditions. FORVIA stated that non-
removable container attachments should be allowed in the chemical
exposure test, noting that the test contributed to the introduction of
container attachments in GTR No. 13.
[[Page 6241]]
Agency Response
NHTSA is maintaining the inclusion of container attachments in the
chemical exposure test unless they were removed prior to the surface
damage test, as discussed above. NHTSA is not including 'EMA's proposed
edit specifying that a different solution is applied to each
preconditioned area. There is no need to specify that a different
solution is applied to each area. This language is consistent with GTR
No. 13, which specifies that each of the five areas ``is exposed to one
of five solutions.''
e. High Temperature Static Pressure Test
Background
Consistent with GTR No. 13, the high temperature static pressure
test involves holding the container for 1000 hours at 85 [deg]C and 125
percent NWP.
Comments Received
Auto Innovators stated that it supports NHTSA's proposal to
harmonize these requirements with GTR No. 13.
Agency Response
NHTSA is maintaining the high temperature static pressure test as
proposed.
f. Extreme Temperature Pressure Cycling Test
Background
Consistent with GTR No. 13, the extreme temperature pressure
cycling test involves pressure cycling at extreme temperatures and
simulates operation (fueling and defueling) in extreme temperature
conditions. The test for performance durability uses the same number of
cycles as required by the baseline initial cycle test before leakage.
This is a total of 7,500 cycles for light vehicles or 11,000 cycles for
heavy vehicles. The extreme temperature pressure cycling test consists
of 40 percent of these total cycles, of which half (20 percent of the
total) are conducted at -40 [deg]C and the other half are conducted at
85 [deg]C.
Comments Received
Quantum Fuel Systems, LLC commented on an ambiguity in GTR No. 13
related to the number of cycles required for the extreme cold and hot
tests. It stated that clarification is needed to determine whether the
total number of cycles for the extreme temperature pressure cycling
test should be 22,000 or 11,000. Quantum also proposed edits to Table 6
of GTR No. 13 to address this ambiguity. Auto Innovators expressed
support for NHTSA's proposal to harmonize these requirements with GTR
No. 13.
Agency Response
NHTSA is maintaining the extreme temperature pressure cycling test
as proposed. The proposed requirement clearly specifies that ``the
container is pressure cycled in accordance with S6.2.3.6 for 40 percent
of the number of cycles specified in S5.1.1.2(a)(1) or S5.1.1.2(b)(1)
as applicable.'' FMVSS No. 308 S5.1.1.2(a)(1) and S5.1.1.2(b)(1)
clearly list 7,500 and 11,000 cycles, respectively. The number of
cycles used for the extreme temperature pressure cycling test is not
based on 22,000 cycles.
g. Residual Pressure Test
Background
Consistent with GTR No. 13, the residual pressure test requires
pressurizing the container to 180 percent NWP and holding this pressure
for 4 minutes.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
the residual pressure test requirements with GTR No. 13. Agility
commented that the residual pressure test requirement should remain at
180 percent NWP, regardless of BPO. It added that
manufacturers would still have incentives to limit performance
degradation due to its effects on cost and repeatability.
Agency Response
NHTSA is maintaining the residual pressure test as proposed. The
requirement of 180 percent NWP with a four-minute hold period is
independent of BPO. The residual pressure test does not
address degradation rate. Degradation rate is addressed by the residual
strength burst test, discussed in the next section.
h. Residual Strength Burst Test
Background
Consistent with GTR No. 13, the residual strength burst test
involves subjecting the end-of-life container to a burst test identical
to the baseline initial burst pressure test. The burst pressure at the
end of the durability test is required to be at least 80 percent of the
BPO specified on the container label. This requirement
effectively controls the burst pressure degradation rate throughout an
extreme service life.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
these requirements with GTR No. 13. Luxfer Gas Cylinders commented on
the likelihood of a rapid rate of degradation in end-of-life burst
pressure, stating that there is a ``vanishingly small likelihood that
this would occur.'' It noted that no manufacturer would produce
containers with a BPO double the specified minimum
requirement and questioned what mechanism would cause such degradation,
suggesting that only severe damage could lead to it, in which case the
container would be removed from service.
Agency Response
NHTSA is maintaining the residual strength burst test as proposed.
As the commenter states, it is unlikely that a container would have
such high degradation as to fail to maintain at least 80 percent of
BPO at its end-of-life burst pressure. However, the residual
strength burst test is straightforward to pass for containers that do
not experience severe burst strength degradation in service. Therefore,
including this requirement does not significantly challenge container
design or create an unnecessary burden on manufacturers. Instead, it
simply prevents the possibility of a poor-performing container from
posing a serious risk to safety due to severe burst strength
degradation while in service.
9. Test for Expected On-Road Performance
Background
Consistent with GTR No. 13, NHTSA proposed the test for expected
on-road performance. The proposed test is closely consistent with the
industry standard SAE J2579_201806, ``Standard for Fuel Systems in Fuel
Cell and Other Hydrogen Vehicles.'' \24\
---------------------------------------------------------------------------
\24\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell
and Other Hydrogen Vehicles. https://www.sae.org/standards/content/j2579_201806/.
---------------------------------------------------------------------------
Comments Received
Luxfer Gas Cylinders commented that the proposed test is time-
consuming and expensive to conduct. It stated that for large 800 liter
containers, there is only one test lab that can conduct the test. It
stated that the cost of testing exceeds $500,000. It questioned if
NHTSA proposing to evaluate containers using the proposed test
procedures.
Agency Response
NHTSA is aware of the burden of the proposed test. FMVSS establish
minimum safety requirements and the FMVSS test procedures establish how
the agency would verify compliance. However, manufacturers are not
[[Page 6242]]
required to conduct the exact test in the FMVSS to certify their
vehicles. The Safety Act requires manufacturers to certify that their
vehicles meet all applicable FMVSS, and specifies that manufacturers
may not certify compliance if, in exercising reasonable care, the
manufacturer has reason to know the certificate is false or misleading.
A manufacturer may use different types of tests or even simulations to
certify its vehicles if the manufacturer exercises reasonable care in
doing so. In other words, manufacturers must ensure that their vehicles
will meet the requirements of FMVSS No. 308 when NHTSA tests the
vehicles in accordance with the test procedures specified in the
standard, but manufacturers may use different test procedures and
evaluation methods to do so. Additionally, as hydrogen vehicles become
more common, the number of test labs performing this test will likely
increase, and the costs associated with testing will likely come down
as a result.
a. Proof Pressure Test
Background
Consistent with GTR No. 13, NHTSA proposed a hydrogen-gas proof
pressure test at the start of the test for expected on-road
performance.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
the proof pressure test with GTR No. 13. Agility questioned the purpose
of performing the proof test with hydrogen instead of using a hydraulic
testing method, commenting that the proposed approach seems
unnecessarily high-risk and costly.
Agency Response
For the reasons discussed above for the test for performance
durability, NHTSA is removing proof pressure testing from FMVSS No.
308. Since 100 percent of all containers already undergo the proof
pressure test during manufacture, including this test would be
redundant and unnecessary.
b. Ambient and Extreme Temperature Gas Pressure Cycling Test
Background
NHTSA proposed an ambient and extreme temperature gas pressure
cycling test that is closely consistent with GTR No. 13.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
the ambient and extreme temperature gas pressure cycling test with GTR
No. 13, stating that tests should be conducted with temperature and
pressure control devices in place, or that equivalent measures should
be used to strictly adhere to the parameters. HATCI requested that
NHTSA either harmonize with GTR No. 13 Phase 2 requirements or ensure
strict adherence to proposed pressure and temperature ranges during
testing. HATCI noted that container pressure should not exceed 100
percent state of charge (SOC) and that the minimum pressure should be 2
MPa. Based on internal testing, HATCI commented that temperatures
outside the specified operational range could lead to o-ring failures,
resulting in leakage. It added that during low-temperature pneumatic
tests, internal temperatures can drop below -40 [deg]C, sometimes
reaching -45 [deg]C, which does not reflect real environmental
conditions and is not considered in container design. HATCI also
recommended that NHTSA test CHSS within the manufacturer's design
limits or within a temperature range of -40 [deg]C to 85 [deg]C, with
manufacturers responsible for providing design temperature data upon
NHTSA's request.
Agency Response
NHTSA is maintaining the ambient and extreme temperature gas
pressure cycling test as proposed. The ambient and extreme temperature
gas pressure cycling test does not subject the container to external
temperature conditions below -30 [deg]C. Additionally, the ambient and
extreme temperature gas pressure cycling test does not consider the
internal temperature of the container; only the ambient temperature
surrounding the container is controlled, along with the fuel delivery
temperature and the initial system equilibration temperature. Neither
GTR No. 13 nor by the commenters provide a method for monitoring the
internal temperature of the container during cycling. Instead, the
container must be able to withstand the internal temperatures that
result from the pressure cycling series as specified. As discussed in
the NPRM, the pressurization rates specified in Table 5 to S6.2.4.1(c)
of FMVSS No. 308 are based on real-world refueling rates, and the
temperatures specified during the test are also based on real-world
conditions, so this test for expected on-road performance is
representative of conditions that can occur in-service.\25\ The other
differences noted by HATCI are related to test tolerances, which are
discussed below.
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\25\ See 89 FR 27520 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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c. Extreme Temperature Static Gas Pressure Leak/Permeation Test
Background
NHTSA proposed the extreme temperature static gas pressure leak/
permeation test consistent with GTR No. 13, except for the removal of
the localize leak requirement in the proposed standard. The localized
leak limit was removed because it is not objectively enforceable due to
the subjective estimation of bubble sizes. NHTSA sought comment on not
including the localize leak requirement during the extreme temperature
static gas pressure leak/permeation test and specifically requested
that if commenters believed it should be included, that they explain
(1) how they believe it could be made more objective and (2) how
specifically it would add to the standard's ability to meet the safety
need.
Comments Received
Commenters provided diverse feedback on the proposed removal of the
localized leak requirement from the extreme temperature static gas
pressure leak/permeation test.
Nikola suggested that while the bubble requirement could be
removed, the single-point leak rate should not be eliminated, and a
mass spectrometer could be used by testing facilities instead. It also
noted that numerous hydrogen performance test facilities that can
evaluate localized leaks.
Luxfer Gas Cylinders stated that permeation rate measurements are
well-established, typically involving the CHSS in an airtight container
with surrounding gas content measured accurately. Luxfer supported the
decision to remove the localized leak requirement.
Auto Innovators agreed with the decision not to include the
localized leak test. Similarly, DTNA commented that the localized leak
test was unnecessary because the full system permeation test evaluates
the overall system. However, if a localized leak test were necessary,
DTNA suggested replacing the bubble test with a concentration-based
hydrogen leak limit of 0.5 percent, derived from standards applied to
CNG and propane vehicles.
TesTneT described its method of using a gas chromatograph or mass
spectrometer in an enclosed, temperature-controlled chamber for
accurate permeation measurement. It also use a mass spectrometer to
quantify leakage after locating potential leak sites
[[Page 6243]]
with a soapy solution. TesTneT raised concerns about hydrogen
permeation risks in enclosed spaces, pointing out that hydrogen can
leak out over time, making it difficult to accumulate in dangerous
amounts.
Newhouse commented that NHTSA's proposed permeation rate of 46 mL/
L/h at 55 [deg]C is unreasonably low and noted several issues, such as
considering worst-case scenarios and ventilation assumptions. Newhouse
suggested allowing a higher limit of 100 percent of the lower
flammability limit (LFL), or 4 percent hydrogen in air, and questioned
the use of 55 [deg]C as a peak temperature, stating that a lower
average would be more representative. Newhouse also recommended
increasing the allowable permeation rate to 184 mL/L/h at 55 [deg]C and
noted that the probability of failure remains low, even with more
conventional ventilation rates in garage spaces.
FORVIA acknowledged that different methods can accurately measure
leakage and permeation and suggested that guidance on measurement could
be provided outside the FMVSS text. It was open to considering
localized leak requirements but noted that the submersion method,
though simple, may require more accurate measurements near the limits.
It indicated that omitting this test for field surveillance would be
acceptable, as production containers typically exhibit far less
leakage. H2MOF proposed exempting all-metal containers from the static
gas leak/permeation test and suggested that procedures from industry
standards be used for guidance.
Agency Response
NHTSA is maintaining the extreme temperature static gas pressure
leak/permeation test as proposed, without the localized leak limit. The
commenters did not provide any explanation for the safety need of the
localized leak limit. Commenters did not provide any evidence that
omitting the localized leakage requirement is less stringent when there
is also an overall permeation limit applied to the CHSS as a whole.
Furthermore, commenters did not provide sufficient explanation of
how, if included, the localized leakage limit could be made more
objective. Some commenters suggested using analytical chemistry
equipment such as mass spectrometers. However, these types of
instruments are highly complex, and additional research would be needed
by NHTSA before they could be used to objectively quantify a leak. Even
if the agency determined that mass spectrometers were viable for
detecting localized leaks, the agency would still need to consider the
safety need being addressed by the requirement.
NHTSA is not changing the overall permeation rate of 46 mL/L/h
based on the comments. This permeation limit is found in GTR No. 13 and
is widely accepted by the industry as an appropriate permeation limit.
Well-developed rationale for this limit is provided in GTR No. 13 and
in the NPRM.\26\ In particular, the conservative 25 percent LFL limit
accounts for concentration non-homogeneities that may be present, and
the choice of 55 [deg]C is a worst-case temperature condition, not one
that is expected to occur commonly. Permeation is higher at higher
temperatures, so NHTSA considered this worst-case condition when
evaluating the permeation limit. This permeation limit is also applied
in the industry standard SAE J2579_201806. The commenters did not
establish sufficient rationale for NHTSA to deviate from the
established 46 mL/L/h.
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\26\ See 89 FR 27522 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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NHTSA is not exempting CHSS with all-metal containers from the
extreme temperature static gas pressure leak/permeation test. All-metal
containers must demonstrate the same level of performance and safety as
other containers. NHTSA is not replacing the proposed test with either
of the standards recommended by H2MOF. The commenter did not establish
any justification for why doing so would improve safety, nor did it
provide any detailed information regarding the alternative standards.
d. Residual Pressure Test & Residual Strength Burst Test
Background
The residual pressure test and residual strength burst test are
conducted in the same manner and for the same reasons discussed above
for the test for performance durability.
Comments Received
Auto Innovators stated support for NHTSA's proposal to harmonize
these requirements with GTR No. 13.
Agency Response
NHTSA is maintaining the residual pressure test and residual
strength burst test as proposed.
10. Test for Service Terminating Performance in Fire
Background
NHTSA proposed a fire test based closely on the GTR No. 13 Phase 2
fire test. The updates to the fire test by the IWG of GTR No. 13 Phase
2 focused on improving the repeatability and reproducibility across
test laboratories. Two significant improvements to the fire test are
(1) the use of a pre-test checkout procedure and (2) basic burner
specifications. The pre-test checkout requires conducting a preliminary
fire exposure on a standardized steel container to verify that
specified fire temperatures can be achieved for the localized and
engulfing fire segments of the test prior to conducting the fire test
on a CHSS. During this pre-test checkout, the fuel flow is adjusted to
achieve fire temperatures within the specified limits as measured on
the surface of the pre-test steel container. The use of a pre-test
steel container instead of an actual CHSS improves the accuracy and
repeatability of the test because it avoids possible container material
degradation that could affect the temperature measurements.
Comments Received
Luxfer Gas Cylinders commented that the recent changes introduced
in GTR No. 13 regarding the fire test are ``excessive'' and do not
enhance test performance. Luxfer stated that the pre-test using a steel
container is only relevant when the steel container matches the size of
the composite container being tested. For larger containers, such as
those used in heavy vehicles, Luxfer stated that the pre-test becomes
unnecessary. Luxfer and H2MOF both suggested that NHTSA consider
adopting the Bonfire test from NGV 2 2019, ``Compressed natural gas
vehicle fuel containers.'' \27\ Additionally, Luxfer expressed concerns
about the increased costs of the new GTR No. 13 fire test. It
questioned whether NHTSA intends to apply this test to containers that
have been withdrawn from service.
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\27\ See https://webstore.ansi.org/standards/csa/csaansingv2019.
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Agility commented that the fire source and pre-test procedures in
GTR No. 13 do not accurately represent vehicle fire scenarios,
particularly for heavy applications. It highlighted that the fire
source width is set at 500 mm regardless of the container's diameter
and that the temperature requirements focus solely on the area beneath
and directly on the container surface. Agility further pointed out the
lack of
[[Page 6244]]
requirements for measuring temperatures around the container, which is
where remotely mounted PRDs are typically located.
Agency Response
NHTSA acknowledges the comments regarding the proposed fire test
based on GTR No. 13 Phase 2 but does not find them persuasive enough to
warrant any significant changes to the proposed test procedures.
Specifically, the concern that the pre-test checkout using a steel
cylinder is only relevant if it matches the size of the composite
container is not valid. The pre-test checkout procedure is designed to
ensure the consistency of fire temperature measurements, which can be
achieved regardless of the difference in size between the pre-test
container and the actual CHSS. The objective of the pre-test checkout
is to verify the fire conditions produce the specified temperatures,
which improves the accuracy and repeatability of the test across
different laboratories.
Regarding the commenters' suggestions to adopt the fire test in NGV
2 2019, NHTSA is aware of ANSI NGV 2 2019, but the GTR No. 13 fire test
remains more representative of real-world conditions. The proposed fire
test procedure based on GTR No. 13 includes both localized and
engulfing fire stages, which are designed based on actual vehicle fire
data, as discussed in the NPRM.\28\ The proposed fire test procedure is
the most realistic fire test available that is representative of a
range of possible real-world vehicle fires. The NGV 2 fire test does
not provide the same level of comprehensiveness as the standard. The
NGV 2 fire test does not include any pre-test procedures to improve
repeatability and reproducibility, nor does it include a localized fire
exposure. The fire test procedure, on the other hand, provides a
rigorous, repeatable test that accounts for both localized and
engulfing fire conditions, addressing various fire exposure scenarios.
Due to the large volumes of hydrogen stored on hydrogen fueled
vehicles, NHTSA maintains that the proposed fire test procedure is
needed to ensure vehicles are designed with a high level of performance
in fire conditions. NHTSA further notes that the pre-test checkout
includes temperature specifications for the bottom, sides, and top of
the pre-test container.
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\28\ See 89 FR 27523 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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Regarding the concern about increased costs, vehicle manufacturers
are already designing their vehicles to meet or exceed the requirements
of the proposed fire test based on GTR No. 13, so NHTSA does not expect
significant increased costs from implementing the proposed fire test.
Regarding applying the requirements to containers that have been
withdrawn from service, NHTSA purchases new vehicles at the point of
sale for compliance testing. NHTSA does not conduct compliance testing
on used vehicles or equipment.
a. Burner Specification
Background
To further improve test reproducibility, a burner configuration is
defined with localized and engulfing fire zones. These specifications
allow the fire test to be performed without a burner development
program. NHTSA explained in the NPRM that it believes that the use of a
standardized burner configuration is a practical way of conducting fire
testing and should reduce variability in test results through
commonality in hardware.\29\ Flexibility is provided to adjust the
length of the engulfing fire zone to match the CHSS length, up to a
maximum of 1.65 m. The width of the burner, however, is fixed at 500 mm
for all fire tests, regardless of the width or diameter of the CHSS
container to be tested, so that each CHSS is evaluated with the same
fire condition regardless of size. The length of the localized fire
zone is also fixed to 250 mm for all fire tests. NHTSA sought comment
on a specification for the burner rail tubing shape and size, which can
affect the spacing between the nozzle tips.
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\29\ See 89 FR 27527 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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Comments Received
MEMA expressed concerns that the burner specifications in FMVSS No.
308 S6.2.5.3 are more rigid than those in GTR No. 13, which specifies a
larger burner assembly, allowing for the testing of larger hydrogen
storage containers. MEMA suggested that the proposed limitations could
create challenges for testing and qualifying hydrogen pressure vessels
for the U.S. market, requesting that NHTSA to align more closely with
GTR No. 13. MEMA also recommended revising the language in FMVSS No.
308 S6.2.5.2(c)(2) regarding nozzle orientation to avoid potential
confusion and align with GTR No. 13, which targets the lowest elevation
of the CHSS.
Auto Innovators recommended harmonizing with GTR No. 13, stating
that industry standards already establish 1.65 meters as the length of
the engulfing fire zone. Auto Innovators recommended maintaining the
basic burner design from GTR No. 13. TesTneT commented that rails
measuring 50 mm square, spaced at 100 mm, provide optimal nozzle tip
spacing. It stated that the square rail is crucial for proper burner
tip installation, and any deviation in rail size could reduce burner
temperatures.
FORVIA emphasized the importance of maintaining equivalence with
GTR No. 13, urging NHTSA to keep the burner configuration consistent
with phase 2 of GTR No. 13. It cautioned that any changes to the burner
specification could lead to ``serious dis-harmonization'' and result in
the need for double testing for products sold across different regions.
Agency Response
In both GTR No. 13 and the proposed FMVSS No. 308, the burner width
is between 450 millimeters and 550 millimeters in width. The additional
length mentioned by TesTneT of 100 mm is intended to be a tolerance.
Tolerances are discussed below. However, to ensure the maximum possible
burner size consistent with GTR No. 13, FMVSS No. 308 S6.2.5.2(b) has
been updated to allow the engulfing burner to extend up to a maximum of
1.75 meters.
NHTSA has determined there is no need to specify square burner
rails. While this shape may be the most convenient shape for the burner
rails, and test labs may prefer square rails, it may be possible to
construct a burner using non-square rails. If such a burner were to
meet all burner specifications and satisfy the prescribed temperature
requirements, it would be considered an acceptable burner. Sufficient
burner specifications, as well as the pre-test checkout procedure
ensure the repeatability and reproducibility of the burner.
GTR No. 13 specifies that ``[t]he pre-test cylinder used for the
pre-test checkout shall be mounted at a height of 100 5 mm
above the burner and located over the burner such that nozzles from the
two centrally-located manifolds are pointing toward the bottom centre''
of the pre-test container. NHTSA similarly proposed mounting the pre-
test container ``such that the nozzles from the two center rails are
pointing toward the bottom center of the pre-test container.'' NHTSA is
[[Page 6245]]
maintaining this language in the final rule. This specification is
sufficiently objective to ensure repeatability and reproducibility of
the test. Furthermore, a specification regarding ``elevation'' may be
ambiguous, and has not been included. For the CHSS fire test, the CHSS
will be positioned for the localized fire test by orienting the CHSS
such that the distance from the center of the localized fire exposure
to the TPRD(s) and TPRD sense point(s) is at or near maximum. NHTSA is
maintaining this orientation in the final rule.
b. Additional Pre-Test Procedurs for Irregularly Shaped Containers
Background
GTR No. 13 specifies additional pre-test checkout procedures
intended for irregularly shaped CHSS which are expected to impede air
flow through the burner. These procedures involve constructing a pre-
test plate having similar dimensions to the CHSS to be tested. A second
pre-test check out is conducted using the pre-test plate and using the
burner monitor thermocouples. If the burner monitor thermocouple
temperatures do not satisfy the specified minimum temperatures, then
the pre-test plate is raised by 50 mm, and a third pre-test checkout is
conducted. GTR No. 13 specifies that this process is repeated until
burner monitor thermocouple temperatures satisfy the required minimum
temperatures. NHTSA considered this additional pre-test process and
determined that it is unnecessary. The goal of the pre-test checkout is
a repeatable and reproducible fire exposure among different testing
facilities. NHTSA has determined there is no need for design-specific
modification to the fire test procedure. Furthermore, the additional
pre-test procedures add considerable complexity to the test procedure,
and as a result could undermine the repeatability and reproducibility
of the fire test. Therefore, NHTSA did not propose these additional
pre-test procedures. NHTSA sought comment on this decision.
Comments Received
Auto Innovators generally agreed with NHTSA's decision to
streamline pre-test procedures but suggested that clarification is
needed to ensure that a repeat test is only required if the pre-test
does not meet the specified requirements. It emphasized that incorrect
pre-test temperatures could result in over or under testing of the
CHSS, potentially leading to a false pass or failure.
FORVIA disagreed with NHTSA's decision, advocating for the
retention of the existing pre-test procedures for irregularly shaped
CHSS as specified in GTR No. 13. It stated that consistency across
global markets is crucial to minimize discrepancies and ensure
manufacturers follow uniform guidelines. FORVIA acknowledged that the
additional pre-test procedures might add time but noted that they would
likely reduce the need for retesting and avoid introducing variables
that could compromise repeatability. It emphasized that GTR No. 13
procedures had been validated through significant work, including round
robin testing, and stated that deviating from these standards could
undermine the enforceability of failed tests.
HATCI also stated that the additional pre-test procedures for
irregularly shaped CHSS are necessary, stating that a lack of uniform
temperature distribution could negatively affect TRPD activation. It
stressed the importance of ensuring proper testing for all CHSS designs
and suggested that the repeatability and reproducibility of the test
could be reassessed as more irregular containers are introduced.
TesTneT, on the other hand, agreed with NHTSA's decision, stating that
additional pre-test procedures are unnecessary.
Agency Response
NHTSA is not including additional pretest procedures for
irregularly shaped containers. NHTSA conducted fire testing of large,
irregularly shaped CHSS according to the proposed test procedure. The
test was highly successful, with the CHSS TPRD activating within one
minute of the ignition of the localize burner. The results of this
testing are summarized in the test report ``GTR No. 13 Fire and
Closures Tests.'' \30\ These results indicate that additional design-
specific procedures are not required and irregularly shaped CHSS can
successfully complete the test for service terminating performance in
fire. The use of the pre-test container is simply to verify the burner
and is not intended to precisely match the size of the CHSS.
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\30\ See the report titled ``GTR No. 13 Fire and Closures
Tests'' which can be found at: https://downloads.regulations.gov/NHTSA-2024-0006-0002/attachment_4.pdf. This report will also be
submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.
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c. Pre-Test Container Length Compared to CHSS
Background
NHTSA conducted CHSS fire testing to verify the feasibility of the
test for service termination performance in fire as proposed. In some
cases during testing, temperatures measured at the burner monitor
thermocouples did not satisfy the required minimum value for the burner
monitor temperature during the engulfing fire stage
(TminENG).\31\ NHTSA's testing indicated that the airflow
during the pre-test may be different from that of the CHSS if the pre-
test container length is substantially different from that of the CHSS
to be tested. The difference in air flow between the two tests could
cause differences in fire input to the CHSS compared to the pre-test
container. Therefore, NHTSA recommended that for CHSS of length between
600 mm and 1650 mm, the difference in the length of the pre-test
container and the CHSS be no more than 200 mm. NHTSA sought comment on
whether this recommendation should be a specification for the pre-test
container.
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\31\ TminENG is calculated by subtracting 50 [deg]C
from the minimum of the 60-second rolling average of the average
burner monitor temperature in the engulfing fire zone of the pre-
test checkout.
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Comments Received
Several commenters disagreed with NHTSA's recommendation to specify
a length difference between the pre-test container and the CHSS being
tested. Nikola stated disagreement with the proposal, explaining that
the pre-test is conducted according to GTR No. 13 and that additional
specifications on length differences are unnecessary. TesTneT also
commented that the pre-test container should align with GTR No. 13 and
argued that since the burner system is uniform, there is no need to
correlate the pre-test container's length with that of the CHSS.
TesTneT added that observations regarding the influence of CHSS length
on pre-test results were incorrect. Auto Innovators similarly
disagreed, stating that the pre-test container's role is to verify the
burner and is not directly related to the CHSS size.
FORVIA expressed opposition as well, recommending that NHTSA keep
the test procedure equivalent to GTR No. 13. It emphasized that adding
length specifications would increase both time and costs for pre-
testing, while the existing GTR No. 13 requirements are sufficient to
ensure reproducible conditions. FORVIA noted that the GTR No. 13 fire
test procedure had been validated through extensive testing and
[[Page 6246]]
provided significant improvements over previous testing methods for CNG
and hydrogen containers.
Agency Response
NHTSA is not including any requirements regarding the difference in
length for the pre-test container and the CHSS. The recommendation that
for CHSS of length between 600 mm and 1650 mm, the difference in the
length of the pre-test container and the CHSS be no more than 200 mm,
will remain a recommendation for future test labs. Following this
recommendation will not be required as part of the testing, and not
adhering to the recommendation will not invalidate test results.
d. Pretest Checkout Frequency
Background
The pre-test checkout is performed at least once before the
commissioning of a new test site. Additionally, if the burner and test
setup is modified to accommodate a test of different CHSS
configurations than originally defined or serviced, then repeat of the
pre-test checkout is needed prior to performing CHSS fire tests. NHTSA
sought comment on the frequency of conducting this pre-test checkout
for ensuring repeatability of the fire test on CHSS.
Comments Received
Several commenters responded to NHTSA's inquiry about the frequency
of the pre-test checkout for CHSS fire testing, with most agreeing that
additional requirements were unnecessary if no modifications were made
to the burner or test setup.
Auto Innovators agreed that a repeat of the pre-test checkout is
necessary if the burner or test setup is modified but recommended that
the pre-test be performed at the manufacturer's discretion if no
modifications have occurred. HATCI similarly commented that the pre-
test checkout should be performed at the manufacturer's discretion.
Nikola stated that the frequency of the pre-test should be determined
by the testing agency, in accordance with ISO 17025, ``General
requirements for the competence of testing and calibration
laboratories,'' accreditation requirements.
TesTneT referred to GTR No. 13, noting that the pre-test only needs
to be conducted once to verify the burner setup, unless modifications
are made. It emphasized that multiple pre-tests are unnecessary if the
test stand remains unchanged between tests. FORVIA disagreed with
adding additional requirements, requesting harmonization with GTR No.
13 and stating that the pre-test checkout before commissioning and
following modifications is sufficient. It suggested that any additional
pre-test checkouts should be at the discretion of the test site
operator, but recommended not adding further requirements to FMVSS.
Agency Response
NHTSA reiterates that the pre-test checkout will be performed at
least once before the commissioning of a new test site and when the
burner or test setup is modified to accommodate different CHSS
configurations. NHTSA believes this approach ensures the consistency
and reliability of testing procedures. No changes are being made to the
proposed requirements based on the comments.
e. Thermocouple Positioning
Background
NHTSA proposed positioning the three burner monitor thermocouples
25 mm below the pre-test container. Since these thermocouples are
intended to monitor the burner, an alternative would be to position
these thermocouples relative to the burner itself. NHTSA sought comment
on whether it is preferable to position the burner monitor
thermocouples relative to the pre-test container or relative to the
burner.
Comments Received
Commenters generally supported harmonizing the positioning of the
burner monitor thermocouples with GTR No. 13 and opposed NHTSA's
proposal to position the thermocouples relative to the burner.
HATCI commented that environmental factors, such as wind and
temperature, could influence test results, recommending alignment with
GTR No. 13, where thermocouples are positioned relative to the pre-test
container. Auto Innovators also recommended positioning the
thermocouples relative to the pre-test container to ensure that
temperatures measured on the container are representative, and for
aiding harmonization with GTR No. 13. It further referenced discussions
during GTR No. 13 Phase 2, highlighting concerns about potential
thermocouple failure due to material expansion from the test article
and noted that GTR No. 13 offers solutions, including backup
thermocouples.
Nikola stated that the purpose of the test is to measure the heat
flux to the container and emphasized the importance of adhering to GTR
No. 13, as the industry standard is to measure heat from the container
being tested. TesTneT added that the thermocouples are positioned
relative to both the pre-test container and the burner, placed 25 mm
below the container and 75 mm above the burner tips, and stated there
is no preferable alternative position. DTNA stated that the distance of
the CHSS to the burner is the key factor that drives the
characterization of the test. DTNA stated that it supports the effort
in the NPRM to establish repeatable and objective test scenarios.
FORVIA disagreed with introducing alternative measurements and stressed
the importance of maintaining equivalency with GTR No. 13 to avoid
unnecessary confusion. It suggested that any clearer requirements
should be introduced in GTR No. 13 Phase 3.
Agency Response
NHTSA will maintain the burner monitor thermocouples 25 mm below
the pre-test container, as specified in GTR No. 13. NHTSA acknowledges
TesTneT's 'point that, due to the prescribed height of the pre-test
container above the burner, specifying a point's distance below the
pre-test container also specifies that point's distance above the
burner.
f. Temperature Variation Greater Than 50 [deg]C and the Associated
Calculations
Background
The minimum value for the burner monitor temperature during the
localized fire stage (TminLOC) is calculated by subtracting
50 [deg]C from the minimum of the 60-second rolling average of the
burner monitor temperature in the localized fire zone of the pre-test
checkout. The minimum value for the burner monitor temperature during
the engulfing fire stage (TminENG) is calculated by
subtracting 50 [deg]C from the minimum of the 60-second rolling average
of the average burner monitor temperature in the engulfing fire zone of
the pre-test checkout.
NHTSA sought comment on the possibility of allowing for a wider
variation than 50 [deg]C below the pre-test temperatures. Furthermore,
as currently specified, the minimum temperatures TminLOC and
TminENG would be time-dependent variables because they are
based on a time-dependent rolling average. Having TminLOC
and TminENG being time-dependent is complex and would make
the testing difficult to monitor. NHTSA sought comment on a simpler
calculation for TminLOC and TminENG that will
result in constant values for TminLOC and
TminENG. NHTSA proposed that TminLOC be
calculated by subtracting 50 [deg]C from the minimum value of the 60-
second rolling average of
[[Page 6247]]
the burner monitor temperature in the localized fire zone of the pre-
test checkout. Similarly, NHTSA proposed that TminENG be
calculated by subtracting 50 [deg]C from minimum value of the 60-second
rolling average of the average of the three burner monitor temperatures
during the engulfing fire stage of the pre-test checkout. NHTSA sought
comment on whether these revised calculations for TminLOC
and TminENG should be required.
Comments Received
Most commenters opposed NHTSA's proposal to allow a wider
temperature variation or change the calculation method for
TminLOC and TminENG, instead requesting
harmonization with GTR No. 13.
HATCI and Auto Innovators both recommended maintaining the 50
[deg]C variation requirement from GTR No. 13, stating that wider
temperature variations could affect test results and impact CHSS
design. Auto Innovators also requested that NHTSA align with GTR No. 13
in terms of calculations for TminLOC and TminENG,
particularly with respect to their time-dependent nature.
TesTneT commented that the requirements in GTR No. 13 are clear. It
stated that there is no need to modify the calculations or allow for
wider temperature variations. It further stated that the revised
calculations proposed by NHTSA are unnecessary, referencing section
6.2.5.4.5.4 of GTR No. 13, which establishes the minimum values for
TminLOC and TminENG.
FORVIA also disagreed with the proposed changes, urging NHTSA to
maintain the test procedure equivalent to GTR No. 13 for simplicity. It
suggested discussing any potential simplifications during the
development of GTR No. 13 Phase 3 rather than changing the existing
method.
Agency Response
NHTSA will maintain calculations for TminLOC and
TminENG that are aligned with those specified in GTR No. 13,
and as proposed in FMVSS No. 308 S6.2.5.3(h). NHTSA will not adopt
wider temperature variations or simplified calculations for
TminLOC and TminENG relative to GTR No. 13. The
calculation method in the final rule specifies a 50 [deg]C variation
from the 60-second rolling average of the burner monitor
thermocouple(s) during the respective stage of the pre-test checkout.
NHTSA notes that this method results in time-dependency of
TminLOC and TminENG. Test labs should plot
TminLOC and TminENG over time to observe the
time-dependency of these variables.
g. Vehicle-Specific Shielding
Background
The test for service terminating performance in fire evaluates the
CHSS. It is possible that vehicle manufacturers may add additional fire
protection features as part of overall vehicle design, and GTR No. 13
includes the option of conducting CHSS fire testing with vehicle
shields, panels, wraps, structural elements, and other features as
specified by the manufacturer. However, adding vehicle-level protection
features is not practical for testing. Furthermore, NHTSA explained in
the NPRM that it believes that it is important for safety that the CHSS
itself can withstand fire and safely vent in the event its shielding is
compromised.\32\ For example, if a crash damages the shielding, and the
shielding was an integral part of the CHSS's ability to withstand fire,
then the CHSS should be able to vent properly before it explodes. As a
result, vehicle-level protection measures are not evaluated by the test
for service terminating performance in fire. However, if a CHSS
includes container attachments, these attachments are included in the
fire test. NHTSA sought comment on excluding vehicle-specific shielding
and on including container attachments as part of the fire test,
particularly in the case of container attachments which can be removed
using a process specified by the manufacturer.
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\32\ See 89 FR 27524 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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Comments Received
Agility commented that there is insufficient justification to
deviate from GTR No. 13 in this area, stating that damaged vehicle
shielding could compromise PRDs as well. It stated that vehicle-level
protection is appropriate for addressing localized fire risks and
stated that vehicle-specific shielding should not be excluded as it is
part of the container's fire protection. TesTneT stated concerns that a
crash could also compromise a CHSS's ability to vent properly in a
fire, suggesting that the test's length, duration, and intensity are
somewhat arbitrary. It stated that surviving the test without
attachments does not necessarily guarantee survival in a real-world
vehicle fire, which could vary significantly.
MEMA commented that NHTSA already acknowledges the importance of
protective attachments in other tests, such as surface damage and
chemical corrosion tests. MEMA requested that NHTSA allow vehicle-
specific shields where applicable.
FORVIA strongly opposed excluding vehicle-specific shielding and
container attachments from CHSS fire testing. It stated that including
shields in the test provides a more accurate representation of real-
world vehicle fire scenarios. FORVIA stated that if shields are
excluded, manufacturers may resort to more complex and costly
protection methods, reducing the practicality of these systems. It
requested that shields remain part of fire testing to fully assess all
safety features. FORVIA requested that shields be specified by
manufacturers, and also stated that it is important to include
container attachments in the fire test. Nikola stated support for the
provisions in GTR No. 13 and stated that allowing container attachments
in the test is appropriate and both options should be permitted.
Agency Response
NHTSA has considered the comments submitted regarding the inclusion
of vehicle-specific shielding and container attachments in the test for
service terminating performance in fire. While several commenters
advocated for allowing vehicle-specific shielding to be part of the
fire test, NHTSA maintains its position to exclude vehicle-specific
shielding from the CHSS fire test.
It is important that the CHSS itself can withstand fire exposure
and properly vent in the event of a failure, regardless of any
additional vehicle-level protection. This approach is based on the
possibility that vehicle shielding or other protective elements could
be compromised in real-world scenarios, such as during a crash. If the
vehicle shielding is damaged or removed, the CHSS must still be able to
perform its critical safety function without relying on external
protection. Including vehicle-specific shielding in the test would not
adequately evaluate the inherent fire resistance and safety performance
of the CHSS.
In addition, vehicle-specific shielding introduces unnecessary
complexity into the testing process which could affect repeatability
and reproducibility of the results. Testing that focuses on the CHSS
itself provides a consistent, uniform assessment that is critical to
safety.
Some commenters expressed concerns that the exclusion of vehicle-
level protection measures may not fully represent real-world fire
scenarios. NHTSA recognizes these concerns but emphasizes that the
primary goal of the fire test is to ensure the resilience of the CHSS
as an independent system. In the
[[Page 6248]]
event of a crash or severe incident that compromises the vehicle's
shielding, it is essential that the CHSS be capable of withstanding
fire exposure and safely venting without the added protection of
vehicle-level components.
Furthermore, the proposed fire test procedure, based on GTR No. 13,
is specifically designed to replicate realistic fire scenarios that
vehicles may encounter. As detailed in the NPRM, the test includes both
localized and engulfing fire stages, which reflect actual vehicle fire
data.\33\ This data-driven approach ensures that the test conditions
are neither arbitrary nor excessive, but instead provide a realistic
assessment of the CHSS's performance during a fire.
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\33\ See 89 FR 27523 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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Regarding container attachments, NHTSA clarifies that if the CHSS
includes container attachments, they may be part of the fire test.
Container attachments, as defined, are considered part of the CHSS
itself.
h. Worst-Case Orientation
Background
GTR No. 13 specifies that the CHSS is rotated relative to the
localized burner to minimize the ability for TPRDs to sense the fire
and respond. GTR No. 13 specifies establishing a worst-case based on
the specific CHSS design. However, NHTSA is concerned that establishing
a worst-case based on a specific design is subjective. NHTSA instead
proposed that the CHSS be positioned for the localized fire by
orienting the CHSS relative to the localized burner such that the
distance from the center of the localized fire exposure to the TPRD(s)
and TPRD sense point(s) is at or near maximum. This positioning
provides a challenging condition where the TPRD(s) may not sense the
localized fire. NHTSA sought comment on the proposed orientation of the
CHSS relative to the localized burner.
Comments Received
TesTneT referenced section 6.2.5.5.2 of GTR No. 13, stating that it
already provides clear instructions on how to identify a worst-case
condition. It commented that while NHTSA proposed some challenging
orientations, these may not necessarily represent the worst-case
scenario, and there is no need to deviate from the guidance in GTR No.
13. On the other hand, Nikola agreed with NHTSA's proposed orientation
of the CHSS relative to the burner.
Auto Innovators agreed with NHTSA on the need to address the
subjectivity in defining a ``worst-case'' orientation but stated that
this issue is already addressed in GTR No. 13, which offers clear
instructions for identifying such conditions. It stated that while
NHTSA's proposal may represent a challenging condition, it may not
always be considered the worst-case scenario.
Agency Response
NHTSA is maintaining the CHSS positioning specifications as
proposed. NHTSA believes that its test procedure aligns well with the
requirements of GTR No. 13 and will provide the level of safety
intended by GTR No. 13's ``worst-case'' orientation. Further, NHTSA
believes that the final standard will simplify determining the
orientation for compliance testing.
NHTSA disagrees with the commenters that GTR No. 13 provides clear
instruction on how a worst-case condition is identified. GTR No. 13
paragraph 6.2.5.5.2 states ``the CHSS test article shall be rotated
relative to the localized burner to minimize the ability to [sic] TPRDs
to sense the fire and respond. Shields, panels, wraps, structural
elements and other features added to the container shall be considered
when establishing the worst-case orientation relative to the localized
fire as parts and features intended to protect sections of the
container but can (inadvertently) leave other potions or joints/seams
vulnerable to attack and/or hinder the ability of TPRDs to respond. For
CHSS where the manufacturer has opted to include vehicle-specific
features (as defined in paragraph 6.2.5.1.), the CHSS test article is
oriented relative to the localized burner to provide the worst-case
fire exposure identified for the specific vehicle.'' This specification
requires the subjective judgement of the test lab and is therefore not
objectively enforceable.
i. Jet Flame Measurement
Background
Jet flames occurring anywhere other than a TPRD outlet, such as the
container walls or joints, cannot exceed 0.5 meters in length. NHTSA
sought comment on how to accurately measure jet flames.
Comments Received
Nikola stated that because most jet fires exceed 0.5 meters, the
presence of jet fire would result in a flame exceeding the length limit
and be a clear test failure. However, it suggested that, if needed, the
test facility can measure the jet flame length using video capture.
Auto Innovators recommended using camera systems or similar imaging
devices, such as infrared, to identify the length of jet flames.
TesTneT commented that fire tests at its facility are monitored using
several video cameras, and the flame length can be measured by
comparing it to the known diameter of the container as seen in the
videos. FORVIA also stated that jet flames are visible in practice, and
the length can be measured by placing an object with a known length
near the TPRD outlet and comparing the jet flame length to this object
in video or pictures taken during the test.
Agency Response
NHTSA will maintain the jet flame requirement as proposed. Jet
flames occurring anywhere other than a TPRD outlet, such as the
container walls or joints, may not exceed 0.5 meters in length. This
0.5 meter limit aligns with GTR 13, as requested by many commenters,
and seeks to minimize the safety risk because this is both the
threshold at which a jet flame is clearly distinguishable from other
flames present during testing and the point where the risk of spread to
the surroundings increases significantly.
NHTSA appreciates the comments regarding the measurement of jet
flames using video capture, reference objects of known length, and
thermal imaging technologies to accurately measure jet flame length
during testing. NHTSA agrees that these methods offer practical ways to
assess flame length in a manner that is consistent with real-time
observations during testing.
At this time, however, NHTSA will not prescribe a specific
measurement methodology in the regulatory text. Instead, the method of
measurement will be left to the discretion of the testing facility.
Test laboratories are encouraged to use suitable techniques for
ensuring compliance with the 0.5-meter jet flame requirement.
j. Heat Release Rate (HRR/A)
Background
In addition to temperature requirements, GTR No. 13 also specifies
required heat release rates per unit area (HRR/A) during the localized
and engulfing fire stages. NHTSA considered the specification for HRR/A
and determined that it could result in over-specification of the test
parameters, potentially making it very difficult to conduct the test.
In addition, NHTSA believes that the detailed temperature
specifications for the pre-test container during the pre-test checkout
are
[[Page 6249]]
sufficient to ensure repeatability and reproducibility of the test.
Therefore, NHTSA did not propose specifications for HRR/A. NHTSA sought
comment on that decision.
Comments Received
Auto Innovators disagreed with NHTSA's decision, recommending that
HRR/A specifications be maintained to ensure test repeatability and
reproducibility. It pointed out that the HRR/A specifications in GTR
No. 13 were introduced to address inconsistencies observed in round-
robin testing between labs. It argued that without HRR/A
specifications, the amount of heat energy delivered during testing
could vary, potentially leading to inconsistent test results. HATCI
also disagreed, stating that the absence of HRR/A specifications could
cause variability in the energy delivered during testing, affecting the
outcome. It recommended that NHTSA adopt the HRR/A specifications in
GTR No. 13 to avoid this issue.
Nikola supported maintaining the GTR No. 13 specification for HRR/
A, noting that the test has already been validated and used by several
test labs globally. TesTneT also disagreed with NHTSA's decision,
stating that HRR/A is important to the fire test because temperature
measurements alone cannot always be relied upon. It explained that
during testing, events like hydrogen venting or coatings dripping onto
thermocouples can disturb temperature readings, and HRR/A provides a
way to ensure that fire conditions remain consistent despite such
disturbances. In contrast, H2MOF agreed with NHTSA's approach not to
specify HRR/A.
Agency Response
NHTSA is not including specifications for HRR/A. Such a
specification could result in over-specification of the test
parameters, potentially making it very difficult to conduct the test.
In addition, NHTSA believes that the detailed temperature
specifications for the pre-test container during the pre-test checkout
are sufficient to ensure repeatability and reproducibility of the test.
Failure to satisfy a temperature specification will result in an
invalid test. Simply adding an additional specification related to HRR/
A will not resolve a failure to meet the temperature specifications. If
the specified temperatures are not met, the test will be invalid
regardless of whether an HRR/A specification is present and satisfied.
k. Wind Speed and Shielding
Background
When testing is conducted outdoors, wind shielding is required to
prevent wind from interfering with the flame temperatures. To ensure
that wind shields do not obstruct the drafting of air to burner, which
could cause variations in test results, the wind shields need to be at
least 0.5 m away from the CHSS being tested. Additionally, for
consistency, the wind shielding used for the pre-test checkout must be
the same as that for the CHSS fire test. NHTSA sought comment on
whether specifications for wind shielding should be provided in the
regulatory text of the standard, and if so, what the specifications
should be. As an additional approach to addressing wind interference
with flame temperatures, NHTSA sought comment on limiting wind speed
during testing to an average wind velocity during testing to 2.24
meters/second, as in FMVSS No. 304.\34\
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\34\ FMVSS No. 304, ``Compressed natural gas fuel container
integrity,'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
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Comments Received
DTNA supported including wind shielding specifications in the
regulatory text, stating that wind is critical to the spread of fire
and that clear wind velocity limits would ensure reproducibility of
test results. Glickenhaus agreed with NHTSA's proposal to limit wind
speed to 2.24 meters per second, while HATCI recommended adding
language to ensure wind does not affect flame direction or
temperatures. HATCI also sought clarity on where wind speed
measurements should be taken, recommending they occur between the wind
shield and the test specimen, with the wind speed at the measuring
point being near 0 meters per second.
In contrast, Nikola commented that maintaining the correct
temperature profile is sufficient and aligned with GTR No. 13, making
wind speed specifications irrelevant. TesTneT argued that specifying
wind speed is unnecessary, as the requirement to meet temperature
specifications already accounts for wind interference. It added that
wind gusts could momentarily exceed the limit, potentially invalidating
the test, even if temperature conditions were maintained. TesTneT also
noted that its use of a large diameter pipe for testing eliminates wind
effects without needing a wind speed specification.
MEMA stated a wind speed limit would be impractical, and that the
fire itself could create an updraft, complicating efforts to limit wind
speed. MEMA expressed concern that this requirement would cause
deviations between GTR No. 13 and FMVSS No. 308, and requested that
NHTSA eliminate the wind speed limit, instead recommending that wind
speed only be measured and recorded, consistent with GTR No. 13. FORVIA
also opposed the wind speed limit, stating it introduces unnecessary
complexities and technical challenges, such as determining where and
how to measure wind speed. It noted that wind can be unpredictable and
suggested that industry practices, which involve conducting tests under
calm conditions and recording wind speed, are sufficient to address
this issue. FORVIA stated that the pre-test checkout already addresses
draft effects from both external wind and the fire itself, making wind
speed limits unnecessary.
Agency Response
NHTSA is not including additional specification for wind or wind
speed. FMVSS No. 308 requires that wind shielding be used for outdoor
fire test sites. It also requires that the separation between the pre-
test container and the walls of the wind shields be at least 0.5
meters. This standard requires test facilities to provide sufficient
protection against wind to prevent an impact on test results.
NHTSA is not including a requirement that air temperature, wind
speed, and/or wind direction be measured and recorded if testing
conducted outdoors. If these parameters are not used to conduct the
test or determine the test result, then there is no reason to require
them to be recorded. Manufacturers and test labs may wish to retain
this information for their own purposes, but collecting this
information is not a specific requirement of the test for service
terminating performance in fire. As some commenters noted, the burner
monitor temperature specifications already account for wind
interference. If the temperature requirements are met during testing,
this result indicates that wind is not interfering with the test to
such a degree that would significantly affect the results.
11. Tests for Performance Durability of Closure Devices
Background
The tests for performance durability of closure devices in GTR No.
13 are closely consistent with the industry standards CSA/ANSI HPRD 1-
2021, ``Thermally activated pressure relief
[[Page 6250]]
devices for compressed hydrogen vehicle fuel containers,'' \35\ and
CSA/ANSI HGV 3.1-2022, ``Fuel System Components for Compressed Hydrogen
Gas Powered Vehicles.'' \36\ The GTR No. 13 tests for performance
durability of closure devices carry a significant test burden. To
evaluate a single TPRD design, 13 TPRD units are required for a total
of 29 individual tests (some units undergo multiple tests in a
sequence). Similarly, to evaluate a single shut-off valve or check
valve, 8 units are required for a total of 17 individual tests. While
NHTSA proposed these requirements to be consistent with GTR No. 13,
NHTSA sought comment on whether testing of this extent is necessary to
meet the need for safety, or whether it is still possible to meet the
need for safety with a less burdensome test approach or with a subset
of the test for performance durability of closure devices. NHTSA
requested that if commenters believe another approach or subset of
tests is appropriate and meets the need for safety, that they provide
specific detail on (1) the alternate approach or subset of tests and
(2) how it meets the need for safety adequately.
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\35\ See https://webstore.ansi.org/standards/csa/csaansihprd2021.
\36\ See https://webstore.ansi.org/standards/csa/csaansihgv2015r2019.
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Furthermore, FMVSS represent minimum performance requirements for
safety. FMVSS does not address issues such as component reliability or
best practices. These considerations are left to industry standards.
NHTSA sought comment on whether a reduced subset of the tests for
performance durability of closure devices could ensure safety with a
lower overall test burden. In such a subset, only those tests directly
linked to critical safety risks would be included.
Comments Received
Auto Innovators expressed support for maintaining consistency with
GTR No. 13 for the tests for performance and durability of closure
devices. Luxfer Gas Cylinders commented that obtaining 13 TPRDs for
testing would not be difficult and stated that the associated costs and
time were not burdensome when compared to container testing. Nikola
also supported adherence to GTR No. 13.
WFS commented that the tests in GTR No. 13, Phase 2, are already
aligned with industry standards such as CSA/ANSI HPRD 1 and CSA/ANSI
HGV 3.1, and that these GTR No. 13 tests were chosen by the IWG of GTR
No. 13 Phase 2 as the minimum required to ensure safety. WFS also
suggested that FMVSS could potentially include a provision allowing
closure devices compliant with relevant industry standards to be
considered compliant with FMVSS requirements, except for occasional
spot checks by NHTSA. FORVIA commented that while the proposed testing
numbers are necessary for initial component validation and type
certification due to their safety relevance, these numbers may not be
needed for field surveillance testing. FORVIA suggested limiting the
sample number to one per test and allowing NHTSA to focus selectively
on specific tests at its discretion.
Agency Response
Based on the comments, NHTSA is maintaining the proposed test
requirements. The commenters indicated the tests are not overly
burdensome and the number of tests has already been minimized to cover
essential safety aspects. NHTSA received no alternative proposals or
specific data showing how a reduced subset of the tests would
adequately meet safety needs. Since commenters did not provide any
evidence for removing tests, NHTSA will maintain the original testing
scope as proposed to ensure safety and maintain consistency with GTR
No. 13. Additionally, there is no option to certify compliance with any
FMVSS requirement by simply stating compliance with a set of industry
standards. Manufacturers must certify direct compliance with the
applicable FMVSS.
a. Hydrogen Impurities and Testing With Inert Gas
Background
NHTSA proposes that testing be conducted at an ambient temperature
of 5[deg]C to 35[deg]C, unless otherwise specified. In addition, GTR
No. 13 specifies that all tests be performed using either:
Hydrogen gas compliant with SAE J2719_202003, ``Hydrogen
Fuel Quality for Fuel Cell Vehicles,'' or
Hydrogen gas with a hydrogen purity of at least 99.97
percent, less than or equal to 5 parts per million of water, and less
or equal to 1 part per million particulate, or
A non-reactive gas instead of hydrogen.
The standard J2719_202003 specifies maximum concentrations of
individual contaminants such as methane and oxygen. Limiting these
individual contaminants is critical for fuel cell operation; however,
these contaminants are unlikely to affect the results of the tests for
performance durability of closure devices.
As a result, FMVSS No. 308 will only require hydrogen with a purity
of at least 99.97 percent, less than or equal to 5 parts per million of
water, and less than or equal to 1 part per million particulate. NHTSA
sought comment on any other impurities that could affect the results of
the tests for performance durability of closure devices.
Using a non-reactive gas for testing would have the benefit of
reducing the test lab safety risk related to handling pressurized
hydrogen. However, it is not clear if replacing hydrogen with a non-
reactive gas reduces stringency and therefore may not adequately
address the safety need. As a result, this option has not been proposed
in FMVSS No. 308. NHTSA sought comment on whether testing with a non-
reactive gas instead of hydrogen reduces test stringency.
Comments Received
Auto Innovators stated the levels of impurities are important and
that other impurities are addressed and limited in SAE J2719. Nikola
agreed that no other impurities would impact the closure device tests.
WFS stated that hydrogen with a purity of 99.97 percent and the
specified water and particulate limits would be adequate, as additional
impurity limits in SAE J2719 are relevant only to fuel cell
performance.
On the subject of testing with inert gas, comments were mixed.
Agility noted that test stringency could vary depending on the specific
test, citing a bonfire test as an example where replacing hydrogen
could be less stringent. Conversely, Agility commented that using inert
gases would not affect the stringency of TPRD flow rate measurements.
Auto Innovators suggested that testing with hydrogen, helium, or a non-
reactive gas mixture containing detectable helium, in line with GTR No.
13, would be acceptable as long as the test conditions, such as
pressure levels and cycle numbers, remained unchanged. HATCI expressed
similar support, stating that using a non-reactive gas under consistent
conditions should not reduce stringency.
Nikola commented that helium is an appropriate replacement for
hydrogen in tests, as it does not compromise test stringency and
facilitates testing procedures. WFS recommended aligning FMVSS with GTR
No. 13, which lists acceptable gases such as hydrogen, helium, and non-
reactive gas mixtures containing detectable helium or hydrogen. WFS
noted that nitrogen would be suitable for tests involving pressure
stress, while helium would be appropriate for leak tests. WFS stated
[[Page 6251]]
that these test gas options are consistent with various industry
standards.
FORVIA expressed concerns about potential material compatibility
issues with impurities not specified in the proposed requirements. It
recommended consulting manufacturers if there are questions about
compatibility. Additionally, FORVIA commented that while hydrogen tests
can help assess resistance to hydrogen embrittlement and fatigue, the
use of alternative gases like dry nitrogen should be suitable.
Agency Response
NHTSA agrees with commenters that using an inert gas will not
reduce the stringency of the tests for performance stability of closure
devices. Therefore, in the final rule, NHTSA has added the option of
using inert gas for conducting the tests for performance durability of
closure devices. NHTSA notes there is no bonfire testing included in
the tests for performance durability of the closure devices, nor any
similar tests where the flammability of hydrogen would play a
significant role in the outcome of the test.
NHTSA does not expect that impurities below 0.03 percent will have
any meaningful impact on the test results. Therefore, NHTSA is
maintaining the specification for hydrogen at 99.97 percent purity,
less than or equal to 5 parts per million of water, and less than or
equal to 1 part per million particulate. As noted in the NPRM, while
fuel cells are highly susceptible to impurities, the test for
performance durability of closure devices does not involve operating or
testing fuel cells, and therefore, strictly controlling the specifics
of the impurities below 0.03 percent is of little importance.
b. TPRD
Background
GTR No. 13 does not consider the possibility of the TPRD activating
during the pressure cycling test, temperature cycling test, salt
corrosion test, vehicle environment test, stress corrosion cracking
test, drop and vibration test, or leak test. The temperatures applied
during these tests are not characteristic of fire and therefore should
not cause the TPRD to activate. TPRD activation in the absence of
temperatures characteristic of a fire indicates that the TPRD is not
functioning as intended and presents a safety risk due to the hazards
associated with TPRD discharge. As a result, NHTSA proposed that if the
TPRD activates at any point during the pressure cycling test,
temperature cycling test, salt corrosion test, vehicle environment
test, stress corrosion cracking test, drop and vibration test, or leak
test, that TPRD will be considered to have failed the test. NHTSA
sought comment on this requirement.
Comments Received
Auto Innovators stated that it agrees with the agency proposal to
integrate the TPRD failure assessment as when evaluating other aspects
of performance. Nikola stated that this requirement aligns with GTR No.
13, which mandates that the TPRD meet the criteria of each subsequent
test. Therefore, Nikola stated, if a TPRD fails, the entire test is
considered failed. Agility and Luxfer Gas Cylinders both stated that
unintended activation could pose a safety risk, indicating support for
the proposal.
WFS, however, recommended leaving the test requirements as they are
currently written in GTR No. 13, noting that pressure cycling is a
unique test that involves pressure fluctuations which could directly
cause TPRD failure. WFS stated that in other tests like corrosion, it
is difficult to detect TPRD activation until a subsequent leak test,
which serves as the main criterion to confirm failure. FORVIA disagreed
with the proposal, arguing that the concept of ``activation'' is not a
clear requirement and may be difficult to measure. FORVIA suggested
that all tests, except for the stress corrosion cracking test, already
use a leak test as the appropriate pass/fail criterion. For the stress
corrosion cracking test, FORVIA noted that a separate pass/fail
criterion is necessary, as exposure to ammonia solution does not
necessarily cause TPRD activation or leakage.
Agency Response
NHTSA is maintaining the requirement that the TPRD not activate
during the pressure cycling test, temperature cycling test, salt
corrosion test, vehicle environment test, stress corrosion cracking
test, drop and vibration test, or leak test. The TPRD should not
activate outside of fire-related conditions. Activation during tests
that do not simulate fire indicates malfunction and poses a safety
risk. While some commenters suggest relying solely on the leak test,
this approach does not fully address the hazards of unintended TPRD
discharge. Unintended activation is a critical failure mode that
warrants a direct requirement. Thus, the requirement to treat TPRD
activation as a test failure is necessary to ensure safety.
A separate test to detect TPRD activation is not necessary. A TPRD
activation event will be evident to the test lab during the existing
tests. TPRD activation is a significant event that will be clear
through visual observation or other monitoring methods already in place
during the tests.
(1) Pressure Cycling Test
Background
The NPRM proposed that one TPRD unit undergo 15,000 internal
pressure cycles with hydrogen gas. While the proposed 15,000 pressure
cycles for the TPRD is consistent with GTR No. 13, NHTSA noted that
this number of cycles is higher than the maximum 11,000 pressure cycles
applied to containers. NHTSA sought comment on the need for 15,000
pressure cycles for TPRDs.
Comments Received
Commenters generally supported NHTSA's proposal to require 15,000
pressure cycles for TPRDs, aligning with GTR No. 13. Auto Innovators
recommended that NHTSA maintain consistency with GTR No. 13 and stated
that the 15,000-cycle requirement is harmonized with other industry
standards. Agility also supported the proposal, stating that 15,000
cycles are consistent with industry standards.
Nikola commented that GTR No. 13 and the industry have agreed on
this higher standard for TPRDs as a safety measure. WFS noted that
during the development of GTR No. 13 Phase 2, Task Force 3 (TF3)
recognized the need for a higher cycle count for primary closure
components compared to containers. WFS stated that TF3 decided to
harmonize TPRD cycle requirements with industry standards, establishing
15,000 cycles to provide a slightly higher safety margin. WFS pointed
out that TF3 applied the same approach to check valve pressure cycle
requirements.
FORVIA expressed support for the proposed 15,000 pressure cycles,
noting that the recently updated UN ECE R134 also mandates 15,000
cycles, aligning with GTR No. 13 Phase 2 and the NHTSA proposal. FORVIA
suggested maintaining this standard as a safety margin and considering
any revisions during Phase 3 of GTR No. 13.
Agency Response
Consistent with GTR No. 13, and based on the comments received,
NHTSA is maintaining 15,000 pressure cycles for TPRDs. NHTSA emphasizes
that maintaining the 15,000 pressure cycle requirement for TPRDs is
consistent with both GTR No. 13 and other relevant standards such as
HPRD-
[[Page 6252]]
1.\37\ As noted by multiple commenters, TPRDs are critical safety
components, and subjecting them to a slightly higher cycle count
compared to containers provides an added safety margin, which is
appropriate given their role in preventing catastrophic failures.
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\37\ See, https://webstore.ansi.org/standards/csa/csaansihprd2021.
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(2) Accelerated Life Test
Background
NHTSA proposed the accelerated life test consistent with GTR No.
13. This test verifies that a TPRD will activate at its intended
activation temperature, but also will not activate prematurely due to a
long-duration exposure to elevated temperature that is below its
activation temperature.
Comments Received
Auto Innovators recommended NHTSA remain consistent with the
requirements of GTR No. 13.
Agency Response
NHTSA is maintaining the accelerated life test as proposed.
(3)Temperature Cycling Test
Background
NHTSA proposed the temperature cycling test consistent with GTR No.
13. This test verifies that a TPRD can withstand extreme temperatures
while in service.
Comments Received
Auto Innovators recommended NHTSA remain consistent with the
requirements of GTR No. 13.
Agency Response
NHTSA is maintaining the temperature cycling test as proposed.
(4) Salt Corrosion Resistance Test
Background
NHTSA sought comment on the clarity and objectivity of the salt
corrosion resistance test procedure. NHTSA asked that if commenters had
suggestions on how to change the salt corrosion resistance test
procedure, that they explain how their suggested changes improve the
clarity and objectivity, and how they continue to meet the need for
safety represented by this test.
Comments Received
Auto Innovators and Nikola both recommended maintaining alignment
with GTR No. 13. WFS also advised against changes, stating that the
procedure aligns with existing industry standards in North America. WFS
acknowledged that the 100-day test duration is more extensive compared
to previous tests, such as a 144-hour salt spray test, but noted that
this longer test reflects best practices adopted by U.S. automakers and
integrated into industry standards for primary closure devices.
FORVIA cautioned against adding additional criteria such as
staining or pitting resistance, stating that these are cosmetic issues
that are almost inevitable in aggressive salt corrosion conditions. It
stated that GTR No. 13 specifies criteria like cracking, softening, and
swelling, and that a requirement that TPRDs must not show signs of
physical degradation would adequately addresses concerns about pitting
and corrosion levels that could impact the device's function. FORVIA
stated that the salt corrosion resistance test is a sufficient minimum
baseline.
Agency Response
Based on the comments received, NHTSA is maintaining the salt
corrosion test as proposed. In GTR No. 13 and in the proposed standard,
after the salt corrosion exposure, the TPRD units are subjected to the
leak test, benchtop activation test, and flow rate test. Neither GTR
No. 13 nor the standard container requirements related to cracking,
softening, swelling, or physical degradation. NHTSA is not including
such requirements in the standard for the salt corrosion test.
Subjecting the TPRD to the leak test, benchtop activation test, and
flow rate test is sufficient to evaluate the performance of the TPRD
after the salt corrosion test exposure.
(5) Vehicle Environment Test
Background
The vehicle environment test exposes the TPRD to the following
fluids for 24 hours each: 19 percent sulfuric acid, 10 percent ethanol,
and 50 percent methanol. GTR No. 13 does not specify the method of
exposure to these chemical solutions. NHTSA sought comment on the
exposure method. GTR No. 13 further specifies that ``cosmetic changes
such as pitting or staining are not considered failures.'' NHTSA sought
comment on including this specification and noted that pitting can be
an aggressive form of corrosion which can ultimately lead to component
failure due to cracking at the pitting site.
Comments Received
Auto Innovators and HATCI both recommended that NHTSA align with
GTR No. 13's criteria, which state that cosmetic changes are not
considered failures. HATCI pointed out that the TPRD undergoes further
performance evaluations, such as leak and flow rate tests, after the
vehicle environment test. It stated that these subsequent tests would
detect any significant degradation in performance caused by corrosion,
ensuring safety.
Luxfer Gas Cylinders commented that the 24-hour exposure is not
aggressive enough to cause pitting and suggested removing references to
cosmetic changes. Nikola added that pitting and cracking issues are
associated with the use of brass, which is not commonly used for TPRDs,
and stated that manufacturers already adhere to these requirements
since they are harmonized with industry standards. WFS suggested that
while the language in GTR No. 13 is sufficient, NHTSA could consider
specifying an exposure method, as outlined in HPRD 1. WFS explained
that this standard provides two methods--periodic spraying or full
immersion--and recommended adopting this language if more detail is
needed. However, WFS agreed that the current approach, which leaves the
exposure method to the test lab, is also acceptable.
FORVIA stated that the existing language provides sufficient
guidance for conducting the test. FORVIA reiterated that cosmetic
changes, like minor pitting, should not result in failure unless they
indicate more significant corrosion issues. FORVIA also suggested
discussing any potential test modifications in the future during GTR
No. 13 Phase 3 development.
Agency Response
Consistent with GTR No. 13, NHTSA will include the statement that
``cosmetic changes such as pitting or staining are not considered
failures'' in S5.1.5.1(e). Cosmetic changes such as pitting or staining
that do not affect the performance of the component do not present a
safety concern and are therefore not considered failures. NHTSA notes
that, after the vehicle environment test, TPRDs must undergo the leak
test, benchtop activation test, and flow rate test, as discussed below.
These subsequent tests are sufficient to ensure the vehicle environment
test has not degraded the performance of the TPRD.
NHTSA agrees that either of the exposure methods described by WFS
would be valid. There could also be other valid exposure methods.
Therefore, NHTSA will not specify exposure by either immersion or by
misting, and instead the test facility may determine an appropriate
exposure method for the component.
[[Page 6253]]
(6) Stress Corrosion Cracking Test
Background
The stress corrosion cracking test exposes the TPRD for ten days to
a moist ammonia air mixture maintained in a glass chamber. Under GTR
No. 13, the moist ammonia-air mixture is achieved using an ammonia-
water mixture with specific gravity of 0.94. Specific gravity is
affected by temperature and, therefore, is an inconvenient metric for
concentration specification because concentrations will need to be
adjusted for different temperatures. NHTSA sought comment on a more
direct metric for ammonia concentration specification, such as 20
weight percent ammonium hydroxide in water.
In GTR No. 13, the only requirement to pass the stress corrosion
cracking test is that the components must not exhibit cracking or
delaminating due to this test. NHTSA sought comment on this performance
requirement and on whether there are alternative requirements for this
test beyond basic visual inspection, such as subjecting the TPRD to the
leak test.
Comments Received
Luxfer Gas Cylinders commented that using a more direct metric for
ammonia concentration, such as 20 weight percent ammonium hydroxide in
water, ``would be an improvement.'' It stated that this test is usually
seen as a material test rather than a component test. Luxfer also
stated that industry cylinder standards require stress corrosion
testing specific to the material, which involves sectioning and
microscopic visual inspection. It suggested that FMVSS No. 308 adopt
the stress corrosion cracking test specified in ISO 11119, ``Gas
cylinders--Refillable composite gas cylinders and tubes--Design,
construction and testing--Part 2: Fully wrapped fibre reinforced
composite gas cylinders and tubes up to 450 l with load-sharing metal
liners,'' or ISO 11515, ``Gas cylinders--Refillable composite
reinforced tubes of water capacity between 450 L and 3000 L--Design,
construction and testing.'' Luxfer stated that a leak test is not an
effective method to detect stress corrosion.
Auto Innovators stated that material requirements for hydrogen
applications are well established in industry standards. It recommended
NHTSA refer to GTR No. 13 Phase 2, which outlines material evaluation
and stress corrosion cracking tests for aluminum alloys. It stated that
if these standards cannot be adopted as performance requirements,
alternative measures should be considered.
HATCI recommended harmonizing with GTR No. 13 Phase 2, in which the
stress corrosion cracking test is confirmed through visual inspection.
They cautioned that adding a leak test could lead to failures due to
affected o-rings rather than actual TPRD issues. HATCI also noted that
under GTR No. 13, the test only applies to TPRDs containing copper
alloys and requested clarity on whether NHTSA intends to follow this
approach.
WFS suggested no changes to the test procedure in GTR No. 13,
emphasizing that it is already harmonized with other standards such as
HPRD 1:21 and ISO 19882, ``Gaseous hydrogen--Thermally-activated
pressure relief devices for compressed hydrogen vehicle fuel
containers.'' They commented that third-party laboratories are capable
of adjusting the moist ammonia concentration and that visual
examination is the appropriate pass criteria.
Regarding the proposed concentration metric of 20 weight percent
ammonium hydroxide, FORVIA disagreed with adding additional measurement
criteria, noting that these tests are performed in temperature-
controlled laboratories with established procedures. They recommended
making any new measurement criteria optional and compatible with the
specific gravity method. FORVIA also stated that a leak test may not be
appropriate and supported visual inspection as sufficient for
identifying cracking or delamination, advocating for consistency with
GTR No. 13.
Agency Response
Regarding the performance requirement for the stress corrosion
cracking test, NHTSA has decided to retain the visual inspection
criterion as the only pass/fail measure. Visual inspection for cracking
or delamination is the appropriate criteria for determining the results
of the test. NHTSA considered the possibility of additional testing
beyond visual inspection, such as leak tests, but concurs with the
commenters that a leak test may not be the best test to evaluate for
stress corrosion. Therefore, introducing a leak test would not
effectively indicate whether stress corrosion cracking has occurred,
and NHTSA has decided against requiring this additional test.
NHTSA is not adopting the stress corrosion cracking test in ISO
11119 or ISO 11515. NHTSA is implementing a stress corrosion cracking
test aligned with GTR No. 13, as proposed in the NPRM.\38\ This test is
sufficient to address the risk of stress corrosion cracking in TPRDs
used in hydrogen vehicles. NHTSA is also not including the humid gas
stress corrosion cracking testing for aluminum alloys from Part I of
GTR No. 13. This test is not a requirement in GTR No. 13 and was not
proposed in the NPRM. Therefore, this test is outside the scope of this
final rule.
---------------------------------------------------------------------------
\38\ See 89 FR 27531 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------
Lastly, NHTSA has decided to specify an ammonia concentration
between 19 weight percent and 21 weight percent ammonium hydroxide
solution in water as the standard concentration for this test. This
decision is based on successful testing conducted by NHTSA, which used
16.7 wt% ammonium hydroxide in water to evaluate closure devices.\39\
NHTSA believes specifying between 19 weight percent and 21 weight
percent ammonium hydroxide in water provides a more practical metric
for ammonia concentration specification than specific gravity, while
still mirroring the effect of an ammonia-water mixtures with a specific
gravity of 0.94. This specification using weight percent also addresses
the ambiguity regarding the variability of specific gravity due to
temperature fluctuations. This concentration of between 19 and 21
weight percent falls with the range of commercially available pre-mixed
ammonium hydroxide solutions.
---------------------------------------------------------------------------
\39\ See the report titled ``GTR No. 13 Fire and Closures
Tests'' which can be found at: https://downloads.regulations.gov/NHTSA-2024-0006-0002/attachment_4.pdf. This report will also be
submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.
---------------------------------------------------------------------------
(7) Drop and Vibration Test
Background
NHTSA proposed the drop and vibration test consistent with GTR No.
13. TPRDs are first dropped in any one of six different orientations.
The units are vibrated for 30 minutes along each of the three
orthogonal axes. The units are vibrated at a resonant frequency which
is determined by using an acceleration of 1.5 g and sweeping through a
sinusoidal frequency range of 10 to 500 Hz with a sweep time of 10
minutes. According to GTR No. 13, the resonance frequency is identified
by a ``pronounced'' increase in vibration amplitude. However, if the
resonance frequency is not found, the test is conducted at 40 Hz. NHTSA
was concerned that specifying a pronounced
[[Page 6254]]
increase in vibration amplitude could be partially subjective. NHTSA
sought comment on more objective criteria for establishing resonance,
such as a frequency where the amplitude of the response of the test
article is at least twice the input energy as measured by response
accelerometers. Furthermore, the acceleration level was not defined in
GTR No. 13 for the resonant dwells. NHTSA sought comment on an
appropriate acceleration level for the resonant dwells.
Comments Received
Nikola stated that GTR No. 13 already has a defined resonance
frequency and that the current test procedure is sufficient. WFS
recommended maintaining the drop and vibration test as harmonized with
GTR No. 13, noting that it is also consistent with HPRD 1:21 and ISO
19882. WFS explained that the phrase ``pronounced increase'' was added
to GTR No. 13 for clarity and stated that a test laboratory with
vibration testing capabilities should be able to detect resonance, as
most shaker table software can automatically identify it. WFS stated
there was no need for additional criteria to establish resonance.
Regarding the acceleration level for resonant dwells or the 40 Hz
default, WFS indicated that it should remain at 1.5 g, which is the
same level as used in the sine sweep portion of the test.
FORVIA also supported keeping the test procedure harmonized with
GTR No. 13, stating that while the measurement method is left open in
the regulation, the definition of a pronounced increase is sufficiently
precise. FORVIA commented that the test setup must be sensitive enough
to identify the highest resonance, which is typically not an issue in
practice. FORVIA expressed confusion over the justification for NHTSA's
proposal to define resonance as a frequency where the amplitude
response is at least twice the input energy, preferring to adhere to
the existing GTR No. 13 criteria.
Agency Response
NHTSA is maintaining the proposed requirement consistent with GTR
No. 13. If a resonant frequency cannot be identified, the test is
conducted at 40 Hz, which is sufficiently objective. As the commenters
note, test facilities will be able to detect and identify the resonant
frequency, and therefore NHTSA will allow test facilities to determine
the appropriate resonant frequency, or otherwise they may use 40 Hz.
(8) Leak Test
Background
NHTSA proposed the leak test consistent with GTR No. 13. The leak
test evaluates the TPRD's ability to contain hydrogen at each of the
following temperatures and pressures:
Ambient temperature: 5[deg]C to 35[deg]C, test at 2 MPa and
125 percent NWP
High temperature: 85[deg]C, test at 2 MPa and 125 percent NWP
Low temperature: -40[deg]C, test at 2 MPa and 100 percent NWP
NHTSA sought comment on the need to perform the leak test at 2 MPa
in addition to the higher pressures.
The leak evaluation involves observing the pressurized unit for
hydrogen bubbles while the unit is immersed in the temperature-
controlled fluid. If hydrogen bubbles are observed, the leak rate is
measured by any method available to the test lab. The total leak rate
must be less than 10 NmL/h, which represents an extremely low leak
rate. NHTSA sought comment on the leak rate requirement of 10 NmL/hour,
noting that this leak rate is much lower than the minimum hydrogen flow
rate of 3.6 NmL/min necessary for initiating a flame.\40\ NHTSA sought
comment on objective methods for measuring the leak rate.
---------------------------------------------------------------------------
\40\ SAE Technical report 2008-01-0726. Flame Quenching Limits
of Hydrogen Leaks. The paper finds that the lowest possible
flammable flow is about 0.005 mg/s (3.6 NmL/min).
---------------------------------------------------------------------------
Comments Received
Agility commented that performing the leak test at higher pressures
is sufficient and that testing at 2 MPa is unnecessary, as leak rates
typically decrease with lower pressures. Nikola stated the opposite,
suggesting that a container is more likely to leak at low pressure and
low temperatures due to decreased rigidity. HATCI agreed with Agility,
indicating that testing at the higher pressure is adequate and
additional testing at 2 MPa does not add to safety assurance. However,
Auto Innovators supported harmonizing with GTR No. 13, stating it is
important to evaluate seal performance under both low- and high-
pressure conditions as well as low temperatures.
DTNA recommended revising the proposed leak rate of 10 NmL/h,
stating that it is significantly lower than the minimum hydrogen flow
rate necessary to initiate a flame and suggesting a limit of 3.6 NmL/
min instead. It stated that this higher limit would reduce the risk of
flame initiation and account for testing variability. Agility, on the
other hand, supported the 10 NmL/h leak rate, stating that it is
consistent with HPRD 1 and GTR No. 13, and suggested using pressure
measurements over time with trace gases as one method to determine
leakage. Nikola acknowledged that although 10 NmL/h is a low rate, the
impact could be amplified when considering multiple devices. It
suggested using bubble tests to confirm the presence of leaks and
employing mass spectrometers or gasometers to quantify the rate if
bubbles are detected.
FORVIA stated disagreement that 10NmL/min is a high leak rate,
given the potential for multiple leakage points. It noted that this
rate would be detectable through submersion and bubble tests but
recommended maintaining consistency with GTR No. 13 for both TPRDs and
valves. FORVIA supported the inclusion of the low-pressure leak test,
stating that poor gasket designs can leak at low pressure but may
become leak-tight at higher pressures.
WFS also advocated for consistency with GTR No. 13, stating that
the test accounts for both empty and full container conditions. It
noted that while the high-pressure condition is typically the most
severe, low pressure can be a challenging scenario in some cases. WFS
supported the 10 NmL/h requirement as it aligns with HPRD 1:21 and ISO
19882 and suggested leaving the choice of measurement methods to the
testing laboratories, which have various available techniques for
detecting leakage at these levels.
MEMA agreed with omitting visual evaluations of bubble formation,
as proposed by NHTSA, acknowledging the agency's aim to avoid
subjective assessments. MEMA also supported the proposed maximum leak
rate of 10 NmL/h.
Agency Response
NHTSA is maintaining the leak test as proposed. The commenters
established reasons for conducting the leak test at low pressure in
addition to high pressure, including gaskets leaking at low pressure
levels and decreasing container rigidity at low pressures and
temperatures. Regarding the leakage limit of 10 NmL/h, NHTSA notes that
there may be more than one TPRD on a vehicle. Therefore, the leakage
from any single TPRD must be very low and the proposed leakage rate of
10 NmL/h is a reasonable limit. Based on the comments, NHTSA will leave
the leakage rate quantification method to the discretion of the test
lab. As stated by the commenters, possible methods for quantification
include capturing bubbles or measurement with sensitive hydrogen or
helium leak detectors.
[[Page 6255]]
(9) Benchtop Activation Test
Background
Three new TRPD units are tested to establish a baseline activation
time, which is the average of the activation time of the three new
TPRDs. TPRD units used in the pressure cycling test, accelerated life
test, temperature cycling test, salt corrosion resistance test, vehicle
environment test, and drop and vibration test are also tested in the
benchtop activation test and these TPRDs must activate within 2 minutes
of the average activation time established from the tests with the new
units.
GTR No. 13 does not provide any information on how to proceed when
a TPRD does not activate at all during the benchtop activation test. A
TPRD that does not activate when inserted into the oven or chimney is
not functioning as intended and therefore presents a safety risk. As a
result, NHTSA proposed that if a TPRD does not activate within 120
minutes from the time of insertion into the oven or chimney, the TPRD
is considered to have failed the test. The time limit of 120 minutes is
selected based on the maximum possible duration of the CHSS fire test.
NHTSA sought comment on this requirement.
Comments Received
Agility supported the proposed 120-minute time limit for TPRD
activation, describing the rationale as reasonable. Auto Innovators
also agreed with NHTSA's proposal regarding the failure assessment for
TPRDs that do not activate within the specified period. However, Nikola
expressed concern, stating that 120 minutes is too long and dangerous,
and that the activation window should be limited to 2 minutes beyond
the baseline established by the new units.
FORVIA agreed that a TPRD must function as intended and activate
within a specified time and temperature range. It stated that a failure
to activate within 120 minutes should be recognizable using sound
engineering judgment. FORVIA suggested that the lack of an explicit
time limit in GTR No. 13 might be intentional and recommended clear
articulation of any additional failure criteria if introduced. It
argued that such a long activation time is unnecessary, as a TPRD
taking this long to activate under 600 [deg]C conditions would not pass
the performance-based fire test.
WFS disagreed with the 120-minute time limit, recommending that the
benchtop activation test remain consistent with GTR No. 13. It noted
that this test is harmonized with HPRD 1:21 and ISO 19882 and differs
from the CHSS fire test. WFS argued that 120 minutes is excessively
long for a chimney test, where activation usually occurs within 5
minutes, and suggested a 10-minute limit as more appropriate. It also
stated that qualified test labs can determine suitable cut-off times
and safely vent gas in case of TPRD failure.
Agency Response
Applying engineering judgment to determine whether a sample has
passed or failed the benchtop activation test is likely to be
subjective. In addition, a test lab determining an appropriate ``cut-
off time'' during the benchtop activation test may also be subjective.
Therefore, NHTSA is maintaining the maximum time limit of 120 minutes
from insertion into the oven or chimney for the TPRD to activate. Any
TPRD that does not activate within 120 minutes from insertion into the
oven or chimney during the benchtop activation test, including any of
the TPRDs used to establish the baseline activation time, will be
considered to have failed the test.
The time limit of 120 minutes is not intended to set the activation
performance timeframe. Instead, it is simply the maximum amount of time
the test lab must wait without an activation before declaring the TPRD
to have failed the test. This standard does not create a dangerous
situation because TPRDs will likely activate much faster than 120
minutes, and the CHSS fire test evaluates the performance of the
overall system in a fire scenario. The CHSS fire test also has a time
limit of 120 minutes for complete CHSS venting to below 1 MPa.
(10) Flow Rate Test
Background
The flow rate test evaluates the TPRD for flow capacity of a TPRD.
Flow rate through the TPRD is measured with the inlet pressurized to 2
MPa and the outlet unpressurized. The lowest measured flow rate must be
no less than 90 percent of a baseline flow rate established as the
measured flow rate of a new TPRD. The number of significant figures
used in the measurement of flow rate can impact the test result. For
example, a test flow rate of 1.7 flow units compared against a baseline
flow rate of 2.0 flow units does not meet the requirement. However, in
this case, if flow rate were measured using only one significant
figure, the two flow rates would be identical (2 flow units). As a
result, NHTSA proposed requiring that the flow rate be measured in
units of kilograms per minute with a precision of at least 2
significant digits. NHTSA sought comment on this proposed requirement.
Comments Received
Auto Innovators and HATCI expressed support for NHTSA's proposal
regarding the use of flow rate measurement in units of kilograms per
minute with a precision of at least two significant digits. Nikola also
agreed with the proposal to use two significant digits. However,
Agility opposed using mass flow rate units, emphasizing that the
properties of different gases must be considered in such an approach.
It stated that the use of percentage difference as specified in GTR No.
13 is clear and not open to interpretation.
WFS recommended no changes to the existing procedure in GTR No. 13,
noting that the test is harmonized with HPRD 1:21 and ISO 19882. It
argued that specifying units as kilograms per minute is unnecessary
since most flow tests for hydrogen components are conducted in grams
per second. It explained that the key aspect of the test is the
comparison of one TPRD flow rate to another, making the specific units
less critical. WFS also cautioned that requiring two significant digits
might suggest a level of precision not achievable with current
equipment, due to minor flow fluctuations during testing. It added that
a flow rate measured in grams per second with one significant digit can
be more precise than a rate in kilograms per hour with two significant
digits. FORVIA provided a neutral stance but noted that GTR No. 13,
HPRD 1, and ISO 19882 also use 2 percent.
Agency Response
NHTSA is maintaining the specification for units of kilograms per
minute with at least two significant digits. NHTSA conducted testing in
which these units were used successfully by the test lab to evaluate
TPRD flowrates.\41\ The test lab used a Coriolis meter to directly
measure the mass flow rate through each TPRD in units of kg/min. NHTSA
also notes that units are interchangeable, so other test labs may use
units such as g/s and simply convert the results to kg/min using the
appropriate conversion factors, while preserving the significant digits
in the measurement.
---------------------------------------------------------------------------
\41\ See the report titled ``GTR No. 13 Fire and Closures
Tests'' which can be found at: https://downloads.regulations.gov/NHTSA-2024-0006-0002/attachment_4.pdf. This report will also be
submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.
---------------------------------------------------------------------------
[[Page 6256]]
(11) Atmospheric Exposure Test
Background
GTR No. 13 includes an atmospheric exposure test to ensure that
non-metallic components that are exposed to the atmosphere and provide
a fuel-containing seal have sufficient resistance to oxygen. This test
requires that the component not crack nor show visible evidence of
deterioration upon exposure to pressurized oxygen for 96 hours at 70
[deg]C. However, NHTSA is concerned that this test is not objectively
enforceable because the requirement involves a subjective determination
of evidence of deterioration. Furthermore, the test would require NHTSA
to determine which components are non-metallic, exposed to the
atmosphere, and provide a fuel-containing seal. As a result, this test
was not included in the proposed FMVSS No. 308. NHTSA sought comment on
not including the atmospheric exposure test.
Comments Received
Agility stated that the atmospheric exposure test is appropriate
for non-metallic materials, but noted that most hydrogen components are
metallic and would not require such a test. It added that this test
could be relevant for electrical components with plastic connectors.
Auto Innovators and HATCI supported NHTSA's proposal to exclude the
atmospheric exposure test, agreeing with the agency's reasoning.
Glickenhaus also agreed with the decision, stating that the requirement
for ``no visible deterioration'' is not objectively measurable and
should be omitted.
WFS commented that the atmospheric exposure test is used in various
industry standards and noted that in third-party laboratories,
determining cracks in rubber materials during testing has been clear
for those incompatible with oxygen exposure. WFS indicated that even if
the test is removed from FMVSS No. 308, manufacturers may still conduct
the test in line with the requirements of industry standards. FORVIA
stated that while it believes the test is feasible and visual
inspection could serve as a pass/fail criterion, it expressed no
objections if NHTSA decides to remove the test.
Agency Response
NHTSA is not including the atmospheric exposure test in FMVSS No.
308. The test criteria are not objectively enforceable, and the
commenters did not provide any alternative criteria for conducting the
test with improved objectivity. The commenters also did not provide any
specific methodology for NHTSA to determine which components are non-
metallic and provide a fuel-containing seal within the closure device
of interest.
c. Check Valves and Shut-Off Valves
(1) Hydrostatic Strength Test
Background
The hydrostatic strength test is conducted to ensure the valves can
withstand extreme pressure of up to 250 percent NWP. Additionally, the
test also ensures that the burst pressure of the valves exposed to
various environmental conditions during prior testing is not degraded
beyond 80 percent of a new unexposed valve's burst pressure.
In the event of a significant leak, it may become impossible for
the test laboratory to increase pressure on the valve. This condition
occurs when any increase in applied pressure is offset by leakage flow,
thereby negating the pressure increase. If it occurs, it is not
possible to complete testing. To address this issue, NHTSA proposed
that valves shall not leak during the hydrostatic strength test, and
that a leak would constitute a test failure. NHTSA sought comment on
the requirement that valves not leak during the hydrostatic strength
test.
Comments Received
Auto Innovators agreed with NHTSA's proposal to require that valves
not leak during this test. WFS also supported NHTSA's proposal,
commenting that leakage during a hydrostatic strength test would
signify a rupture of the pressure-containing boundary and thus
constitute a failure. It pointed out that this detail is implied in HGV
3.1-2022 and further clarified in ISO 19887, ``Gaseous Hydrogen--Fuel
system components for hydrogen-fuelled vehicles,'' which states: ``The
components shall be examined to verify that leakage or rupture has not
occurred.'' WFS added that adopting this language could help with
clarity and harmonization if NHTSA deems it necessary.
In contrast, FORVIA disagreed with the proposal, stating that leak
tightness above 125 percent NWP is not required and that such a
requirement would not correspond to actual service conditions. It
suggested that in the event of a leak during hydrostatic testing, there
should be no test result, and the test should be repeated. FORVIA also
commented that the leak test should sufficiently address this potential
failure mode.
Agency Response
While NHTSA proposed the requirement that the valve not leak during
the hydrostatic strength test, this requirement is not intended to test
specifically for leakage above 125 percent NWP. Unlike the leak test,
the valve will not be submerged in a fluid and observed for bubbles
from leakage during the hydrostatic strength test. Instead, this
requirement is intended to avoid a situation where a test lab cannot
complete testing due to significant leakage from the valve that
prevents continued pressurization to the required pressures. Even if
such a test were considered ``no result'' and repeated, the same leak
could occur with subsequent test samples. Therefore, there needs to be
a requirement that the valve not leak to an extent that prevents
continued pressurization in accordance with S6.2.6.2.1(c) during the
hydrostatic strength test. Accordingly, NHTSA is revising this part of
the requirement to state the valve ``shall not leak to an extent that
prevents continued pressurization in accordance with S6.2.6.2.1(c).''
Regarding adding the language proposed by WFS, NHTSA is revising
the language as stated above. This is the most clear and concise way to
state the requirement.
(2) Leak Test
Background
NHTSA proposed the leak test consistent with GTR No. 13, and
similar to the leak test discussed above for TPRDs. NHTSA sought
comment on objective methods for measuring the leak rate.
Comments Received
Nikola stated that the specified leak rate of 10 NmL/h, while
applicable to a single point, could accumulate quickly when considering
multiple leak points throughout the CHSS. WFS commented that the leak
test is harmonized with industry standards and can be measured using
various methods, including bubble capture or sensitive hydrogen or
helium leak detectors capable of measuring levels lower than visible
bubbles. It stated there is no need for NHTSA to specify a particular
measurement method, as it can be determined by the testing facility
based on available equipment.
FORVIA disagreed with the proposed leak rate of 10 NmL/h, stating
that it is relatively high, especially if multiple leakage points in
the vehicle are at this level. It suggested that the leak rate can be
identified using submersion and bubble tests, but noted that more
[[Page 6257]]
accurate testing methods, such as global accumulation tests, are
available.
Agency Response
NHTSA is maintaining the leak test as proposed. NHTSA notes that
there may be more than one closure device on a vehicle. Therefore, the
leakage from any single closure device must be very low and the
proposed leakage rate of 10 NmL/h is a reasonable limit. Based on the
comments, NHTSA will leave the leakage rate quantification method to
the test lab. As stated by the commenters, possible methods for
quantification include capturing bubbles or measurement with sensitive
hydrogen or helium leak detectors.
(3) Extreme Temperature Pressure Cycling Test
Background
The extreme temperature pressure cycling test simulates extreme
temperature conditions that may lead to gas release failures when
combined with pressure cycling. The total number of operational cycles
is 15,000 for the check valve, consistent with the 15,000 cycles used
for the TPRD above. The total number of operational cycles is 50,000
for the shut-off valve. The higher 50,000 cycles for the shut-off valve
reflects the multiple pressure pulses the shut-off valve experiences as
it opens and closes repeatedly during service. In contrast, the check
valve only experiences a pressure pulse during fueling. NHTSA sought
comment on the number of pressure cycles for check valves and shut-off
valves.
Pressure cycling is conducted at different environmental
temperatures and pressures:
Ambient: Between 5.0[deg]C and 35.0[deg]C, 100 percent NWP
High: 85[deg]C, 125 percent NWP
Low: -40 [deg]C, 80 percent NWP
After cycling, each valve is subjected to 24 hours of ``chatter
flow'' to simulate the chatter condition described above. Chatter flow
means the application of a flow rate of gas through the valve that
results in chatter as described above. NHTSA was concerned, however,
that the application of chatter flow could be partially subjective.
NHTSA sought comment on the following aspects of the chatter flow test:
Appropriate methodology or a procedure for inducing
chatter flow.
Appropriate instrumentation and criteria to measure and
quantify chatter flow such as a decibel meter and minimum sound
pressure level.
How to proceed in cases where no chatter occurs.
The specific safety risks that are addressed by the
chatter flow test.
The possibility of not including the chatter flow test.
In the case of shut-off valves, GTR No. 13 specifies that the
chatter flow test is required only in the case of a shut-off valve
which functions as a check valve during fueling and that the flow rate
used to induce chatter should be within the normal operating conditions
of the valve. However, NHTSA has no way of determining whether a shut-
off valve is functioning as a check valve during fueling or the normal
operating conditions of the valve. As a result, NHTSA proposed that the
chatter flow test will apply to all shut-off valves and will not
specify flow rate limitations for the chatter flow test. NHTSA sought
comment on this decision.
Comments Received
Auto Innovators recommended aligning the number of pressure cycles
with GTR No. 13. FORVIA expressed support for the proposed minimum
values, confirming that 15,000 cycles for check valves and 50,000
cycles for shut-off valves are consistent with GTR No. 13. Similarly,
Nikola commented that safety devices should adhere to higher standards,
in alignment with GTR No. 13. Agility suggested using 50,000 cycles for
both check valves and shut-off valves.
Regarding the chatter flow test, HATCI requested that NHTSA exclude
this requirement if a CHSS component prevents chatter within the shut-
off valve, suggesting that manufacturers could provide documentation to
demonstrate this. WFS stated that the test is harmonized with industry
standards and stated it is sufficiently defined. It commented that GTR
No. 13 already describes an appropriate methodology for inducing
chatter flow by specifying a gas flow rate through the valve at the
level that causes the most chatter. WFS stated that additional
instrumentation, such as decibel meters, is unnecessary since chatter
is detectable by ear. WFS also stated that if no chatter occurs during
the flow test, GTR No. 13 specifies that the 24-hour chatter test is
not necessary. Regarding the specific safety risks that are addressed
by the chatter flow test, WFS stated that chatter could lead to
premature wear and failure of the valve's check functionality. WFS
recommended keeping the procedure as written in GTR No. 13, noting that
if a shut-off valve lacks check valve functionality, the test should
not be required since chatter only occurs during unidirectional flow
through a check valve.
Agency Response
NHTSA is maintaining the number of pressure cycles as proposed. For
the reasons discussed in the NPRM, and confirmed by the commenters,
15,000 pressure cycles for check-valves and 50,000 pressure cycles for
shut-off valves are the industry standard for minimum safety of these
components.\42\
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\42\ See 89 FR 27530, 27533 (Apr. 17, 2024), available at
https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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NHTSA is maintaining the chatter flow test as proposed. NHTSA will
leave it to test labs to determine the flowrate that cases the most
valve flutter. As the commenters note, this determination could be
accomplished by listening for audible sound changes. In the case of
valves that do not experience chatter, or vehicles with components that
prevent chatter, the chatter flow test should not adversely impact the
test results because these valves will not experience chatter.
Therefore, a specific exemption is not required for shut-off valves
that do not experience chatter or for vehicles that have components to
prevent chatter flow.
As stated above, NHTSA has no way of determining whether a shut-off
valve is functioning as a check valve during fueling or the normal
operating conditions of the valve; therefore NHTSA is maintaining the
test as proposed. This determination is not expected to adversely
impact test results because, as stated by the commenters, chatter only
occurs during unidirectional flow through a check valve. Therefore, if
a shut-off valve is not functioning as a check valve, it will not
experience unidirectional flow nor chatter.
(4) Salt Corrosion Resistance Test
Background
NHTSA proposed a salt corrosion resistance test for check valves
and shut-off valves equivalent to the salt corrosion resistance test
for TPRDs discussed above.
Comments Received
Auto Innovators recommended that NHTSA maintain consistency with
GTR No. 13. Nikola agreed with the proposal, noting that it is
harmonized with industry standards.
Agency Response
Based on the comments received, NHTSA is maintaining the salt
corrosion test as proposed.
[[Page 6258]]
(5) Vehicle Environment Test
Background
NHTSA proposed a vehicle environment test for check valves and
shut-off valves equivalent to the vehicle environment test for TPRDs
discussed above.
Comments Received
Auto Innovators recommended that NHTSA remain consistent with GTR
No. 13. Nikola stated that the tests from GTR No. 13 are aligned with
industry standards and would be conducted by manufacturers regardless.
Agency Response
Based on the comments received, NHTSA is maintaining the vehicle
environment test as proposed.
(6) Atmospheric Exposure Test
Background
For the reasons discussed above to the TPRD atmospheric exposure
test, NHTSA did not propose the atmospheric test for check valves and
shut-off valves.
Comments Received
Auto Innovators and HATCI both expressed support for NHTSA's
proposal to not include the atmospheric exposure test for check valves
and shut-off valves. WFS suggested leaving the requirement in the
FMVSS, consistent with its feedback on the atmospheric exposure test
for TPRDs. However, it noted that if NHTSA chooses to remove the test,
manufacturers will still perform it in accordance with HGV 3.1. FORVIA
commented that the test is feasible, and a visible inspection could
serve as a pass/fail criterion, but indicated that it would find it
acceptable if NHTSA decided to eliminate this test.
Agency Response
NHTSA is not including the atmospheric exposure test for check
valves and shut-off valves for the same reasons discussed above for
TPRDs.
(7) Electrical Tests
Background
The electrical tests apply to the shut-off valve only. The
electrical tests evaluate the shut-off valve for:
Leakage, unintentional valve opening, fire, and/or melting
after exposure to an abnormal voltage.
Failure of the electrical insulation between the power
conductor and casing when the valve is exposed to a high voltage.
The exposure to abnormal voltage is conducted by applying twice the
valve's rated voltage or 60 V, whichever is less to the valve for at
least one minute. After the test, the valve is subject to the leak test
and leak requirements. The test for electrical insulation is conducted
by applying 1000 V between the power conductor and the component casing
for at least two seconds. The isolation resistance between the valve
and the casing must be 240 k[Omega] or more.
Some valves may have requirements specified by their manufacturers
for peak and hold pulse width modulation duty cycle. NHTSA sought
comment on whether and how to adjust the proposed test procedure to
account for a manufacturer's specified peak and hold pulse width
modulation (PWM) duty cycle requirements.
Comments Received
Commenters provided various perspectives on potential adjustments
to the proposed test procedure to account for a manufacturer's
specified peak and hold PWM duty cycle requirements. Auto Innovators
stated that more information is needed to understand NHTSA's intent,
emphasizing that ``operation of the valve has no bearing on insulation
resistance'' and that the insulation resistance should be verified
between a single conductor and the component casing, regardless of the
modulation type. HATCI similarly stated that the PWM or peak
specification is not relevant to the electrical tests, arguing that
these tests are meant to check compliance under abnormal conditions,
such as atypical voltages. Agility suggested that any inclusion of PWM
requirements would go beyond the requirements of GTR No. 13 and would
require further investigation, adding that it did not recommend
including such requirements. WFS commented that the test should be
consistent with GTR No. 13 and noted that peak and hold modulation is
only applicable when testing to open a valve and keep it open, which is
not the purpose of this insulation resistance test. WFS stated that the
coil is not actually energized during this test, as it is similar to a
Hipot test where one lead is attached to the coil and the other to the
body to confirm insulation.
FORVIA stated that NHTSA appears to be proposing new test
procedures for valves, specifically related to PWM duty cycle
requirements, and acknowledged concerns about additional certification
tests to address specific manufacturer-set operational requirements. It
stated that these operational conditions would already be thoroughly
evaluated during the manufacturer's Design Validation (DV) and
Production Validation (PV) phases, where the valve's performance is
tested against specified requirements. FORVIA concluded that the
existing DV and PV processes adequately address concerns about PWM duty
cycles and stated that additional test scenarios are unnecessary. It
also recommended maintaining equivalence with GTR No. 13 and noted that
the test is independent of peak/hold or modulation of the voltage, as
it validates the component's ``electrical robustness.''
Agency Response
NHTSA is maintaining the electrical tests as proposed. As supported
by the commenters, NHTSA has determined that procedures to account for
pulse width modulation specifications are not necessary. The electrical
tests expose the valve to abnormal voltages and evaluate its insulation
resistance. The results of these tests will not be affected by PWM
variations during testing.
(8) Vibration Test
Background
The vibration test evaluates a valve's resistance to vibration. The
valve is pressurized to 100 percent NWP and exposed to vibration for 30
minutes along each of the three orthogonal axes (vertical, lateral, and
longitudinal). After vibration, the valve shall comply with the leak
test and the hydrostatic strength test to verify it retains its basic
ability to contain hydrogen and resist burst due to over-
pressurization. GTR No. 13 also contains a requirement that ``each
sample shall not show visible exterior damage that indicates that the
performance of the part is compromised.'' Showing signs of damage is a
subjective measure and lacks the objectivity needed per the Motor
Vehicle Safety Act. Therefore, this language was removed.
Comments Received
Auto Innovators expressed agreement with NHTSA's assessment,
stating that the lack of an objective measure for evaluating vibrations
justified the removal of the language. Nikola also indicated its
agreement with this decision.
Agency Response
NHTSA is maintaining the vibration test as proposed, which does not
include the requirement regarding visible exterior damage indicating
that the performance of the part is compromised.
(9) Stress Corrosion Cracking Test
Background
NHTSA proposed conducting the stress corrosion cracking test in the
[[Page 6259]]
same manner and for the same reasons discussed above for TPRDs.
Comments Received
Auto Innovators agreed with NHTSA's proposal.
Agency Response
NHTSA will maintain an equivalent stress corrosion cracking test
for check-valves and shut-off valves as the stress corrosion cracking
test for TPRDs, discussed above.
12. Labeling Requirements
Background
NHTSA proposed that the container label(s) include the following
information:
Manufacturer, serial number, and date of manufacture.
The statement ``Compressed Hydrogen Only.''
The container's NWP in MPa and pounds per square inch
(psi).
Date when the system should be removed from service.
BPO in MPa and psi.
Comments Received
Nikola recommended adding a DOT/FMVSS compliance statement to the
label. MEMA agreed with NHTSA's proposal to list information such as
the manufacturer's name and contact details, serial number, NWP, fuel
type, and the container's service removal date. However, MEMA objected
to including an inspection schedule on the label. It also pointed out
that such a requirement is not part of GTR No. 13 and requested NHTSA
reconsider its inclusion. Glickenhaus noted a lack of sufficient
information to specify a performance standard for label attachment that
would prevent localized degradation or stress.
Agency Response
As discussed above, NHTSA will not require BPO to be
listed on the container label. NHTSA is maintaining the other labeling
requirements as proposed. These labeling and inspection requirements
are consistent with the established labeling requirements for CNG fuel
containers in FMVSS No. 304.\43\ Having this information on the
container label will help operators properly maintain their vehicles
through regular safety inspections.
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\43\ FMVSS No. 304, ``Compressed natural gas fuel container
integrity.'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
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Additionally, since FMVSS No. 308 is a vehicle-level standard, the
DOT/FMVSS compliance statement should be located on the vehicle itself,
not directly on the container. Lastly, while concerns were raised about
label attachment durability, label attachment methods are expected to
be developed based on best practices, and this issue does not affect
the requirement to specify information on the container label.
C. FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles''
Background
FMVSS No. 307 sets requirements for the vehicle fuel system to
mitigate hazards associated with hydrogen leakage and discharge from
the fuel system, as well as requirements to ensure hydrogen leakage,
hydrogen concentration in enclosed spaces of the vehicle, and hydrogen
container displacement are within safe limits post-crash. The fuel
system integrity requirements for normal vehicle operations would apply
to all hydrogen-fueled vehicles, while the post-crash fuel system
integrity requirements only apply to light vehicles and compressed
hydrogen-fueled school buses regardless of GVWR. NHTSA sought comment
on the application of FMVSS No. 307 to all vehicles, including heavy
vehicles (vehicles with a GVWR greater than 4,536 kg (10,000 pounds).
As proposed, portions of FMVSS No. 307 would apply to all hydrogen
vehicles regardless of GVWR. However, not all vehicles would be subject
to crash testing under FMVSS No. 307. As described below, passenger
cars, multipurpose passenger vehicles, trucks and buses with a GVWR of
less than or equal to 4,536 kg would be subject to barrier crash
testing, as would school buses with a GVWR greater than 4,536 kg. Heavy
vehicles other than school buses with a GVWR greater than 4,536 kg
would not be subject to crash testing under the proposed standard.
Comments Received
Agility commented that FMVSS No. 307 should not apply to all
vehicles, citing significant differences between light and heavy
vehicles that warrant separate consideration. It stated that while some
requirements could be the same, fuel system-specific configurations and
integration into the vehicle body should be addressed separately, given
the differences in vehicle accelerations and impacts based on GVWR.
Luxfer Gas Cylinders supported the application of FMVSS No. 307 to all
vehicles. Auto Innovators stated that while the safety and integrity of
hydrogen vehicles are priorities regardless of size, it does not
support the inclusion of heavy vehicles under FMVSS No. 307 at this
time. Auto Innovators cited the design implications for heavy vehicles,
which have not been previously subject to such requirements, and called
for further research to justify this inclusion. It recommended that if
NHTSA considers including heavy vehicles, a comprehensive regulatory
impact analysis should be conducted, and a new rulemaking proposal
issued as either a separate rulemaking notice or a supplemental notice
of proposed rulemaking. Auto Innovators also stated the need for
additional research to determine if alternative test procedures are
required to evaluate heavy vehicle performance and understand the
potential impact on vehicle design. Nikola stated ``leave it to the OEM
to decide.''
Agency Response
NHTSA is maintaining the application of FMVSS No. 307 as proposed,
consistent with GTR No. 13, which applies to both light and heavy
vehicles.\44\ While Auto Innovators cited need for more research to
support application of FMVSS No. 307 to heavy vehicles, Hyundai Motor
Group noted that heavy commercial vehicles and buses will be important
types of hydrogen powered vehicles. Indeed, NHTSA and industry expect
heavy vehicles to comprise a significant portion of the hydrogen fleet.
In 2023, about 33 percent of hydrogen-powered vehicles were commercial
vehicles and this percentage is expected to grow in the coming
years.\45\ Because hydrogen fuel poses risks regardless of a vehicle's
GVWR, safety need compels that the requirements for normal vehicle
operation apply to heavy vehicles just as they apply to light vehicles
so long as the standard is able to be practicable and objective. The
performance tests under normal vehicle operations adopted in the final
rule are aligned with GTR No. 13 and have already been implemented for
hydrogen powered vehicles (regardless of GVWR) in other
[[Page 6260]]
countries.\46\ These tests are simple and can be performed similarly
for light and heavy vehicles. Therefore, the same minimum safety
requirements must be applied to all vehicles that use compressed
hydrogen as a fuel source. Specifically, heavy vehicles must meet the
same requirements as light vehicles for fueling receptacles, hydrogen
discharge systems, protection against flammable conditions, fuel system
leakage, and tell-tale warnings provided to the driver. This approach
also harmonizes with commenters' requests for harmonization with GTR No
13.\47\
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\44\ The scope of GTR No. 13 states that ``[t]his regulation
applies to all hydrogen-fueled vehicles of Categories 1 and 2 with a
maximum design speed exceeding 25 km/h.'' ``Category 1 vehicle''
means a power-driven vehicle with four or more wheels designed and
constructed primarily for the carriage of (a) person(s). ``Category
2 vehicle'' means a power-driven vehicle with four or more wheels
designed and constructed primarily for the carriage of goods. See
TRANS-WP29-1045e, Annex 2, https://unece.org/DAM/trans/doc/2005/wp29/TRANS-WP29-1045e.pdf.
\45\ See Global Market Insights: Hydrogen Vehicle Market size,
https://www.gminsights.com/industry-analysis/hydrogen-vehicle-
market#:~:text=Hydrogen%20Vehicle%20Market%20size%20was,expenses%20as
sociated%20with%20hydrogen%20vehicles.
\46\ See ECE R.134, ``Uniform provisions concerning the approval
of motor vehicles and their components with regard to the safety-
related performance of hydrogen fuelled vehicles,'' https://unece.org/transport/documents/2024/10/standards/addendum-133-regulation-no-134-revision-1.
\47\ Hyundai and Nikola are already producing vehicles that
comply with GTR No. 13 fuel system integrity requirements. As of
October 2024, Nikola has sold 235 fuel cell electric Class 8 heavy-
duty trucks in the United States. About 70 Hyundai Class 8 XCIENT
fuel cell trucks have already been sold in the United States.
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Furthermore, NHTSA will not leave it to vehicle manufacturers to
decide whether to apply FMVSS No. 307 to their vehicles. Allowing
manufacturers to decide whether to apply FMVSS No. 307 to their
vehicles would not be consistent with the application of other FMVSS.
As discussed below, NHTSA agrees more research would be beneficial
before the crash test requirements of FMVSS No. 307 are applied to all
heavy vehicles. Hyundai suggested post-crash requirements similar to
that proposed for heavy school buses. EMA suggested use of component
level tests, while Nikola stated it is developing its own crash test
requirements based on the FMVSS No. 214 side impact moving barrier
crash test. This final rule only requires heavy vehicles to comply with
the fuel system integrity requirements under normal vehicle operations.
As discussed below, NHTSA is considering conducting research on post-
crash requirements for heavy vehicles and will consider the commenters'
suggestions on this matter.
1. Enclosed or Semi-Enclosed Spaces Definition
Background
GTR No. 13 defines ``enclosed or semi-enclosed spaces' as ``the
special volumes within the vehicle (or the vehicle outline across
openings) that are external to the hydrogen system (storage system,
fuel cell system, internal combustion engine (ICE) and fuel flow
management system) and its housings (if any) where hydrogen may
accumulate (and thereby pose a hazard).'' NHTSA proposed a similar
definition of ``enclosed or semi-enclosed spaces means the volumes
external to the hydrogen fuel system such as the passenger compartment,
luggage compartment, and space under the hood.'' NHTSA also proposed
defining that ``hydrogen fuel system means the fueling receptacle,
CHSS, fuel cell system or internal combustion engine, fuel lines, and
exhaust systems.''
Comments Received
EMA raised concerns about the proposed definition of ``enclosed or
semi-enclosed spaces,'' calling it ambiguous and a departure from
NHTSA's intent to harmonize with GTR No. 13. It commented that NHTSA's
use of ``such as'' implies a non-exhaustive list, potentially
encompassing unintended areas outside the vehicle's hydrogen system. It
cited various references in the NPRM where NHTSA repeatedly linked
``enclosed or semi-enclosed spaces'' to volumes that allow hydrogen
accumulation. EMA highlighted specific alleged problems with the
proposed definition's broadness, such as in the fueling receptacle
requirements of S5.1.1, arguing the term's literal interpretation would
limit receptacle mounting to components within the hydrogen system,
leading to potentially unsafe situations. Similarly, in section
S5.1.3.1(c) on pressure relief systems, EMA argued that directing
hydrogen discharge solely towards the hydrogen system is unsafe. It
noted that the proposed term appears nine times outside the definition
in FMVSS No. 307, with several instances relating to hydrogen
detection. EMA suggested revising the definition to align with GTR No.
13 or adding a specification that such spaces are where hydrogen can
accumulate and pose a hazard.
FORVIA also expressed the need for clearer criteria, recommending
NHTSA define ``semi-enclosed spaces'' by specifying volumes and
enclosed sides to avoid testing ambiguities. Meanwhile, Auto Innovators
opposed the inclusion of ``space under the hood'' in the definition,
stating it diverged from GTR No. 13.
Agency Response
NHTSA agrees with the commenters that the proposed definition of
``enclosed or semi-enclosed spaces'' is vague and ambiguous. To avoid
ambiguity, NHTSA has revised the definition of enclosed or semi-
enclosed spaces to mean ``the passenger compartment, luggage
compartment, and space under the hood.'' This definition no longer
contains the words ``such as,'' so it no longer implies the inclusion
of ambiguous additional volumes beyond those listed in the definition.
The ``space under the hood'' is included in the definition of
enclosed or semi-enclosed spaces because there is a risk of hydrogen
accumulation under the hood just as there is a risk of hydrogen
accumulation in the passenger compartment and/or in the luggage
compartment. If hydrogen were to accumulate heavily in the space under
the hood, it could result in a fire if an ignition source were present.
By including the ``space under the hood'' in the definition of enclosed
or semi-enclosed spaces, the requirements of FMVSS No. 307 S5.1.3(b)
apply, thereby preventing accumulation of hydrogen to unsafe levels
under the hood.
Furthermore, NHTSA believes that including ``space under the hood''
in the enclosed and semi-enclose spaces is consistent with GTR No. 13.
GTR No. 13 defines enclosed or semi-enclosed spaces as ``the special
volumes within the vehicle (or the vehicle outline across openings)
that are external to the hydrogen system (storage system, fuel cell
system, internal combustion engine (ICE) and fuel flow management
system) and its housings (if any) where hydrogen may accumulate (and
thereby pose a hazard).'' Space under the hood can be considered a
special volume within the vehicle, external to the hydrogen system and
its housings, where hydrogen may accumulate.
2. Fuel System Integrity During Normal Vehicle Operations
a. Fueling Receptacles
Background
The first proposed requirement for the fueling receptacle was to
prevent reverse flow to the atmosphere. The second proposed requirement
was for a label with the statement, ``Compressed Hydrogen Only'' as
well as the statement ``Service pressure ______ MPa (_____ psig).'' The
label must also contain the statement, ``See instructions on fuel
container(s) for inspection and service life.'' The third proposed
requirement was for positive locking that prevents the disconnection of
the fueling hose during fueling. The fourth proposed requirement was
for protection against ingress of dirt and water to protect the fueling
receptacle from contamination that could lead to degradation of the
fuel system over time. The fifth proposed requirement was to prevent
the receptacle from being mounted in a location that would be highly
susceptible to crash deformations in order to prevent degradation in
the
[[Page 6261]]
event of a crash. NHTSA also proposed that the receptacle be prevented
from being mounted in the enclosed or semi-enclosed spaces of the
vehicle because these areas can accumulate hydrogen.
NHTSA proposed that the assessment for all five receptacle
requirements would be by visual inspection. NHTSA sought comment on the
proposed requirements for the fueling receptacle and on the objectivity
of assessment by visual inspection.
Comments Received
Luxfer Gas Cylinders questioned how NHTSA intends to conduct visual
inspections of the fueling receptacle and inquired about the number of
receptacles that would be tested annually. It also questioned how
positive locking would be assessed for the variety of vehicle designs
in service. Luxfer further commented on the requirement that the
fueling receptacle should not be mounted in impact energy-absorbing
areas, stating that since receptacles are typically mounted on a
vehicle's outer surface for accessibility, any such surface is
inherently vulnerable in a crash, making this requirement appear
unnecessary.
Auto Innovators noted that there is no reference test provided for
the requirement to prevent reverse flow to the atmosphere and
recommended using the GTR No. 13 leak test for check valves and shut-
off valves. It also requested clarification on the label location. Air
Products recommended adding a disconnect switch to fueling receptacles
for medium and heavy vehicles to prevent starting or drive-away, as
used in light vehicles. It stated that GTR No. 13 Phase 2 standardizes
references to fueling receptacle profiles to ensure vehicles are fueled
only with appropriate pressure classes and prevent cross-fueling with
other compressed gas dispensing stations. Air products cited standards
ISO 17268, ``Gaseous hydrogen land vehicle refuelling connection
devices,'' and SAE J2600, ``Compressed Hydrogen Surface Vehicle Fueling
Connection Devices,'' in this context.
HATCI expressed concerns about the lack of space for the proposed
labeling requirements and recommended omitting additional lines of text
compared to GTR No. 13. It supported the requirement to prevent ingress
of water and oil, agreeing that this could affect the closure device
tests. Nikola and Agility both stated that visual inspection is an
acceptable means of assessment. FORVIA disagreed with the proposed
requirements and requested that NHTSA align them exactly with GTR No.
13.
Agency Response
Regarding the requirement for the fueling receptacle to not be
mounted in locations ``highly susceptible to crash deformations,'' the
proposed requirements do not use the term ``highly susceptible.''
Instead, NHTSA proposed that ``[t]he fueling receptacle shall not be
mounted to or within the impact energy-absorbing elements of the
vehicle.'' However, in response to concerns raised, NHTSA has
reconsidered the necessity of this requirement.
The commenters correctly note that it is generally expected for the
fueling receptacle to be mounted on the exterior of the vehicle to
facilitate fuel filling, which inherently exposes it to potential
damage in the event of a crash. NHTSA agrees that this reality limits
the effectiveness and practicality of restricting the mounting location
based on energy-absorbing elements of the vehicle. Given that any
surface-mounted device, by its nature, could be subject to damage in a
collision, maintaining the proposed restriction would not significantly
enhance vehicle safety and could introduce unnecessary design
constraints.
Therefore, after careful review, NHTSA has decided to remove the
requirement that fueling receptacles shall not be mounted in the
energy-absorbing elements of the vehicle. This decision aligns with the
practical considerations raised by commenters and reflects the
understanding that modern vehicle design incorporates various safety
mechanisms, such as reinforced mounting systems and advanced materials,
that can adequately protect external components like fueling
receptacles from damage without the need for this specific regulation.
NHTSA believes that removing this requirement will not compromise
safety objectives while allowing for greater flexibility in vehicle
design.
NHTSA is maintaining the other fueling receptacle requirements as
proposed. NHTSA will conduct visual inspection by observation of the
fueling receptacle, its location within the vehicle, and through basic
operation of the vehicle such as attaching a fueling nozzle to the
receptacle to test for positive locking. NHTSA has discretion regarding
how many vehicles it inspects per year.
NHTSA notes that the referenced GTR No. 13 leak test outlines the
check valve and shut-off valve leak test. While a fueling receptacle
may contain a check valve, the test procedure is not written to
accommodate fueling receptacles. In addition, testing of CHSS check
valves is already covered under FMVSS No. 308 S5.1.5.2, and it would be
redundant to apply the same test to the receptacle. As a result, NHTSA
is maintaining visual inspection as the evaluation method for the
requirements of FMVSS No 307 S5.1.1.
NHTSA is not requiring a disconnect switch to prevent vehicle
starting and drive away on light duty vehicles. However, vehicle
manufacturers are free to include this technology in their designs.
NHTSA is also not including requirements for the fueling receptacle
profile or setting requirements for different ``Pressure Classes.''
Such specification would be design restrictive.
There is no exact location specified for the location of the
fueling receptacle label. The presence of this label will be verified
by visual inspection. Manufacturers may consider this inspection method
when determining where to locate the label. The additional statement
``See instructions on fuel container(s) for inspection and service
life'' is consistent with FMVSS No. 303.\48\ This statement is
important for the purpose of helping operators properly maintain their
vehicles through regular safety inspections.
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\48\ FMVSS No. 303, ``Fuel system integrity of compressed
natural gas vehicles,'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.303.
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Lastly, NHTSA notes that the fueling receptacle design is not
standardized by GTR No. 13. The preamble to GTR No. 13 simply
references industry standards where examples of fueling receptacles can
be found. This language in GTR No. 13does not constitute a requirement
or a standardization of the fueling receptacle. NHTSA believes fueling
receptacle designs may still be evolving. Therefore, while there may be
safety benefits to standardizing fueling receptable designs, to do so
at this time would be premature.
b. Over-Pressure Protection for Low-Pressure Systems
Background
NHTSA proposed GTR No. 13's requirement of over-pressure protection
for low-pressure systems. Accordingly, the agency proposed requiring
countermeasures to prevent failure of downstream components in the
event a pressure regulator fails to properly reduce the fuel pressure
from the much higher pressure in the CHSS. The activation pressure of
the overpressure protection device shall be lower than or equal to the
maximum allowable working pressure for the appropriate
[[Page 6262]]
section of the hydrogen system as determined by the manufacturer. NHTSA
sought comment on the requirement for an overpressure protection device
in the fuel system and how to test the performance of such a device.
Comments Received
Auto Innovators recommended that NHTSA align with GTR No. 13 and
avoid requiring an additional test. It stated that the main areas of
GTR No. 13 cover CHSS, high-pressure closures, PRD, fuel lines,
electrical safety, and performance and other subsystem requirements in
the vehicle. It commented that the proposed overpressure protection
falls under the ``Hydrogen Delivery'' system of a hydrogen fuel cell
vehicle, which it stated should be outside the scope of this
regulation. Auto Innovators noted that while low-pressure systems are
not covered by GTR No. 13, it clearly defines overpressure protection
for these systems as ensuring that ``the hydrogen system downstream of
a pressure regulator shall be protected against overpressure due to the
possible failure of the pressure regulator,'' which each manufacturer
will verify. Thus, it stated that there is no need to add this
requirement to FMVSS No. 307.
HATCI supported NHTSA's proposal to harmonize with GTR No. 13 and
agreed that an overpressure protection device should be included in the
system. However, it stated that evaluating every overpressure
protection device in a system would need to end with regulator failure
and compromise the whole system. It suggested that if such evaluation
is necessary, the device's operation could be verified at the component
level by applying a reverse pressure. Agility found the requirement
acceptable and proposed testing the component on a bench by measuring
its activation pressure. It also noted the possibility of testing it on
the vehicle by deliberately exposing a PRD to its activation pressure,
though it cautioned that this exposure could pose risks to vehicle
safety.
Nikola commented that no additional test is needed since this
component falls outside the scope of the regulation. FORVIA agreed with
keeping alignment to GTR No. 13 Phase 2 and recommended using visual
inspection as the test procedure. It argued that conducting an actual
test on the vehicle would be difficult due to vehicle-dependent
factors.
Agency Response
Based on the comments received, NHTSA is removing the requirement
for an overpressure protection device in the fuel system. There is no
test available to evaluate the performance of the over-pressure
protection device, and therefore the proposed requirement that ``the
activation pressure of the over-pressure protection device be lower
than or equal to the maximum allowable working pressure for the
respective downstream section of the hydrogen system'' is
unenforceable. Simply requiring a device to be present with no test to
evaluate its performance does not improve safety, and therefore, the
requirement for an over-pressure protection device has been removed.
c. Hydrogen Discharge Systems
(1) TPRD Discharge Direction
Background
Consistent with GTR No. 13, NHTSA proposed that the TPRD vent line
be protected from ingress of dirt or water to prevent contamination
that could degrade or compromise the TPRD. NHTSA proposed several
requirements related to the TPRD vent discharge direction, requiring
that the TPRD discharge must not be directed towards nor impinge upon:
1. Any enclosed or semi-enclosed spaces where hydrogen could
unintentionally accumulate, such as the trunk, passenger compartment,
or engine compartment.
2. The vehicle wheel housing.
3. Hydrogen containers.
4. Rechargeable electrical energy storage system (REESS).
5. Any emergency exit(s) or service door(s).
In addition to these requirements, NHTSA proposed an additional
requirement to protect potential occupants attempting to exit the
vehicle or first responders approaching the vehicle. This requirement
stated that hydrogen vented through the TPRD(s) be directed upwards
within 20[deg] of vertical relative to the level surface or downwards
within 45[deg] of vertical relative to the level surface. NHTSA sought
comment on this additional requirement for TPRD discharge direction,
and on the proposed discharge angles.
Comments Received
Air Products commented that venting downward could be acceptable
for light vehicles but recommended any downward TPRD vent flow should
be diffused to minimize a jet fire scenario. It also proposed specific
considerations for heavy vehicles, suggesting that venting should be
oriented away from cargo and vertically positioned outside the CHSS
enclosure and vehicle. It stated the importance of designing vent
stacks to withstand back pressure, thrust forces, and vehicle
accidents.
Air Products also stated that venting high-pressure hydrogen in
confined areas increases the likelihood of deflagration or detonation.
It described the possibility of flame impingement at the TPRD outlet
potentially leading to a cascading effect and larger hydrogen releases.
It proposed modifications to include ``enclosed or semi-enclosed spaces
including portions of the CHSS'' as a location the discharge shall not
impinge upon.
Agility stated that the proposed requirement for a discharge angle
within 20 degrees of vertical does not align with existing standards.
It suggested using the wording from GTR No. 13 and commented that while
venting within 45 degrees of vertical from the top could be acceptable,
venting from the bottom at any angle other than vertical could lead to
horizontal gas/flame plumes, posing risks to passengers and first
responders. Agility also noted that these requirements could become
irrelevant in vehicle rollovers.
Nikola and FORVIA both expressed concerns over the prescriptiveness
of specifying venting angles. Nikola stated that discussions among
experts concluded that manufacturers should be given the responsibility
to determine safe venting designs. It cited GTR No. 13, which only
specifies prohibited venting directions rather than mandating specific
angles. FORVIA similarly stated that the topic is highly vehicle-
specific and should be addressed on a case-by-case basis. FORVIA noted
that the phrase ``not be directed towards'' could be interpreted
subjectively, leading to compliance challenges. FORVIA agreed with the
requirements other than the venting direction angles, but recommended
aligning the wording exactly with GTR No. 13.
Luxfer Gas Cylinders viewed the proposed requirements as an
improvement but indicated uncertainty about manufacturers' ability to
comply. Auto Innovators did not support the proposed requirements in
S5.1.3.1(b), citing extensive discussions within GTR No. 13 Phase 2,
which highlighted structural differences among vehicles, especially
heavy vehicles, that complicate establishing a ``one-size-fits-all''
requirement. It stated that prescribing discharge directions could
limit design flexibility without improving safety. It also recommended
deleting the proposed S5.1.3.1(c)(5) and
[[Page 6263]]
(6), because these requirements are inconsistent with GTR No. 13 and
because the intent is not clear.
Agency Response
NHTSA acknowledges commenters' stated concerns that setting
specific discharge angles was extensively discussed during GTR No. 13
Phase 2, and that the Informal Working Group ultimately chose not to
include such specific requirements due to the complexities involved,
especially given that vehicles--especially larger vehicles--have
heterogenous designs and that a specific approach that works for some
vehicles may not work for other vehicles. NHTSA also acknowledges that
in certain situations, such as vehicle rollovers, angle requirements
could become less relevant. After reviewing the comments and
considering the real-world scenarios presented, NHTSA has decided to
remove the proposed discharge angle requirements until more information
is available to determine whether a generalized discharge angle is
reasonable and beneficial. NHTSA will, however, retain the other TPRD
discharge direction requirements as proposed. NHTSA notes that the
requirements specify that ``[t]he hydrogen gas discharge from TPRD(s)
of the CHSS shall not impinge upon'' as opposed to ``shall not be
directed towards.''
NHTSA is not adding any additional requirements based on cargo
locations within the vehicle or vent stack design at this time. Similar
to the above discussion, cargo-specific TPRD directional venting
requirements may be overly prescriptive, and until more data is
available, it could potentially be unworkable given the variety of
vehicle designs and cargo configurations or be a suboptimal safety
solution. Furthermore, requirements for vent stack design, such as
ensuring mechanical support for thrust forces, are design
considerations that NHTSA does not intend to regulate and are outside
the scope of the proposed standards.
Additionally, there is no need to specify additional portions of
the CHSS to avoid venting onto, because the requirements list the
container, which is the main component of the CHSS. Not directing TPRD
discharge towards the container will effectively avoid the CHSS as
well, so an additional specification regarding the CHSS would be
redundant.
Lastly, NHTSA is retaining the specifications regarding ``emergency
exit(s) as identified in FMVSS No. 217'' and ``service door(s).'' As
stated in the NPRM, the purpose of these requirements is to prevent
safety hazards due to hydrogen discharge from the TPRD that could
inhibit the ability of passengers to safely exit the vehicle.\49\
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\49\ See 89 FR 27536 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
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(2) Possible Test To Evaluate TPRD Discharge Direction
Background
NHTSA proposed that the discharge direction from TPRDs and other
pressure relief devices be evaluated through visual inspection. NHTSA
sought comment on whether there is a more appropriate test.
Comments Received
Nikola recommended relying on a visual inspection for evaluating
TPRD discharge direction. In contrast, HATCI suggested that NHTSA adopt
a detailed emission measurement method, which would use the end of the
valve angle relative to horizontal, instead of solely depending on
visual inspection.
Agency Response
NHTSA will maintain visual inspection as the evaluation for TPRD
discharge direction. It will be clear from the orientation of the TPRD
and/or the TPRD vent lines where the TPRD discharge is being directed.
While the suggestion to use valve angle measurements to verify
compliance is plausible, the commenters did not provide a specific
procedure for conducting an objective valve angle measurement. If a
more comprehensive and detailed testing procedure is identified in the
future, the agency may consider incorporating it in the future.
d. Vehicle Exhaust Systems
Background
NHTSA proposed the vehicle exhaust requirements outlined in GTR No.
13. NHTSA proposed that the test procedure be conducted after the
vehicle has been set to the ``on'' or ``run'' position for at least
five minutes prior to testing. A hydrogen measuring device is placed in
the center line of the exhaust within 100 mm from the external
discharge point. The fuel system would undergo a shutdown, start-up,
and idle operation to stimulate normal operating conditions. The
measurement device used should have a response time of less than 0.3
seconds to ensure an accurate three second moving average calculation.
Response times higher than 0.3 seconds could result in inaccurate data
collection because the sensor may not have time to register the true
concentration levels before recording each data point.
The time period of three seconds for the rolling average ensures
that the space around the vehicle remains non-hazardous in the case of
an idling vehicle in a closed garage. This time period is
conservatively determined by assuming that a standard size vehicle
purges the equivalent of a 250 kW (340 HP) fuel cell system.\50\ The
time is then calculated for a nominal space occupied by a standard
passenger vehicle (4.6 meters x 2.6 meters x 2.6 meters) to build up to
25 percent of the LFL, or one percent by volume in air. The time limit
for this rolling-average situation is determined to be three
seconds.\51\
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\50\ In comparison, the power system output of a Toyota Mirai is
182 HP.
\51\ SAE 2578_201408. Recommended Practice for General Fuel Cell
Vehicle Safety. Appendix C3. https://www.sae.org/standards/content/j2578_201408/.
---------------------------------------------------------------------------
Comments Received
Luxfer Gas Cylinders questioned how NHTSA intends to ensure
compliance with these requirements. Auto Innovators expressed support
for harmonizing the exhaust requirements with GTR No. 13 but suggested
revising the terminology from ``on'' or ``run'' position to align with
the GTR standard, which specifies that ``the propulsion system of the
test vehicle is started, warmed up to its normal operating temperature,
and left operating for the test duration.'' Nikola stated agreement
with adopting the requirements in GTR No. 13.
Agency Response
NHTSA will ensure compliance with the requirements of FMVSS No. 307
S5.1.2.2, Vehicle exhaust system, by testing vehicles in accordance
with FMVSS No. 307 S6.5, Test for the vehicle exhaust system.
Additionally, for the reasons discussed below in section IV.C.2.f.,
Protection against flammable conditions, NHTSA has revised the
requirement that ``the vehicle shall be set to the `on' or `run'
position for at least 5 minutes prior to testing, and left operating
for the test duration.'' The new requirement will specify that ``the
vehicle propulsion system shall be operated for at least five minutes
prior to testing and shall continue to operate throughout the test.''
This change ensures the safe operation of fuel cell vehicles during
testing while still meeting the intended objectives of the proposed
test protocol.
[[Page 6264]]
e. Fuel System Leakage
Background
GTR No. 13 includes fuel system leakage requirements specifying no
leakage from the fuel lines. A flammable or explosive condition can
arise if hydrogen leaks from the fuel lines and accumulates. However,
the safety risk of a leak applies to the entire fuel system, not only
to the fuel lines. As a result, NHTSA proposed that the fuel system
leakage requirement for no leakage apply to the entire hydrogen fuel
system downstream of the shut-off valve, which includes the fuel lines
and the fuel cell system. NHTSA further proposed to define fuel lines
to include all piping, tubing, joints, and any components such as flow
controllers, valves, heat exchangers, and pressure regulators. From a
safety standpoint, there is no difference between a leak coming from
fuel line piping, and a leak coming from a valve, pressure regulator,
or the fuel cell system itself. Consistent with GTR No. 13, NHTSA
proposed a strict no leakage standard. NHTSA sought comment on whether
there is a safe level of hydrogen that may leak, and if so, what would
be an objective leakage limit and how to accurately quantify hydrogen
leakage from the fuel system.
NHTSA proposed to test this requirement using either a gas leak
detector or leak detecting liquid (bubble test). NHTSA sought comment
if one of these tests is preferrable. NHTSA also proposed that the test
be conducted with the fuel system at NWP after having been in the
``on'' or ``run'' position for at least five minutes. NHTSA sought
comment on whether alternative conditions would better simulate
realistic scenarios when downstream lines are more likely to leak.
Comments Received
Luxfer Gas Cylinders commented that either a gas leak detector or a
bubble test is acceptable, noting the long-standing effectiveness of
the bubble test and expressing support for the proposed five-minute
warm-up period. Ballard Power Systems stated that achieving a strict no
leakage standard is likely impractical due to the extensive use of
elastomeric seals and non-metallic materials in fuel cell vehicles. It
stated that fuel cell stacks typically have a leakage rate around 200
mL/min hydrogen at the beginning of life, and that standards such as
HGV 3.1 permit a maximum leak rate of 10 Ncc/h. It recommended
establishing a leakage requirement that ensures flammable releases are
negligible, suggesting that gas mixtures with hydrogen concentrations
below the lower flammability limit do not pose combustion risks.
Ballard proposed mitigation techniques like enclosing components prone
to leaks and using ventilation and hydrogen detection to manage non-
flammable releases.
Auto Innovators disagreed with a strict no leakage requirement,
stating that leakage can be detected at very low levels well below
hazardous thresholds using sensitive equipment. It advocated for
aligning the allowable leakage rate with the single-point leakage
definition in GTR No. 13. It also supported NHTSA's proposal for the
five-minute warm-up but suggested adopting GTR No. 13's terminology and
test conditions. Air Products recommended conducting the leak check at
1.25 times NWP to align with industry standards.
HATCI supported harmonizing with GTR No. 13 and advised adopting
criteria that focus on leak detection at accessible fuel line sections,
especially at joints, as specified in GTR No. 13 section 6.1.5. HATCI
also proposed adopting a 3 percent hydrogen concentration limit as a
flammability condition and suggested clarifying regulatory text
regarding the vehicle's ``on'' or ``run'' position during testing.
Agility noted that complete leak-free connections are impossible and
referenced SAE J1267, which states that ``absolute leak tightness is an
absolute impossibility.'' It recommended specifying maximum allowable
leak rates consistent with existing standards, emphasizing that both
bubble solutions and electronic leak detection are feasible methods.
Nikola proposed adopting GTR No. 13's leak rate requirement of
0.005 mg/s and supported the bubble test as a reliable method to check
for joint leaks, suggesting that more advanced instrumentation be
required only if a bubble test indicates leakage. Hyzon expressed
concerns about the subjectivity of bubble testing and recommended that
NHTSA use additional accurate testing methods, including detection
devices that meet industry standards. NFA commented that a safe level
of hydrogen leak should reference standards like SAE technical paper
2008-01-0726, ``Flame Quenching Limits of Hydrogen Leaks,'' and SAE
J2579, which limit leak rates to prevent hazardous concentrations. It
questioned why FMVSS No. 308 would apply a different standard to the
CHSS compared with the standard that applies to the rest of the fuel
system. NFA emphasized the practicality of bubble tests for detecting
localized leaks and noted that metallic ferrule style tube fittings can
be validated to be bubble-tight.
FORVIA suggested revising the wording of the proposal to specify
``no detectable leakage'' based on a test method or minimum measurement
sensitivity. DTNA argued that a zero percent leak rate is not feasible
due to hydrogen's chemical properties and current measurement
technology limitations. It proposed a leak rate below 3.6 NmL/min,
which it stated is the lowest flow necessary for flame initiation.
Agency Response
NHTSA has determined that a demonstratable ``no leakage'' standard
as evaluated by a bubble test is consistent with GTR No. 13, which
specifies that ``the hydrogen fueling line downstream of the main shut-
off valve(s) shall not leak.'' GTR No. 13 does not provide any leakage
limit in either section 5.2.1.5 or 6.1.5. Thus, NHTSA's application of
a demonstratable no-leakage requirement as evaluated by a bubble test
aligns with GTR No. 13.
NHTSA acknowledges the concerns regarding the practicality of
achieving a true no-leakage standard, noting that very low levels of
hydrogen leakage may occur due to the tiny size of hydrogen molecules
and the materials and sealing technologies used in hydrogen fuel
systems. However, NHTSA emphasizes that any detectable hydrogen leakage
poses potential safety risks. Even minimal levels of hydrogen leakage
present the possibility of gas accumulation in enclosed spaces, which
could create hazardous conditions. Multiple individual points of
leakage could produce an additive effect where the cumulative leakage
rate becomes significant.
In response to suggestions that NHTSA define specific test methods
for leak detection, the proposed regulation already includes objective
test procedures for verifying compliance with the no-leakage
requirement in FMVSS No. 307 S6.6. As such, suggestions to include
additional specificity in test methods are redundant, as the regulation
already addresses this concern. Furthermore, NHTSA is not including in
S6.6 the statement ``primarily at joints'' that is found in GTR No. 13.
This language is unnecessary, as NHTSA will be able to evaluate joints
as well as other portions of the fuel system for leakage regardless of
whether this language is included or not. Additionally, it is not
possible to define a fuel system leakage limit based on a concentration
of hydrogen in the surrounding air, as some commenters
[[Page 6265]]
suggested. Doing so would require several assumptions to be made
regarding factors such as the volume of air in which the hydrogen may
accumulate, the location of leakage points relative to the air volume,
number of leakage points, and the possibility of air-exchange rates.
To address concerns about the high sensitivity of leak detection
equipment, NHTSA has decided to remove the option of using an
electronic leak detector and will instead require the use of the bubble
test method exclusively. As some commenters noted, the bubble test has
been effectively used for decades and provides a practical, reliable
means of visually detecting leaks. This method, which is less sensitive
than advanced electronic leak detectors, is based on simple visual
observation as to the expansion and/or propagation of bubbles and is
not dependent on the subjective opinions of individuals. It addresses
the need for an objective evaluation of leakage while acknowledging the
concerns about detecting insignificant background levels of hydrogen
that do not present a direct hazard. The bubble test will allow for a
practical assessment of compliance with the no-leakage requirement
without the possibility of test equipment detecting harmless levels of
hydrogen. If no leakage is detectable using the bubble test specified
in S6.6, then the vehicle will be deemed to have acceptable
performance. To further clarify this standard, FMVSS No. 307 S5.1.4 has
been revised to read: ``When tested in accordance with S6.6, the
hydrogen fuel system downstream of the shut-off valve(s) shall not
exhibit observable leakage.'' Adding the words ``exhibit observable
leakage'' clarifies that leaks which do not result in observable bubble
expansion during the S6.6 test procedure are not considered failures.
Additionally, for the reasons discussed below in section IV.C.2.f.,
Protection against flammable conditions, NHTSA has revised the
requirement that ``the vehicle shall be set to the `on' or `run'
position for at least 5 minutes prior to testing, and left operating
for the test duration.'' If the vehicle is not a fuel cell vehicle, it
shall be warmed up and kept idling. If the test vehicle has a system to
stop idling automatically, measures shall be taken to prevent the
engine from stopping.'' The new requirement will specify that ``the
vehicle propulsion system shall be operated for at least five minutes
prior to testing and shall continue to operate throughout the test.''
This change ensures the safe operation of fuel cell vehicles during
testing while still meeting the intended objectives of the proposed
test protocol.
f. Protection Against Flammable Conditions
Background
NHTSA proposed requiring a visual warning within 10 seconds in the
event that the hydrogen concentration in an enclosed or semi-enclosed
space exceeds 3.0 percent (75 percent of the LFL). Additionally,
consistent with GTR No. 13, NHTSA proposed requiring the shut-off valve
to close within 10 seconds if at any point the concentration in an
enclosed or semi-enclosed space exceeds 4.0 percent (the LFL).
GTR No. 13 provides two options for evaluating this requirement.
The first option is to use a remote-controlled release of hydrogen to
simulate a leak, along with laboratory-installed hydrogen concentration
detectors in the enclosed or semi-enclosed spaces. The laboratory-
installed hydrogen concentration detectors are used to verify that the
required warning and shut-off valve closure occur at the appropriate
hydrogen concentrations in the enclosed or semi-enclosed spaces. GTR
No. 13 allows for the remote-controlled release of hydrogen to be drawn
from the vehicle's own CHSS. Therefore, by using this option, it is
possible for a vehicle to meet the requirements without a built-in
hydrogen concentration detector. This objective is accomplished by the
vehicle monitoring hydrogen outflow from its CHSS. The vehicle can then
trigger the required warning and shut-off valve closure if significant
hydrogen outflow from the CHSS is detected that is not accounted for by
fuel cell hydrogen consumption.
The second option for evaluating the requirement is to use an
induction hose and a cover to apply hydrogen test gas directly to the
vehicle's built-in hydrogen concentration detector(s) within the
enclosed or semi-enclosed spaces. Test gas with a hydrogen
concentration of 3.0 to 4.0 percent is used to verify the warning, and
test gas with a hydrogen concentration of 4.0 to 6.0 percent is used to
verify the closure of the shut-off valve. The warning and shut-off
valve closure must occur within 10 seconds of applying the respective
test gas to the detector. The warning is verified by visual inspection,
and the shut-off valve closure can be verified by monitoring the
electric power to the shut-off valve or by the sound of the shut-off
valve activation.
This second option indirectly requires the presence of at least one
hydrogen concentration detector in the enclosed or semi-enclosed spaces
that can detect the hydrogen test gas and trigger the warning and shut-
off valve closure at appropriate hydrogen concentration levels. NHTSA
proposed this second option as the only test method in FMVSS No. 307,
which would thereby require each vehicle to have at least one built-in
hydrogen concentration detector. NHTSA sought comment on requiring
built-in hydrogen concentration detectors and on the reliability of the
required warning and shut-off valve closure for vehicles that do not
have built-in hydrogen concentration detectors.
In addition to the above requirement regarding a warning and shut-
off valve closure, GTR No. 13 includes a requirement that any failure
downstream of the main hydrogen shut off valve shall not result in any
level of hydrogen concentration in the passenger compartment. This
requirement is evaluated by applying a remote-controlled release of
hydrogen simulating a leak in the fuel system, along with laboratory-
installed hydrogen concertation detectors in the passenger compartment.
After remote release of hydrogen, GTR No. 13 requires that the hydrogen
concentration in the passenger compartment not exceed 1.0 percent. The
number, location, and flow capacity of the release points for the
remote-controlled release of hydrogen are determined by the vehicle
manufacturer.
NHTSA instead proposed that the remote-controlled release of
hydrogen shall not result in a hydrogen concentration exceeding 3.0
percent in the enclosed or semi-enclosed spaces of the vehicle
(including the passenger compartment). NHTSA sought comment on this
requirement and on specific test procedures for initiating a remote-
controlled release of hydrogen in a vehicle.
To evaluate this requirement, NHTSA proposed that a hydrogen
concentration detector be installed in any enclosed or semi-enclosed
space where hydrogen may accumulate from the simulated hydrogen
release. After the remote-controlled release of hydrogen, the hydrogen
concentration would be measured continuously using the laboratory-
installed hydrogen concertation detector. The test would be completed
five minutes after initiating the simulated leak or when the hydrogen
concentration does not change for three minutes, whichever is longer.
Five minutes was selected as the minimum time for monitoring the
hydrogen concentration because five
[[Page 6266]]
minutes is generally considered a sufficient time frame for vehicle
occupants to evacuate in the event of an emergency.
Comments Received
Agility commented that using built-in hydrogen detectors is
feasible and analogous to requirements for liquified natural gas (LNG)
vehicle systems. It emphasized the need for electronic detection due to
hydrogen's odorless nature, comparing it to the established reliability
of natural gas sensors. Agility also stated that any remote release of
hydrogen should not be built into every vehicle directly, citing
potential safety risks and increased costs. Instead, it recommended
using separate testing equipment operated by qualified personnel.
Luxfer Gas Cylinders expressed concern that requiring detectors and
warnings for all enclosed and semi-enclosed spaces might be excessively
difficult due to the number of such spaces in both light and heavy
vehicles. Air Products suggested incorporating passive or mechanical
ventilation into the CHSS to help dissipate leaks before they
accumulate to hazardous levels, in addition to other safety measures.
Glickenhaus raised safety concerns regarding the idling of fuel
cell electric vehicles during tests, commenting that forcing fuel cell
vehicles to idle could be dangerous or even impossible depending on the
fuel cell's minimum output and battery capacity. Glickenhaus stated
that while hydrogen internal combustion vehicles might idle safely,
fuel cell vehicles could face significant risks of overcharging or
electrical failure.
HATCI sought clarity on specific test requirements. It questioned
the definition of the air component in the mixed hydrogen gases for
testing and expressed concerns over the difficulty of obtaining the
specified mixtures based on geographical availability. Additionally,
HATCI supported the flexibility in defining release points downstream
of the shut-off valve, as proposed by NHTSA, allowing manufacturers to
determine these parameters.
Nikola recommended not adding an additional 10-second requirement
for visual warnings beyond what is specified in GTR No. 13. It also
preferred allowing OEMs to decide how to meet safety requirements
rather than requiring built-in hydrogen detectors. It requested that
NHTSA maintain the lower leakage concentration limit of one percent
inside the passenger compartment to align with GTR No. 13. FORVIA
disagreed with deviations from GTR No. 13, requesting that NHTSA keep
the requirements fully aligned and avoid requiring hydrogen detectors
in enclosed spaces, suggesting that ventilation might suffice as a
safety measure.
Agency Response
After careful consideration of the comments received, NHTSA has
decided to maintain the proposed requirements, with the exception of
revisions related to the idling requirements, discussed below, and the
revision to the definition of enclosed and semi-enclosed spaces,
discussed above.
Regarding the use of built-in hydrogen detectors, some commenters
supported their use, drawing parallels to systems required in LNG
vehicles due to the lack of odorant in the fuel, which makes electronic
detection necessary. NHTSA has determined that built-in hydrogen
detectors are critical for safety. Hydrogen's odorless and highly
flammable properties necessitate on-board hydrogen detection capability
to mitigate risks. The proposed test method verifies that hydrogen
detectors can activate a warning and shut-off valve closure within the
prescribed time frame and concentration thresholds, thereby ensuring
that vehicles can detect and respond to hydrogen leaks promptly. There
will not be an excessive number of spaces that will require hydrogen
detectors because, as discussed above, the definition of ``enclosed and
semi-enclosed spaces'' has been revised to be very specific, including
only the passenger compartment, luggage compartment, and space under
the hood.
With respect to concerns about remote-controlled hydrogen release
for testing purposes, some commenters stated that incorporating this
feature into every vehicle could introduce safety risks or unnecessary
costs. This is not a correct interpretation of the proposal. FMVSS No.
307 S6.4.2(b) states that ``[p]rior to the test, the vehicle is
prepared to simulate remotely controllable hydrogen releases from the
fuel system or from an external fuel supply.'' This language indicates
the use of separate, specialized test equipment that is only applied to
the test vehicle(s) rather than integrating the capability into all
vehicles.
Regarding the hydrogen concentration limit in the passenger
compartment, some commenters advocated for maintaining the 1.0 percent
limit specified in GTR No. 13, citing it as more conservative. However,
NHTSA proposed a 3.0 percent limit in the enclosed and semi-enclosed
spaces (not just the passenger compartment). The 3.0 percent limit
aligns with the lower flammability limit (LFL) of hydrogen, and
providing a more balanced requirement across all the enclosed and semi-
enclosed spaces and ensures that hydrogen concentrations remain below
hazardous levels. NHTSA has therefore chosen to maintain this
requirement as proposed. Note that the definition for enclosed and
semi-enclosed spaces has been revised to eliminate ambiguity, as
discussed above in section IV.C.1.
Regarding the comment that the components of the air in the mixed
gas were not defined in S6.4.1(b), this concern is unfounded. The
proposed regulatory text specifies the required hydrogen concentrations
in the test gas mixtures: ``The first test gas has any hydrogen
concentration between 3.0 and 4.0 percent by volume in air to verify
function of the warning, and the second test gas has any hydrogen
concentration between 4.0 and 6.0 percent by volume in air to verify
function of the shut-down.'' NHTSA can clarify that ``air'' refers to
the natural atmospheric air composition, which is globally consistent
across the surface of the Earth. Atmospheric air is primarily composed
of approximately 78% nitrogen, 21% oxygen, and trace amounts of other
gases such as argon and carbon dioxide. This standard atmospheric
composition is well understood and used in numerous industrial and
scientific applications. Therefore, the air component in the hydrogen-
air mixture is inherently defined and does not require additional
specification or definition within the regulatory text.
Regarding the time of 10 seconds to activate the warning or the
shut-off valve closure, GTR No 13 does not contain a time limit for
activation. The test can continue indefinitely if the warning has not
come on or the shut-off valve has not closed. NHTSA cannot have a test
that may continue indefinitely; therefore, the agency is maintain the
proposed 10-second time limit to activate the warning and close the
shut-off valve after the respective mixtures of hydrogen gas are
applied.
Lastly, concerns were raised about the idling requirements for fuel
cell vehicles during testing. One commenter emphasized that forcing
fuel cell vehicles to idle for extended periods could pose significant
safety risks, including the potential for battery overcharging or fuel
cell malfunction. NHTSA recognizes these concerns and has revised the
regulatory language. The new requirement will specify that ``the
vehicle propulsion system shall be operated for at least five minutes
prior
[[Page 6267]]
to testing and shall continue to operate throughout the test.'' This
change ensures the safe operation of fuel cell vehicles during testing
while still meeting the intended objectives of the proposed test
protocol.
(1) Wind Control During Testing
Background
The proposed test procedures in this section would be conducted
without the influence of any wind. NHTSA sought comment on providing
more specific wind protection requirements and sought comment on
limiting the maximum wind velocity during testing to 2.24 meters/
second, as in FMVSS No. 304.\52\
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\52\ FMVSS No. 304, ``Compressed natural gas fuel container
integrity.'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
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Comments Received
Nikola commented that including wind influence in testing would not
be feasible unless tests were conducted indoors, which would introduce
additional complexities. It supported using the same wind velocity
requirement as FMVSS No. 304. Auto Innovators agreed with NHTSA on the
need to establish more specific wind protection requirements.
Agency Response
After careful consideration, NHTSA has determined that it will not
impose specific limits on wind velocity or require wind shielding
measures as part of the testing protocol. While some commenters
suggested adopting a wind velocity limit similar to that in FMVSS No.
304, NHTSA has decided against incorporating explicit wind control
specifications. Establishing objective wind control requirements, such
as specifications for shielding or velocity limits, present logistical
challenges. Furthermore, requiring all tests to be conducted indoors to
completely eliminate wind effects could introduce additional safety and
operational difficulties, further complicating the testing process.
These challenges make prescriptive wind control requirements
impractical across different test environments.
Therefore, while NHTSA is maintaining the requirement that ``the
test shall be conducted without influence of wind,'' the agency will
allow individual test facilities the discretion to manage wind
conditions according to their capabilities and procedures. This
approach offers necessary flexibility, enabling laboratories to conduct
tests under conditions suited to their operational constraints, while
still ensuring the accuracy and reliability of test results.
g. Warning for Elevated Hydrogen Concentration
Background
NHTSA proposed requiring a telltale warning when hydrogen
concentration exceeds 3.0 percent in the enclosed or semi-enclosed
spaces of the vehicle. NHTSA also proposed the visual warning be red in
color and remain illuminated while the vehicle is in operation with
hydrogen concentration levels exceeding 3.0 percent in enclosed or
semi-enclosed spaces of the vehicle. The visual warning must be in
clear view of the driver. For a vehicle with an Automated Driving
System (ADS) and without manually operated driving controls, the visual
warning must be in clear view of all the front seat occupants. NHTSA
sought comment on whether the warning should be in clear view of all
occupants, including occupants in rear seating positions, in vehicles
equipped with an ADS. NHTSA also sought comment on whether an auditory
warning should be required when hydrogen concentration exceeds 3.0
percent in the enclosed or semi-enclosed spaces of the vehicle.
NHTSA also proposed that a telltale be activated if the hydrogen
warning system malfunctions, such as in the case of a circuit
disconnection, short circuit, sensor fault, or other system failure.
NHTSA proposed that when the telltale activates for these
circumstances, it illuminate as yellow to distinguish a malfunction of
the warning system from that of excess hydrogen concentration.
Comments Received
Nikola expressed agreement with the proposal. Auto Innovators
highlighted the need to align with the requirements in FMVSS No. 101,
``Controls and displays,'' for vehicles equipped with ADS and
recommended maintaining current placement requirements for visual
warnings. It noted that defining ``clear view'' lacks objectivity and
stated that auditory warnings should not be required in ADS-equipped
vehicles until further research is conducted. It stated that ``near-
term flexibility'' may be needed to prevent consumer confusion. Auto
Innovators supported the proposed activation criteria and color scheme,
noting consistency with GTR No. 13.
DTNA suggested adding an audible warning to supplement the visual
warning, particularly for heavy vehicles and school buses with complex
seating arrangements where occupants might not have clear visibility of
the visual indicator. It stated that an audible warning would be
essential for crew cabs, trucks with sleeper berths, and school buses,
where a visual warning alone would not suffice to communicate risk
effectively. Similarly, Glickenhaus supported the addition of an
auditory warning and favored the placement of visual warnings in clear
view of all seating positions in ADS-equipped vehicles.
HATCI supported harmonization with GTR No. 13 and recommended
determining visual warning requirements based on a vehicle's automation
level. It stated that visual warnings should be in the driver's view
for vehicles at SAE Levels 0 to 3 but more broadly visible for vehicles
at SAE Levels 4 or 5. However, HATCI advised against requiring auditory
warnings, citing concerns about potential confusion due to the numerous
existing auditory alerts.
NFA supported the inclusion of a visual telltale in red for high
hydrogen concentration levels, in line with FMVSS No. 307, and agreed
with the requirement for a yellow malfunction warning. NFA also
provided context for its current hydrogen detection system, which
includes warnings at 20 percent and 50 percent of the LFL, indicating
that its system already meets the proposed standard. Regarding ADS-
equipped vehicles, NFA agreed with NHTSA's proposal as written, noting
that transit buses are likely to retain an attendant or driver in the
front seating position due to the additional duties they perform. NFA
recommended that NHTSA consider how to address the requirements in
scenarios where no front seat passengers are present.
Agency Response
After careful consideration, NHTSA is maintaining the proposal as
originally outlined. With respect to the inclusion of an auditory
warning, NHTSA agrees that further research is necessary to assess the
most appropriate auditory alerting mechanisms for hydrogen-fueled
vehicles. While some commenters advocated for the inclusion of an
auditory warning, NHTSA has determined that additional research is
needed to evaluate the use of auditory alerts. For example, the
possibility of voice alerts may need to be considered. Voice alerts may
offer a clearer communication of the hazard without contributing to
confusion. Additionally, NHTSA is cognizant that the proliferation of
crash avoidance and driving automation systems has resulted in an
increased number of telltales and auditory alerts, many of which are
[[Page 6268]]
voluntarily added by manufacturers. As such, NHTSA will not require
auditory warnings at this time. The absence of a requirement for an
auditory warning does not preclude manufacturers from voluntarily
including such warnings based on their vehicle-specific configurations.
Regarding visual warning placement, NHTSA will not adopt specific
requirements based on SAE automation levels at this time. The scope of
this final rule is not contingent on a particular vehicle type. NHTSA's
focus remains on ensuring that the visual warning is in clear view of
the driver or, for ADS-equipped vehicles without manual controls, in
view of the front-seat occupants. This approach provides manufacturers
with flexibility while maintaining safety for occupants in these
advanced vehicles. This approach is also consistent with past updates
to the crashworthiness FMVSS to account for ADS-equipped vehicles.\53\
The suggestion to include rear-seat occupants in ADS-equipped vehicles
is not being implemented at this time, as NHTSA believes that further
consideration is needed to determine the most effective and appropriate
hydrogen warning systems for rear-seat occupants.
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\53\ See 87 FR 18560 (Mar. 30, 2022), available at https://www.federalregister.gov/documents/2022/03/30/2022-05426/occupant-protection-for-vehicles-with-automated-driving-systems.
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Finally, regarding the distinction between malfunction and hydrogen
concentration warnings, NHTSA will retain the proposed color scheme,
with yellow indicating a system malfunction and red indicating an
elevated hydrogen concentration. This color differentiation is
essential to ensure that drivers and occupants can quickly distinguish
between a system malfunction and an immediate hydrogen-related hazard.
3. Post-Crash Fuel System Integrity
Background
Consistent with GTR No. 13, NHTSA proposed that the post-crash
requirements for vehicles that use hydrogen fuel for propulsion power
only apply to passenger cars, multipurpose passenger vehicles, trucks,
and buses with a GVWR less than or equal to 4,536 kg (10,000 pounds)
and to all school buses. NHTSA did not propose that the post-crash
requirements apply to all heavy vehicles with a GVWR greater than 4,536
kg (10,000 pounds). NHTSA sought comment on whether heavy vehicles
should be subject to these proposed post-crash requirements and, if so,
what crash tests should NHTSA conduct on heavier vehicles.
NHTSA proposed to use the crash tests equivalent to those applied
to conventionally fueled vehicles in accordance with FMVSS No. 301. For
light vehicles with a GVWR under 4,536 kg, these crash tests include an
80 kilometers per hour (km/h) (~50 miles per hour (mph)) impact of a
rigid barrier into the rear of the vehicle, a 48 km/h (~30 mph) frontal
crash test into a rigid barrier, and a 53 km/h (~33 mph) impact of a
moving deformable barrier into the side of the vehicle. For school
buses with a GVWR greater than or equal to 4,536 kg, the crash test is
a moving contoured barrier impact at 48 km/h. NHTSA sought comment on
whether there are alternative crash tests that should be used for the
forthcoming proposed regulations.
NHTSA proposed that there be no fire during the test, and that
vehicles meet three additional post-crash requirements described by GTR
No. 13. The first proposed requirement is the volumetric flow of
hydrogen gas leakage from the CHSS must not exceed an average of 118
normal liters per minute (NL/min) from the time of vehicle impact
through a time interval [Delta]t of at least 60-minutes after impact.
The volumetric leak rate of hydrogen post-crash is determined as a
function of the pressure in the container before and after the crash
test. The interval [Delta]t is at least 60 minutes after impact and the
pressure drop measurement should be at least 5 percent of the pressure
sensor's full range. Helium may be used in place of hydrogen during
crash-testing with an allowable leakage limit for helium of 88.5 NL/
min.
The second requirement is a hydrogen concentration limit set to
four percent by volume (for helium, this corresponds to a concentration
of three percent by volume) in enclosed or semi-enclosed spaces. This
requirement is satisfied if the CHSS shut-off valve(s) are confirmed to
be closed within five seconds of the crash and there is no hydrogen
leakage from the CHSS.
For the purpose of measuring the hydrogen concentration, GTR No. 13
specifies that data from the sensors shall be collected at least every
five seconds and continue for a period of 60 minutes. GTR No. 13 also
discusses filtering of the data to provide smoothing of the data, but
is unclear about the exact data filtration method to be used. NHTSA
proposed using a three-data-point rolling average for filtering the
data steam. Since a data point will be collected at least every five
seconds, this rolling average will be, at most, a 15-second rolling
average. NHTSA sought comment on this proposed data filtration method.
The third proposed requirement is that the container(s) remain
attached to the vehicle by at least one component anchorage, bracket,
or any structure that transfers loads from the device to the vehicle
structure. This requirement is evaluated by visual inspection of the
container attachment points. NHTSA will evaluate the presence of
vehicle fire by visual inspection for the duration of the test, which
includes the time needed to determine fuel leakage from the CHSS.
In addition to these requirements, NHTSA sought comment on the
safety need for a heavy vehicle sled test. NHTSA sought input and
comment with supporting data on implementing a possible alternative
heavy vehicle impact test for the CHSS. NHTSA sought comment on the
possibility of including a moving contoured barrier impact test on
heavy vehicles (other than school buses) in accordance with S6.5 of
FMVSS No. 301.
Comments Received
Auto Innovators supported NHTSA's decision to limit the scope of
FMVSS No. 307 to light vehicles with a GVWR under 10,000 pounds and
school buses. It requested that NHTSA conduct a regulatory impact
analysis before including heavy vehicles. Auto Innovators noted that
heavy vehicles have varied designs and are produced in low volumes,
making full-scale crash testing complex and potentially cost-
prohibitive. It recommended that if NHTSA considers including heavy
vehicles, it should issue a new rulemaking proposal through either a
separate rulemaking notice or supplemental notice of proposed
rulemaking. Regarding the proposed crash tests, Auto Innovators agreed
with using existing crash tests for vehicles under 10,000 pounds GVWR,
stating that existing crash tests are representative of commonly
occurring crashes in the field and should be suitable for assessing the
post-crash fuel system integrity of hydrogen vehicles. Auto Innovators
opposed adding alternative crash tests for hydrogen vehicles without
supporting data. Auto Innovators also stated that it agrees with
NHTSA's proposed data filtration method.
Hyundai concurred with NHTSA's initial decision to apply the post-
crash requirements for heavy vehicles only to school buses but
highlighted the potential significance of heavy commercial vehicles for
hydrogen applications. It stated that post-crash fuel system integrity
should be a
[[Page 6269]]
consideration for these vehicles. It stated that the moving deformable
barrier test for heavy school buses could be adapted to include other
heavy vehicles. However, if the adaptation would delay the rulemaking,
Hyundai suggested that NHTSA consider a follow-on rulemaking to address
heavy vehicle standards once those procedures have been developed.
Agility agreed with NHTSA's decision to keep the post-crash
requirements separate for heavy vehicles, stating that these vehicles
differ significantly from light vehicles and require careful
consideration and research before establishing specific crash testing
requirements. It suggested benchmarking existing standards for light
vehicles as a starting point and adapting similar procedures with
appropriate performance criteria for heavy vehicle applications.
Agility proposed focusing on fuel system-specific tests, such as a sled
test, to account for the complexity of heavy vehicle configurations,
stating that such tests could yield consistent results independent of
the vehicle's body type or chassis. It also noted that current
practices under FMVSS Nos. 303 and 304 have been adequate for heavy CNG
vehicles and that a sled test could serve as a viable alternative to
full vehicle crash tests, potentially simplifying the process. Agility
also supported the use of a 15-second rolling average for data
filtration.
DTNA supported NHTSA's decision to exclude heavy vehicles, other
than school buses, from the proposed post-crash requirements, citing
the lack of existing comparable crash tests and the high costs of
conducting full-scale tests for heavy vehicle configurations. DTNA
recommended a partial vehicle impact test using a moving deformable
barrier (MDB), which allows for evaluating crash protection components
like shields and panels without the need for full-vehicle tests. It
suggested that vehicle simulations could also be used to assess these
components. DTNA supported retaining the moving contoured barrier test
for school buses over 10,000 pounds GVWR, as it aligns with current
FMVSS No. 301 standards. It proposed a simulation similar to the
Federal Motor Carrier Safety Administration's 30-foot drop test
requirements outlined in 49 CFR 393.67(e)(1) but advised against
conducting a 30-foot drop test solely on the container, stating that
this test would not reflect real-world conditions since hydrogen
containers often have additional protective components.
EMA supported component-level testing for heavy vehicles, noting
that full-scale crash tests would be impractical due to the custom
designs and low production volumes of these vehicles. It stated that
international standards such as GTR No. 20, ``Electric Vehicle
Safety,'' and UN ECE R100, ``Uniform provisions concerning the approval
of vehicles with regard to specific requirements for the electric power
train,'' rely on mechanical shock tests at the component level. EMA
agreed with the inclusion of crash tests for hydrogen-fueled school
buses, as these tests align with FMVSS No. 301 and provide consistent
safety standards with liquid-fueled buses. EMA stated that heavy school
buses have relatively few model offering and vehicle configurations.
Nikola supported applying side impact tests when the CHSS falls
within the MDB impact zone defined by FMVSS No. 214, ``Side impact
protection,'' and suggested allowing manufacturers to determine the
specific impact zones based on vehicle design. Nikola completed
frontal, side, and rear impact tests for its own designs and proposed
that each manufacturer should be responsible for identifying the
relevant strike zones on its vehicles. Nikola also stated that the
proposed post-crash CHSS retention and leakage requirements seemed
reasonable, but it did not see a need for a sled test.
Hyzon agreed with NHTSA's decision not to introduce new post-crash
requirements for hydrogen-powered heavy vehicles (HPHV) in FMVSS No.
307, aligning the standard with GTR No. 13 Phase 2. It stated that
NHTSA has not set crash test requirements for any other heavy vehicles,
and there is no justification for unique post-crash requirements
specifically for HPHVs. Hyzon suggested that further research be
conducted before considering additional standards. Hyzon suggested
waiting for more data from GTR No. 13 Phase 3 before deciding on any
new crash tests.
Glickenhaus expressed safety concerns about crash testing vehicles
with hydrogen onboard, stating that the proposed regulations do not
reference procedures and processes to make that crash test safe. It
pointed out that while NHTSA typically includes safety protocols in its
standards, such as substituting Stoddard solvent for gasoline during
FMVSS No. 301 testing, the proposed regulations under FMVSS Nos. 307
and 308 would allow crashes with hydrogen or helium. It requested that
if manufacturers are expected to choose between testing with hydrogen
or helium, this expectation should be explicitly stated in the
regulation. Glickenhaus stated that two testing laboratories have
expressed reluctance to perform crash tests with hydrogen due to safety
concerns, preferring helium or other inert gases. It argued that if
these experienced labs are not comfortable testing with hydrogen, it is
unlikely that manufacturers could safely conduct these tests on their
own. Additionally, Glickenhaus recommended using thermal imaging
cameras for fire detection, as hydrogen fires are clear and colorless,
making them difficult to identify through visual inspection alone.
NFA commented on the need for mechanical shock testing for heavy
vehicles but noted a lack of comprehensive data to conclusively assess
the relevance of a sled test. It stated that both NFA and its CHSS
manufacturers adhere to the mechanical shock requirements in NGV 6.1,
``Compressed natural gas (CNG) fuel storage and delivery systems for
road vehicles,'' which requires 8g inertia loading in all three primary
axes without failure, and referenced UN ECE R134, which specifies lower
inertia loading requirements of 6.6g longitudinally and 5g
transversely. NFA commented that harmonizing regulations across North
America and Europe would provide consistency. It recommended continuing
testing at the CHSS component level, including the mounting system, to
ensure tests reflect real-world installations and establish a baseline
performance standard applicable to all vehicle types, regardless of
available crash data. It also suggested that NHTSA allow calculation or
simulation methods, like Finite Element Analysis, to demonstrate
compliance to reduce prototyping and testing costs for OEMs. NFA noted
the infrequency of crashes involving its vehicles and the limited full-
vehicle testing required by current regulations, adding that it
currently position CHSS in less vulnerable areas, such as roof-mounted
or protected luggage compartments. However, it stated that if
sufficient data becomes available to support a performance requirement,
testing should be standardized at the CHSS component or assembly level
instead of full-vehicle testing.
HATCI stated that it supports the Agency's harmonization with GTR
No. 13 for post-crash fuel system integrity.
Agency Response
After consideration of the comments received, NHTSA has decided to
maintain the scope of the post-crash requirements as initially proposed
for vehicles that use hydrogen fuel for propulsion power, limiting the
applicability to passenger cars, multipurpose passenger vehicles,
[[Page 6270]]
trucks, and buses with a GVWR of less than or equal to 4,536 kg (10,000
pounds), as well as all school buses. NHTSA will not extend the post-
crash requirements to include all heavy vehicles with a GVWR greater
than 4,536 kg at this time.
NHTSA agrees with the commenters that limiting the post-crash
requirements to light vehicles with a GVWR of 10,000 pounds or less and
to all school buses regardless of GVWR is appropriate at this time, as
it helps minimize the testing burden and addresses the practical
limitations of conducting full-scale vehicle tests on heavier vehicles.
NHTSA agrees that more research is needed before considering the
inclusion of heavy vehicles other than school buses in the post-crash
requirements, given the complexity of these vehicles and the absence of
existing crash tests for heavy vehicles. NHTSA is considering future
research to address the comments that component-level testing, rather
than full vehicle crash testing, may be appropriate for heavy vehicle
fuel systems at this time and that benchmarking against existing light
vehicle crash testing procedures is a reasonable starting point for
future heavy vehicle applications.
Furthermore, NHTSA is not implementing a moving contoured barrier
impact test for heavy vehicles at this time due to the complexity
associated with developing an objective test applicable to various
heavy vehicle designs. Further research is needed to determine
appropriate testing methods for tests involving heavy vehicles, and
current data is insufficient to justify the inclusion of such tests.
Regarding the use of helium as an alternative to hydrogen for crash
testing, NHTSA proposed this option in the regulatory text to provide
flexibility for manufacturers. NHTSA will maintain the proposal that
the test gas for compliance testing may be either hydrogen or helium,
with the choice of test gas being at the manufacturer's option.
Hydrogen and helium gas have similar leak characteristics, so it is
expected that a vehicle that meets the performance requirements when
tested with one gas will also meet the performance requirements when
tested with the other.
NHTSA is not currently specifying the use of thermal imaging
cameras as a means to detect post-crash fire. However, test labs are
encouraged to use available technology such as thermal cameras or other
heat detection equipment when evaluating for the presence of post-crash
fire.
D. Tolerances
Background
The concept of test parameter tolerances refers to the allowable
variations in the conditions or parameters under which a test is
conducted, without impacting the validity or reliability of the test
results. In regulatory testing, it is often impractical or impossible
to maintain exact, fixed values for all parameters throughout the
testing process. Therefore, tolerances are established to allow for
slight deviations that are considered acceptable within a specified
range. These tolerances ensure that even though the exact conditions
may not be strictly identical in each test, the outcomes will remain
consistent and comparable, as long as they fall within the defined
tolerance limits. NHTSA proposed test parameter tolerances that are
generally consistent with the suggested tolerances specified in the GTR
No. 13. By adopting these established tolerances, NHTSA ensures that
test conditions remain controlled and reliable while allowing for
practical flexibility in testing environments.
Comments Received
TesTneT stated that in its 35 years of experience with hydraulic
pressure cycle testing, it has not faced issues meeting a low-pressure
tolerance of 1 MPa. Nikola stated that the proposed low-pressure range
for container pressure cycling was ``adequate.'' However, Luxfer Gas
Cylinders commented that the proposed lower limits of 1 MPa to 2 MPa
for pressure cycling tests are ``too low and too tight.'' Luxfer stated
that few containers would likely reach 1 or 2 MPa during actual
service, making the test conditions unrealistic. It also noted
challenges in maintaining these limits due to industrial testing
equipment constraints and recommended revising the range to align with
NGV 2, where cycling occurs between no greater than 10 percent of the
service pressure and 125 percent of the service pressure.
Auto Innovators expressed concern over NHTSA's application of GTR
No. 13 tolerances. It noted that GTR No. 13 specifies target values and
allowable tolerances ([alpha]), but the NPRM proposed a
range between (X-[alpha]) and (X+[alpha]) without defining a target.
Auto Innovators argued that this proposal could compel manufacturers to
set equipment at either extreme of the range, potentially testing at
various points in between, which it argued deviates from the test's
purpose. Auto Innovators cited the low-pressure cycling test, where
NHTSA proposed a range of ``between 1 MPa and 2 MPa.'' It stated that
this approach could lead to impractical testing conditions and
recommended NHTSA align with GTR No. 13. It also provided a table
listing parameters in GTR No. 13 that use minimum (>=) and maximum (<=)
values.
H2MOF proposed setting the lower bound of the pressure cycle at no
more than 10 percent of the upper cycle, with an absolute maximum of 3
MPa, in line with the standard ISO 11515. H2MOF stated that the upper
bound in ISO 11515 is defined as the maximum developed pressure at 65
[deg]C, or approximately 117 percent of NWP. HATCI generally supported
harmonizing with GTR No. 13. FORVIA stated that indicators for
conditions like 85 degrees Celsius should use ``greater than or equal
to'' and for -40 degrees Celsius, ``less than or equal to.'' It also
requested maintaining the low-pressure range of 1 MPa to 2 MPa to
ensure a margin above ambient pressure.
Agency Response
The use of open-ended tolerances, such as ``greater than or equal
to'' (>=) and ``less than or equal to'' (<=) symbols, does not provide
the necessary clarity for conducting robust and consistent tests. The
use of ``>='' or ``<='' without specific upper or lower limits could
result in impractical testing conditions, potentially leading to tests
at unreasonably high or low values that are irrelevant to real-world
performance or safety objectives. Without a defined range, the test
could extend to extreme values of temperature or pressure, for example,
making the test results unrealistic and inconsistent. A specific range
with both upper and lower bounds is essential to ensure the tests
reflect conditions relevant to vehicle safety, while also providing a
controlled and repeatable environment for assessment.
Furthermore, tolerance ranges allow for slight variation in test
parameters during testing while maintaining the validity of the
results. Testing at any point within the proposed range will not affect
the overall outcome, nor will fluctuations within the range impact the
results. This concept allows for flexibility within the defined range
that does not materially affect the test results because the allowed
variation is small enough to be considered insignificant in relation to
the overall test objectives.
NHTSA maintains that the test parameter tolerances proposed in the
NPRM are generally consistent with GTR No. 13. When GTR No. 13 provides
an open-ended range, such as ``<= 2 MPa,'' the GTR No. 13 suggested
tolerance is not listed with ``'' because
[[Page 6271]]
it is not intended to be applied to both sides of range endpoint.
Instead, the tolerance is only intended to be applied to the open end
of the range. Hence NHTSA's proposal of between 1 MPa and 2 MPa, based
on the GTR No. 13 suggested tolerance of 1 MPa.
GTR No. 13 paragraph 245 provides another example, citing GTR No.
13 paragraph 6.2.3.5., where the static hold pressure is specified as
>=125 per cent NWP. In this case, there is a minimum value of the
range, but no maximum. GTR No. 13 paragraph 245 states that in this
case, ``the tolerance of 5 percent NWP in the table could be applied,
which results in a maximum of 130 percent NWP.''
Hence, for the low-pressure range during hydraulic cycling, NHTSA
proposed a tolerance of between 1 MPa and 2 MPa, based on the GTR No.
13 suggested tolerance of 1 MPa. Regarding Luxfer Gas Cylinders'
comment that the proposed lower limits of 1 MPa to 2 MPa for pressure
cycling tests are ``too low and too tight,'' NHTSA notes that the test
tolerances proposed in the NPRM are supported by TestNet's comment that
in its 35 years of experience with hydraulic pressure cycle testing, it
has not faced issues meeting a low-pressure of 1 MPa.
The argument that tolerances would force manufacturers or test labs
to test at extreme ends of the range, such as the lowest or highest
allowable point and at all points within the range, is inaccurate.
NHTSA believes all of the proposed test procedures are robust enough to
accommodate minor fluctuations in parameters without affecting the
outcome of the test or repeatability of the results. The entire range
is designed to ensure consistent and valid test results, regardless of
where within the range the test is performed, or whether there are
fluctuations within the range during testing. The parameters, as
proposed, provide the necessary testing flexibility without sacrificing
the repeatability and reproducibility of the testing procedure.
Moreover, the use of a specified range prevents the need for excessive
precision, which could make testing more difficult and unnecessarily
increase the burden on test laboratories.
E. General Comments
Background
NHTSA received several general comments about the proposed
standard, reflecting broad perspectives on the overall proposal. These
comments did not address specific technical or procedural issues but
instead addressed general aspects of the proposed standards.
Comments Received
An anonymous commenter stated that the establishment of new
standards for hydrogen fuel systems was an ``excellent next step''
given the increasing prevalence of hydrogen-powered vehicles. It stated
that it was important to consider the risks associated with pressurized
hydrogen containers, which differ from non-pressurized gasoline or
diesel containers, and noted that hydrogen is highly flammable,
particularly in a compressed state. The commenter suggested that
implementing a safety standard could reduce risks of death and injury
related to the integrity of these containers.
Consumer Reports supported the proposed creation of FMVSS Nos. 307
and 308, stating that while hydrogen fuel cell vehicle sales have been
limited, manufacturers are making advancements in this technology. It
described the standards as necessary for both fuel system integrity and
the compressed hydrogen storage system.
Auto Innovators echoed this support but also recommended that NHTSA
revise its proposal to better align with GTR No. 13. It highlighted
potential challenges due to differences in certification testing,
especially when tests are conducted in series, which could lead to
increased costs. Ford similarly supported the proposed standards and
highlighted its experience in hydrogen technology research. Ford
endorsed Auto Innovators' call for close alignment with GTR No. 13 and
stated that GTR No. 13 guides its North American product development.
Hyundai expressed support for the proposed adoption of FMVSS Nos. 307
and 308 and agreed with NHTSA's statement that the standards address an
emerging safety need. Hyundai acknowledged the rationale behind
deviations from GTR No. 13 but suggested exploring additional ways to
harmonize with the global regulation, and referred to Auto Innovators'
comments for specific recommendations.
Glickenhaus commented that the Department of Transportation (DOT)
already has extensive regulations prescribing testing and certification
requirements for compressed hydrogen storage containers used for
transporting hydrogen on public roads under the Hazardous Materials
Regulations (HMR) in 49 CFR Subchapter C. It specifically referenced 49
CFR 172, which lists hazardous materials that include compressed
hydrogen and hydrogen fuel cell vehicles, and stated that DOT's
requirements for cryogenic and compressed hydrogen storage containers,
including their manufacturing, testing, and certification, are outlined
in 49 CFR part 173. Glickenhaus stated that it does not appear that any
of these requirements are referenced or incorporated into the container
requirements for FMVSS No. 308. It suggested that if the pressure
vessel or components making up a CHSS have already undergone DOT
hazardous material transportation certification, it could potentially
reduce additional testing requirements specific to using those
containers for fuel storage in hydrogen fuel cell vehicles. Glickenhaus
expressed concern that the lack of harmony between DOT's HMR standards
for compressed hydrogen containers and FMVSS No. 308's requirements
could result in a scenario where a container certified for transporting
hydrogen over roads, ships, and airways in the United States might not
be legal for use in vehicles on those same roads. Alternatively, it
stated, if a container were certified under FMVSS No. 308 but not under
DOT's hazardous materials transport standards, any towing company might
inadvertently violate hazardous material transportation regulations by
transporting a hydrogen fuel cell vehicle and its stored hydrogen. It
stated that it does not want this responsibility to fall to towing
companies. They stated that they do not want NHTSA to create a
regulation that would make it a violation of other DOT requirements to
tow or transport a hydrogen fuel cell vehicle.
TTP commented that the proposal is not consistent with existing
FMVSS Nos. 303 and 304, and that the intent is unclear regarding
establishing standards specifically for fuel systems or for the vehicle
as a whole. They expressed uncertainty about how the proposed
standards, if required by new FMVSS, would be enforced and noted that
testing and verification by NHTSA would be costly and impractical. TTP
questioned if the intent was to approach enforcement differently from
the current methodology under FMVSS Nos. 303 and 304. They recommended
that NHTSA harmonize with existing methodologies and allow industry
standards to control certification and compliance wherever possible to
maintain consistency. TTP also stated there are significant differences
between the production processes for light and heavy vehicle
applications and that enforcement of the proposals would not be
practical for both. They stated that
[[Page 6272]]
light vehicle OEMs build a complete vehicle, which simplifies
homologation due to consistent configurations, whereas the heavy market
involves a mix of suppliers and intermediate manufacturers, making
enforcement of vehicle-specific requirements impractical. TTP further
commented that the proposal does not align with existing industry
standards for container requirements, such as HGV 2, ``Compressed
Hydrogen Gas Vehicle Fuel Containers,'' and NGV 2, and stated that some
proposed requirements may compromise safety or prevent the use of
containers with good safety records. They stated the proposal is not
consistent with industry standards for component-level fuel system
requirements specified in HPRD 1 and HGV 3.1, and they requested
harmonization with these standards. Additionally, TTP requested
clarification on whether the intent of the proposed FMVSS Nos. 307 and
308 would differ from FMVSS Nos. 303 and 304.
Agency Response
Some commenters raised concerns regarding potential misalignment
between FMVSS No. 308 and the DOT hazardous materials regulations for
compressed hydrogen storage systems. The regulation of the
transportation of hydrogen over roads as cargo within tanker trucks in
the United States is governed by the PHMSA through 49 CFR Subchapter C-
Hazardous Materials Regulations (HMR).\54\ PHMSA standards focus on the
safe transportation of hazardous materials like hydrogen across all
modes of transport, including trucks, and prioritizes minimizing risks
during transport and handling of hydrogen, including potential leaks or
spills. On the other hand, FMVSS Nos. 307 and 308 focus on the fuel
system integrity of motor vehicles that use compressed hydrogen as a
fuel source to propel the vehicle with the purpose of reducing deaths
and injuries occurring from fires that result from hydrogen fuel
leakage during vehicle operation and after motor vehicle crashes and
from explosions resulting from the bursting of pressurized hydrogen
containers.
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\54\ https://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C.
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FMVSS No. 308 addresses vehicle-specific safety needs with a focus
on vehicle occupant safety that go beyond the PHMSA regulations for the
transportation of hazardous materials. While PHMSA regulations govern
hydrogen storage containers during transportation and are designed to
mitigate safety risks during transport and handling of hydrogen, FMVSS
No. 308 is specifically designed to ensure safety in the context of
real-world driving, fueling, and crash conditions. Hydrogen storage
systems in vehicles used for vehicle propulsion must meet performance
standards that address risks unique to vehicle operation, including
repeated fueling in different fueling conditions, dynamic driving
environments, and potential accidents. Therefore, while DOT regulations
and FMVSS No. 308 serve related functions, the standards are distinct
and necessary for their respective purposes.
Several commenters also questioned the practicality and intent of
the proposed FMVSS Nos. 307 and 308, particularly in relation to
existing standards like FMVSS Nos. 303 and 304, which apply to CNG
systems. NHTSA believes that hydrogen vehicles present distinct safety
challenges that require specific regulatory measures. The unique
properties of compressed hydrogen, such as its higher storage pressures
and greater flammability, necessitate separate performance requirements
to mitigate the associated risks. Hydrogen fuel systems have
characteristics that differ significantly from CNG systems, and as a
result, the proposed standards reflect the distinct differences
presented by hydrogen. While FMVSS Nos. 303 and 304 remain effective
for CNG, they are not sufficient to address the safety risks unique to
hydrogen fueled vehicles.
Some commenters expressed concerns about the potential lack of
harmonization between FMVSS Nos. 307 and 308 and GTR No. 13. As
discussed above, NHTSA acknowledges these concerns but emphasizes that
the proposed standards have been tailored specifically to address the
safety needs of hydrogen vehicles in the context of the FMVSS. While
GTR No. 13 is the primary basis for the proposed FMVSS Nos. 307 and
308, exact alignment with GTR No. 13 is not possible in FMVSS, for the
reasons discussed above in section IV.A.
Similarly, some commenters suggested that existing industry
standards for component-level fuel system requirements should be used
as the primary basis for FMVSS Nos. 307 and 308. NHTSA acknowledges the
value of the standards HGV 2, HGV 3.1, and HPRD 1, and notes that they
were considered during the development of GTR No. 13. However, FMVSS
are intended to establish minimum vehicle-level safety performance
standards, and it is not necessary nor practical to adopt the entirety
of industry standards into the FMVSS. While industry standards play an
important role in ensuring the safety of individual components, FMVSS
Nos. 307 and 308 set baseline requirements for hydrogen fuel systems to
ensure that they function safely as part of the overall vehicle system.
NHTSA's focus was in aligning the proposed FMVSS Nos. 307 and 308 with
GTR No. 23 to enable global harmonization of regulations for hydrogen
powered vehicles.
FMVSS establish minimum safety requirements and the FMVSS test
procedures provide notice to establish how the agency would verify
compliance. However, this does not mean that manufacturers must conduct
the exact test in the FMVSS to certify their vehicles. The Motor
Vehicle Safety Act \55\ requires manufacturers to certify that their
vehicles meet all applicable FMVSS, and specifies that manufacturers
may not certify compliance if, in exercising reasonable care, the
manufacturer has reason to know the certificate is false or misleading.
A manufacturer may use component-level tests to certify its vehicles if
it exercises reasonable care in doing so. Manufacturers must ensure
that their vehicles will meet the requirements of FMVSS Nos. 307 and
308 when NHTSA tests the vehicles in accordance with the test
procedures specified in the standards, but manufacturers may use
different test procedures to do so.
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\55\ 49 U.S.C. Ch. 301: Motor Vehicle Safety, https://uscode.house.gov/view.xhtml?req=granuleid%3AUSC-prelim-title49-chapter301&edition=prelim.
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In response to concerns about the enforceability of the proposed
standards, particularly for heavy vehicles with complex production
processes, NHTSA believes that the proposed FMVSS Nos. 307 and 308
standards are practical and enforceable across vehicle types. Although
the heavy vehicle market involves a diverse supply chain with multiple
intermediate manufacturers, the performance-based nature of these
standards allows for flexibility in design. The regulations do not
prescribe specific design solutions but instead set performance
criteria, which manufacturers can meet using various engineering
approaches. This adaptability ensures that both light and heavy
vehicles can comply with the safety requirements without imposing
impractical regulatory burdens. NHTSA is confident that these standards
will not result in undue complexity or unnecessary cost in terms of
enforcement.
[[Page 6273]]
F. Lead Time
Background
In the NPRM, NHTSA proposed two key dates regarding the
implementation of FMVSS Nos. 307 and 308. First, the effective date was
proposed as 180 days after the publication of the final rule in the
Federal Register. This is the date when the final rule would officially
go into effect. Second, NHTSA proposed a compliance date for
manufacturers to fully adhere to the new requirements. The compliance
date was initially stated as September 1, two years after the
publication of the final rule. However, in the ``Lead Time'' section, a
different compliance date was proposed as September 1 in the year
following the rule's publication. This was a clerical error, as both
compliance dates should have stated ``the first September 1 that is two
years after the publication of the final rule.''
Comments Received
Nikola stated they agree with the rule taking effect the following
September. EMA commented that heavy vehicle manufacturers would need at
least five years from the final rule's publication to comply, stating
that GTR No. 13 Phase 2 had only been recently approved and the
revision broadened its scope to include heavy vehicles. EMA cited the
need for manufacturers to evaluate the new requirements, conduct
validation testing, and potentially redesign components. Similarly,
Auto Innovators raised concerns about the proposed compliance period,
suggesting that an additional five years beyond the one-year compliance
date would be necessary. They noted a lack of harmonization with GTR
No. 13, which they stated would require significant design, hardware,
and software adjustments for manufacturers.
Several commenters, including Auto Innovators, HATCI, and
Glickenhaus, also pointed out conflicting compliance dates within the
NPRM. Auto Innovators and HATCI pointed out inconsistencies between the
Dates section, which stated the compliance date as two years after
publication, and the Lead Time section, which stated it as one year.
Both organizations requested additional lead time due to a lack of
harmonization with GTR No. 13 and the substantial vehicle design
changes they stated will be required. HATCI requested a compliance date
of five years from the first September 1 after the final rule's
publication, and cited potential impacts on pre-production vehicles due
to a lack of harmonization which will prevent manufacturers from
utilizing existing hardware and software.
Glickenhaus requested a three-year extension for low volume
manufacturers to avoid disruption to current pilot projects. Hyundai
also recommended a five-year compliance period after the September 1
following the rule's publication, stating that this is justified by the
signi[filig]cant number of changes from GTR No. 13 in FMVSS Nos. 307
and 308, the inclusion of substantive new requirements, and the time
required for design changes, validation and certi[filig]cation. Hyundai
also noted that these proposed requirements are generally consistent
with current industry practices, so there is no immediate safety
necessity warranting a shorter lead time.
Agency Response
NHTSA acknowledges the comments regarding the proposed lead time
and the concerns raised about the inconsistency between the compliance
dates mentioned in the NPRM. NHTSA acknowledges that the ``Lead Time''
section was not updated correctly to reflect the intended proposed
compliance timeline. To clarify this issue, first, NHTSA confirms that
the effective date remains as proposed: 180 days after the publication
of the final rule in the Federal Register.
Second, in response to commenters' requests for additional lead
time for the compliance date, particularly from heavy vehicle
manufacturers and others citing the need for additional time, NHTSA has
revised the compliance date in the final rule. The final rule will
adopt a compliance date that will be September 1, 2028, more than 3
years after the publication of the final rule. This extension provides
additional time for manufacturers to ensure compliance without causing
significant disruption.
However, NHTSA emphasizes that the requirements proposed under
FMVSS Nos. 307 and 308 are closely aligned with GTR No. 13 and current
industry practices. Many manufacturers have already implemented safety
systems and testing procedures that meet the requirements of the final
rule, and thus an extended lead time beyond the three-year period is
not necessary. NHTSA is not aware of any peculiarities of the U.S.
market that would necessitate lead times double or triple the lead
times in other markets.\56\
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\56\ NHTSA knows from its involvement in UN ECE that the lead
times in other markets are sometimes substantially shorter than
those often requested by manufacturers in the United States. As an
example, Europe's General Safety Regulation was adopted in late 2019
and required that manufacturers equip vehicles with certain vehicle
safety features by July 2022. See https://www.tuvsud.com/en-us/resource-centre/stories/revision-of-the-eu-general-safety-regulation. This period of less than 3 years is less than the
timelines often requested by American industry, who often seek much
longer lead times.
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V. Other Changes to the Regulatory Text
A clerical correction was made to the S3 Application section of
FMVSS No. 308 to add the words ``to propel the vehicle.'' These words
were included in S3 Application of FMVSS No. 307, but were
inadvertently omitted from FMVSS No. 308 S3. This edit is editorial in
nature to improve the clarity of the section, and does not intend to
change the application of the standard.
A clerical correction was made to S6.2.2.2(e), deleting the word
``container'' from ``container manufacture may specify.'' The inclusion
of the word ``container'' before manufacturer was erroneous since the
standard is being applied as a vehicle-level standard, as discussed
above. The section will now simply state that the ``manufacturer may
specify.''
A clerical correction was made to the definition of ``hydrogen fuel
system'' to replace the word ``mean'' with ``means'' for grammatical
accuracy.
S5.2.2 was updated to include the words ``The vehicle shall meet at
least'' to clarify that the vehicle must meet at least one of the
requirements listed in S5.2.2 (a) though (c).
S6.1 was updated to include the words ``individual test'' before
vehicle to clarify that the statement is referring to a specific
individual test vehicle, not a line or model of vehicle.
S6.4.2(c) was updated to replace the word ``volumes'' with
``spaces.'' The section is referring to enclosed or semi-enclosed
spaces, which are defined in the standard, whereas enclosed or semi-
enclosed volumes are not defined.
NHTSA replaced all instances of the word ``manufacturer'' with
``vehicle manufacturer'' to clarify that the vehicle manufacturer is
responsible for all aspects of the two standards.
VI. Rulemaking Analyses and Notices
Executive Order 12866, Executive Order 13563, and DOT Regulatory
Policies and Procedures
We have considered the potential impact of this final rule under
Executive Order 12866, Executive Order 13563, and DOT Order 2100.6A.
This final rule is nonsignificant under E.O. 12866 and was not reviewed
by the Office of Management and Budget. It is also not considered ``of
special note to the Department'' under DOT Order
[[Page 6274]]
2100.6A, Rulemaking and Guidance Procedures.
Today, there are only two publicly available vehicle models that
may be affected by the final rule, which collectively equal less than
5,000 vehicles sold per model year. Most manufacturers and vehicle
lines currently in production would be unaffected by this rule. Of
those vehicles that would be covered by today's standards, we expect
the compliance cost to be minimal. As discussed earlier, the few
manufacturers that already offer hydrogen vehicles in the marketplace
already take safety precautions to attempt to emulate the safety of
conventional and battery electric vehicles, and adhere to the industry
guidelines that informed the creation of GTR No. 13. Because the final
rule is intended to coalesce industry practice and future designs
through harmonized regulations, we do not expect that the rule would
pose a significant cost to current manufacturers, or for manufacturers
that may be planning to enter the market.
Given NHTSA is establishing these standards during the early
development of hydrogen vehicles, there is no baseline to compare
today's rule against. While we anticipate the regulations will promote
safer hydrogen vehicles, we cannot quantify this benefit with any
degree of certainty, especially given that we cannot forecast what the
industry would look like in the absence of our proposed standard.
Furthermore, most of the safety benefits that will accrue to this rule
will only be realized when hydrogen vehicles become more prevalent. The
net present value of these future costs and benefits is minimal.
Regulatory Flexibility Act
Pursuant to the Regulatory Flexibility Act (5 U.S.C. 601 et seq.,
as amended by the Small Business Regulatory Enforcement Fairness Act
(SBREFA) of 1996), whenever an agency is required to publish a notice
of proposed rulemaking or final rule, it must prepare and make
available for public comment a regulatory flexibility analysis that
describes the effect of the rule on small entities (i.e., small
businesses, small organizations, and small governmental jurisdictions).
The Small Business Administration's regulations at 13 CFR part 121
define a small business, in part, as a business entity ``which operates
primarily within the United States.'' (13 CFR 121.105(a)(1)). No
regulatory flexibility analysis is required if the head of an agency
certifies the proposed or final rule will not have a significant
economic impact on a substantial number of small entities. SBREFA
amended the Regulatory Flexibility Act to require Federal agencies to
provide a statement of the factual basis for certifying that a proposed
or final rule will not have a significant economic impact on a
substantial number of small entities.
I certify that these standards will not have a significant impact
on a substantial number of small entities. This action creates FMVSS
Nos. 307 and 308 to establish minimum safety requirements for the CHSS
and fuel system integrity of hydrogen vehicles. FMVSS Nos. 307 and 308
are vehicle standards. We anticipate any burdens of the standard will
fall onto manufacturers of hydrogen vehicles. NHTSA is unaware of any
small entities that currently manufacture or are planning to
manufacture hydrogen vehicles. Furthermore, NHTSA is adopting standards
similar to those already in place across industry. Thus, we anticipate
the impacts of this final rule on all manufacturers to be minimal
regardless of manufacturer size.
Executive Order 13132
NHTSA has examined this final rule pursuant to Executive Order
13132 (64 FR 43255, August 10, 1999) and concluded that no additional
consultation with States, local governments or their representatives is
mandated beyond the rulemaking process. The Agency has concluded that
this action would not have ``federalism implications'' because it would
not have ``substantial direct effects on States, on the relationship
between the national government and the States, or on the distribution
of power and responsibilities among the various levels of government,''
as specified in section 1 of the Executive order. This final rule would
apply to motor vehicle manufacturers. Further, no State has adopted
requirements regulating the CHSS or fuel integrity of hydrogen powered
vehicles. Thus, Executive Order 13132 is not implicated and
consultation with State and local officials is not required.
NHTSA rules can preempt in two ways. First, the National Traffic
and Motor Vehicle Safety Act contains an express preemption provision:
When a motor vehicle safety standard is in effect under this chapter, a
State or a political subdivision of a State may prescribe or continue
in effect a standard applicable to the same aspect of performance of a
motor vehicle or motor vehicle equipment only if the standard is
identical to the standard prescribed under this chapter. 49 U.S.C.
30103(b)(1). It is this statutory command by Congress that preempts any
non-identical State legislative and administrative law addressing the
same aspect of performance.
The express preemption provision described above is subject to a
savings clause under which compliance with a motor vehicle safety
standard prescribed under this chapter does not exempt a person from
liability at common law. 49 U.S.C. 30103(e). Pursuant to this
provision, State common law tort causes of action against motor vehicle
manufacturers that might otherwise be preempted by the express
preemption provision are generally preserved.
NHTSA rules can also preempt State law if complying with the FMVSS
would render the motor vehicle manufacturers liable under State tort
law. Pursuant to Executive Order 13132 and 12988, NHTSA has considered
whether this rule could or should preempt State common law causes of
action. The agency's ability to announce its conclusion regarding the
preemptive effect of one of its rules reduces the likelihood that
preemption will be an issue in any subsequent tort litigation. To this
end, the agency has examined the nature (i.e., the language and
structure of the regulatory text) and objectives of this rule and finds
that this rule, like many NHTSA rules, would prescribe only a minimum
safety standard. As such, NHTSA does not intend this NPRM to preempt
State tort law that would effectively impose a higher standard on motor
vehicle manufacturers rule. Establishment of a higher standard by means
of State tort law will not conflict with the minimum standard adopted
here. Without any conflict, there could not be any implied preemption
of a State common law tort cause of action.
Executive Order 12988 (Civil Justice Reform)
When promulgating a regulation, Executive Order 12988 specifically
requires that the agency must make every reasonable effort to ensure
that the regulation, as appropriate: (1) Specifies in clear language
the preemptive effect; (2) specifies in clear language the effect on
existing Federal law or regulation, including all provisions repealed,
circumscribed, displaced, impaired, or modified; (3) provides a clear
legal standard for affected conduct rather than a general standard,
while promoting simplification and burden reduction; (4) specifies in
clear language the retroactive effect; (5) specifies whether
administrative proceedings are to be required before parties may file
suit in court; (6) explicitly or implicitly defines key terms; and (7)
addresses other important issues affecting clarity
[[Page 6275]]
and general draftsmanship of regulations.
Pursuant to this Order, NHTSA notes as follows. The preemptive
effect of this final rule is discussed above in connection with E.O.
13132. NHTSA notes further that there is no requirement that
individuals submit a petition for reconsideration or pursue other
administrative proceeding before they may file suit in court.
Executive Order 13609 (Promoting International Regulatory Cooperation)
Executive Order 13609, ``Promoting International Regulatory
Cooperation,'' promotes international regulatory cooperation to meet
shared challenges involving health, safety, labor, security,
environmental, and other issues and to reduce, eliminate, or prevent
unnecessary differences in regulatory requirements.
The final rule adopts the technical requirements of GTR No.13, a
technical standard for hydrogen vehicles adopted by the United Nations
Economic Commission for Europe (UN ECE) World Forum for Harmonization
of Vehicle Regulations (WP.29). As a Contracting Party that voted in
favor of GTR No. 13, NHTSA was obligated to initiate rulemaking to
incorporate safety requirements and options specified in GTR, which the
agency satisfied when it published its notice of proposed rulemaking
NHTSA is not required to finalize the text of the GTR.
While the final rule does contain some differences from GTR No. 13
to reflect U.S. law, they are consistent with the regulatory process
envisioned and encouraged from the outset of GTR No. 13. NHTSA will
continue to participate with the international community on GTR No. 13
and evaluate further amendments on their merits as they are adopted by
WP.29.
NHTSA has analyzed this final rule under the policies and agency
responsibilities of Executive Order 13609 and has determined this rule
would have no effect on international regulatory cooperation.
National Environmental Policy Act
NHTSA has analyzed this rule for the purposes of the National
Environmental Policy Act (42 U.S.C. 4321 et. seq.), as amended. In
accordance with 49 C.F.R Sec. 1.81, 42 U.S.C. 4336, and DOT NEPA Order
5610.1C, NHTSA has determined that this rule is categorically excluded
pursuant to 23 CFR 771.118(c)(4) (planning and administrative
activities, such as promulgation of rules, that do not involve or lead
directly to construction).
This rulemaking establishes two new FMVSS, FMVSS No. 307, ``Fuel
system integrity of hydrogen vehicles,'' which specifies requirements
for the integrity of the fuel system in hydrogen vehicles during normal
vehicle operations and after crashes, and FMVSS No. 308, ``Compressed
hydrogen storage system integrity,'' which specifies requirements for
the compressed hydrogen storage system to ensure the safe storage of
hydrogen onboard vehicles. This rulemaking is not anticipated to result
in any environmental impacts, and there are no extraordinary
circumstances present in connection with this rulemaking.
NHTSA expects the changes to new and existing vehicles to be
minimal, and mitigating the hazards associated with fires that result
from hydrogen fuel leakage during vehicle operation and after motor
vehicle crashes and from explosions resulting from the burst of
pressurized hydrogen containers would result in a public health and
safety benefit. For these reasons, the agency has determined that
implementation of this action will not have any adverse impact on the
quality of the human environment.
Paperwork Reduction Act
Under the procedures established by the Paperwork Reduction Act of
1995 (PRA) (44 U.S.C. 3501, et. seq.), Federal agencies must obtain
approval from the OMB for each collection of information they conduct,
sponsor, or require through regulations. A person is not required to
respond to a collection of information by a Federal agency unless the
collection displays a valid OMB control number. The Information
Collection Request (ICR) for a revision of a previously approved
collection described below will be forwarded to OMB for review and
comment. In compliance with these requirements, NHTSA asks for public
comments on the following proposed collection of information for which
the agency is seeking approval from OMB. In this final rule, we are
finalizing a revision and reinstatement to a previously approved OMB
collection, OMB Clearance No. 2127-0512, Consolidated Labeling
Requirements for Motor Vehicles (except the VIN).\57\
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\57\ In compliance with the requirements of the PRA, NHTSA is
separately publishing a notice to request comment on NHTSA's
reinstatement with modification of the previously approved
information collection request.
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Title: Consolidated Labeling Requirements for Motor Vehicles
(except the VIN).
OMB Control Number: OMB Control No. 2127-0512.
Type of Request: Revision of a previously approved collection.
Type of Review Requested: Regular.
Requested Expiration Date of Approval: 3 years from the date of
approval.
Summary of the Collection of Information: FMVSS No. 307 specifies
requirements for the integrity of motor vehicle fuel systems using
compressed hydrogen as a fuel source. Each hydrogen vehicle must have a
permanent label which lists the fuel type, service pressure, and a
statement directing vehicle users/operators to instructions for
inspection and service life of the fuel container. FMVSS No. 308
specifies requirements for the integrity of compressed hydrogen storage
systems (CHSS). Each hydrogen container must have a permanent label
containing manufacturer contact information, the container serial
number, manufacturing date, date of removal from service, and
applicable BPO burst pressure. If the proposed requirements
are made final, we will submit a request for OMB clearance of the
proposed collection of information and seek clearance prior to the
effective date of the final rule.
Description of the likely respondents: Vehicle manufacturers.
Estimated Number of Respondents: 10.
Estimated Total Annual Burden Hours: $8,616.
It is estimated that vehicle manufacturers will provide labels on
10 different hydrogen vehicle models. Since manufacturers have provided
CNG vehicles with similar required labels for many years, it is
estimated that manufacturers will have a generalized label template
which only requires minor adjustments for hydrogen and population with
the required information. There is an annual 1.0 hour burden for
manufacturers to have a Mechanical Drafter put the correct information
into a label template to create a model specific label. The annual
burden for this label creation is 10 hours (10 hydrogen vehicle model
labels * 1 hour per model label) and $478 (10 hydrogen vehicle model
labels * 1 hour per model label * $33.62 labor rate per hour / 70.3% of
labor rate as total wage compensation). Manufacturers will also bear a
cost burden of $1,884 (2,850 hydrogen vehicles * $0.73 per label) for
the required labels to be attached to the hydrogen vehicles. The
combined total annual burden to vehicle manufacturers from the
requirements to have the specified label text on hydrogen vehicles is
10 hours and $2,362. These hour and cost burdens represent a new
[[Page 6276]]
addition to this information collection request.
It is estimated that vehicle manufacturers will provide labels on
10 different hydrogen container models. Since manufacturers have
provided CNG containers with similar labels for many years, it is
estimated that manufacturers will have a generalized label template
which requires only minor adjustments for hydrogen and then population
with their current contact information, the container serial number,
manufacturing date, and date of removal from service. There is an
annual 1.0 hour burden for manufacturers to have a Mechanical Drafter
put the correct information into a label template to create a model
specific label. The annual burden for this label creation is 10 hours
(10 hydrogen container model labels * 1.0 hours per model label) and
$478 (10 hydrogen container models labels * 1.0 hours per model label *
$33.62 labor rate per hour / 70.3% of labor rate as total wage
compensation). Manufacturers will also bear a cost burden of $5,776
(7,910 hydrogen containers * $0.730 per label) for the required labels
to be attached to the hydrogen containers. The combined total annual
burden to vehicle manufacturers from the requirements to have the
specified label text on hydrogen containers is 10 hours and $6,254.
These hour and cost burdens represent a new addition to this
information collection request.
National Technology Transfer and Advancement Act
Under the National Technology Transfer and Advancement Act of 1995
(NTTAA) (Pub. L. 104) Section 12(d) of the National Technology Transfer
and Advancement Act (NTTAA) requires NHTSA to evaluate and use existing
voluntary consensus standards in its regulatory activities unless doing
so would be inconsistent with applicable law (e.g., the statutory
provisions regarding NHTSA's vehicle safety authority) or otherwise
impractical. Voluntary consensus standards are technical standards
developed or adopted by voluntary consensus standards bodies. Technical
standards are defined by the NTTAA as ``performance-based or design-
specific technical specification and related management systems
practices.'' They pertain to ``products and processes, such as size,
strength, or technical performance of a product, process or material.''
Examples of organizations generally regarded as voluntary consensus
standards bodies include ASTM International, the Society of Automotive
Engineers (SAE), and the American National Standards Institute (ANSI).
If NHTSA does not use available and potentially applicable voluntary
consensus standards, we are required by the Act to provide Congress,
through OMB, an explanation of the reasons for not using such
standards.
Today's final rule establishes standards that are consistent with
voluntary standards cited above such as SAEJ2579_201806, HPRD-1 2021,
and HGV 3.1 2022.
This final rule adopting key aspects of GTR No. 13 is consistent
with the goals of the NTTAA. This final rule adopts much of a global
consensus standard. However this final rule includes some minor
deviations from GTR No. 13. As discussed above, FMVSS must maintain
objectivity, clarity, and practicability, ensuring that every
requirement is measurable and enforceable, with unambiguous test
procedures. These adjustments ensure FMVSS remain clear, objective, and
enforceable. For example, NHTSA is removing subjective requirements
such as the TPRD atmospheric exposure test and the and localized leak
requirement from the ambient and extreme gas permeation test. NHTSA is
also requiring the testing of only one component for some tests instead
of multiple components (as specified in GTR No. 13 for assessing
variability in response), and eliminating duplicative requirements like
the proof pressure tests. NHTSA has also removed unnecessary
requirements for burst pressure variability, and removed a requirement
for an overpressure protection device that had no corresponding
performance test. NHTSA also selected a more balanced requirement for
the hydrogen concentration limit in the enclosed and semi-enclosed
spaces, rather than applying the GTR's zero limit to only the passenger
compartment.
The GTR was developed by a global regulatory body and is designed
to increase global harmonization of differing vehicle standards. The
GTR leverages the expertise of governments in developing safety
requirements for hydrogen fueled vehicles. NHTSA's consideration of GTR
No. 13 accords with the principles of NTTAA as NHTSA's consideration of
an established, proven regulation has reduced the need for NHTSA to
expend significant agency resources on the same safety need addressed
by GTR No. 13.
Incorporation by Reference
Under regulations issued by the Office of the Federal Register (1
CFR 51.5(a)), an agency, as part of a proposed rule that includes
material incorporated by reference, must summarize material that is
proposed to be incorporated by reference and discuss the ways the
material is reasonably available to interested parties or how the
agency worked to make materials available to interested parties. At the
final rule stage, regulations require that the agency seek formal
approval, summarize the material that it incorporates by reference in
the preamble of the final rule, discuss the ways that the materials are
reasonably available to interested parties, and provide other specific
information to the Office of the Federal Register.
NHTSA is incorporating by reference two documents into the Code of
Federal Regulations. First, NHTSA is incorporating by reference ASTM
D1193-06 (Reapproved 2018), Standard Specification for Reagent Water.
ASTM D1193-06 is an industry standard that defines the requirements for
the purity of water used in laboratories, ensuring that experiments and
tests are not compromised by water impurities. NHTSA will use a water
supply conforming to Type IV requirements of ASTM D1193-06 in testing
the compliance of closure devices with the salt corrosion resistance
test in 571.308 S6.2.6.1.4.
NHTSA is also incorporating by reference ISO 6270-2:2017, Paints
and Varnishes--Determination of Resistance to Humidity--Part 2:
Condensation (In-Cabinet Exposure with Heated Water Reservoir). ISO
6270-2:2017 specifies methods for assessing the resistance of materials
to humidity by focusing on how materials behave when exposed to high
humidity. ISO 6270-2:2017 provides detailed procedures and materials
for conducting tests where humidity is the primary variable. NHTSA will
use the apparatus described within ISO 6270-2:2017 in testing the
compliance of closure devices with the salt corrosion resistance test
in 571.308 S6.2.6.1.4.
All standards incorporated by reference in this rule are available
for review at NHTSA's headquarters in Washington, DC, and for purchase
from the organizations promulgating the standards. The ASTM standard is
also available for review at ASTM's online reading room.\58\
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\58\ https://www.astm.org/READINGLIBRARY/.
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Unfunded Mandates Reform Act
Section 202 of the Unfunded Mandates Reform Act of 1995 (UMRA),
Public Law 104-4, requires Federal agencies to prepare a written
assessment of the costs, benefits, and other effects
[[Page 6277]]
of proposed or final rules that include a Federal mandate likely to
result in the expenditure by State, local, or tribal governments, in
the aggregate, or by the private sector, of more than $100 million
annually (adjusted for inflation with base year of 1995). Adjusting
this amount by the implicit gross domestic product price deflator for
the year 2022 results in $177 million (111.416/75.324 = 1.48). This
rule will not result in a cost of $177 million or more to State, local,
or tribal governments, in the aggregate, or the private sector. Thus,
this rule is not subject to the requirements of sections 202 of the
UMRA.
Executive Order 13045 (Protection of Children From Environmental Health
and Safety Risks)
Executive Order 13045, ``Protection of Children from Environmental
Health and Safety Risks,'' (62 FR 19885, April 23, 1997) applies to any
proposed or final rule that: (1) Is determined to be ``economically
significant,'' as defined in E.O. 12866, and (2) concerns an
environmental health or safety risk that NHTSA has reason to believe
may have a disproportionate effect on children. If a rule meets both
criteria, the agency must evaluate the environmental health or safety
effects of the rule on children and explain why the rule is preferable
to other potentially effective and reasonably feasible alternatives
considered by the agency.
This rulemaking is not subject to the Executive Order because it is
not economically significant as defined in E.O. 12866.
Executive Order 13211
Executive Order 13211 (66 FR 28355, May 18, 2001) applies to any
rulemaking that: (1) is determined to be economically significant as
defined under E.O. 12866, and is likely to have a significantly adverse
effect on the supply of, distribution of, or use of energy; or (2) that
is designated by the Administrator of the Office of Information and
Regulatory Affairs as a significant energy action. This rulemaking is
not subject to E.O. 13211 as this rule is not economically significant
and should not have an adverse effect on the supply of, distribution
of, or use of energy for the same reasons explained in our discussion
of Executive Orders 12866 and 13563.
Plain Language
Executive Order 12866 requires each agency to write all rules in
plain language. Application of the principles of plain language
includes consideration of the following questions:
Have we organized the material to suit the public's needs?
Are the requirements in the rule clearly stated?
Does the rule contain technical language or jargon that
isn't clear?
Would a different format (grouping and order of sections,
use of headings, paragraphing) make the rule easier to understand?
Would more (but shorter) sections be better?
Could we improve clarity by adding tables, lists, or
diagrams?
What else could we do to make the rule easier to
understand?
If you have any responses to these questions, please include them
in your comments on this proposal.
Regulation Identifier Number (RIN)
The Department of Transportation assigns a regulation identifier
number (RIN) to each regulatory action listed in the Unified Agenda of
Federal Regulations. The Regulatory Information Service Center
publishes the Unified Agenda in April and October of each year. You may
use the RIN contained in the heading at the beginning of this document
to find this action in the Unified Agenda.
List of Subjects in 49 CFR Part 571
Imports, Incorporation by reference, Motor vehicle safety,
Reporting and recordkeeping requirements, Tires.
In consideration of the foregoing, NHTSA amends 49 CFR part 571 as
set forth below.
PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS
0
1. The authority citation for part 571 continues to read as follows:
Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166;
delegation of authority at 49 CFR 1.95.
0
2. Amend Sec. 571.5 by:
0
a. Redesignating paragraphs (d)(20) through (33) as paragraphs (d)(21)
through (34), respectively;
0
b. Adding new paragraph (d)(20);
0
d. Redesignating paragraphs (i)(1) through (4) as paragraphs (i)(2)
through (5), respectively; and
0
e. Adding new paragraph (i)(1).
The additions read as follows:
Sec. 571.5 Matter incorporated by reference.
* * * * *
(d) * * *
(20) ASTM D1193-06 (Reapproved 2018), Standard Specification for
Reagent Water, approved March 15, 2018, into Sec. 571.308.
* * * * *
(i) * * *
(1) ISO 6270-2:2017(E), Paints and Varnishes--Determination of
Resistance to Humidity--Part 2: Condensation (In-Cabinet Exposure with
Heated Water Reservoir), Second edition, November 2017, into Sec.
571.308.
* * * * *
0
3. Section 571.307 is added to read as follows:
Sec. 571.307 Standard No. 307; Fuel system integrity of hydrogen
vehicles
S1. Scope. This standard specifies requirements for the integrity
of motor vehicle hydrogen fuel systems.
S2. Purpose. The purpose of this standard is to reduce deaths and
injuries occurring from fires that result from hydrogen fuel leakage
during vehicle operation and after motor vehicle crashes.
S3. Application. This standard applies to each motor vehicle
manufactured on or after September 1, 2028, that uses compressed
hydrogen gas as a fuel source to propel the vehicle.
S4. Definitions.
Check valve means a valve that prevents reverse flow.
Closure devices mean the check valve(s), shut-off valve(s), and
thermally-activated pressure relief device(s) that control the flow of
hydrogen into and/or out of a CHSS.
Container means a pressure-bearing component of a compressed
hydrogen storage system that stores a continuous volume of hydrogen
fuel in a single chamber or in multiple permanently interconnected
chambers.
Container attachments mean non-pressure bearing parts attached to
the container that provide additional support and/or protection to the
container and that may be removed only with the use of tools for the
specific purpose of maintenance and/or inspection.
Compressed hydrogen storage system (CHSS) means a system that
stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed
of a container, container attachments (if any), and all closure devices
required to isolate the stored hydrogen from the remainder of the fuel
system and the environment.
Enclosed or semi-enclosed spaces means the passenger compartment,
luggage compartment, and space under the hood.
Fuel cell system means a system containing the fuel cell stack(s),
air processing system, fuel flow control system, exhaust system,
thermal management system, and water management system.
[[Page 6278]]
Fueling receptacle means the equipment to which a fueling station
nozzle attaches to the vehicle and through which fuel is transferred to
the vehicle.
Fuel lines means all piping, tubing, joints, and any components
such as flow controllers, valves, heat exchangers, and pressure
regulators.
Hydrogen concentration means the percentage of the hydrogen
molecules within the mixture of hydrogen and air (equivalent to the
partial volume of hydrogen gas).
Hydrogen fuel system means the fueling receptacle, CHSS, fuel cell
system or internal combustion engine, fuel lines, and exhaust systems.
Luggage compartment means the space in the vehicle for luggage,
cargo, and/or goods accommodation, bounded by a roof, hood, floor, side
walls being separated from the passenger compartment by the front
bulkhead or the rear bulkhead.
Maximum allowable working pressure (MAWP) means the highest gauge
pressure to which a component or system is permitted to operate under
normal operating conditions.
Nominal working pressure (NWP) means the settled pressure of
compressed gas in a container or CHSS fully fueled to 100 percent state
of charge and at a uniform temperature of 15 [deg]C.
Normal milliliter means a quantity of gas that occupies one
milliliter of volume when its temperature is 0 [deg]C and its pressure
is 1 atmosphere.
Passenger compartment means the space for occupant accommodation
that is bounded by the roof, floor, side walls, doors, outside glazing,
front bulkhead, and rear bulkhead or rear gate.
Pressure relief device (PRD) means a device that, when activated
under specified performance conditions, is used to release hydrogen
from a pressurized system and thereby prevent failure of the system.
Rechargeable electrical energy storage system (REESS) means the
rechargeable energy storage system that provides electric energy for
electrical propulsion.
Service door means a door that allows for the entry and exit of
vehicle occupants under normal operating conditions.
Shut-off valve means a valve between the container and the
remainder of the hydrogen fuel system that must default to the
``closed'' position when unpowered.
State of charge (SOC) means the density ratio of hydrogen in the
CHSS between the actual CHSS condition and that at NWP with the CHSS
equilibrated to 15 [deg]C, as expressed as a percentage using equation
1 to this section, where [rho] is the density of hydrogen (g/L) at
pressure (P) in MegaPascals (MPa) and temperature (T) in Celsius
([deg]C) as listed in table 1 to S4 or linearly interpolated therein:
Equation 1 to Sec. 571.307 S4
[GRAPHIC] [TIFF OMITTED] TR17JA25.000
Table 1 to Sec. 571.307 S4
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Pressure (MPa)
Temperature ([deg]C) ---------------------------------------------------------------------------------------------------------------------------------
1 10 20 30 35 40 50 60 65 70 75 80 87.5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-40........................................................... 1.0 9.7 18.1 25.4 28.6 31.7 37.2 42.1 44.3 46.4 48.4 50.3 53.0
-30........................................................... 1.0 9.4 17.5 24.5 27.7 30.6 36.0 40.8 43.0 45.1 47.1 49.0 51.7
-20........................................................... 1.0 9.0 16.8 23.7 26.8 29.7 35.0 39.7 41.9 43.9 45.9 47.8 50.4
-10........................................................... 0.9 8.7 16.2 22.9 25.9 28.7 33.9 38.6 40.7 42.8 44.7 46.6 49.2
0............................................................. 0.9 8.4 15.7 22.2 25.1 27.9 33.0 37.6 39.7 41.7 43.6 45.5 48.1
10............................................................ 0.9 8.1 15.2 21.5 24.4 27.1 32.1 36.6 38.7 40.7 42.6 44.4 47.0
15............................................................ 0.8 7.9 14.9 21.2 24.0 26.7 31.7 36.1 38.2 40.2 42.1 43.9 46.5
20............................................................ 0.8 7.8 14.7 20.8 23.7 26.3 31.2 35.7 37.7 39.7 41.6 43.4 46.0
30............................................................ 0.8 7.6 14.3 20.3 23.0 25.6 30.4 34.8 36.8 38.8 40.6 42.4 45.0
40............................................................ 0.8 7.3 13.9 19.7 22.4 24.9 29.7 34.0 36.0 37.9 39.7 41.5 44.0
50............................................................ 0.7 7.1 13.5 19.2 21.8 24.3 28.9 33.2 35.2 37.1 38.9 40.6 43.1
60............................................................ 0.7 6.9 13.1 18.7 21.2 23.7 28.3 32.4 34.4 36.3 38.1 39.8 42.3
70............................................................ 0.7 6.7 12.7 18.2 20.7 23.1 27.6 31.7 33.6 35.5 37.3 39.0 41.4
80............................................................ 0.7 6.5 12.4 17.7 20.2 22.6 27.0 31.0 32.9 34.7 36.5 38.2 40.6
85............................................................ 0.7 6.4 12.2 17.5 20.0 22.3 26.7 30.7 32.6 34.4 36.1 37.8 40.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Thermally-activated pressure relief device (TPRD) means a non-
reclosing PRD that is activated by temperature to open and release
hydrogen gas.
S5. Hydrogen fuel system.
S5.1. Fuel system integrity during normal vehicle operations.
S5.1.1. Fueling receptacle requirements. (a) A compressed hydrogen
fueling receptacle shall prevent reverse flow to the atmosphere.
(b) A label shall be affixed close to the fueling receptacle
showing the following information:
(1) The statement, ``Compressed hydrogen gas only.''
(2) The statement, ``Service pressure ______MPa (_____psig).''
(3) The statement, ``See instructions on fuel container(s) for
inspection and service life.''
(c) The fueling receptacle shall ensure positive locking of the
fueling nozzle.
(d) The fueling receptacle shall be protected from the ingress of
dirt and water.
(e) The fueling receptacle shall not be installed in enclosed or
semi-enclosed spaces.
S5.1.2. Hydrogen discharge systems.
S5.1.2.1. Pressure relief systems. (a) If present, the outlet of
the vent line for hydrogen gas discharge from the TPRD(s) of the CHSS
shall be protected from ingress of dirt and water.
(b) The hydrogen gas discharge from TPRD(s) of the CHSS shall not
impinge upon:
(1) Enclosed or semi-enclosed spaces;
(2) Any vehicle wheel housing;
(3) Container(s);
(4) REESS(s);
(5) Any emergency exit(s) as identified in Sec. 571.217 (FMVSS No.
217); nor
(6) Any service door(s).
S5.1.2.2. Vehicle exhaust system. When tested in accordance with
S6.5 of this standard, the hydrogen concentration at the vehicle
exhaust system's point of discharge shall not:
(a) Exceed an average of 4.0 percent by volume during any moving
three-second time interval; nor
(b) Exceed 8.0 percent by volume at any time.
S5.1.3. Protection against flammable conditions. (a) When tested in
accordance with S6.4.1 of this standard, a warning in accordance with
S5.1.6 shall be provided within 10 seconds of the application of the
first test gas.
[[Page 6279]]
When tested in accordance with S6.4.1, the main shut-off valve shall
close within 10 seconds of the application of the second test gas.
(b) When tested in accordance with S6.4.2 of this standard, the
hydrogen concentration in the enclosed or semi-enclosed spaces shall be
less than 3.0 percent.
S5.1.4. Fuel system leakage. When tested in accordance with S6.6 of
this standard, the hydrogen fuel system downstream of the shut-off
valve(s) shall not exhibit observable leakage.
S5.1.5 Tell-tale warning. A warning shall be given to the driver,
or to all front seat occupants for vehicles without a driver's
designated seating position, by a visual signal or display text with
the following properties:
(a) Visible to the driver while seated in the driver's designated
seating position or visible to all front seat occupants of vehicles
without a driver's designated seating position;
(b) Yellow in color if the warning system malfunctions;
(c) Red in color if hydrogen concentration in enclosed or semi-
enclosed spaces exceeds 3.0 percent by volume;
(d) When illuminated, shall be visible to the driver (or to all
front seat occupants in vehicles without a driver's designated seating
position) under both daylight and nighttime driving conditions; and
(e) Remains illuminated when hydrogen concentration in any of the
vehicle's enclosed or semi-enclosed spaces exceeds 3.0 percent by
volume or when the warning system malfunctions, and the ignition
locking system is in the ``On'' (``Run'') position or the propulsion
system is activated.
S5.2. Post-crash fuel system integrity. Each vehicle with a gross
vehicle weight rating (GVWR) of 4,536 kg or less to which this standard
applies must meet the requirements in S5.2.1 through S5.2.4 when tested
according to S6 under the conditions of S7. Each school bus with a GVWR
greater than 4,536 kg to which this standard applies must meet the
requirements in S5.2.1 through S5.2.4 when tested according to S6 under
the conditions of S7 of this standard.
S5.2.1. Fuel leakage limit. If hydrogen gas is used for testing,
the volumetric flow of hydrogen gas leakage shall not exceed an average
of 118 normal liters per minute for the time interval, [Delta]t, as
determined in accordance with S6.2.1 of this standard. If helium is
used for testing, the volumetric flow of helium leakage shall not
exceed an average of 88.5 normal litres per minute for the time
interval, [Delta]t, as determined in accordance with S6.2.2 of this
standard.
S5.2.2. Concentration limit in enclosed spaces. The vehicle shall
meet at least one of the requirements in S5.2.2(a), (b), or (c).
(a) Hydrogen gas leakage shall not result in a hydrogen
concentration in the air greater than 4.0 percent by volume in enclosed
or semi-enclosed spaces for 60 minutes after impact when tested in
accordance with S6.3 of this standard.
(b) Helium gas leakage shall not result in a helium concentration
in the air greater than 3.0 percent by volume in enclosed or semi-
enclosed spaces for 60 minutes after impact when tested in accordance
with S6.3 of this standard.
(c) The shut-off valve of the CHSS shall close within 5 seconds of
the crash.
S5.2.3. Container displacement. The container(s) shall remain
attached to the vehicle by at least one component anchorage, bracket,
or any structure that transfers loads from the container to the vehicle
structure.
S5.2.4. Fire. There shall be no fire in or around the vehicle for
the duration of the test.
S6. Test Requirements.
S6.1. Vehicle Crash Tests. A test vehicle with a GVWR less than or
equal to 4,536 kg, under the conditions of S7 of this standard, is
subject to any one single barrier crash test of S6.1.1, S6.1.2, and
S6.1.3. A school bus with a GVWR greater than 4,536 kg, under the
conditions of S7, is subject to the contoured barrier crash test of
S6.1.4. A particular vehicle need not meet further test requirements
after having been subjected and evaluated to a single barrier crash
test.
S6.1.1. Frontal barrier crash. The test vehicle, with test dummies
in accordance with S6.1 of 571.301 of this chapter, traveling
longitudinally forward at any speed up to and including 48.0 km/h,
impacts a fixed collision barrier that is perpendicular to the line of
travel of the vehicle, or at an angle up to 30 degrees in either
direction from the perpendicular to the line of travel of the vehicle.
S6.1.2. Rear moving barrier impact. The test vehicle, with test
dummies in accordance with S6.1 of Sec. 571.301, is impacted from the
rear by a barrier that conforms to S7.3(b) of Sec. 571.301 and that is
moving at any speed up to and including 80.0 km/h.
S6.1.3. Side moving deformable barrier impact. The test vehicle,
with the appropriate 49 CFR part 572 test dummies specified in Sec.
571.214 (FMVSS No. 214) at positions required for testing by S7.1.1,
S7.2.1, or S7.2.2 of Standard 214, is impacted laterally on either side
by a moving deformable barrier moving at any speed between 52.0 km/h
and 54.0 km/h.
S6.1.4. Moving contoured barrier crash. The test vehicle is
impacted at any point and at any angle by the moving contoured barrier
assembly, specified in S7.5 and S7.6 in Sec. 571.301, traveling
longitudinally forward at any speed up to and including 48.0 km/h.
S6.2. Post-crash CHSS leak test.
S6.2.1. Post-crash leak test for CHSS filled with compressed
hydrogen. (a) The hydrogen gas pressure, P0 (MPa), and
temperature, T0 ([deg]C), shall be measured immediately
before the impact. The hydrogen gas pressure Pf (MPa) and
temperature, Tf ([deg]C) shall also be measured immediately
after a time interval [Delta]t (in minutes) after impact. The time
interval, [Delta]t, starting from the time of impact, shall be the
greater of S6.2.1(a)(1) or (2):
(1) 60 minutes; or
(2) The time interval calculated with equation 2 to this section,
where Rs = Ps/NWP, Ps is the pressure
range of the pressure sensor (MPa), NWP is the Nominal Working Pressure
(MPa), and VCHSS is the volume of the CHSS (L):
Equation 2 to Sec. 571.307 S6.2.1(a)(2)
[Delta]t = VCHSS x NWP/1000 x ((-0.027 x NWP + 4) x
Rs -0.21) - 1.7 x Rs
(b) The initial mass of hydrogen M0 (g) in the CHSS
shall be calculated from equations 3 through 5 to this section:
Equation 3 to Sec. 571.307 S6.2.1(b)
P0' = P0 x 288/(273 + T0)
Equation 4 to Sec. 571.307 S6.2.1(b)
[rho]0' = -0.0027 x (P0')\2\ + 0.75 x
P0' + 1.07
Equation 5 to Sec. 571.307 S6.2.1(b)
M0 = [rho]0' x VCHSS
(c) The final mass of hydrogen in the CHSS, Mf (in
grams), at the end of the time interval, [Delta]t, shall be calculated
from equations 6 through 8 to this section, where Pf is the
measured final pressure (MPa) at the end of the time interval, and
Tf ([deg]C) is the measured final temperature:
Equation 6 to Sec. 571.307 S6.2.1(c)
Pf' = Pf x 288/(273 + Tf)
Equation 7 to Sec. 571.307 S6.2.1(c)
[rho]f' = -0.0027 x (Pf')\2\ + 0.75 x
Pf' + 1.07
Equation 8 to Sec. 571.307 S6.2.1(c)
Mf = [rho]f' x VCHSS
(d) The average hydrogen flow rate over the time interval shall be
calculated from equation 9 to this section, where VH2 is the
average volumetric flow rate (normal millilitres per min) over the time
interval:
[[Page 6280]]
Equation 9 to Sec. 571.307 S6.2.1(d)
VH2 = (Mf-M0)/[Delta]t x 22.41/2.016 x
(Ptarget/P0)
S6.2.2 Post-crash leak test for CHSS filled with compressed helium.
(a) The helium pressure, P0 (MPa), and temperature,
T0 ([deg]C), shall be measured immediately before the impact
and again immediately after a time interval starting from the time of
impact. The time interval, [Delta]t (min), shall be the greater of the
values in S6.2.2(a)(1) or (2):
(1) 60 minutes; or
(2) The time interval calculated with equation 10 to this section,
where Rs = Ps/NWP, Ps is the pressure
range of the pressure sensor (MPa), NWP is the Nominal Working Pressure
(MPa), and VCHSS is the volume of the CHSS (L):
Equation 10 to Sec. 571.307 S6.2.2(a)(2)
[Delta]t = VCHSS x NWP/1000 x (-0.028 x NWP + 5.5) x
Rs-0.3)-2.6 x Rs
(b) The initial mass of helium M0 (g) in the CHSS shall
be calculated from equations 11 through 13 to this section:
Equation 11 to Sec. 571.307 S6.2.2(b)
P0' = P0 x 288/(273 + T0)
Equation 12 to Sec. 571.307 S6.2.2(b)
[rho]0' = -0.0043 x (P0')\2\ + 1.53 x
P0' + 1.49
Equation 13 to Sec. 571.307 S6.2.2(b)
M0 = [rho]0' x VCHSS
(c) The final mass of helium Mf (g) in the CHSS at the
end of the time interval, [Delta]t (min), shall be calculated from
equations 14 through 16 to this section, where Pf is the
measured final pressure (MPa) at the end of the time interval, and
Tf ([deg]C) is the measured final temperature:
Equation 14 to Sec. 571.307 S6.2.2(c)
Pf' = Pf x 288/(273 + Tf)
Equation 15 to Sec. 571.307 S6.2.2(c)
[rho]f' = -0.0043 x (Pf')\2\ + 1.53 x
Pf' + 1.49
Equation 16 to Sec. 571.307 S6.2.2(c)
Mf = [rho]f' x VCHSS
(d) The average helium flow rate over the time interval shall be
calculated from equation 17 to this section, where VHe is
the average volumetric flow rate (normal millilitres per min) of helium
over the time interval:
Equation 17 to Sec. 571.307 S6.2.2(d)
VHe = (Mf-M0)/[Delta]t x 22.41/4.003 x
(Ptarget/P0)
S6.3. Post-crash concentration test for enclosed spaces. (a)
Sensors shall measure either the accumulation of hydrogen or helium
gas, as appropriate, or the reduction in oxygen.
(b) Sensors shall have an accuracy of at least 5 percent at 4.0
percent hydrogen or 3.0 percent helium by volume in air, and a full-
scale measurement capability of at least 25 percent above these
criteria. The sensor shall be capable of a 90 percent response to a
full-scale change in concentration within 10 seconds.
(c) Prior to the crash impact, the sensors shall be located in the
passenger and luggage compartments of the vehicle as follows:
(1) At any interior point at any distance between 240 mm and 260 mm
of the headliner above the driver's seat or near the top center of the
passenger compartment.
(2) At any interior point at any distance between 240 mm and 260 mm
of the floor in front of the rear (or rear most) seat in the passenger
compartment.
(3) At any interior point at any distance between 90 mm and 110 mm
below the top of luggage compartment(s).
(d) The sensors shall be securely mounted on the vehicle structure
or seats and protected from debris, air bag exhaust gas and
projectiles.
(e) The vehicle shall be located either indoors or in an area
outdoors protected from direct and indirect wind.
(f) Post-crash data collection in enclosed spaces shall commence
from the time of impact. Data from the sensors shall be collected at
least every 5 seconds and continue for a period of 60 minutes after the
impact.
(g) The data shall be compiled into a three-data-point rolling
average prior to evaluating the applicable concentration limit in
accordance with S5.2.2(a) or (b) of this standard.
S6.4. Test procedure for protection against flammable conditions.
S6.4.1. Test for hydrogen gas leakage detectors. (a) The vehicle
propulsion system shall be operated for at least five minutes prior to
testing and shall continue to operate throughout the test.
(b) Two mixtures of air and hydrogen gas shall be used in the test:
The first test gas has any hydrogen concentration between 3.0 and 4.0
percent by volume in air to verify function of the warning, and the
second test gas has any hydrogen concentration between 4.0 and 6.0
percent by volume in air to verify function of the shut-down.
(c) The test shall be conducted without influence of wind.
(d) A vehicle hydrogen leakage detector located in the enclosed or
semi-enclosed spaces is enclosed with a cover and a test gas induction
hose is attached to the hydrogen gas leakage detector.
(e) The hydrogen gas leakage detector is exposed to continuous flow
of the first test gas specified in S.6.4.1(b) until the warning turns
on.
(f) Then the hydrogen gas leakage detector is exposed to continuous
flow of the second test gas specified in S.6.4.1(b) until the main
shut-off valve closes to isolate the CHSS. The test is completed when
the shut-off valve closes.
S6.4.2. Test for integrity of enclosed spaces and detection
systems. (a) The test shall be conducted without influence of wind.
(b) Prior to the test, the vehicle is prepared to simulate remotely
controllable hydrogen releases from the fuel system or from an external
fuel supply. The number, location, and flow capacity of the release
points downstream of the shut-off valve are defined by the vehicle
manufacturer.
(c) A hydrogen concentration detector shall be installed in any
enclosed or semi-enclosed spaces where hydrogen may accumulate from the
simulated hydrogen release.
(d) Vehicle doors, windows and other covers are closed.
(e) The vehicle propulsion system shall be operated for at least
five minutes and shall continue to operate throughout the remainder of
the test.
(f) A leak shall be simulated using the remote controllable
function.
(g) The hydrogen concentration is measured continuously until the
end of the test.
(h) The test is completed 5 minutes after initiating the simulated
leak or when the hydrogen concentration does not change for 3 minutes,
whichever is longer.
S6.5. Test for the vehicle exhaust system. (a) The vehicle
propulsion system shall be operated for at least five minutes prior to
testing and shall continue to operate throughout the test, except for
times when the propulsion system becomes deactivated by the steps taken
during S6.5(c).
(b) The measuring section of the measuring device shall be placed
along the centerline of the exhaust gas flow within 100 mm of where the
exhaust is released to the atmosphere.
(c) The exhaust hydrogen concentration shall be continuously
measured during the following steps:
(1) The fuel cell system shall be shut down.
(2) The fuel cell system shall be immediately restarted.
(3) After one minute, the vehicle shall be set to the ``off''
position and measurement continues until the until the vehicle shutdown
is complete.
[[Page 6281]]
(d) The measurement device shall have a resolution time of less
than 300 milliseconds;
(e) The measurement device shall have a measurement response time
(t0-t90) of less than 2 seconds, where
t0 is the moment of hydrogen concentration switching, and
t90 is the time when 90 percent of the final indication is
reached and shall have a resolution time of less than 300 milliseconds
(sampling rate of greater than 3.33 Hz).
S6.6. Test for fuel system leakage. The vehicle CHSS shall be
filled with hydrogen to any pressure between 90 percent NWP and 100
percent NWP for the duration of the test for fuel system leakage.
(a) The vehicle propulsion system shall be operated for at least
five minutes prior to testing and shall continue to operate throughout
the test.
(b) Hydrogen leakage shall be evaluated at accessible sections of
the hydrogen fuel system downstream of the shut-off valve(s) using a
leak detecting liquid. Hydrogen gas leak detection shall be performed
immediately after applying the liquid.
S7. Test conditions. The requirements of S5.2 shall be met under
the following conditions. Where a range of conditions is specified, the
vehicle must be capable of meeting the requirements at all points
within the range.
(a) Prior to conducting the crash test, instrumentation is
installed in the CHSS to perform the required pressure and temperature
measurements if the vehicle does not already have instrumentation with
the required accuracy.
(b) The CHSS is then purged, if necessary, following vehicle
manufacturer directions before filling the CHSS with compressed
hydrogen or helium gas, as specified by the vehicle manufacturer.
(c) The target fill pressure Ptarget shall be calculated
from equation 18 to this section, where NWP is in MPa, To is
the ambient temperature in [deg]C to which the CHSS is expected to
settle, and Ptarget is the target fill pressure in MPa after
the temperature settles:
Equation 18 to Sec. 571.307 S7
Ptarget = NWP x (273 + To)/288
(d) The container(s) shall be filled to any pressure between 95.0
percent and 100.0 percent of the calculated target fill pressure.
(e) After fueling, the vehicle shall be maintained at rest for any
duration between 2.0 and 3.0 hours before conducting a crash test in
accordance with S6.1 of this standard.
(f) The CHSS shut-off valve(s) and any other shut-off valves
located in the fuel system downstream hydrogen gas piping shall be in
normal driving condition immediately prior to the impact.
(g) The parking brake is disengaged and the transmission is in
neutral prior to the crash test.
(h) Tires are inflated to manufacturer's specifications.
(i) The vehicle, including test devices and instrumentation, is
loaded as follows:
(1) A passenger car, with its fuel system filled as specified in
S7(d), is loaded to its unloaded vehicle weight plus its rated cargo
and luggage capacity weight, secured in the luggage area, plus the
necessary test dummies as specified in S6, restrained only by means
that are installed in the vehicle for protection at its seating
position(s).
(2) A multipurpose passenger vehicle, truck, or bus with a GVWR of
10,000 pounds or less, whose fuel system is filled as specified in
S7(d), is loaded to its unloaded vehicle weight, plus the necessary
test dummies as specified in S6 of this standard, plus 136.1 kg, or its
rated cargo and luggage capacity weight, whichever is less, secured to
the vehicle and distributed so that the weight on each axle as measured
at the tire-ground interface is in proportion to its gross axle weight
rating (GAWR). Each dummy shall be restrained only by means that are
installed in the vehicle for protection at its seating position(s).
(3) A school bus with a GVWR greater than 10,000 pounds, whose fuel
system is filled as specified in S7(d), is loaded to its unloaded
vehicle weight, plus 54.4 kg of unsecured weight at each designated
seating position.
0
4. Section 571.308 is added to read as follows:
Sec. 571.308 Standard No. 308; Compressed hydrogen storage system
integrity
S1. Scope. This standard specifies requirements for compressed
hydrogen storage systems used in motor vehicles.
S2. Purpose. The purpose of this standard is to reduce deaths and
injuries occurring from fires that result from hydrogen fuel leakage
during vehicle operation and to reduce deaths and injuries occurring
from explosions resulting from the burst of pressurized hydrogen
containers.
S3. Application. This standard applies to each motor vehicle
manufactured on or after September 1, 2028, that is equipped with
compressed hydrogen gas as a fuel source to propel the vehicle. The
standard does not apply to vehicles that are only equipped with cryo-
compressed hydrogen storage systems and/or solid-state hydrogen storage
system to propel the vehicle.
S4. Definitions.
BPO means the vehicle manufacturer-supplied median burst
pressure for a batch of new containers.
Burst means to break apart or to break open.
Burst pressure means the highest pressure achieved for a container
tested in accordance with S6.2.2.1 of this standard.
Check valve means a valve that prevents reverse flow.
Closure devices mean the check valve(s), shut-off valve(s), and
thermally-activated pressure relief device(s) that control the flow of
hydrogen into and/or out of a CHSS.
Container means a pressure-bearing component of a compressed
hydrogen storage system that stores a continuous volume of hydrogen
fuel in a single chamber or in multiple permanently interconnected
chambers.
Container attachments mean non-pressure bearing parts attached to
the container that provide additional support and/or protection to the
container and that may be removed only with the use of tools for the
specific purpose of maintenance and/or inspection.
Compressed hydrogen storage system (CHSS) means a system that
stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed
of a container, container attachments (if any), and all closure devices
required to isolate the stored hydrogen from the remainder of the fuel
system and the environment.
Cryo-compressed hydrogen storage system means a system that stores
hydrogen by compressing it to high pressure while simultaneously
cooling it to very low temperatures, allowing for a higher density of
hydrogen storage compared to standard compressed hydrogen systems.
Hydrogen fuel system means the fueling receptacle, CHSS, fuel cell
system or internal combustion engine, fuel lines, and exhaust systems.
Nominal working pressure (NWP) means the settled pressure of
compressed gas in a container or CHSS fully fueled to 100 percent state
of charge and at a uniform temperature of 15 [deg]C.
Normal milliliter means a quantity of gas that occupies one
milliliter of volume when its temperature is 0 [deg]C and its pressure
is 1 atmosphere.
Pressure relief device (PRD) means a device that, when activated
under specified performance conditions, is used to release hydrogen
from a
[[Page 6282]]
pressurized system and thereby prevent failure of the system.
Service life (of a container) means the time frame during which
service (usage) is authorized by the vehicle manufacturer.
Shut-off valve means a valve between the container and the
remainder of the hydrogen fuel system that must default to the
``closed'' position when unpowered.
Solid-state hydrogen storage system means a system that stores
hydrogen at ambient temperatures and low pressures within solid
materials that can either physically absorb the hydrogen gas or
chemically combine with it.
State of charge (SOC) means the density ratio of hydrogen in the
CHSS between the actual CHSS condition and that at NWP with the CHSS
equilibrated to 15 [deg]C, as expressed as a percentage using the
equation 1 to this section, where [rho] is the density of hydrogen (g/
L) at pressure (P) in MegaPascals (MPa) and temperature (T) in Celsius
([deg]C) as listed below in Table 1 or linearly interpolated therein:
Equation 1 to Sec. 571.308 S4
[GRAPHIC] [TIFF OMITTED] TR17JA25.001
Table 1 to Sec. 571.308 S4
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Pressure (MPa)
Temperature ([deg]C) ---------------------------------------------------------------------------------------------------------------------------------
1 10 20 30 35 40 50 60 65 70 75 80 87.5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-40........................................................... 1.0 9.7 18.1 25.4 28.6 31.7 37.2 42.1 44.3 46.4 48.4 50.3 53.0
-30........................................................... 1.0 9.4 17.5 24.5 27.7 30.6 36.0 40.8 43.0 45.1 47.1 49.0 51.7
-20........................................................... 1.0 9.0 16.8 23.7 26.8 29.7 35.0 39.7 41.9 43.9 45.9 47.8 50.4
-10........................................................... 0.9 8.7 16.2 22.9 25.9 28.7 33.9 38.6 40.7 42.8 44.7 46.6 49.2
0............................................................. 0.9 8.4 15.7 22.2 25.1 27.9 33.0 37.6 39.7 41.7 43.6 45.5 48.1
10............................................................ 0.9 8.1 15.2 21.5 24.4 27.1 32.1 36.6 38.7 40.7 42.6 44.4 47.0
15............................................................ 0.8 7.9 14.9 21.2 24.0 26.7 31.7 36.1 38.2 40.2 42.1 43.9 46.5
20............................................................ 0.8 7.8 14.7 20.8 23.7 26.3 31.2 35.7 37.7 39.7 41.6 43.4 46.0
30............................................................ 0.8 7.6 14.3 20.3 23.0 25.6 30.4 34.8 36.8 38.8 40.6 42.4 45.0
40............................................................ 0.8 7.3 13.9 19.7 22.4 24.9 29.7 34.0 36.0 37.9 39.7 41.5 44.0
50............................................................ 0.7 7.1 13.5 19.2 21.8 24.3 28.9 33.2 35.2 37.1 38.9 40.6 43.1
60............................................................ 0.7 6.9 13.1 18.7 21.2 23.7 28.3 32.4 34.4 36.3 38.1 39.8 42.3
70............................................................ 0.7 6.7 12.7 18.2 20.7 23.1 27.6 31.7 33.6 35.5 37.3 39.0 41.4
80............................................................ 0.7 6.5 12.4 17.7 20.2 22.6 27.0 31.0 32.9 34.7 36.5 38.2 40.6
85............................................................ 0.7 6.4 12.2 17.5 20.0 22.3 26.7 30.7 32.6 34.4 36.1 37.8 40.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Thermally-activated pressure relief device (TPRD) means a non-
reclosing PRD that is activated by temperature to open and release
hydrogen gas.
TPRD sense point means instrumentation that detects elevated
temperature for the purpose of activating a TPRD.
S5. Requirements.
S5.1. Requirements for the CHSS. Each vehicle CHSS shall include
the following functions: shut-off valve, check valve, and TPRD. Each
vehicle CHSS shall have a NWP of 70 MPa or less. Each vehicle
container, closure device, and CHSS shall meet the applicable
performance test requirements listed in table 2 to this section.
Table 2 to Sec. 571.308 S5.1
------------------------------------------------------------------------
Requirement section Test article
------------------------------------------------------------------------
S5.1.1. Tests for baseline metrics........ Container.
S5.1.2. Test for performance durability... Container.
S5.1.3. Test for expected on-road CHSS.
performance.
S5.1.4. Test for service terminating CHSS.
performance in fire.
S5.1.5. Tests for performance durability Closure devices.
of closure devices.
------------------------------------------------------------------------
S5.1.1. Tests for baseline metrics.
S5.1.1.1. Baseline initial burst pressure. The vehicle manufacturer
shall immediately and irrevocably specify upon request, in writing and
within 15 business days: whether the primary constituent of the
container is glass fiber composite. When a new container with its
container attachments (if any) is tested in accordance with S6.2.2.1 of
this standard, both of the following requirements shall be met:
(a) The burst pressure of the container shall not be less than 2
times NWP.
(b) The burst pressure of the container having glass-fiber
composite as a primary constituent shall not be less than 3.5 times
NWP.
S5.1.1.2. Baseline initial pressure cycle test. When a new
container with its container attachments (if any) is hydraulically
pressure cycled in accordance with S6.2.2.2 of this standard to any
pressure between 125.0 percent NWP and 130.0 percent NWP,
(a) Containers for vehicles with a GVWR of 10,000 pounds or less
(1) Shall not leak nor burst for at least 7,500 cycles, and
(2) Thereafter shall not burst for an additional 14,500 cycles. If
a leak occurs while conducting the test as specified in S5.1.1.2(a)(2),
the test is stopped and not considered a failure.
(b) Containers for vehicles with a GVWR of over 10,000 pounds
(1) Shall not leak nor burst for at least 11,000 cycles, and
(2) Thereafter shall not burst for an additional 11,000 cycles. If
a leak occurs while conducting the test as specified in S5.1.1.2(b)(2),
the test is stopped and not considered a failure.
S5.1.2. Test for performance durability. A new container shall not
leak nor burst when subjected to the sequence of tests in S5.1.2.1
through S5.1.2.6. Immediately following S5.1.2.6, and without
depressurizing the container, the container is subjected to a burst
test in accordance with S6.2.2.1(c) and (d) of this standard. The burst
pressure of the container at the end of the sequence of tests in this
[[Page 6283]]
section shall not be less than 0.8 times the BPO value
specified by the vehicle manufacturer. The sequence of tests and the
burst pressure test are illustrated in figure 1 to S5.1.2. The vehicle
manufacturer shall immediately and irrevocably specify upon request, in
writing and within 15 business days: the BPO of the
container.
S5.1.2.1. Drop test. The container with its container attachments
(if any) is dropped once in accordance with S6.2.3.2 of this standard
in any one of the four orientations specified in that section. Any
container with damage from the drop test that prevents further testing
of the container in accordance with S6.2.3.4 of this standard shall be
considered to have failed to meet the test for performance durability
requirements. In the case of an asymmetric container, the vehicle
manufacturer shall immediately and irrevocably specify upon request, in
writing, and within 15 business days: the center of gravity of the
container.
S5.1.2.2. Surface damage test. The container, except if an all-
metal container, is subjected to the surface damage test in accordance
with the S6.2.3.3 of this standard. Container attachments designed to
be removed shall be removed and container attachments that are not
designed to be removed shall remain in place. Container attachments
that are removed shall not be reinstalled for the remainder of S5.1.2;
container attachments that are not removed shall remain in place for
the remainder of S5.1.2.
S5.1.2.3. Chemical exposure and ambient-temperature pressure
cycling test. The container is exposed to chemicals in accordance with
S6.2.3.4 and then hydraulically pressure cycled in accordance with
S6.2.3.4 of this standard for 60 percent of the number of cycles as
specified in S5.1.1.2(a)(1) or (b)(1) as applicable. For all but the
last 10 of these cycles, the cycling pressure shall be any pressure
between 125.0 percent NWP and 130.0 percent NWP. For the last 10
cycles, the pressure shall be any pressure between 150.0 percent NWP
and 155.0 percent NWP.
S5.1.2.4. High temperature static pressure test. The container is
pressurized to any pressure between (or equal to) 125 percent NWP and
130 percent NWP and held at that pressure no less than 1,000 and no
more than 1,050 hours in accordance with S6.2.3.5 of this standard and
with the temperature surrounding the container at any temperature
between 85.0 [deg]C and 90.0 [deg]C.
S5.1.2.5. Extreme temperature pressure cycling test. The container
is pressure cycled in accordance with S6.2.3.6 for 40 percent of the
number of cycles specified in S5.1.1.2(a)(1) or (b)(1) as applicable.
The pressure for the first half of these cycles equals any pressure
between 80.0 percent NWP and 85.0 percent NWP with the temperature
surrounding the container equal to any temperature between -45.0 [deg]C
and -40.0 [deg]C. The pressure for the next half of these cycles equals
any pressure between 125.0 percent NWP and 130.0 percent NWP and the
temperature surrounding the container equal to any temperature between
85.0 [deg]C and 90.0 [deg]C and the relative humidity surrounding the
container not less than 80 percent.
S5.1.2.6. Residual pressure test. The container is hydraulically
pressurized in accordance with S6.2.3.1 of this standard to a pressure
between 180.0 percent NWP and 185.0 percent NWP and held for any
duration between 240 to 245 seconds.
[[Page 6284]]
[GRAPHIC] [TIFF OMITTED] TR17JA25.002
Figure 1 to Sec. 571.308 S5.1.2. Performance Durability Test; (for
Illustration Purposes Only)
S5.1.3. Test for expected on-road performance. When subjected to
the sequence of tests in S5.1.3.1, the CHSS shall meet the permeation
and leak requirements specified in S5.1.3.2 and shall not burst.
Thereafter, the container of the CHSS shall not burst when subjected to
a residual pressure test in accordance with S5.1.3.3. Immediately
following the test specified in S5.1.3.3, and without depressurizing
the container, the container of the CHSS is subjected to a burst test
in accordance with S6.2.2.1(c) and (d) of this standard. The burst
pressure of the container at the end of the sequence of tests in this
section shall not be less than 0.8 times the BPO specified
by the vehicle manufacturer under S5.1.2.
S5.1.3.1. Ambient and extreme temperature gas pressure cycling
test. The CHSS is pressure cycled using hydrogen gas for 500 cycles
under any temperature and pressure condition for the number of cycles
as specified in table 3 to S5.1.3.1, and in accordance with the
S6.2.4.1 of this standard test procedure. A static gas pressure leak/
permeation test performed in accordance with S5.1.3.2 is conducted
after the first 250 pressure cycles and after the remaining 250
pressure cycles.
Table 3 to Sec. 571.308 S5.1.3.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Initial system Fuel delivery Cycle initial and
Number of cycles Ambient conditions equilibration temperature final pressure Cycle peak pressure
--------------------------------------------------------------------------------------------------------------------------------------------------------
5.................................. -30.0 [deg]C to -25.0 -30.0 [deg]C to -25.0 15.0 [deg]C to 25.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C. [deg]C. [deg]C. SOC.
5.................................. -30.0 [deg]C to -25.0 -30.0 [deg]C to -25.0 -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C. [deg]C. [deg]C. SOC.
15................................. -30.0 [deg]C to -25.0 not appliable......... -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C. [deg]C. SOC.
5.................................. 50.0 [deg]C to 55.0 50 [deg]C to 55 -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C, 80% to 100% [deg]C, 80% to 100% [deg]C. SOC.
relative humidity. relative humidity.
20................................. 50.0 [deg]C to 55.0 not appliable......... -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C, 80% to 100% [deg]C. SOC.
relative humidity.
200................................ 5.0 [deg]C to 35.0 not appliable......... -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C. [deg]C. SOC.
[[Page 6285]]
Extreme temperature static gas 55.0 [deg]C to 60.0 55.0 [deg]C to 60.0 not appliable........ not appliable........ 100.0% SOC to 105.0%
pressure leak/permeation test [deg]C. [deg]C. SOC.
S5.1.3.2.
25................................. 50.0 [deg]C to 55.0 not appliable......... -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C, 80% to 100% [deg]C. SOC.
relative humidity.
25................................. -30.0 [deg]C to -25.0 not appliable......... -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C. [deg]C. SOC.
200................................ 5.0 [deg]C to 35.0 not appliable......... -40.0 [deg]C to -33.0 1.0 MPa to 2.0 MPa... 100.0% SOC to 105.0%
[deg]C. [deg]C. SOC.
Extreme temperature static gas 55.0 [deg]C to 60.0 55.0 [deg]C to 60.0 not appliable........ not appliable........ 100.0% SOC to 105.0%
pressure leak/permeation test [deg]C. [deg]C. SOC.
S5.1.3.2.
--------------------------------------------------------------------------------------------------------------------------------------------------------
S5.1.3.2. Extreme temperature static gas pressure leak/permeation
test. When tested in accordance with S6.2.4.2 of this standard after
each group of 250 pneumatic pressure cycles in S5.1.3.1, the CHSS shall
not discharge hydrogen more than 46 millilitres per hour (mL/h) for
each litre of CHSS water capacity.
S5.1.3.3. Residual pressure test. The container of the CHSS is
hydraulically pressurized in accordance with S6.2.3.1 to any pressure
between 1.800 times NWP and 1.850 times NWP and held at that pressure
for any duration between 240 to 245 seconds.
S5.1.4. Test for service terminating performance in fire. When the
CHSS is exposed to the two-stage localized or engulfing fire test in
accordance with S6.2.5 of this standard, the container shall not burst.
The pressure inside the CHSS shall fall to 1 MPa or less within the
test time limit specified in S6.2.5.3(o) of this standard. Any leakage
or venting, other than that through TPRD outlet(s), shall not result in
jet flames greater than 0.5 m in length. If venting occurs though the
TPRD, the venting shall be continuous.
S5.1.5. Tests for performance durability of closure devices. All
tests are performed at ambient temperature of 5 [deg]C to 35 [deg]C
unless otherwise specified.
S5.1.5.1. TPRD requirements. The TPRD shall not activate at any
point during the test procedures specified in S6.2.6.1.1, S6.2.6.1.3,
S6.2.6.1.4, S6.2.6.1.5, S6.2.6.1.6, S6.2.6.1.7, and S6.2.6.1.8 of this
standard.
(a) A TPRD subjected to pressure cycling in accordance with
S6.2.6.1.1 of this standard shall be sequentially tested in accordance
with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this standard;
(1) When tested in accordance with S6.2.6.1.8, the TPRD shall not
exhibit leakage greater than 10 normal milliliters per minute (NmL/
hour).
(2) When tested in accordance with S6.2.6.1.9 of this standard, the
TPRD shall activate within no more than 2 minutes of the average
activation time of three new TPRDs tested in accordance with
S6.2.6.1.9;
(3) When tested in accordance with S6.2.6.1.10 of this standard,
the TPRD shall have a flow rate of at least 90 percent of the highest
baseline flow rate established in accordance with S6.2.6.1.10;
(b)(1) A TPRD shall activate in less than ten hours when tested at
the vehicle manufacturer's specified activation temperature in
accordance with S6.2.6.1.2 of this standard;
(2) When tested at the accelerated life temperature in accordance
with S6.2.6.1.2 of this standard, a TPRD shall not activate in less
than 500 hours and shall not exhibit leakage greater than 10 NmL/hour
when tested in accordance with S6.2.6.1.8 of this standard;
(c) A TPRD subjected to temperature cycling testing in accordance
with S6.2.6.1.3 of this standard shall be sequentially tested in
accordance with S6.2.6.1.8(a)(3), S6.2.6.1.9, and S6.2.6.1.10 of this
standard;
(1) When tested in accordance with S6.2.6.1.8(a)(3) of this
standard, the TPRD shall not exhibit leakage greater than 10 NmL/hour;
(2) When tested in accordance with S6.2.6.1.9 of this standard, the
TPRD shall activate within no more than 2 minutes of the average
activation time of three new TPRDs tested in accordance with
S6.2.6.1.9;
(3) When tested in accordance with S6.2.6.1.10 of this standard,
the TPRD shall have a flow rate of at least 90 percent of the highest
baseline flow rate established in accordance with S6.2.6.1.10;
(d) A TPRD subjected to salt corrosion resistance testing in
accordance with S6.2.6.1.4 of this standard shall be sequentially
tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of
this standard;
(1) When tested in accordance with S6.2.6.1.8 of this standard, the
TPRD shall not exhibit leakage greater than 10 NmL/hour;
(2) When tested in accordance with S6.2.6.1.9 of this standard, the
TPRD shall activate within no more than 2 minutes of the average
activation time of three new TPRDs tested in accordance with
S6.2.6.1.9;
(3) When tested in accordance with S6.2.6.1.10 of this standard,
the TPRD shall have a flow rate of at least 90 percent of the highest
baseline flow rate established in accordance with S6.2.6.1.10;
(e) A TPRD subjected to vehicle environment testing in accordance
with S6.2.6.1.5 of this standard shall not show signs of cracking,
softening, or swelling, and thereafter shall be sequentially tested in
accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this
standard. Cosmetic changes such as pitting or staining are not
considered failures.
(1) When tested in accordance with S6.2.6.1.8 of this standard, the
TPRD shall not exhibit leakage greater than 10 NmL/hour.
(2) When tested in accordance with S6.2.6.1.9 of this standard, the
TPRD shall activate within no more than 2 minutes of the average
activation time of three new TPRDs tested in accordance with
S6.2.6.1.9,
(3) When tested in accordance with S6.2.6.1.10 of this standard,
the TPRD shall have a flow rate of at least 90 percent of the highest
baseline flow rate established in accordance with S6.2.6.1.10;
(f) A TPRD subjected to stress corrosion cracking testing in
accordance with S6.2.6.1.6 of this standard shall not exhibit visible
cracking or delaminating;
(g) A TPRD shall be subjected to drop and vibration testing in
accordance with
[[Page 6286]]
S6.2.6.1.7 of this standard. If the TPRD progresses beyond
S6.2.6.1.7(c) to complete testing under S6.2.6.1.7(d), it shall then be
sequentially tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and
S6.2.6.1.10 of this standard.
(1) When tested in accordance with S6.2.6.1.8 of this standard, the
TPRD shall not exhibit leakage greater than 10 NmL/hour.
(2) When tested in accordance with S6.2.6.1.9 of this standard, the
TPRD shall activate within no more than 2 minutes of the average
activation time of three new TPRDs tested in accordance with
S6.2.6.1.9,
(3) When tested in accordance with S6.2.6.1.10 of this standard,
the TPRD shall have a flow rate of at least 90 percent of the highest
baseline flow rate established in accordance with S6.2.6.1.10;
(h) One new TPRD subjected to leak testing in accordance with
S6.2.6.1.8 of this standard shall not exhibit leakage greater than 10
NmL/hour;
(i) Three new TPRDs are subjected to a bench top activation test in
accordance with S6.2.6.1.9 of this standard. The maximum difference in
the activation time between any two of the three TPRDs shall be 2
minutes or less.
S5.1.5.2. Check valve and shut-off valve requirements. This section
applies to both check valves and shut-off valves.
(a) A valve subjected to hydrostatic strength testing in accordance
with S6.2.6.2.1 of this standard shall not leak to an extent that
prevents continued pressurization in accordance with S6.2.6.2.1(c) nor
burst at less than 250 percent NWP;
(b) A valve subjected to leak testing in accordance with S6.2.6.2.2
of this standard shall not exhibit leakage greater than 10 NmL/hour;
(c)(1) A check valve shall meet the requirements when tested
sequentially as follows:
(i) The check valve shall reseat and prevent reverse flow after
each cycle when subjected to 13,500 pressure cycles in accordance with
S6.2.6.2.3 of this standard to any pressure between 100.0 and 105.0
percent NWP and at any temperature between 5.0 [deg]C and 35.0 [deg]C;
(ii) The same check valve shall reseat and prevent reverse flow
after each cycle when subjected to 750 pressure cycles in accordance
with S6.2.6.2.3 of this standard to any pressure between 125.0 and
130.0 percent NWP and at any temperature between 85.0 [deg]C and 90.0
[deg]C;
(iii) The same check valve shall reseat and prevent reverse flow
after each cycle when subjected to 750 pressure cycles in accordance
with S6.2.6.2.3 of this standard to any pressure between 80.0 and 85.0
percent NWP and at any temperature between -45.0 [deg]C and -40.0
[deg]C;
(iv) The same check valve shall be subjected to chatter flow
testing in accordance with S6.2.6.2.4 of this standard;
(v) When tested in accordance with S6.2.6.2.2 of this standard, the
same check valve shall not exhibit leakage greater than 10 NmL/hour;
(vi) When tested in accordance with S6.2.6.2.1 of this standard,
the same check valve shall not leak to an extent that prevents
continued pressurization in accordance with S6.2.6.2.1(c), nor burst at
less than 250 percent NWP, nor burst at less than 80 percent of the
burst pressure of the new unit tested in accordance with S5.1.5.2(a)
unless the burst pressure of the valve exceeds 400 percent NWP.
(2) A shut-off valve shall meet the requirements when tested
sequentially as follows:
(i) The shut-off valve shall be subjected to 45,000 pressure cycles
in accordance with S6.2.6.2.3 to any pressure between 100.0 and 105.0
percent NWP and at any temperature between 5.0 [deg]C and 35.0 [deg]C;
(ii) The same shut-off valve shall be subjected to 2,500 pressure
cycles in accordance with S6.2.6.2.3 of this standard to any pressure
between 125.0 and 130.0 percent NWP and at any temperature between 85.0
[deg]C and 90.0 [deg]C;
(iii) The same shut-off valve shall be subjected to 2,500 pressure
cycles in accordance with S6.2.6.2.3 of this standard to any pressure
between 80.0 and 85.0 percent NWP and at any temperature between -45.0
[deg]C and -40.0 [deg]C;
(iv) The same shut-off valve shall be subjected to chatter flow
testing in accordance with S6.2.6.2.4 of this standard;
(v) When tested in accordance with S6.2.6.2.2 of this standard, the
same shut-off valve shall not exhibit leakage greater than 10 NmL/hour;
(vi) When tested in accordance with S6.2.6.2.1 of this standard,
the same shut-off valve shall not leak to an extent that prevents
continued pressurization in accordance with S6.2.6.2.1(c), nor burst at
less than 250 percent NWP, nor burst at less than 80 percent of the
burst pressure of the new unit tested in accordance with S5.1.5.2(a)
unless the burst pressure of the valve exceeds 400 percent NWP.
(d) A valve subjected to salt corrosion resistance testing in
accordance with S6.2.6.1.4 of this standard shall be tested
sequentially in accordance with S6.2.6.2.2 followed by S6.2.6.2.1 of
this standard.
(1) When tested in accordance with S6.2.6.2.2 of this standard, the
valve shall not exhibit leakage greater than 10 NmL/hour;
(2) When tested in accordance with S6.2.6.2.1 of this standard, the
valve shall not leak to an extent that prevents continued
pressurization in accordance with S6.2.6.2.1(c), nor burst at less than
250 percent NWP, nor burst at less than 80 percent of the burst
pressure of the new unit tested in accordance with S5.1.5.2(a) unless
the burst pressure of the valve exceeds 400 percent NWP.
(e) A valve subjected to vehicle environment testing in accordance
with S6.2.6.1.5 of this standard shall not show signs of cracking,
softening, or swelling and shall be tested sequentially in accordance
with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard. Cosmetic
changes such as pitting or staining are not considered failures.
(1) When tested in accordance with S6.2.6.2.2 of this standard, the
valve shall not exhibit leakage greater than 10 NmL/hour;
(2) When tested in accordance with S6.2.6.2.1 of this standard, the
valve shall not leak to an extent that prevents continued
pressurization in accordance with S6.2.6.2.1(c), nor burst at less than
250 percent NWP, nor burst at less than 80 percent of the burst
pressure of the new unit tested in accordance with S5.1.5.2(a) unless
the burst pressure of the valve exceeds 400 percent NWP;
(f) A shut-off valve shall have a minimum resistance of 240
k[Omega] between the power conductor and the valve casing, and shall
not exhibit open valve, smoke, fire, melting, or leakage greater than
10 NmL/hour when subjected to electrical testing in accordance with
S6.2.6.2.5 followed by leak testing in accordance with S6.2.6.2.2 of
this standard;
(g) A valve subjected to vibration testing in accordance with
S6.2.6.2.6 of this standard shall be tested sequentially in accordance
with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard.
(1) When tested in accordance with S6.2.6.2.2 of this standard, the
valve shall not exhibit leakage greater than 10 NmL/hour;
(2) When tested in accordance with S6.2.6.2.1 of this standard, the
valve shall not leak to an extent that prevents continued
pressurization in accordance with S6.2.6.2.1(c), nor burst at less than
250 percent NWP, nor burst at less than 80 percent of the burst
pressure of the new unit tested in accordance with
[[Page 6287]]
S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent
NWP.
(h) A valve shall not exhibit visible cracking or delaminating when
subjected to stress corrosion cracking testing in accordance with
S6.2.6.1.6 of this standard.
S5.1.6. Labeling. Each vehicle container shall be permanently
labeled with the information specified in paragraphs S5.1.6(a) through
(g). Any label affixed to the container in compliance with this section
shall remain in place and be legible for the vehicle manufacturer's
recommended service life of the container. The information shall be in
English and in letters and numbers that are at least 6.35 millimeters
(\1/4\ inch) high.
(a) The statement: ``If there is a question about the proper use,
installation, or maintenance of this compressed hydrogen storage
system, contact ______,'' inserting the vehicle manufacturer's name,
address, and telephone number. The name provided shall be consistent
with the vehicle manufacturer's filing in accordance with 49 CFR part
566.
(b) The container serial number.
(c) The statement: ``Manufactured in ______,'' inserting the month
and year of manufacture of the container.
(d) The statement ``Nominal Working Pressure ______MPa
(_____psig),'' Inserting the nominal working pressure which shall be no
greater than 70 MPa.
(e) The statement ``Compressed Hydrogen Gas Only.''
(f) The statement: ``Do Not Use After ______,'' inserting the month
and year that mark the end of the vehicle manufacturer's recommended
service life for the container.
(g) The statement: ``This container should be visually inspected
for damage and deterioration after a motor vehicle accident or fire,
and either: (i) at least every 12 months when installed on a vehicle
with a GVWR greater than 4,536 kg, or (ii) at least every 36 months or
36,000 miles, whichever comes first, when installed on a vehicle with a
GVWR less than or equal to 4,536 kg.''
S6. Test procedures.
S6.1. [Reserved]
S6.2. Test procedures for compressed hydrogen storage.
S6.2.1. Unless otherwise specified, data sampling for pressure
cycling under S6.2 shall be at least 1 Hz.
S6.2.2. Test procedures for baseline performance metrics.
S6.2.2.1. Burst test. (a) The container is filled with a hydraulic
fluid.
(b) The container, the surrounding environment, and the hydraulic
fluid are at any temperature between 5.0 [deg]C and 35.0 [deg]C.
(c) The rate of pressurization shall be less than or equal to 1.4
MPa per second for pressures higher than 1.50 times NWP. If the rate
exceeds 0.35 MPa per second at pressures higher than 1.50 times NWP,
then the container is placed in series between the pressure source and
the pressure measurement device.
(d) The container is hydraulically pressurized until burst and the
burst pressure of the container is recorded.
S6.2.2.2. Pressure cycling test. (a) The container is filled with a
hydraulic fluid.
(b) The container surface, or the surface of the container
attachments if present, the environment surrounding the container, and
the hydraulic fluid are at any temperature between 5.0 [deg]C and 35.0
[deg]C at the start of testing and maintained at the specified
temperature for the duration of the testing.
(c) The container is pressure cycled at any pressure between 1.0
MPa and 2.0 MPa up to the pressure specified in the respective section
of S5. The cycling rate shall be any rate up to 10 cycles per minute.
(d) The temperature of the hydraulic fluid entering the container
is maintained and monitored at any temperature between 5.0 [deg]C and
35.0 [deg]C.
(e) The vehicle manufacturer may specify a hydraulic pressure cycle
profile within the specifications of S6.2.2.2(c). Vehicle manufacturers
shall submit this profile to NHTSA immediately and irrevocably, upon
request, in writing, and within 15 business days; otherwise, NHTSA
shall determine the profile. At NHTSA's option, NHTSA shall cycle the
container within 10 percent of the vehicle manufacturer's specified
cycling profile.
S6.2.3. Performance durability test.
S6.2.3.1. Residual pressure test. The container is pressurized
smoothly and continually with hydraulic fluid or hydrogen gas as
specified until the pressure level is reached and held for the
specified time.
S6.2.3.2. Drop impact test. The container is drop tested without
internal pressurization or attached valves. The surface onto which the
container is dropped shall be a smooth, horizontal, uniform, dry,
concrete pad or other flooring type with equivalent hardness. No
attempt shall be made to prevent the container from bouncing or falling
over during a drop test, except for the vertical drop test, during
which the test article shall be prevented from falling over. The
container shall be dropped in any one of the following four
orientations described below and illustrated in figure 2 to S6.2.3.2.
(a) From a position within 5[deg] of horizontal with the lowest
point of the container at any height between 1.800 meters and 1.820
meters above the surface onto which it is dropped. In the case of a
non-axisymmetric container, the largest projection area of the
container shall be oriented downward and aligned horizontally;
(b) From a position within 5[deg] of vertical with the center of
any shut-off valve interface location upward and with any potential
energy of between 488 Joules and 538 Joules. If a drop energy of
between 488 Joules and 538 Joules would result in the height of the
lower end being more than 1.820 meters above the surface onto which it
is dropped, the container shall be dropped from any height with the
lower end between 1.800 meters and 1.820 meters above the surface onto
which it is dropped. If a drop energy of between 488 Joules and 538
Joules would result in the height of the lower end being less than
0.100 meters above the surface onto which it is dropped, the container
shall be dropped from any height with the lower end between 0.100
meters and 0.120 meters above the surface onto which it is dropped. In
the case of a non-axisymmetric container, the center of any shut-off
valve interface location and the container's center of gravity shall be
aligned vertically, with the center of that shut-off valve interface
location upward;
(c) From a position within 5[deg] of vertical with the center of
any shut-off valve interface location downward with any potential
energy of between 488 Joules and 538 Joules. If a potential energy of
between 488 Joules and 538 Joules would result in the height of the
lower end being more than 1.820 meters above the surface onto which it
is dropped, the container shall be dropped from any height with the
lower end between 1.800 meters and 1.820 meters above the surface onto
which it is dropped. If a drop energy of between 488 Joules and 538
Joules would result in the height of the lower end being less than
0.100 meters above the surface onto which it is dropped, the container
shall be dropped from any height with the lower end between 0.100
meters and 0.120 meters above the surface onto which it is dropped. In
the case of a non-axisymmetric container, the center of any shut-off
valve interface location and the container's center of gravity shall be
aligned vertically, with the center of that shut-off valve interface
location downward;
(d) From any angle between 40[deg] and 50[deg] from the vertical
orientation with the center of any shut-off valve interface location
downward, and with the container center of gravity between 1.800 meters
and 1.820 meters above the
[[Page 6288]]
surface onto which it is dropped. However, if the lowest point of the
container is closer to the ground than 0.60 meters, the drop angle
shall be changed so that the lowest point of the container is between
0.60 meters and 0.62 meters above the ground and the center of gravity
is between 1.800 meters and 1.820 meters above the surface onto which
it is dropped. In the case of a non-axisymmetric container, the line
passing through the center of any shut-off valve interface location and
the container's center of gravity shall be at any angle between 40[deg]
and 50[deg] from the vertical orientation. If this specification
results in more than one possible container orientation, the drop shall
be conducted from the orientation that results in the lowest
positioning of the center of the shut-off valve interface location.
[GRAPHIC] [TIFF OMITTED] TR17JA25.003
Figure 2 to Sec. 571.308 S6.2.3.2. The Four Drop Orientations; (for
Illustration Purposes Only)
S6.2.3.3. Surface damage test. The surface damage test consists of
surface cut generation and pendulum impacts as described below.
(a) Surface cut generation: Two longitudinal saw cuts are made at
any location on the same side of the outer surface of the unpressurized
container, as shown in Figure 3, or on the container attachments if
present. The first cut is 0.75 millimeters to 1.25 millimeters deep and
200 millimeters to 205 millimeters long; the second cut, which is only
required for containers affixed to the vehicle by compressing its
composite surface, is 1.25 millimeters to 1.75 millimeters deep and 25
millimeters to 28 millimeters long.
(b) Pendulum impacts: Mark the outer surface of the container, or
the container attachments if present, with five separate, non-
overlapping circles each having any linear diameter between 100.0
millimeters and 105.0 millimeters, as shown in Figure 3. The marks
shall be located on the side opposite from the saw cuts, or located on
a different chamber in the case of a container with more than one
chamber. Within 30 minutes following preconditioning for any duration
from 12 hours to 24 hours in an environmental chamber at any
temperature between -45.0 [deg]C and -40.0 [deg]C, impact the center of
each of the five areas with a pendulum having a pyramid with
equilateral faces and square base, and the tip and edges being rounded
to a radius of between 2.0 millimeters and 4.0 millimeters. The center
of impact of the pendulum shall coincide with the center of gravity of
the pyramid. The energy of the pendulum at the moment of impact with
each of the five marked areas on the container is any energy between
30.0 Joules and 35.0 Joules. The container is secured in place during
pendulum impacts and is not pressurized above 1 MPa.
[[Page 6289]]
[GRAPHIC] [TIFF OMITTED] TR17JA25.004
Figure 3 to Sec. 571.308 S6.2.3.3. Locations of Surface Damage for
S6.2.3.3(a) and Pendulum Impacts for S6.2.3.3(b); (for Illustration
Purposes Only)
S6.2.3.4. Chemical exposure and ambient temperature pressure
cycling test. (a) Each of the 5 areas preconditioned by pendulum impact
in S6.2.3.3(b) is exposed to any one of five solutions:
(1) 19 to 21 percent by volume sulfuric acid in water;
(2) 25 to 27 percent by weight sodium hydroxide in water;
(3) 5 to 7 percent by volume methanol in gasoline;
(4) 28 to 30 percent by weight ammonium nitrate in water; and
(5) 50 to 52 percent by volume methyl alcohol in water.
(b) The container is oriented with the fluid exposure areas on top.
A pad of glass wool approximately 0.5 centimeters thick and 100
millimeters in diameter is placed on each of the five preconditioned
areas. A sufficient amount of the test fluid is applied to the glass
wool to ensure that the pad is wetted across its surface and through
its thickness for the duration of the test. A plastic covering shall be
applied over the glass wool to prevent evaporation.
(c) The exposure of the container with the glass wool is maintained
for at least 48 hours and no more than 60 hours with the container
hydraulically pressurized to any pressure between 125.0 percent NWP and
130.0 percent NWP. During exposure, the temperature surrounding the
container is maintained at any temperature between 5.0 [deg]C and 35.0
[deg]C.
(d) Hydraulic pressure cycling is performed in accordance with
S6.2.2.2 at any pressure within the specified ranges according to
S5.1.2.3 for the specified number of cycles. The glass wool pads are
removed and the container surface is rinsed with water after the cycles
are complete.
S6.2.3.5. Static pressure test. The container is hydraulically
pressurized to the specified pressure in a temperature-controlled
chamber. The temperature of the chamber and the container surface, or
the surface of the container attachments if present, are held at the
specified temperature for the specified duration.
S6.2.3.6. Extreme temperature pressure cycling test. (a) The
container is filled with hydraulic fluid for each test;
(b) At the start of each test, the container surface, or the
surface of the container attachments if present, the hydraulic fluid,
and the environment surrounding the container are at any temperature
and relative humidity (if applicable) within the ranges specified in
S5.1.2.5 of this standard and maintained for the duration of the
testing.
(c) The container is pressure cycled from any pressure between 1.0
MPa and 2.0 MPa up to the specified pressure at a rate not exceeding 10
cycles per minute for the specified number of cycles;
(d) The temperature of the hydraulic fluid entering the container
shall be measured as close as possible to the container inlet.
S6.2.4. Test procedures for expected on-road performance.
S6.2.4.1. Ambient and extreme temperature gas pressure cycling
test. (a) In accordance with table 3 to S5.1.3.1 of this standard, the
specified ambient conditions of temperature and relative humidity, if
applicable, are maintained within the test environment throughout each
pressure cycle. When required in accordance with table 3 to S5.1.3.1,
the CHSS temperature shall be in the specified initial system
equilibration temperature range between pressure cycles.
(b) The CHSS is pressure cycled from any pressure between 1.0 MPa
and 2.0 MPa up to any pressure within the specified peak pressure range
in accordance with table 3 to this section. The temperature of the
hydrogen fuel dispensed to the container is controlled to within the
specified temperature range within 30 seconds of fueling initiation.
The specified number of pressure cycles are conducted.
(c) The ramp rate for pressurization shall be greater than or equal
to the ramp rate given in table 4 to S6.2.4.1(c) according to the CHSS
volume, the ambient conditions, and the fuel delivery temperature. If
the required ambient temperature is not available in table 4 to this
section, the closest ramp rate value or a linearly interpolated
[[Page 6290]]
value shall be used. The pressure ramp rate shall be decreased if the
gas temperature in the container exceeds 85 [deg]C.
Table 4 to Sec. 571.308 S6.2.4.1(c)
--------------------------------------------------------------------------------------------------------------------------------------------------------
CHSS pressurization rate (MPa/min)
---------------------------------------------------------------------------------------------------
50.0 [deg]C to 55.0 5.0 [deg]C to 35.0 -30.0 [deg]C to -25.0 -30.0 [deg]C to -25.0
CHSS volume (L) [deg]C ambient [deg]C ambient [deg]C ambient [deg]C ambient
conditions -33.0 [deg]C conditions -33.0 [deg]C conditions -33.0 [deg]C conditions 15.0 [deg]C
to -40.0 [deg]C fuel to -40.0 [deg]C fuel to -40.0 [deg]C fuel to 25.0 [deg]C fuel
delivery temperature delivery temperature delivery temperature delivery temperature
--------------------------------------------------------------------------------------------------------------------------------------------------------
50.................................................. 7.6 19.9 28.5 13.1
100................................................. 7.6 19.9 28.5 7.7
174................................................. 7.6 19.9 19.9 5.2
250................................................. 7.6 19.9 19.9 4.1
300................................................. 7.6 16.5 16.5 3.6
400................................................. 7.6 12.4 12.4 2.9
500................................................. 7.6 9.9 9.9 2.3
600................................................. 7.6 8.3 8.3 2.1
700................................................. 7.1 7.1 7.1 1.9
1,000............................................... 5.0 5.0 5.0 1.4
1,500............................................... 3.3 3.3 3.3 1.0
2,000............................................... 2.5 2.5 2.5 0.7
2,500............................................... 2.0 2.0 2.0 0.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
(d) The de-fueling rate shall be any rate greater than or equal to
the intended vehicle's maximum fuel-demand rate. Out of the 500
pressure cycles, any 50 pressure cycles are performed using a de-
fueling rate greater than or equal to the maintenance de-fueling rate.
S6.2.4.2. Gas permeation test. (a) A CHSS is filled with hydrogen
gas to any SOC between 100.0 percent and 105.0 percent and placed in a
sealed container. The CHSS is held for any duration between 12 hours
and 24 hours at any temperature between 55.0 [deg]C and 60.0 [deg]C
prior to the start of the test.
(b) The permeation from the CHSS shall be determined hourly
throughout the test.
(c) The test shall continue for 500 hours or until the permeation
rate reaches a steady state. Steady state is achieved when at least 3
consecutive leak rates separated by any duration between 12 hours and
48 hours are within 10 percent of the previous rate.
S6.2.5. Test procedures for service terminating performance in
fire. The fire test consists of two stages: a localized fire stage
followed by an engulfing fire stage. The burner configuration for the
fire test is specified in S6.2.5.1. The overall test configuration of
the fire test is verified using a pre-test checkout in accordance with
S6.2.5.2 prior to the fire test of the CHSS. The fire test of the CHSS
is conducted in accordance with S6.2.5.3.
S6.2.5.1. Burner configuration. (a) The fuel for the burner shall
be liquefied petroleum gas (LPG).
(b) The width of the burner shall be between 450 millimeters and
550 millimeters.
(c) The length of the burner used for the localized fire stage
shall be between 200 millimeters and 300 millimeters.
(d) The length of the burner used for the engulfing fire stage
shall be in accordance with S6.2.5.3(m).
(e) The burner nozzle configuration and installation shall be in
accordance with table 5 to S6.2.5.1. The nozzles shall be installed
uniformly on six rails.
Table 5 to Sec. 571.308 S6.2.5.1
------------------------------------------------------------------------
Item Description
------------------------------------------------------------------------
Nozzle type............................ Liquefied petroleum gas fuel
nozzle with air pre-mix.
LPG orifice in nozzle.................. 0.9 to 1.1 millimeter inner
diameter.
Air ports in nozzle.................... Four (4) holes, 5.8 to 7.0
millimeter inner diameter.
Fuel/Air mixing tube in nozzle......... 9 to 11 millimeter inner
diameter.
Number of rails........................ 6.
Center-to-center spacing of rails...... 100 to 110 millimeter.
Center-to-center nozzle spacing along 45 to 55 millimeter.
the rails.
------------------------------------------------------------------------
S6.2.5.2. Pre-test checkout. (a) The pre-test checkout procedure in
this section shall be performed to verify the fire test configuration
for the CHSS tested in accordance with S6.2.5.3.
(b) A pre-test container is a 12-inch Schedule 40 Nominal Pipe Size
steel pipe with end caps. The cylindrical length of the pre-test
container shall be equal to or longer than the overall length of the
CHSS to be tested in S6.2.5.3, but no shorter than 0.80 m and no longer
than 1.75 m.
(c) The pre-test container shall be mounted over the burner:
(1) At any height between 95 millimeters and 105 millimeters above
the burner;
(2) Such that the nozzles from the two center rails are pointing
toward the bottom center of the pre-test container; and
(3) Such that the container's position relative to the localized
and engulfing zones of the burner is consistent with the positioning of
the CHSS over the burner in S6.2.5.3.
(d) For outdoor test sites, wind shielding shall be used. The
separation between the pre-test container and the walls of the wind
shields shall be at least 0.5 meters.
[[Page 6291]]
(e) Temperatures during the pre-test check-out shall be measured at
least once per second using 3.2 millimeter diameter or less K-type
sheath thermocouples.
(f) The thermocouples shall be located in sets to measure
temperatures along the cylindrical section of the pre-test container.
These thermocouples are secured by straps or other mechanical
attachments within 5 millimeters from the pre-test container surface.
One set of thermocouples consists of:
(1) One thermocouple located at the bottom surface exposed to the
burner flame,
(2) One thermocouple located mid-height along the left side of the
cylindrical surface,
(3) One thermocouple located mid-height along the right side of the
cylindrical surface, and
(4) One thermocouple located at the top surface opposite to the
burner flame.
(g) One set of thermocouples shall be centrally located at the
localized fire zone of the CHSS to be tested as determined in S6.2.5.3.
Two additional sets of thermocouples shall be spread out over the
remaining length of the engulfing fire zone of the CHSS to be tested
that is not part of the localized fire zone of the CHSS to be tested.
(h) Burner monitor thermocouples shall be located between 20
millimeters and 30 millimeters below the bottom surface of the pre-test
container in the same three horizontal locations described in
S6.2.5.2(g). These thermocouples shall be mechanically supported to
prevent movement.
(i) With the localized burner ignited, the LPG flow rate to the
burner shall be set such that the 60-second rolling averages of
individual temperature readings in the localized fire zone shall be in
accordance with the localized stage row in the table below.
(j) With the entire burner ignited, the LPG flow rate to the burner
shall be set such that the 60-second rolling averages of individual
temperature readings shall be in accordance with the engulfing stage
row in table 6 to S6.2.5.2.
Table 6 to Sec. 571.308 S6.2.5.2
----------------------------------------------------------------------------------------------------------------
Temperature range on
Fire stage Temperature range on bottom sides of pre-test Temperature range on top of
of pre-test container container pre-test container
----------------------------------------------------------------------------------------------------------------
Localized................... 450 [deg]C to 700 [deg]C.... less than 750 [deg]C... less than 300 [deg]C.
Engulfing................... Average temperatures of the Not applicable......... Average temperatures of the
pre-test container surface pre-test container surface
measured at the three measured at the three top
bottom locations shall be locations shall be at
greater than 600 [deg]C. least 100 [deg]C, and when
greater than 750 [deg]C,
shall also be less than
the average temperatures
of the pre-test container
surface measured at the
three bottom locations.
----------------------------------------------------------------------------------------------------------------
S6.2.5.3. CHSS fire test. (a) The CHSS to be fire tested shall
include TPRD vent lines.
(b) The CHSS to be fire tested shall be mounted at any height
between 95 millimeters and 105 millimeters above the burner.
(c) CHSS shall be positioned for the localized fire test by
orienting the CHSS such that the distance from the center of the
localized fire exposure to the TPRD(s) and TPRD sense point(s) is at or
near maximum.
(d) When the container is longer than the localized burner, the
localized burner shall not extend beyond either end of the container in
the CHSS.
(e) The CHSS shall be filled with compressed hydrogen gas to any
SOC between 100.0 percent and 105.0 percent.
(f) For outdoor test sites, the same wind shielding shall be used
as was used for S6.2.5.2. The separation between the CHSS and the walls
of the wind shields shall be at least 0.5 meters.
(g) Burner monitor temperatures shall be measured below the bottom
surface of the CHSS in the same positions as specified in S6.2.5.2(h).
(h) The allowable limits for the burner monitor temperatures during
the CHSS fire test shall be established based on the results of the
pre-test checkout as follows:
(1) The minimum value for the burner monitor temperature during the
localized fire stage (TminLOC) shall be calculated by
subtracting 50 [deg]C from the 60-second rolling average of the burner
monitor temperature in the localized fire zone of the pre-test
checkout. If the resultant TminLOC exceeds 600 [deg]C,
TminLOC shall be 600 [deg]C.
(2) The minimum value for the burner monitor temperature during the
engulfing fire stage (TminENG) shall be calculated by
subtracting 50 [deg]C from the 60-second rolling average of the average
of the three burner monitor temperatures during the engulfing fire
stage of the pre-test checkout. If the resultant TminENG
exceeds 800 [deg]C, TminENG shall be 800 [deg]C.
(i) The localized fire stage is initiated by starting the fuel flow
to the localized burner and igniting the burner.
(j) The 10-second rolling average of the burner monitor temperature
in the localized fire zone shall be at least 300 [deg]C within 1 minute
of ignition and for the next 2 minutes.
(k) Within 3 minutes of the igniting the burner, using the same LPG
flow rate as S6.2.5.2(i), the 60-second rolling average of the
localized zone burner monitor temperature shall be greater than
TminLOC as determined in S6.2.5.3(h)(1).
(l) After 10 minutes from igniting the burner, the engulfing fire
stage is initiated.
(m) The engulfing fire zone includes the localized fire zone and
extends in one direction towards the nearest TPRD or TPRD sense point
along the complete length of the container up to a maximum burner
length of 1.65 m.
(n) Within 2 minutes of the initiation of the engulfing fire stage,
using the same LPG flow rate as S6.2.5.2(j), the 60-second rolling
average of the engulfing burner monitor temperature shall be equal or
greater than TminENG as determined in S6.2.5.3(h)(2).
(o) The fire testing continues until the pressure inside the CHSS
is less than or equal to 1.0 MPa or until:
(1) A total test time of 60 minutes for CHSS on vehicles with a
GVWR of 10,000 pounds or less or;
(2) A total test time of 120 minutes for CHSS on vehicles with a
GVWR over 10,000 pounds.
S6.2.6. Test procedures for performance durability of closure
devices.
[[Page 6292]]
S6.2.6.1. TPRD performance tests. Unless otherwise specified,
testing is performed with either hydrogen gas with a purity of at least
99.97 percent, less than or equal to 5 parts per million of water, and
less or equal to 1 part per million particulate, or with an inert gas.
All tests are performed at any temperature between 5.0 [deg]C and 35.0
[deg]C unless otherwise specified.
S6.2.6.1.1. Pressure cycling test. A TPRD undergoes 15,000 internal
pressure cycles at a rate not exceeding 10 cycles per minute. The table
below summarizes the pressure cycles. Any condition within the ranges
specified in table 7 to this section may be selected for testing.
(a) The first 10 pressure cycles shall be from any low pressure of
between 1.0 MPa and 2.0 MPa to any high pressure between 150.0 percent
NWP and 155.0 percent NWP. These cycles are conducted at any sample
temperature between 85.0 [deg]C to 90.0 [deg]C.
(b) The next 2,240 pressure cycles shall be from any low pressure
between 1.0 MPa and 2.0 MPa to any high pressure of between 125.0
percent NWP and 130.0 percent NWP. These cycles are conducted at any
sample temperature between 85.0 [deg]C to 90.0 [deg]C.
(c) The next 10,000 pressure cycles shall be from any low pressure
of between 1.0 MPa and 2.0 MPa to any high pressure between 125.0
percent NWP and 130.0 percent NWP. These cycles are conducted at a
sample temperature between 5.0 [deg]C to 35.0 [deg]C.
(d) The final 2,750 pressure cycles shall be from any low pressure
between 1.0 MPa and 2.0 MPa to any high pressure between 80.0 percent
NWP and 85.0 percent NWP. These cycles are conducted at any sample
temperature between -45.0 [deg]C to -40.0 [deg]C.
Table 7 to Sec. 571.308 S6.2.6.1.1
----------------------------------------------------------------------------------------------------------------
Sample temperature
Number of cycles Low pressure High pressure for cycles
----------------------------------------------------------------------------------------------------------------
First 10........................... 1.0 MPa to 2.0 MPa.... 150.0% NWP to 155.0% NWP... 85.0 [deg]C to 90.0
[deg]C.
Next 2,240......................... 1.0 MPa to 2.0 MPa.... 125.0% NWP to 130.0% NWP... 85.0 [deg]C to 90.0
[deg]C.
Next 10,000........................ 1.0 MPa to 2.0 MPa.... 125.0% NWP to 130.0% NWP... 5.0 [deg]C to 35.0
[deg]C.
Final 2,750........................ 1.0 MPa to 2.0 MPa.... 80.0% NWP to 85.0% NWP..... -45.0 [deg]C to -40.0
[deg]C.
----------------------------------------------------------------------------------------------------------------
S6.2.6.1.2. Accelerated life test. (a) Two TPRDs undergo testing;
one at the vehicle manufacturer's specified activation temperature, and
one at an accelerated life temperature, TL, given in [deg]C using
equation 2 to this section, where [beta] = 273.15 [deg]C, TME is 85
[deg]C, and Tf is the vehicle manufacturer's specified activation
temperature in [deg]C.:
Equation 2 to Sec. 571.308 S6.2.6.1.2
[GRAPHIC] [TIFF OMITTED] TR17JA25.005
(b) The TPRDs are placed in an oven or liquid bath maintained
within 5.0 [deg]C of the specified temperature per S6.2.6.1.2(a). The
TPRD inlets are pressurized with hydrogen to any pressure between 125.0
percent NWP and 130.0 percent NWP and time until activation is
measured.
S6.2.6.1.3. Temperature cycling test. (a) An unpressurized TPRD is
placed in a cold liquid bath maintained at any temperature between -
45.0 [deg]C and -40.0 [deg]C. The TPRD shall remain in the cold bath
for any duration not less than 2 hours and not more than 24 hours. The
TPRD is removed from the cold bath and transferred, within five minutes
of removal, to a hot liquid bath maintained at any temperature between
85.0 [deg]C and 90.0 [deg]C. The TPRD shall remain in the hot bath for
any duration not less than 2 hours and not more than 24 hours. The TPRD
is removed from the hot bath and, within five minutes of removal,
transferred back into the cold bath maintained at any temperature
between -45.0 [deg]C and -40.0 [deg]C.
(b) Step (a) is repeated until 15 thermal cycles have been
achieved.
(c) The TPRD remains in the cold liquid bath for any duration not
less than 2 and not more than 24 additional hours, then the internal
pressure of the TPRD is cycled with hydrogen gas from any pressure
between 1.0 MPa and 2.0 MPa to any pressure between 80.0 percent NWP
and 85.0 percent NWP for 100 cycles. During cycling, the TPRD remains
in the cold bath and the cold bath is maintained at any temperature
between -45.0 [deg]C and -40.0 [deg]C.
S6.2.6.1.4. Salt corrosion resistance test. (a) Each closure device
is exposed to a combination of cyclic conditions of salt solution,
temperatures, and humidity. One test cycle is equal to any duration not
less than 22 and not more than 26 hours, and is in accordance with
table 8 to S6.2.6.1.4.
Table 8 to Sec. 571.308 S6.2.6.1.4
----------------------------------------------------------------------------------------------------------------
Accelerated cyclic corrosion conditions (1 cycle = 22 hours to 26 hours)
-----------------------------------------------------------------------------------------------------------------
Cycle condition Temperature Relative humidity Cycle duration
----------------------------------------------------------------------------------------------------------------
Ambient stage........................ 22.0 [deg]C to 28.0 35 percent to 55 470 minutes to 490
[deg]C. percent. minutes
----------------------------------------------------------------------------------------------------------------
Transition 55 min to 60 min
----------------------------------------------------------------------------------------------------------------
Humid stage.......................... 47.0 [deg]C to 51.0 95 percent to 100 410 minutes to 430
[deg]C. percent. minutes
----------------------------------------------------------------------------------------------------------------
Transition 170 minutes to 190 minutes
----------------------------------------------------------------------------------------------------------------
Dry stage............................ 55.0 [deg]C to 65.0 less than 30 percent... 290 minutes to 310
[deg]C. minutes
----------------------------------------------------------------------------------------------------------------
(b) The apparatus used for this test shall consist of a fog/
environmental chamber as defined in ISO 6270-2:2017(E) (incorporated by
reference, see Sec. 571.5), with a suitable water supply conforming to
Type IV
[[Page 6293]]
requirements in ASTM D1193-06 (Reapproved 2018) (incorporated by
reference, see Sec. 571.5). The chamber shall include a supply of
compressed air and one or more nozzles for fog generation. The nozzle
or nozzles used for the generation of the fog shall be directed or
baffled to minimize any direct impingement on the closure devices.
(c) During ``wet-bottom'' generated humidity cycles, water droplets
shall be visible on the samples.
(d) Steam generated humidity may be used provided the source of
water used in generating the steam is free of corrosion inhibitors and
visible water droplets are formed on the samples to achieve proper
wetness.
(e) The drying stage shall occur in the following environmental
conditions: any temperature not less than 60 [deg]C and not greater
than 65 [deg]C and relative humidity no more than 30 percent with air
circulation.
(f) The impingement force from the salt solution application shall
not remove corrosion and/or damage the coatings of the closure devices.
(g) The complex salt solution in percent by mass shall be as
specified in S6.2.6.1.4(g)(1) through (5):
(1) Sodium Chloride: not less than 0.08 and not more than 0.10
percent.
(2) Calcium Chloride: not less than 0.095 and not more than 0.105
percent.
(3) Sodium Bicarbonate: not less than 0.07 and not more than 0.08
percent.
(4) Sodium Chloride must be reagent grade or food grade. Calcium
Chloride must be reagent grade. Sodium Bicarbonate must be reagent
grade. For the purposes of S6.2.6.1.4, water must meet ASTM D1193-06
(Reapproved 2018) Type IV requirements (incorporated by reference, see
Sec. 571.5).
(5) Either calcium chloride or sodium bicarbonate material must be
dissolved separately in water and added to the solution of the other
materials.
(h) The closure devices shall be installed in accordance with the
vehicle manufacturer's recommended procedure and exposed to the 100
daily corrosion cycles, with each corrosion cycle in accordance with
table 8 to S6.2.6.1.4.
(i) For each salt mist application, the solution shall be sprayed
as an atomized mist, using the spray apparatus to mist the components
until all areas are thoroughly wet and dripping. Suitable application
techniques include using a plastic bottle, or a siphon spray powered by
oil-free regulated air to spray the test samples. The quantity of spray
applied should be sufficient to visibly rinse away salt accumulation
left from previous sprays. Four salt mist applications shall be applied
during the ambient stage. The first salt mist application occurs at the
beginning of the ambient stage. Each subsequent salt mist application
should be applied not less than 90 and not more than 95 minutes after
the previous application.
(j) The time from ambient to the wet condition shall be any
duration not less than 60 and not more than 65 minutes and the
transition time between wet and dry conditions shall be any duration
not less than 180 and not more than 190 minutes.
S6.2.6.1.5. Vehicle environment test. (a) The inlet and outlet
connections of the closure device are connected or capped in accordance
with the vehicle manufacturer's installation instructions. All external
surfaces of the closure device are exposed to each of the following
fluids for any duration between 24 hours and 26 hours. The temperature
during exposure shall be any temperature between 5.0 [deg]C and 35.0
[deg]C. A separate test is performed with each of the fluids
sequentially on a single closure device.
(1) Sulfuric acid: not less than 19 and not more than 21 percent by
volume in water;
(2) Ethanol/gasoline: not less than 10 and not more than 12 percent
by volume ethanol and not less than 88 and not more than 90 percent by
volume gasoline; and
(3) Windshield washer fluid: not less than 50 and not more than 52
percent by volume methanol in water.
(b) The fluids are replenished as needed to ensure complete
exposure for the duration of the test.
(c) After exposure to each fluid, the closure device is wiped off
and rinsed with water.
S6.2.6.1.6. Stress corrosion cracking test. (a) All components
exposed to the atmosphere shall be degreased. For check valves and
shut-off valves, the closure device shall be disassembled, all
components degreased, and then reassembled.
(b) The closure device is continuously exposed to a moist ammonia
air mixture maintained in a glass chamber having a glass cover. The
exposure lasts any duration not less than 240 hours and not more than
242 hours. The aqueous ammonia shall have a composition of between 19
weight percent and 21 weight percent ammonium hydroxide in water.
Aqueous ammonia shall be located at the bottom of the glass chamber
below the sample at any volume not less than 20 mL and not more than 22
mL of aqueous ammonia per liter of chamber volume. The bottom of the
sample is positioned any distance not less than 30 and not more than 40
millimeters above the aqueous ammonia and supported in an inert tray.
(c) The moist ammonia-air mixture is maintained at atmospheric
pressure and any temperature not less than 35 [deg]C and not more than
40 [deg]C.
S6.2.6.1.7. Drop and vibration test. (a) The TPRD is aligned
vertically to any one of the six orientations covering the opposing
directions of three orthogonal axes: vertical, lateral and
longitudinal.
(b) A TPRD is dropped in free fall from any height between 2.00
meters and 2.02 meters onto a smooth concrete surface. The TPRD is
allowed to bounce on the concrete surface after the initial impact.
(c) Any sample with damage from the drop that results in the TPRD
not being able to be tested in accordance with S6.2.6.1.7(d) shall not
proceed to S6.2.6.1.7(d) and shall not be considered a failure of this
test.
(d) Each TPRD dropped in S6.2.6.1.7(a) that did not have damage
that results in the TPRD not being able to be tested is mounted in a
test fixture in accordance with vehicle manufacturer's installation
instructions and vibrated for any duration between 30.0 minutes and
35.0 minutes along each of the three orthogonal axes (vertical, lateral
and longitudinal) at the most severe resonant frequency for each axis.
(1) The most severe resonant frequency for each axis is determined
using any acceleration between 1.50 g and 1.60 g and sweeping through a
sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time
between 10.0 minutes and 20.0 minutes. The most severe resonant
frequency is identified by a pronounced increase in vibration
amplitude.
(2) If the resonance frequency is not found, the test shall be
conducted at any frequency between 35 Hz and 45 Hz.
S6.2.6.1.8. Leak test. Unless otherwise specified, the TPRD shall
be thermally conditioned to the ambient temperature condition, then
checked for leakage, then conditioned to the high temperature
condition, then checked for leakage, then conditioned to low
temperature, then checked for leakage.
(a) The TPRD shall be thermally conditioned at test temperatures in
each of the test conditions and held for any duration between 1.0 hour
and 24.0 hours. The TPRD is pressurized with hydrogen at the inlet. The
required test conditions are:
(1) Ambient temperature: condition the TPRD at any temperature
between 5.0 [deg]C and 35.0 [deg]C; test in accordance with
S6.2.6.1.8(b) at any pressure between 1.5 MPa and 2.5 MPa and then
[[Page 6294]]
at any pressure between 125.0 percent NWP and 130.0 percent NWP.
(2) High temperature: condition the TPRD at any temperature between
85.0 [deg]C and 90.0 [deg]C; test in accordance with S6.2.6.1.8(b) at
any pressure between 1.5 MPa and 2.5 MPa and then at any pressure
between 125.0 percent NWP and 130.0 percent NWP.
(3) Low temperature: condition the TPRD at any temperature between
-45.0 [deg]C and -40.0 [deg]C; test in accordance with S6.2.6.1.8(b) at
any pressure between 1.5 MPa and 2.5 MPa and then at any pressure
between 100.0 percent NWP and 105.0 percent NWP.
(b) Following conditioning at each of the specified test
temperature ranges, the TPRD is observed for leakage while immersed in
a temperature-controlled liquid at the same specified temperature range
for any duration between 1.0 minutes and 2.0 minutes at each of the
pressure ranges listed above. If no bubbles are observed for the
specified time period, it is not considered a failure. If bubbles are
detected, the leak rate is measured.
S6.2.6.1.9. Bench top activation test. (a) The test apparatus
consists of either a forced air oven or chimney with air flow. The TPRD
is not exposed directly to flame. The TPRD is mounted in the test
apparatus according to the vehicle manufacturer's installation
instructions.
(b) The temperature of the oven or chimney is at any temperature
between 600.0 [deg]C and 605.0 [deg]C for any duration between 2
minutes and 62 minutes prior to inserting the TPRD.
(c) Prior to inserting the TPRD, pressurize the TPRD to any
pressure between 1.5 MPa and 2.5 MPa.
(d) The pressurized TPRD is inserted into the oven or chimney, the
temperature within the oven or chimney is maintained at any temperature
between 600.0 [deg]C and 605.0 [deg]C, and the time for the TPRD to
activate is recorded. If the TPRD does not activate within 120 minutes
from the time of insertion into the oven or chimney, the TPRD shall be
considered to have failed the test.
S6.2.6.1.10. Flow rate test. (a) At least one new TPRD is tested to
establish a baseline flow rate.
(b) After activation in accordance with S6.2.6.1.9, and without
cleaning, removal of parts, or reconditioning, the TPRD is subjected to
flow testing using hydrogen, air or an inert gas;
(c) Flow rate testing is conducted with any inlet pressure between
1.5 MPa and 2.5 MPa. The outlet is at atmospheric pressure.
(d) Flow rate is measured in units of kilograms per minute with a
precision of at least 2 significant digits.
S6.2.6.2. Check valve and shut-off valve performance tests. Unless
otherwise specified, testing shall be performed with either hydrogen
gas with a purity of at least 99.97 percent, less than or equal to 5
parts per million of water, and less than or equal to 1 part per
million particulate, or with an inert gas. All tests are performed at
any temperature between 5.0 [deg]C and 35.0 [deg]C unless otherwise
specified.
S6.2.6.2.1. Hydrostatic strength test. (a) The outlet opening is
plugged and valve seats or internal blocks are made to assume the open
position.
(b) Any hydrostatic pressure between 250.0 percent NWP and 255.0
percent NWP is applied using water to the valve inlet for any duration
between 180.0 seconds and 185.0 seconds. The unit is examined to ensure
that burst has not occurred.
(c) The hydrostatic pressure is then increased at a rate of less
than or equal to 1.4 MPa/sec until component failure. The hydrostatic
pressure at failure is recorded.
S6.2.6.2.2. Leak test. Each unit shall be thermally conditioned to
the ambient temperature condition, then checked for leakage, then
conditioned to the high temperature condition, then checked for
leakage, then conditioned to low temperature, then checked for leakage.
(a) Each unit shall be pressurized to any pressure between 2.0 MPa
and 3.0 MPa and held for any duration between 1.0 hours and 24.0 hours
in the specified temperature range before testing. The outlet opening
is plugged. The test conditions are:
(1) Ambient temperature: condition the unit at any temperature
between 5.0 [deg]C and 35.0 [deg]C; test at any pressure between 1.5
MPa and 2.5 MPa and at any pressure between 125.0 percent NWP and 130.0
percent NWP.
(2) High temperature: condition the unit at any temperature between
85.0 [deg]C and 90.0 [deg]C; test at any pressure between 1.5 MPa and
2.5 MPa and at any pressure between 125.0 percent NWP and 130.0 percent
NWP.
(3) Low temperature: condition the unit at any temperature between
-45.0 [deg]C and -40.0 [deg]C; test at any pressure between 1.5 MPa and
2.5 MPa and at any pressure between 100.0 percent NWP and 105.0 percent
NWP.
(b) While within the specified temperature and pressure range, the
unit is observed for leakage while immersed in a temperature-controlled
liquid held within the same specified temperature range as the test
condition for any duration between 1.0 minutes and 2.0 minutes at each
of the test pressures. If no bubbles are observed for the specified
time period, the sample passes the leak test. If bubbles are detected,
the leak rate is measured.
S6.2.6.2.3. Extreme temperature pressure cycling test. (a) The
valve unit is connected to a test fixture.
(b) For a check valve, the pressure is applied in six incremental
pulses to the check valve inlet with the outlet closed. The pressure is
then vented from the check valve inlet. The pressure is lowered on the
check valve outlet side to any pressure between 55.0 percent NWP and
60.0 percent NWP prior to the next cycle.
(c) For a shut-off valve, the specified pressure is applied through
the inlet port. The shut-off valve is then energized to open the valve
and the pressure is reduced to any pressure less than 50 percent of the
specified pressure range. The shut-off valve shall then be de-energized
to close the valve prior to the next cycle.
S6.2.6.2.4. Chatter flow test. The valve is subjected to between
24.0 hours and 26.0 hours of chatter flow at a flow rate that causes
the most valve flutter.
S6.2.6.2.5. Electrical Tests. This section applies to shut-off
valves only.
(a) The solenoid valve is connected to a variable DC voltage
source, and the solenoid valve is operated as follows:
(1) Held for any duration between 60.0 and 65.0 minutes at any
voltage between 0.50 V and 1.5 times the rated voltage.
(2) The voltage is increased to any voltage between 0.5 V to two
times the rated voltage, or between 60.0 V and 60.5 V, whichever is
less, and held for any duration between 60.0 seconds and 70.0 seconds.
(b) Any voltage between 1,000.0 V DC and 1,010.0 V DC is applied
between the power conductor and the component casing for any duration
between 2.0 seconds to 4.0 seconds.
S6.2.6.2.6. Vibration test. (a) The valve is pressurized with
hydrogen to any pressure between 100.0 percent NWP and 105.0 percent
NWP, sealed at both ends, and vibrated for any duration between 30.0
and 35.0 minutes along each of the three orthogonal axes (vertical,
lateral and longitudinal) at the most severe resonant frequencies.
(b) The most severe resonant frequencies are determined using any
acceleration between 1.50 g and 1.60 g and sweeping through a
sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time
between 10.0 minutes and 20.0 minutes. The resonance frequency is
identified by a pronounced increase in vibration amplitude.
[[Page 6295]]
(c) If the resonance frequency is not found, the test shall be
conducted at any frequency between 35 Hz and 45 Hz.
Issued in Washington, DC, under authority delegated in 49 CFR
1.95 and 501.
Adam Raviv,
Chief Counsel.
[FR Doc. 2024-31367 Filed 1-16-25; 8:45 am]
BILLING CODE 4910-59-P