                             Response to Comments
                                       
                    For the Notice of Proposed Rulemaking:
                                       
                    Protection of the Stratospheric Ozone:
New Substitute in the Motor Vehicle Air Conditioning Sector under the Significant New Alternatives Policy (SNAP) Program
                                       
                                       
                         Docket: EPA-HQ-OAR-2008-0664
                                       
                               February 24, 2011
                                       
                                       
                                       
                     U.S. Environmental Protection Agency
                          Office of Air and Radiation
                       Stratospheric Protection Division
                         1200 Pennsylvania Avenue, NW
                             Washington, DC 20460
Contents
lIST OF TERMS AND ACRONYMS	4
1.	List of COmments REceived and Summarized	6
2.	Acceptability Decision	8
2.1	Acceptability of HFO-1234yf	8
2.2	Use of Other Alternative Refrigerants	8
3.	Use Conditions for HFO-1234yf	9
3.1	Overall Comments on Use Conditions	9
3.2	Recommended Language for Revising Use Conditions	11
3.3	Concentration in Passenger Compartment	12
3.3.1	Mitigation Strategies and Implications on the Risk of HFO-1234yf	13
3.3.2	Ignition Specifications	14
3.3.3	Appropriateness of the Simulated Charge Size	14
3.4	Concentration in Engine Compartment	15
3.5	Controlling Concentrations near Electric Sources for Hybrid Vehicles or Electric Vehicles	16
3.6	Unique Fittings	17
3.7	Labeling Requirements	17
3.8	High-Pressure Cutoff Switch	17
3.9	Failure Mode and Effects Analysis (FMEA)	17
3.10	Legal Authority for Use Conditions	18
4.	Environmental Impacts of HFO-1234yf	18
4.1	Ozone Depletion Potential (ODP) of HFO-1234yf	18
4.2	Global Warming Potential (GWP) of HFO-1234yf	18
4.3	Contribution to Ground Level Ozone	19
4.4	Degradation of HFO-1234yf into Trifluoroacetic Acid (TFA)	21
4.5	Lifecycle Emissions of HFO-1234yf	22
5.	Health and safety concerns	23
5.1	Toxicity of HFO-1234yf	23
5.2	Flammability of HFO-1234yf	26
5.3	Generation of Hydrogen Fluoride (HF)	28
6.	Retrofits of MVAC Systems	31
6.1	Use of HFO-1234yf as a Retrofit	31
6.2	Use of Other Alternative Refrigerants as Retrofits in HFO-1234yf MVAC Systems	32
7.	Use by "do-it-yourselfers"	33
8.	servicing issues	35
8.1	Servicing Specifications	35
8.2	Technician Certification Specification	36
8.3	Required Servicing Equipment	36
9.	TSCA Significant New Use Rule (SNUR)	37
10.	End of Life Vehicle Recycling Concerns	38
10.1	Regulatory Impacts on End-of-Life Vehicle (ELV) Recyclers	38
10.2	Occupational Risks at End-of-Life Vehicle Recycling	40
11.	Cost of HFO-1234yF	39
12.	Timely Completion of the Rule	43
13.	Other	44
 REFERENCES............................................................................................. 46
List of Terms and Acronyms 

AC, A/C	Air conditioning
AIST	National Institute of Advanced Industrial Science and Technology 
ASHRAE	American Society of Heating, Refrigerating and Air Conditioning Engineers
BAM	Bundesanstalt für Materialforschung und-prüfung (Federal Institute for Materials Research and Testing)
CAA		Clean Air Act
CFC		Chlorofluorocarbon
CFD		Computational Fluid Dynamics
CFR		Code of Federal Regulations
CO2		Carbon dioxide
CRP 		Cooperative Research Program
DIN	Deutsches Institut für Normung (German Institute for Standards)
DIY		Do-it-yourself
DOT		U.S. Department of Transportation
ELV		End-of-Life Vehicle
EPA		U.S. Environmental Protection Agency
EU		European Union
FMEA		Failure Mode and Effects Analysis
FR		Federal Register
FRAND	Fair, Reasonable and Non-Discriminatory
GWP		Global Warming Potential 
HC		Hydrocarbon
HCFC		Hydrochlorofluorocarbon
HF		Hydrogen Fluoride
HFC		Hydrofluorocarbon
HFO		Hydrofluoro-olefin
HI		Hazard Index
ISO		International Organization for Standardization
JAMA		Japan Automobile Manufacturers Association
kg		Kilogram
LCCP		Lifecycle Climate Performance 
LFL		Lower Flammability Limit
MAC 		Mobile Air Conditioning
MACS		Mobile Air Conditioning Society
MOE		Margin of Exposure
MIR		Maximum Incremental Reactivity
MVAC	Motor Vehicle Air Conditioning
NHTSA 	National Highway Traffic Safety Administration
NOAEL	No Observed Adverse Effect Level
ODP		Ozone Depletion Potential
ODS		Ozone Depleting Substance
OEM		Original Equipment Manufacturer
OSHA 		Occupational Safety and Health Administration
PAG		Polyalkylene Glycol
PFC		Perfluorocarbon
PMN		Pre-Manufacture Notice
POCP		Photochemical Ozone Creation Potential
ppb		Parts per billion
ppm		Parts per million
RCRA		Resource Conservation and Recovery Act
SAE		Society of Automotive Engineers
SNAP		Significant New Alternatives Policy
SNUN		Significant New Use Notice
SNUR		Significant New Use Rule
SO2		Sulfur dioxide
TFA		Trifluoroacetic acid
TSCA		Toxic Substances Control Act
TWA		Time-weighted Average
UBA		Umwelt Bundesamt (Federal Agency for the Environment)
UMRA	Unfunded Mandates Reform Act
VOC		Volatile Organic Compound
WEEL		Workplace Environmental Exposure Limit
μg/L		Micrograms per liter

List of COmments REceived and Summarized

Public Comments Received by EPA on the New Substitute in the Motor Vehicle Air Conditioning End Use under the SNAP Program
                                     Count
Document ID No.
Commenter Name
Organization
                                       1
EPA-HQ-OAR-2008-0664-0039
Nancy Baker
NA
                                       2
EPA-HQ-OAR-2008-0664-0040
Anonymous
Anonymous
                                       3
EPA-HQ-OAR-2008-0664-0051.1
Gregory Buffalino
Volvo
                                       4
EPA-HQ-OAR-2008-0664-0052.1
Taner Eryilmaz
DuPont
                                       5
EPA-HQ-OAR-2008-0664-0053.1
Gabriele Hoffmann
Federal Environmental Agency in Germany (UBA)
                                       6
EPA-HQ-OAR-2008-0664-0054.1
Christianna Papazahariou
Shecco
                                       7
EPA-HQ-OAR-2008-0664-0055.1
Frank J. Diertl
Daimler AG (DAG)[a] 
                                       8
EPA-HQ-OAR-2008-0664-0056.1
Gary Pollak
SAE International
                                       9
EPA-HQ-OAR-2008-0664-0057.1
Michael Sonnekalb
Konvekta
                                      10
EPA-HQ-OAR-2008-0664-0058.1
Robert D. Brown
Ford
                                      11
EPA-HQ-OAR-2008-0664-0059
James Irvine
Jaguar Land Rover
                                      12
EPA-HQ-OAR-2008-0664-0060.1
Julie Becker
The Alliance of Automobile Manufacturers[b]
                                      13
EPA-HQ-OAR-2008-0664-0061.1
Deborah Bakker
Hyundai
                                      14
EPA-HQ-OAR-2008-0664-0062.1
John Cabaniss
Association of International Automobile Manufacturers (AIAM)
                                      15
EPA-HQ-OAR-2008-0664-0063.1
Douglas I. Greenhaus
National Automobile Dealers Association (NADA)
                                      16
EPA-HQ-OAR-2008-0664-0064.1
Kevin Webber
Toyota
                                      17
EPA-HQ-OAR-2008-0664-0065.1
Ward Atkinson and William Hill
SAE Interior Climate Control Standards Committee (ICCC)
                                      18
EPA-HQ-OAR-2008-0664-0066.1
Michael Conlon
Conlon, Frantz & Phelan LLP
                                      19
EPA-HQ-OAR-2008-0664-0069.1
Elvis Hoffpauir
Mobile Air Conditioning Society (MACS) Worldwide
                                      20
EPA-HQ-OAR-2008-0664-0077
Michael Conlon
Conlon, Frantz & Phelan LLP
                                      21
EPA-HQ-OAR-2008-0664-0078.1
Gregory Buffalino
Volvo
                                      22
EPA-HQ-OAR-2008-0664-0079
Anonymous
Anonymous
                                      23
EPA-HQ-OAR-2008-0664-0080.1
Gabriele Hoffmann
Federal Environmental Agency in Germany (UBA)
                                      24
EPA-HQ-OAR-2008-0664-0081.1
Matt Kevnick
Toyota
                                      25
EPA-HQ-OAR-2008-0664-0082
Nick Hanna
Greater Cleveland Automobile Dealers Association (GCADA)
                                      26
EPA-HQ-OAR-2008-0664-0083.1
Frederick Sciance
General Motors (GM)
                                      27
EPA-HQ-OAR-2008-0664-0085.1
Douglas I. Greenhaus
National Automobile Dealer's Association (NADA)
                                      28
EPA-HQ-OAR-2008-0664-0087.1
Michael E. Wilson
Automotive Recycler's Association
                                      29
EPA-HQ-OAR-2008-0664-0088
Claudette Papathanasopoulos
Greenpeace
                                      30
EPA-HQ-OAR-2008-0664-0089.1
Christianna Papazahariou
Shecco
                                      31
EPA-HQ-OAR-2008-0664-0089.2
Christianna Papazahariou
Shecco
                                      32
EPA-HQ-OAR-2008-0664-0090.1
Robert L. Redding, Jr.
Automotive Service Association
                                      33
EPA-HQ-OAR-2008-0664-0091.1
Thomas A. Lewandowski
Gradient
                                      34
EPA-HQ-OAR-2008-0664-0094
Anonymous
Anonymous
                                      35
EPA-HQ-OAR-2008-0664-0095.1
Taner Eryilmaz
DuPont
                                      36
EPA-HQ-OAR-2008-0664-0095.2
Taner Eryilmaz
DuPont
                                      37
EPA-HQ-OAR-2008-0664-0097.1
Christianna Papazahariou
Shecco
                                      38
EPA-HQ-OAR-2008-0664-0097.2
Christianna Papazahariou
Shecco
                                      39
EPA-HQ-OAR-2008-0664-0097.3
Christianna Papazahariou
Shecco
                                      40
EPA-HQ-OAR-2008-0664-0097.4
Christianna Papazahariou
Shecco
                                      41
EPA-HQ-OAR-2008-0664-0099
Gary Pivotto
NA
                                      42
EPA-HQ-OAR-2008-0664-0100.1
Maleesa M. Williams
Lee's Auto Repair Incorporated
                                      43
EPA-HQ-OAR-2008-0664-0101.1
Michael J Conlon
Conlon, Frantz & Phelan, LLP
                                      44
EPA-HQ-OAR-2008-0664-0103.1
Diana H Hull
AutoZone
                                      45
EPA-HQ-OAR-2008-0664-0104.1
Anonymous
Anonymous
                                      46
EPA-HQ-OAR-2008-0664-0106.1
David Doniger
Natural Resources Defense Council (NRDC)
                                      47
EPA-HQ-OAR-2008-0664-0108
John Francis III
John Francis III
                                      48
EPA-HQ-OAR-2008-0664-0110
Douglas I. Greeithaus
National Automobile Dealer's Association (NADA)
                                      49
EPA-HQ-OAR-2008-0664-0111.1
David L. Wagger
Institute of Scrap Recycling Industries, Inc. (ISRI)
                                      50
EPA-HQ-OAR-2008-0664-0113.1
Michael J Conlon
Conlon, Frantz & Phelan, LLP
                                      51
EPA-HQ-OAR-2008-0664-0114.2
Christianna Papazahariou
Shecco
                                      52
EPA-HQ-OAR-2008-0664-0115.2
David Diggs
Honeywell
                                      53
EPA-HQ-OAR-2008-0664-0116.1
David Diggs
Honeywell
                                      54
EPA-HQ-OAR-2008-0664-0116.2
David Diggs
Honeywell
                                      55
EPA-HQ-OAR-2008-0664-0120
Tom Massey
Auto Air and More Inc.
                                      56
EPA-HQ-OAR-2008-0664-0118.2
Giedrius Ambrozaitis
The Alliance of Automobile Manufacturers[b], d
                                      57 
EPA-HQ-OAR-2008-0664-0119
Greg Henslee
O'Reilly Auto Partsd
                                      58 
EPA-HQ-OPPT-2008-0664-0121.1
David Diggs
Honeywell[c], d
                                      59 
EPA-HQ-OAR-2008-0664-0135.1[c]
Taner Eryilmaz
DuPontd
                                      60 
EPA-HQ-OAR-2008-0664-0131.1
Donald Elliott
Arkemad
                                      61 
EPA-HQ-OAR-2008-0664-0132.1
Michael Conlon
Conlon, Frantz & Phelan LLPd
a. Submitted by Mercedes-Benz on behalf of its parent company, Daimler AG.
b. The Alliance of Automobile Manufacturers is comprised of the BMW Group, Chrysler LLC, Ford Motor Company, General Motors, Jaguar Land Rover, Mazda, Mercedes-Benz, Mitsubishi Motors, Porsche, Toyota, and Volkswagen.  In addition to supporting the comments submitted by the Alliance, Ford Motor Company, General Motors, Jaguar Land Rover, Mercedes-Benz, and Toyota also submitted supplemental comments on the proposed rule.
c. Published in response to SNUR FedReg. Vol. 75, No. 63 (April 2, 2010) under docket ID EPA-HQ-OPPT-2008-0918. Comments relevant to the SNAP proposed rule (docket ID EPA-HQ-OAR-2008-0664) are included in this summary of comments.
d. Comments submitted after the close of the comment period.
Acceptability Decision
Acceptability of HFO-1234yf
Comment:  Several commenters supported EPA's proposal to find HFO-1234yf as an acceptable substitute for CFC-12 in motor vehicle air conditioners (MVACs).  These commenters stated that available information indicates that HFO-1234yf will not pose significant health risks or environmental concerns under foreseeable use and leak conditions and that it has a strong potential to reduce greenhouse gas emissions from motor vehicles.  Also, these commenters declared that HFO-1234yf's risks are similar to or less than those of other available alternatives, such as HFC-134a, HFC-152a, and CO2.  A commenter referenced the work of the SAE CRP (CRP, 2008 and 2009), which concluded that HFO-1234yf can be used safely through established industry practices for vehicle design, engineering, manufacturing, and service. 
Other commenters opposed finding HFO-1234yf acceptable or stated that there was insufficient information to support a conclusion.  These commenters stated that the risks of HFO-1234yf are greater than those of other available alternatives, such as HFC-134a, CO2, and hydrocarbons. 
 Response:  See section VII.A of the preamble, "Acceptability decision," for our response to these comments.
Comment:  A commenter stated that specific justification should be given for why HFO-1234yf should not be used in medium and heavy-duty vehicle MVACs.
Response:  The submission to the SNAP program (EPA-HQ-OAR-2008-0664-0013.1) was specifically "for use as a refrigerant in OEM mobile air conditioning units for new cars and servicing of those cars by professionals" as a substitute for CFC-12.  Thus, the original submission does not specifically address medium or heavy duty vehicles or vehicles that traditionally used HCFC-22 as the refrigerant, such as buses or trains, and so EPA is not addressing these other uses.  Thus, EPA's risk screen (HQ-OAR-2008-0664-0038), as well as the SAE CRP's risk assessments (CRP, 2008 and 2009), were based on the use of HFO-1234yf in light-duty vehicles.  Because there is no indication from the manufacturer that this substitute should apply more broadly, and because of lack of risk information related to broader usage, this final rule is for use of HFO-1234yf in light-duty vehicles (i.e., cars and light-duty passenger vehicles including vans, pickup trucks, and sport utility vehicles).
Use of Other Alternative Refrigerants
Comment:  Three commenters suggested that EPA should consider other substitutes for CFC-12 in MVAC systems, such as CO2 or hydrocarbons. An organization representing the automotive industry stated that the risks from using CO2 in MVAC systems are below the probability of other adverse events which society considers acceptable and are roughly 1.5 orders of magnitude greater than the risks from using HFO-1234yf.  
Response:  See section VII.A of the preamble, "Acceptability decision," for our response to these comments. 
Use Conditions for HFO-1234yf
Overall Comments on Use Conditions
Comment:  Several commenters stated that the proposed use conditions limiting concentrations of HFO-1234yf below the lower flammability limit are overly stringent or even impossible to meet and are not needed for safe usage.  Some automobile manufacturers suggested relying upon established standards and practices, such as SAE protocols and standards, instead of use conditions.  Some commenters suggested alternative language for use conditions.  Other commenters expressed concern that the proposed use conditions limiting concentrations of HFO-1234yf would preclude the use of HFO-1234yf by any vehicle that is not initially designed to use this refrigerant. 
Response:  See section VII.B of the preamble, "Use conditions," for our response to these comments.
Comment:  Two commenters stated that established standards and practices would be adequate for safe use of HFO-1234yf. 
Response:  EPA agrees that the three proposed use conditions limiting the concentration of HFO-1234yf are not required, so long as specific practices identified in SAE standards are followed.  The final rule references the 2011 version of the SAE J639 standard, requiring the safety provisions that were identified in the proposal as necessary (e.g., labels, unique fittings, high pressure cut-off switch).  In addition, the final rule requires the unique fittings for refrigerant containers from the 2011 version of the SAE J2844 standard.  These fittings were the unique fittings selected by the manufacturer and provided to EPA as required by appendix D to subpart G of 40 CFR part 82.  They also are the same fittings required for the low-side service port on a vehicle -- quick connect fittings with an outside diameter of 14 mm (0.551 inches).  See the following sections in the preamble for further discussion:  IV. "What are the final use conditions and why did EPA finalize these conditions?", V. "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and VII.B. "Use conditions."
Comment:  In late comments, one commenter stated that EPA has not established that HFO-1234yf poses a real world flammability risk.  Another commenter stated that significant engineering restrictions proposed by EPA on the use of HFO-1234yf are unnecessary.  The commenter based this on statements made by Honeywell on July 15, 2010 at the SAE Refrigerant Symposium that discussed the testing conducted under the Cooperative Research Program (CRP) for HFO-1234yf and the results of the SAE risk assessment for that refrigerant based on that testing.  Specifically, the commenter referred to the following statements: "Extensive testing at third-party facilities did not identify significant risks for the use of R-1234yf in mobile air-conditioning systems." "R-1234yf does not pose an exposure risk due to chemical toxicity." "Risks for Repair Workers of using R-1234yf MAC systems are very small."  
Some commenters requested that EPA re-evaluate its position on the first three use conditions. One of these commenters stated that EPA should only require such cost-effective use controls as are necessary to reduce risks to acceptable levels without compromising MVAC or other vehicle performance attributes. 
Response:  We have reevaluated the first three use conditions with engineering restrictions on concentration.  Based on the information available to the Agency, including the SAE risk assessment mentioned by commenters (CRP, 2009; EPA-HQ-OAR-2008-664-0132.2) and the summary of that document provided by one of the commenters (EPA-HQ-OAR-2008-0664-0132), we believe that the flammability risk from HFO-1234yf is extremely low and have removed the first three use conditions from the final rule accordingly.  The remaining use conditions related to industry standards are a cost-effective means to reduce risks to acceptable levels.  See the following sections in the preamble for further discussion:  IV. "What are the final use conditions and why did EPA finalize these conditions?", V. "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and VII.B. "Use conditions."
Comment:  One commenter provided test results from the Bundesanstalt fuer Materialforschung und  - pruefung (BAM -- Federal Institute for Materials Research and Testing) that tested various mixtures of HFO-1234yf and ethane (EPA-HQ-OAR-2008-0664-0053.3).  The commenter stated that the tests show that explosions can occur at HFO-1234yf concentrations below its lower flammability limit (LFL) of 6.2% when minimal amounts of gaseous hydrocarbons are available.  This commenter stated that the maximum concentrations of HFO-1234yf allowed under any use condition need to be far below the 6.2% LFL to ensure safety.  Other commenters agreed with these concerns.  Yet other commenters looked at the same test data and stated that the testing was not relevant to real-world situations in MVAC because it is unlikely that such large amounts of ethane or other gaseous hydrocarbons (0.8-2.4% by volume) would form in a vehicle.  One commenter stated that HFO-1234yf reduces the flammability of ethane compared to ethane alone, and that HFO-1234yf reduces flammability of ethane more than CO2 or argon, substances used as fire suppressants (EPA-HQ-OAR-2008-0664-0115.1).
Response:  See section VII.B of the preamble, "Use conditions," for our response to these comments.  
Comment:  A commenter noted that a safety margin of 0.2% below the lower flammability limit was proposed for the concentration limit for HFC-152a in document EPA-HQ-OAR-2008-0664-0005. 
Response:  EPA notes that the safety margin for HFC-152a mentioned by the commenter was for purposes of performing a conservative risk assessment, rather than for setting an enforceable limit.  However, when EPA issued a rule for HFC-152a (proposal at 71 FR 55140, final at 73 FR 33304), we used the lowest measured LFL of 3.7%.  In any case, since the estimated risks of fire from HFO-1234yf are so low, with only one fire expected every hundred years across the entire U.S. fleet, EPA does not find it necessary to require a regulatory limit on concentrations of HFO-1234yf.  Also see section VII.B of the preamble, "Use conditions," for further information.
Comment:  One commenter provided data from a presentation showing that the lower flammability limit of HFO-1234yf decreases as temperature increases.  The commenter stated that the proposed LFL of 6.2% may not be conservative enough. 
Response:  See section VII.B of the preamble, "Use conditions," for our response to this comment.

Recommended Language for Revising Use Conditions
Comment:  Three commenters recommended that the following language be used to replace the first three use conditions that limit concentrations of HFO-1234yf: "HFO-1234yf MVAC systems must incorporate protective engineering strategies in areas where processes, procedures or upset conditions such as leaks have the potential to generate HFO-1234yf concentrations at or above 6.2% v/v in proximity to any potential ignition source."  
One commenter proposed the following language in place of  the first three use conditions that limit concentrations of HFO-1234yf: "Vehicle manufacturers shall perform risk assessments as described in SAE J1739 (FMEA) and based on this analysis, implement necessary design measures in order to have similar or reduced risk level compared to current HFC-134a MVAC systems." 
One commenter recommended eliminating the first three use conditions that limit concentrations of HFO-1234yf, or alternatively using the following to replace those conditions: "HFO-1234yf MVAC systems must incorporate protective engineering strategies in areas reasonably likely to generate HFO-1234yf concentrations at or above 6.2% v/v in proximity to any reasonably likely ignition source.  Such strategies shall be based on risk assessments based on SAE J1739 (FMEA), or its equivalent." 
One commenter recommended the following text to replace the three proposed design-related use conditions: "HFO-1234yf mobile air conditioning (MAC) systems shall incorporate engineering strategies reasonably necessary to manage risks of injury and/or property damage caused by HFO-1234yf, similar to R-134a MAC systems risk. Such strategies shall be based on risk assessments using SAE J1739 (FMEA) or its equivalent." 
Response:  In the final rule, we are removing the three use conditions that restrict the concentration of HFO-1234yf below the lower flammability limit (LFL) because of the low risks of flammability and generation of hydrogen fluoride (HF) and the fact that those risks are comparable to or less than risks from other available or potentially available alternatives in this end use.  As discussed in the preamble, EPA believes that the use conditions based upon industry standards are sufficient to address risks without adding the new use conditions suggested by the commenters.  See the following sections in the preamble:  IV. "What are the final use conditions and why did EPA finalize these conditions?", V. "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and VII.B. "Use conditions."  
Comment:  One commenter suggested that the use conditions for limiting concentrations in the passenger cabin should require the incorporation of engineering strategies and/or devices "such that foreseeable leaks" rising to the specified concentration levels can be avoided.  Similarly, the commenter stated that any use condition limiting concentrations in the engine compartment should be limited to "prevention of ignition caused by foreseeable leaks."  The commenter noted that EPA did this in a similar use condition in its final SNAP rule for HFC-152a, another flammable refrigerant for MVAC with greater flammability risk.  The commenter stated that this would be consistent with safety requirements of the National Highway Traffic Safety Administration (NHTSA) and would ensure that EPA's use conditions are feasible.  
Response:  See section VII.B of the preamble, "Use conditions," for our response to this comment.

Concentration in Passenger Compartment
Comment:  Regarding the first proposed use condition that would limit the concentration of HFO-1234yf below the LFL in the passenger cabin, several commenters stated that the risks of refrigerant leaking into the passenger compartment and exceeding the LFL are very low.  Some automobile manufacturers stated that it may not be possible to keep the concentration below the LFL in the event of a collision; however, the commenters said that even if concentrations in the passenger cabin exceeded the LFL, it would be extremely difficult to ignite the refrigerant.  Some commenters stated that the engineering strategies that would be necessary to implement the proposed use condition would actually increase overall risk by increasing the risk of conveying smoke and fumes from the engine compartment into the passenger compartment in the event of an accident.  Some commenters suggested alternative language for the use condition to give greater flexibility in engineering responses to allow for differences between vehicles.  
Response:  See section VII.B of the preamble, "Use conditions," for our response to these comments.
Comment:  Ten commenters do not support the proposed use condition limiting concentrations of HFO-1234yf in the passenger compartment. Two commenters further stated that unless this condition is modified, the changeover to a new refrigerant will be delayed and could be completely forestalled. 
Response:  As discussed in section IV of the preamble, "What are the final use conditions and why did EPA finalize these conditions?", EPA is not including the proposed use condition requiring that a specific level of refrigerant concentration inside the passenger cabin is not exceeded.  
Comment:  One commenter stated that if EPA determines to include a passenger compartment use condition, the condition should include the same limitation applicable to the more flammable HFC-152a. The commenter further stated that a probing area and time must be specified for compliance to the concentration limit, as well as the situations for which such a requirement holds (i.e., normal use conditions and/or vehicle crash). 
Response:  As discussed in section IV of the preamble, "What are the final use conditions and why did EPA finalize these conditions?", EPA is not including the proposed use condition requiring that a specific level of refrigerant concentration inside the passenger cabin is not exceeded.  
Comment:  Four commenters compared the risk of HFO-1234yf with other refrigerants.  Two commenters stated that even without concentration limits, it has been shown that HFO- 1234yf is safer than HFC-152a in a secondary loop system and that HFO-1234yf has almost the same risk profile as HFC-134a.  
Response:  EPA agrees that the overall risks associated with HFO-1234yf are less than or comparable to those from other available refrigerants for MVAC, provided that the use conditions in this final rule are observed.  Thus, we are finding HFO-1234yf acceptable as a substitute for CFC-12 in MVAC systems in new light-duty vehicles, subject to use conditions. 
Comment:  Two commenters stated that the use condition is not conservative enough. One commenter further stated that the maximum concentrations of HFO-1234yf need to be far below the 6.2% LFL, and that they are unsure whether or not additional measures can effectively avoid the risk of explosive mixtures. 
Response:  See the following sections in the preamble:  IV. "What are the final use conditions and why did EPA finalize these conditions?", V. "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and VII.B. "Use conditions."  In the final rule, we are removing the three use conditions that restrict the concentration of HFO-1234yf below the LFL because of the low risks of flammability and generation of HF and the fact that those risks are comparable to or less than risks from other available or potentially alternatives in this end use.  
Mitigation Strategies and Implications on the Risk of HFO-1234yf
[Refer also to comments on HF generation for further discussion on risks associated with HFO-1234yf.]
Comment:  Two commenters stated that the mitigation strategies that would need to be adopted to meet the refrigerant concentration limit for the interior compartment in the proposed use condition would increase overall risk compared to not having such strategies.  One commenter stated that to meet the concentration limit, the two prominent strategies that could be used -- 1) a squib valve to purge the refrigerant to an outside location during a crash and 2) turning the blower on high in crash situations -- would both result in increased overall risk. Purging the refrigerant during a crash with a squib valve would create leaks in many crashes in which no leak would normally occur, possibly creating new risks where the refrigerant is purged. Turning the blower on high would disperse any high concentrations of HFO-1234yf near the floor; however, in all crashes it would also bring into the passenger compartment air from near the engine compartment, which could include smoke and fumes from that area following a crash.  The commenter also stated that a secondary loop could prevent high interior concentrations, but the loss of efficiency [of the MVAC system] would be prohibitive for HFO-1234yf. 
One commenter stated that adopting a requirement for a "blower off switch" as a use restriction would eliminate or reduce the ignition risks associated with collisions. 
One commenter does not support the use of directed discharge devices in the engine compartment (which would be one way to meet the proposed use condition limiting the refrigerant concentration in the engine compartment). 
Response:  EPA recognizes that there may be risks associated with mitigation techniques and we consider these risks when establishing use conditions. In determining whether a use condition is necessary and appropriate, EPA balances any risks that may result from meeting that use condition with the risks that are presented in the absence of such a use condition.  As explained more fully in the preamble, EPA is not including the use conditions that limit concentrations of HFO-1234yf in the interior compartment or in the engine compartment in the final rule.  Instead, we are requiring original equipment manufacturers and users to meet safety requirements consistent with those in SAE J639 and to meet requirements for risk assessment consistent with those in SAE J1739.  See the following sections in the preamble:  IV "What are the final use conditions and why did EPA finalize these conditions?", V "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and VII B "Use conditions."  

Ignition Specifications
Comment:  Some commenters responded to EPA's request for comment as to whether the use conditions should apply only when the car ignition is on.  These commenters indicated that it is unnecessary for the use conditions on refrigerant concentrations within the passenger compartment to apply while a vehicle's ignition is off because it is unlikely that a collision would occur, that high temperatures would occur, or that refrigerant would enter the passenger cabin when the ignition, and thus the MVAC system, is off.  Another commenter stated that it should be mandatory for all electric power sources to be shut off when the ignition is off. 
Response:  See section VII.B of the preamble, "Use conditions" for our response to these comments.
Appropriateness of the Simulated Charge Size 
Comment:  One commenter stated that vehicle A/C refrigerant charge amounts vary from vehicle to vehicle (from 0.4 kg to 1.5 kg) dependant on specific design characteristics, and hence there is not one size that is appropriate for all simulations and thus there is no simple answer to EPA's question about what charge sizes to use in analyzing potential interior refrigerant concentrations. The commenter further noted that industry efforts such as the SAE CRP have tried to include vehicles with worst-case charges, and for interior refrigerant concentrations these have tended to be the smallest vehicles.  
Response:  EPA believes that worst-case charge sizes are appropriate for risk assessment and agrees that these tend to be for the smallest vehicles.  We have based our analysis on smaller charge sizes with a large ratio of charge to free space in analyzing risks, as might be found in small vehicles.
Comment:  One commenter disagreed with a statement in section IV.F of the preamble to the proposed rule regarding charge sizes in the SAE International/DuPont (CRP, 2008) and Exponent reports.  This portion of the preamble stated that, based upon presentations from Honeywell that HFO-1234yf charge sizes should be 90-95% of a HFC-134a charge size, and therefore the Crown Victorias described in the SAE International/DuPont report and in the Exponent report were undercharged.  The commenter disagreed, stating that the Large Car CFD analysis was done with appropriate guidance from vehicle manufacturers regarding charge size. 
Response:  EPA believes the commenter is referencing the following statement in the preamble to the proposed rule (74 FR 53449):  
      The Agency requests public comment on the SAE International/DuPont and Exponent reports.  Specifically, the Agency requests comment on the appropriateness of the simulated charge size that was used by each report.  The SAE International/DuPont report simulated a 2001 Ford Crown Victoria with a 691 gram HFO-1234yf charge.  The Exponent report used a 1997 Ford Crown Victoria with a charge size of 693 grams.  The 1997 and 2001 Ford Crown Victorias were originally designed with approximately 966 gram and 1097 grams HFC-134a charge size systems (MACS, 2005).  Honeywell presentations have indicated the HFO-1234yf charge size is 90-95% of a HFC-134a charge size (Honeywell, 2008).  Based on the original refrigerant charge size of these Crown Victorias, the HFO-1234yf charge sizes, in both simulations, are not consistent with the 90-95% HFC-134a charge sizes described in Honeywell presentations and the Crown Victorias are undercharged.  Charge size is an important element in determining the probability of a flammable concentration.  EPA requests comment on whether the charge sizes used in the DuPont and Exponent simulations are consistent with the actual charge sizes that would need to be used in MVAC for these vehicles.  
It is not clear from the comment what guidance vehicle manufacturers gave regarding charge size or why this differed from statements in a Honeywell presentation that HFO-1234yf charge size is 90-95% of a HFC-134a charge size.  Starting with charge sizes for the Crown Victoria of 966 g and 1097 g in 1997 and 2001, 90-95% of those values would be 869-918 g or 987-1042 g, rather than 691 or 693 g, the values used in the SAE International/DuPont and Exponent reports.  However, additional information from the SAE CRP (CRP, 2009) indicates that there is low overall probability of ignition occurring, with an estimate of roughly 9 x 10[-13] occurrences per vehicle operating hour.  Thus, the specific charge size does not have a significant impact on EPA's conclusion that HFO-1234yf is acceptable for use in new light-duty vehicles for MVAC, subject to use conditions, nor does it impact EPA's conclusions about the final use conditions.
Concentration in Engine Compartment
Comment:  Several commenters stated that the proposed limits on concentrations of HFO-1234yf in the engine compartment cannot be met, even hypothetically, and that imposition of such a use condition would delay or even prevent the use of HFO-1234yf.  Other commenters stated that the engineering required to meet the proposed use condition is almost certain to preclude the use of HFO-1234yf by any vehicle that was not initially designed to use this refrigerant.  
Response:  See section VII.B of the preamble, "Use conditions," for our response to these comments.
Comment:  Ten commenters do not support the proposed use condition on engine compartment concentrations. One commenter also recommended that the proposed use conditions be eliminated because they have not shown to improve real world safety and because they would interfere with good engineering practices. 
Two commenters stated that the use condition is not conservative enough. One of the commenters stated that the maximum concentrations of HFO-1234yf need to be far below the 6.2% LFL and further stated that they are unsure whether or not additional measures can effectively avoid the risk of explosive mixtures. The other commenter referenced a graph showing the LFL of HFO-1234yf vs. temperature and stated that the elevated temperatures at which the LFL is lowered could possibly occur at least in the engine compartment.  
Response:  EPA is removing the proposed use condition that sets a specific limit for refrigerant concentrations inside the engine compartment in the final rule.  See the following sections in the preamble for further detail:  IV. "What are the final use conditions and why did EPA finalize these conditions?", V. "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and VII.B. "Use conditions."
Comment:  One commenter suggested that the use conditions for limiting concentrations in the passenger cabin should require the incorporation of engineering strategies and/or devices "such that foreseeable leaks" rising to the specified concentration levels can be avoided.  Similarly, the commenter stated that any use condition limiting concentrations in the engine compartment should be limited to "prevention of ignition caused by foreseeable leaks."  The commenter noted that EPA did this in a similar use condition in its final SNAP rule for HFC-152a, another flammable refrigerant for MVAC with greater flammability risk.  The commenter stated that this would be consistent with safety requirements of the National Highway Traffic Safety Administration (NHTSA) and would ensure that EPA's use conditions are feasible.  
Response:  See section VII.B of the preamble, "Use conditions," for our response to this comment.
Controlling Concentrations near Electric Sources for Hybrid Vehicles or Electric Vehicles
Comment:  A number of commenters did not support the proposed use condition on concentrations of HFO-1234yf in hybrid and electric vehicles.  One commenter recommended eliminating this use condition, as the SAE CRP risk assessment concludes there are no real world safety risks.  Another commenter suggested referring to the SAE or ISO International Organization for Standardization (ISO) standards in place of a specific use condition.  One commenter stated that electric terminals on hybrid vehicles are well protected to prevent fires and should not ignite the refrigerant.  Another commenter stated that an accident severe enough to cause refrigerant leakage would also result in damage to the duct between the evaporator [in the MVAC system] and the battery pack, preventing an increase in refrigerant concentrations at the battery pack.  One commenter stated that it is difficult to establish generic SNAP use conditions for hybrid vehicles, and individual manufacturers need to understand particular design features of their hybrid vehicles to ensure safe refrigerant application.  Three commenters expressed concern for using HFO-1234yf in hybrid and electric vehicles and stated that the use condition is not conservative enough.  One commenter stated that the maximum concentrations of HFO-1234yf need to be far below the 6.2% LFL based on new tests done at the Federal Institute for Materials Research and Testing (BAM) and that they are unsure whether or not additional measures can effectively avoid the risk of explosive mixtures.  Another commenter stated that HFO-1234yf would raise concerns in the field of battery cooling needed in electric vehicles because flammability and chemical reactions would pose major risks, which could lead to legal consequences for OEMs. 
Response:  See section VII.B of the preamble, "Use conditions" for our response to these comments.
Comment:  One commenter stated that the conclusions drawn from the SAE CRP presentation overstate the risks of HFO-1234yf, and its real world vehicle data provides for a more realistic risk assessment (see Toyota Study: MAC Refrigerant Risk Assessment -- EPA-HQ-OAR-2008-0664-0081.1 and -0081.2). 
Response:  Based on the information available, including the information provided by the commenter, the risks of sparking from an electrical source are not high enough to warrant a use condition.  EPA is removing the proposed use condition that would have required design with protective devices, isolation and/or ventilation techniques where levels of refrigerant concentration may exceed the LFL in proximity to exhaust manifold surfaces or near hybrid or electric vehicle power sources in the final rule.  See the following sections in the preamble for further rationale:  IV "What are the final use conditions and why did EPA finalize these conditions?" and VII.B "Use conditions."
Unique Fittings
Comment:  Several commenters agreed with EPA's proposal to require use of unique fittings and a warning label that identify the new refrigerant and restrict the possibility of cross-contamination with other refrigerants.  Other commenters suggested that no use conditions are necessary because established standards and practices would be adequate for safe use of HFO-1234yf.  
Response:  See section VII.B of the preamble, "Use conditions," for our response to these comments. 
Labeling Requirements
Comment:  Six commenters support the proposed labeling requirement. One commenter recommended the label comply with SAE J639 design requirements. 
Response:  EPA is retaining the requirement for a warning label in the final rule by reference to the SAE J639 standard (2011).  See section VII.B of the preamble, "Use conditions," for further detail.
High-Pressure Cutoff Switch
Comment:  Some commenters agreed with EPA's proposal to require a high-pressure compressor cut-off switch, as per SAE J639.  
Another commenter suggested that the compressor cut-off switch would be useful for all systems in which the discharge pressure can reach the burst pressure, not just those systems with pressure relief devices.  
Response:  See section VII.B of the preamble, "Use conditions" for our response to these comments.
Failure Mode and Effects Analysis (FMEA)
Comment:  Several commenters supported the requirement for vehicle makers to conduct and maintain FMEAs.  Other automobile manufacturers stated that the final SNAP rule finding HFC-152a acceptable as a substitute for CFC-12 in MVAC included this as a comment rather than as a use condition, and suggested that EPA do the same in the final rule for HFO-1234yf.  Another commenter stated that FMEAs for each vehicle design are standard industry practice, and so no use condition is required; this commenter provided language for an alternate use condition should EPA choose to specify a use condition for vehicle design.
Response:  See section VII.B of the preamble, "Use conditions" for our response to these comments. 
Comment:  A commenter requested that EPA specifically allow manufacturers to perform FMEAs according to equivalent standards developed by organizations other than SAE (e.g., the International Organization for Standardization [ISO], the German Institute for Standards [DIN], or the Japan Automobile Manufacturers Association [JAMA]).
Response:  See section VII.B of the preamble, "Use conditions," for our response to this comment.
Legal Authority for Use Conditions
Comment:  A commenter expressed that EPA's approach to setting use conditions infringes upon the Department of Transportation's motor vehicle safety jurisdiction and that EPA does not have the authority to protect against any fire risk associated with motor vehicles.  
Response:  See section VII.B of the preamble, "Use conditions," for our response to this comment.
Environmental Impacts of HFO-1234yf
Ozone Depletion Potential (ODP) of HFO-1234yf
Comment:  Several commenters agreed with EPA's proposed finding that HFO-1234yf would not contribute significantly to stratospheric ozone depletion, and that the ODP of HFO-1234yf is at or near zero. Two commenters commented that the ODP of HFO-1234yf should be stated as "zero" instead of "nearly zero," and one commenter requested that EPA clarify that HFO-1234yf has an ODP less than that of HFC-134a. 
Other commenters disagreed with EPA's statement that the ODP of HFO-1234yf is at or near zero. One commenter expressed concern that ODS may be used in the HFO-1234yf manufacturing process or emissions may break down into gases with ODPs.  This commenter advised EPA against listing HFO-1234yf as an acceptable replacement for HFC-134a in MVACs. Another commenter stated that HFO-1234yf requires further investigation since unsaturated HFCs such as HFO-1234yf might break down into gases that are ozone depleting.
Response:  See section VII.C.1 of the preamble, "Ozone depletion potential," for our response to these comments.  Concerning the potential use of ODS in the process of manufacturing HFO-1234yf, EPA reviewed the identity and emission rates of the chemicals used in manufacturing HFO-1234yf in confidential business information provided to EPA as part of the Pre-Manufacture Notice and the SNAP submission.  This information indicates it is highly unlikely that substances used in the manufacturing process will have a significant impact on human health and the environment, including the ozone layer.  
      4.2 Global Warming Potential (GWP) of HFO-1234yf
Comment:  Several commenters agreed with EPA's statement that HFO-1234yf has a global warming potential (GWP) of 4 over a 100-year time horizon.  Some commenters noted the potential environmental benefits of having a lower GWP refrigerant available. 
Other commenters stated that HFO-1234yf would not be a solution to high global warming impacts because of environmental and health impacts of breakdown products, including HF, trifluoroacetic acid (TFA), and aldehydes. 
Response:  See the discussion in section VII.C.2 of the preamble, "Global warming potential" for our response to these comments.
Comment:  A commenter stated that environmental, meteorological, and space agencies are casting doubts about the claims that olefins might solve the problem of high global warming impacts.  [Note:  Hydrofluoroolefins are a subset of olefins.  Olefins are carbon-containing compounds with a double bond.]
Response:  EPA finds this statement vague and unsupported.  The commenter has not stated which agencies have raised doubts or the basis of any doubts.  See also the discussion in section VII.C.2 of the preamble, "Global warming potential."
Comment:  One commenter stated that if HFO-1234yf is not decomposed to TFA then there might be a risk for building high-GWP substances, and noted that Bera et al. (2009) found the fluorine atom to be responsible for the most powerful GWP substances.  
 Response:  EPA disagrees.  Available information on expected decomposition products of HFO-1234yf does not identify any with a high GWP.  Expected breakdown pathways include hydroxyl mediated oxidation (Luecken et al., 2009), which would create CF3COF and then trifluoroacetic acid (Papadimitrou et al., 2007), and chlorine initiated oxidation reactions in a marine environment.  The latter would create predominantly CF3COF and some HCOCl, CO, and NO2 (ICF, 2010d).  Other expected breakdown products from HFO-1234yf include formaldehyde and hydroperoxyl radical (HO2) (ICF, 2010d).  Available information indicates that close to 100% of fluorinated breakdown products of HFO-1234yf will degrade to trifluoroacetyl fluoride that then degrades to TFA in the environment (ICF, 2010d).
Although it is true that the fluorine atom is responsible for creating significant greenhouse gas impacts from compounds such as CFCs, HFCs, and perfluorocarbons (PFCs), it is also true that the article cited from Bera et al. (2009) only considered saturated compounds with single bonds.  Single bonds are inherently more stable than the double bond found in HFOs such as HFO-1234yf.  Thus, saturated HFCs such as HFC-134a have a much longer lifetime and significantly higher GWP than unsaturated HFOs such as HFO-1234yf, even though both compounds contain four bonds between carbon and fluorine.  HFO-1234yf has an estimated atmospheric lifetime of approximately 11 days and a 100-year GWP of 4 (Papadimitrou et al., 2007), compared to a lifetime of 14 years and an estimated GWP of 1430 for HFC-134a (IPCC, 2007).
  1.1 Contribution to Ground Level Ozone
Comment:  Some commenters expressed concern about a potential increase in ground-level ozone of  >1-4% calculated in EPA's initial assessment (ICF, 2009) of environmental impacts of HFO-1234yf.  Other commenters stated that HFO-1234yf will not contribute significantly to ground-level ozone.  One commenter suggested that EPA provide an updated assessment of the potential contribution of HFO-1234yf to ground-level ozone, considering the additional information provided in public comments (e.g., Luecken et al., 2009, and Wallington et al., 2009).
Response:  See the discussion in section VII.C.4 of the preamble, "Ground-level ozone formation." 
Comment:  A commenter noted that the Scientific Assessment Panel to the Montreal Protocol recently raised its concerns about the potential for tropospheric ozone pollution formation from HFOs, citing Newman et al. (2009).  
Response:  The presentation to the Scientific Assessment Panel for the Montreal Protocol (Newman et al., 2009) cited by the commenter specifically asks "Does it [olefins] lead to ozone pollution production?"  Based on all available information, we conclude that HFO-1234yf will not create significant impacts on ground level ozone formation or on local air quality, as we originally proposed.  Our revised analysis (ICF, 2010b) estimates that emissions of HFO-1234yf might cause increases in ground-level ozone of approximately 0.08 ppb or 0.1% of the ozone standard in the worst case, rather than an increase of 1.4 to 4% as determined in our initial analysis (ICF, 2009).  Also see the discussion in section VII.C.4 of the preamble, "Ground-level ozone formation." 
Comment:  Some commenters disagreed with EPA's statement that HFO-1234yf has a photochemical ozone creation potential (POCP) comparable to that of ethylene (100), while others agreed with this conclusion. One commenter provided a peer-reviewed study that estimated the POCP of HFO-1234yf to be 7 (Wallington et al., 2010). 
Response:  See section VII.C.4 of the preamble, "Ground-level ozone formation," for our response to these comments. 
Comment:  A commenter provided a link to a paper (Carter, 2009) that found the maximum incremental reactivity (MIR) for HFO-1234yf to be about the same as that for ethane.  Based on the MIR value for HFO-1234yf, some commenters stated that EPA should find HFO-1234yf to be exempt from the definition of volatile organic compound (VOC).  
Response:  See section VII.C.4 of the preamble, "Ground-level ozone formation." 
Comment:  A commenter stated that EPA should not present the VOC status of HFO-1234yf for regulatory purposes as a settled matter, since the manufacturer has petitioned the Agency to exempt HFO-1234yf from the list of VOCs in 40 CFR 51.100(s).  
Response:  EPA's proposal described the legal situation at that time. The definition of "volatile organic compound" at 40 CFR CFR 51.100(s) begins, "(a) Volatile organic compounds (VOC) means any compound of carbon ... which participates in atmospheric photochemical reactions.  (1) This includes any such organic compound other than the following, which have been determined to have negligible photochemical reactivity..."  Periodically, EPA adds negligibly reactive compounds, or so-called "VOC-exempt" chemicals, to the list at 40 CFR 51.100(s)(a)(1).  These compounds are not regulated as VOCs for purposes of meeting the National Ambient Air Quality Standards under regulations for implementing State Implementation Plans.  Since HFO-1234yf is a compound of carbon, it is regulated as a VOC at 40 CFR 51.100(s) until and unless we issue a final rule that adds HFO-1234yf to the list of organic compounds which have been determined to have negligible photochemical reactivity.  We recognize that the regulatory status of HFO-1234yf as a VOC could change, depending on the outcome of EPA's response to the manufacturer's petition to exempt HFO-1234yf from the regulatory definition of VOC.  
Degradation of HFO-1234yf into Trifluoroacetic Acid (TFA)
Comment:  Two commenters agreed with the SNAP finding that TFA is formed from the atmospheric oxidation of HFO-1234yf, citing Orkin et al. (1997). 
Response:  EPA agrees.  Also see section VII.C.5, of the preamble, "Formation of trifluoroacetic acid and ecosystem impacts" for further discussion.
Comment:  Several commenters agreed with EPA's proposed finding that the projected maximum concentration of TFA in rainwater from degradation of HFO-1234yf does not pose a significant aquatic toxicity risk.  Other commenters raised concern about the potential impacts of TFA on biodiversity, ecosystems, and human health.  One commenter questioned the sustainability of HFO-1234yf, so long as there are questions remaining about its environmental fate and degradation.  One commenter stated that artificial input of TFA into the environment should be avoided because of its toxicity and chemical properties.  Another commenter stated that HFO-1234yf poses additional environmental concerns compared to HFC-134a and advised against finding it acceptable while the issue of TFA production is being further researched.
Response:  See section VII.C.5 of the preamble, "Formation of trifluoroacetic acid and ecosystem impacts" for our response to these comments.
Comment:  Some commenters stated that further research on TFA is necessary.  
Response:  See section VII.C.5 of the preamble, "Formation of trifluoroacetic acid and ecosystem impacts" for our response to these comments.
Comment:  Another commenter stated that TFA leached out from the atmosphere through precipitation could develop an herbicide effect and pose a risk to plants and other living organisms.  The commenter also stated that National Institute of Advanced Industrial Science and Technology (AIST) researchers estimate the maximum concentrations of TFA in rainwater and surface water to be 0.45 and 1.3 μg/L, respectively, citing Kajihara et al. (2010).  The commenter further noted that the authors of the AIST paper warn that TFA is known to be extremely stable in the environment and that there is an ample risk that the adoption of HFO-1234yf could lead to the development of aquatic eco-toxicity. 
Response:  EPA continues to conclude that the degradation of HFO-1234yf into TFA does not pose a significant risk of aquatic toxicity or ecosystem impacts.  The AIST researchers also stated that the most conservative estimate of impacts finds levels of TFA to be less than 1/80[th] of the NOAEL for this compound.  This is an ample margin compared to that under EPA's guidelines for pesticides (ORD, 2010).  See section VII.C.5 of the preamble, "Formation of trifluoroacetic acid and ecosystem impacts" for further discussion.
Comment:  Some commenters disagreed with a statement in the ICF (2009) analysis concerning TFA concentrations in surface waters, that "the exception to this is vernal pools and similar seasonal water bodies that have no significant outflow capacity."  These commenters believe that Boutonnet et al. (1999) showed that accumulation of trifluoroacetate, a compound closely related to TFA, was rather limited in seasonal water bodies.  The commenters also stated that Benesch et al. (2002) conducted an experimental study of the impacts of TFA on vernal pools, in which no impacts were observed.  
Response:  See section VII.C.5 of the preamble, "Formation of trifluoroacetic acid and ecosystem impacts" for our response to these comments. 
Comment:  Two commenters stated that EPA's initial modeling (EPA-HQ-OAR-2008-0664-0037) greatly overestimates the local deposition of TFA from oxidation of HFO-1234yf.  In particular, one commenter claimed that the modeling's use of the oxidation of SO2 to sulfate ion, SO3[-], as a proxy for the oxidation of HFO-1234yf is overly conservative because a large portion of SO2 is in aerosol form, unlike for HFO-1234yf.  This commenter also referred to the impacts found in the peer-reviewed paper by Luecken et al. (2009).  
Response:  See section VII.C.5, of the preamble, "Formation of Trifluoroacetic Acid and Ecosystem Impacts" for our response to these comments.
Lifecycle Emissions of HFO-1234yf
Comment: One commenter stated that HFO-1234yf has the best global lifecycle climate performance (LCCP) and lower CO2 [equivalent] emissions compared to other alternatives.  However, another commenter stated that HFO-1234yf has a lower thermodynamic efficiency than HFC-134a and that its use could lead to increases in CO2 and other air pollutant emissions.  The same commenter stated that there is no assurance that automakers would voluntarily add technologies to maintain current levels of MVAC efficiency when using HFO-1234yf. 
 Response:  See section VII.C.3 of the preamble, "Lifecycle emissions of HFO-1234yf."
Comment:  A commenter cautioned EPA against drawing conclusions regarding HFO-1234yf efficiency from the GREEN-MAC-LCCP model.  The commenter expressed concerns about discrepancies between the model and real world findings (e.g., difference between model results finding CO2 less efficient than HFC-134a vs. test and field experience showing large climate benefits and efficiency gains of up to 25% when using CO2 as cited in ATZ (2008), Meyer (2008), and a 2009 UBA press release).  The commenter believes some model data may be outdated or otherwise inaccurate. 
 Response:  Concerning the GREEN-MAC-LCCP model, it is not clear that there are discrepancies between the results of the model and real world experience, as the commenter has claimed.  The UBA press release cited provides no data on real world experience.  The real-world tests cited by the commenter from Meyer (2008) and ATZ (2008) involved CO2 MVAC systems that (1) had been optimized for efficiency and (2) took place in a temperate climate where CO2 cools more efficiently compared to its performance in hotter climates.  In contrast, the GREEN-MAC-LCCP model considers fundamental thermodynamic differences and performance under a variety of environmental conditions.  HFO-1234yf is expected to be more efficient relative to HFC-134a and CO2 at higher temperatures, such as in Arizona (JAMA, 2008).  We believe the highly favorable conditions for the real world testing for CO2 may explain why the cited tests show remarkable efficiency gains with CO2 that are not seen in results from the GREEN-MAC-LCCP model. 
Comment:  Concerning an appropriate rate of emissions for estimating environmental impacts of HFO-1234yf, three commenters recommended that EPA use 50 g per vehicle per year total lifecycle emission rate.  These commenters cited the work of Wallington et al. (2008) and Papasavva et al. (2009).  Another commenter stated that HFO-1234yf is very likely to have a lower leak rate than HFC-134a, citing data on permeability for both refrigerants. 
Response:  See section VII.C.3 of the preamble, "Lifecycle emissions of HFO-1234yf."
Health and safety concerns
Toxicity of HFO-1234yf
Comment:  Three commenters stated that there are no toxicity concerns with using HFO-1234yf, and two commenters noted that HFO-1234yf is comparable to HFC-134a in terms of human health effects. One commenter also stated that HFO-1234yf does not present a developmental toxicity or lethality risk. 
Seven commenters stated that there are potential toxicity concerns with use of HFO-1234yf. One commenter cautioned EPA against listing HFO-1234yf as acceptable for use in MVACs on the grounds of increased concerns over developmental effects and other toxic effects on human health.  
Response:  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf," for our response to these comments.
Comment:  Based on a risk assessment conducted by one commenter, the commenter concluded in late comments that if HFO-1234yf is used under the conditions specified in the commenter's risk assessment, adverse health impacts would not be expected to car occupants, to servicing personnel, or to do-it-yourselfer (DIY) consumers (see Table 1 in docket item EPA-HQ-OAR-2008-0664-0135.2 for exposure input parameters used in the EPA [2009] and DuPont Risk Assessments [DuPont, 2010]). This commenter noted differences between the margin-of-exposure approach to assessing risk, as in EPA's risk assessment (EPA-HQ-OAR-2008-0664-0036), and the commenter's hazard index (HI) approach.  The commenter further stated that in all cases, the predicted HI for HFO-1234yf was only one-half of the values predicted for R-134a, and in some cases, only one-third of the R-134a values, demonstrating from a health perspective that HFO-1234yf is a viable alternative to R-134a.  
Response:  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf."  
Comment:  In response to supporting document EPA-HQ-OAR-2008-0664-0036, one commenter disagreed with the use of a 2-week study for the use of evaluating 30 minute exposures and stated that acute toxicity or cardiac sensitization test results would be more appropriate for acute exposure evaluations.
Response:  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf," for our response to these comments.
Comment:  A commenter asserted that EPA's methodology to estimate the exposure levels associated with the DIY use, using the SAE CRP Phase II Report (CRP, 2008), greatly exaggerates the exposure that could be experienced in actual use conditions.  Another commenter calculated exposure to a DIYer, assuming that the refrigerant fills a garage, and concluded that exposure would be less than the manufacturer's recommended exposure limit of 1000 ppm. The first commenter stated that the 30 minute TWA value used by the EPA is unrealistic as are the exposure estimates presented in scenarios 1 and 2 of the supporting document EPA-HQ-OAR-2008-0664-0036. The specific exposure parameters that the commenters questioned were assumptions regarding:
       garage volume;
       time the user spent under the hood during recharging operations;
       the size of the space where any leaking gas would disperse;
       the air exchange rate in a service area that should be well-ventilated when the engine is running;
       use of the refrigerant in a closed garage with no ventilation; and
       the amount of refrigerant used during recharge operations.
During the comment period for the proposed SNUR, the PMN and SNAP submitter conducted a simulated vehicle service leak testing, using HFC-134a as a surrogate, indicating that exposures from use of a 12-oz can during consumer DIY use are below the Agency's level of concern for HFO-1234yf (Honeywell, 2010a). 
Response:  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf," for our response to these comments.  
Comment: One commenter stated that HFOs could harm the human nervous system. The commenter cited a diagram of breakdown products in a slide presentation given by the Montreal Protocol Scientific Assessment Panel in July 2009 and suggested that the toxic impact of aldehydes would be higher than that of carbonic acids.  
Response: See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf," for our response to this comment.
Comment:  Some commenters stated that additional research and review of the available information regarding toxicity of HFO-1234yf needs to be conducted.
Response:  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf," for our response to these comments.  
Comment:  In late comments, a commenter stated that EPA appears to be relying on a SNUR to reduce risks to human health from exposure to HFO-1234yf.  This commenter stated that EPA must re-open the comment period on the proposed SNAP rule so that commenters may reassess the extent to which the final restrictions of the SNUR will be effective at limiting adverse human health effects.  The same commenter noted that information on new price levels and availability is needed to assess the effectiveness of the SNUR. 
Response:  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf," for our response to these comments.  
Comment:  One commenter stated that the safety of humans in direct and constant contact with HFO-1234yf would be seriously threatened and engineers, maintenance workers, and employees in automotive recycling facilities would be exposed to a yet unknown risk. 
Response:  EPA's risk screen found that risks to workers during repair, maintenance, and vehicle end-of-life (including automotive recycling) were minimal because exposure levels were expected to be well below EPA's workplace exposure level of 250 ppm and well below the lower flammability limit of HFO-1234yf (EPA-HQ-OAR-2008-0664-0038).  Also see sections V and VII.D.1 of the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and "Toxicity of HFO-1234yf."  
Comment:  A commenter recommended that independent testing be performed and published in a peer reviewed scientific journal before a full assessment can be made on the developmental toxicity and environmental impact of HFO-1234yf.  
Response:  We believe that such testing is not necessary.  While certainly further scientific studies can always shed new or additional light, EPA cannot delay necessary rulemaking actions in order to perform or await the results of future tests where adequate information is already available. We note that other new compounds reviewed under SNAP have not been required to have independent toxicological testing or publication of that testing in a peer-reviewed journal. 
Comment:  In late comments, a commenter did not agree with EPA's statement that HFO-1234yf has human health concerns for developmental toxicity and lethality via inhalation. The commenter stated that HFO-1234yf has been evaluated in a 2-generation reproductive toxicity study and extensively studied for developmental toxicity in multiple species.  The commenter stated that HFO-1234yf was not uniquely toxic to the developing fetus in any species tested and displayed no maternal toxicity in the rat.  The commenter also stated that after repeated exposures to high concentrations, rabbit maternal toxicity was observed, and the No Adverse Effect Level (NOAEL) was 4000 ppm.  The commenter concluded that given that the maternal toxicity occurred only after extended exposure to high concentrations and that when evaluated within the context of plausible exposure scenarios, HFO-1234yf does not represent a developmental toxicity or lethality risk. 
Response:  See sections V and VII.D.1 of the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and "Toxicity of HFO-1234yf."  
Comment:  One commenter stated in late comments that he identified several potential errors or irregularities in interpreting data in the memorandum, ``Risk Assessment: P070601 Reflecting Deliberations and Decisions from the 3/4/09 Dispo[sition] Meeting'' (docket number EPA - HQ - OAR - 2008 - 0664-0036/EPA-HQ-OPPT-2008-0918-0034). The commenter stated that they were unable to replicate EPA's output for passenger car exposure values and can charging technician exposure values.  The commenter also stated that EPA used different input parameters than were used in the Gradient Risk Assessment report (CRP, 2008) to estimate the air concentration in a car cabin after a leak and to characterize risk to vehicle repair workers and do-it-yourselfers (DIYers).  The commenter further stated that it was not clear what was the basis for EPA to use values which deviated from the Gradient Risk Assessment, nor was it clear from which industry study EPA's numbers were derived. 
Response:  Concerning exposure estimates for DIYers, the exposure values in the EPA risk assessment (EPA-HQ-OAR-2008-0664-0036) are bounding estimates of the maximum possible theoretical concentrations.  The EPA assessment used the industry-modeled DIY scenarios and assumptions in a 2008 report by Gradient Corporation for the SAE CRP (CRP, 2008) as a starting point for creating the bounding estimates.  To do so, EPA assumed that the entire leakage mass of each industry-modeled scenario was released to its corresponding volume with no air exchange.  Also see section VII.D.1 of the preamble, "Toxicity of HFO-1234yf."  
Comment:  One commenter stated that HFO-1234yf has a lower workplace exposure limit than HFC-134a because of links to developmental toxicity and lethality when inhaled, and thus, poses additional concerns to human health compared to HFC-134a.  
Response:  EPA's risk screen and risk assessment [EPA-HQ-OAR-2008-0664-0038 and -0036] both found that workplace exposures of HFO-1234yf were expected to be well below the workplace exposure limit of 250 ppm (or corresponding margin of exposure of 30) that EPA used in its analysis.  Thus, we expect workplace exposure from HFO-1234yf to result in no workplace risk from direct toxicity, as for HFC-134a.  Although the American Industrial Hygiene Association has assigned a lower workplace exposure environmental limit (WEEL) of 500 ppm for HFO-1234yf compared to a WEEL of 1000 ppm for HFC-134a, this does not mean that there is a greater risk of toxicity for workers using HFO-1234yf.  In either case, the exposure concentrations are expected to be significantly below the workplace exposure limit.  The derivation of the workplace exposure limit that EPA used in our risk screen, document EPA-HQ-OAR-2008-0064-0038, is discussed in section V of the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" under the heading, "Occupational risks."  Also see sections V and VII.D.1 of the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and "Toxicity of HFO-1234yf."
Comment:  One commenter commented that the risk of exposure is reduced if workers are certified. 
Response:  EPA expects that this is true, and that risks of worker exposure are reduced even more significantly through use of certified refrigerant handling equipment.  Also see sections VII.D.1 and VI.F of the preamble, "Toxicity of HFO-1234yf" and "Use by `do-it-yourselfers.'"
Flammability of HFO-1234yf
Comment:  One commenter stated that although HFO-1234yf is technically flammable, ISO and American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) have classified HFO-1234yf to be in a new category of extremely low flammability refrigerant. Another commenter stated that even if HFO-1234yf has to be classified as an A2 substance, it deviates substantially from other A2 substances. 
Response:  EPA recognizes that ASHRAE standard 34 and a corresponding ISO standard classify HFO-1234yf as an "A2L" refrigerant.  This is a new subclass of refrigerant with relatively low toxicity ("A"), and relatively low flammability ("2L"), signifying flammable refrigerants with an LFL > 0.1 kg/m[3] at 21 °C and 101 kPa, a heat of combustion < 19,000 kJ/kg, and a burning velocity less than or equal to 10 cm/s. This classification is not directly relevant to EPA's decision.
Comment:  Five commenters stated that HFO-1234yf has a low likelihood to ignite, especially under the conditions encountered in an automotive application. One commenter stated that the mere presence of high refrigerant concentrations does not contribute to a hazardous condition because an ignition source of sufficient energy must also be present.  Another commenter disagreed with EPA's view that a flammability risk exists. 
Other commenters stated that additional review of the available information regarding flammability of HFO-1234yf needs to be conducted.  Some commenters stated that EPA should consider restricting concentrations of HFO-1234yf to much lower concentrations than to the lower flammability limit (LFL) of 6.2%.  
Response:  See section VII.D.2 of the preamble, "Flammability," for our response to these comments.
Comment:  Three commenters stated that HFO-1234yf is flammable and that the proposed regulation does not offer any restrictions to protect those persons handling HFO-1234yf nor does it restrict the sale and use by the general public. 
Response:  See section VII.D.2 of the preamble, "Flammability," for our response to these comments.
Comment:  One commenter stated that compared with HFC-134a, the explosion probability of HFO-1234yf is much higher based on testing done at the Federal Institute for Materials Research and Testing (Bundesanstalt für Materialforschung und  -  prüfung, BAM). 
Other commenters disagreed with those flammability conclusions, finding the testing results to be expected but not representative of real-world use in MVAC.  These commenters stated that the flammability risks of HFO-1234yf were not significant and that the mixtures of HFO-1234yf and ethane used in the testing would not be seen in MVAC in actual operations.
Response:  See section VII.D.2 of the preamble, "Flammability," for our response to these comments.
Comment:  One commenter stated that the change in LFL by addition of another refrigerant is an expected result and known within industry, citing LeChatelier (1891) and Bodurtha (1980), and that when mixing more flammable HCs with less flammable refrigerants, the LFL of the mixture will be between those of two pure refrigerants. Another commenter stated that PAG lubricant would not be expected to transform into ethane at the levels used in the BAM report.  A third commenter stated that another commenter's interpretation of the BAM test report is misleading, and specifically noted that the following statement made by the commenter could lead uninformed readers to the incorrect conclusion that an ethane and HFO-1234yf mixture is more flammable than the individual components: "only 0.5 to 1.3% of ethane with low amounts [HFO-]1234yf are sufficient enough to form explosive mixtures in air." 
Response:  Overall, the available information shows that there are very low risks from the flammability of HFO-1234yf.  See sections V, VII.B and VII.D.2 of the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" "Use conditions," and "Flammability."
Comment:  Another commenter also commented that regarding flammability, European standards used in the BAM testing are much more conservative than U.S. standards, creating the widest potential flammability limits. 
Response:  From the commenter's discussion, it appears that the DIN 51649 standard used by BAM may result in a broader range of concentrations that would be flammable than indicated by testing according to ASTM E681, the standard required by ANSI/ASHRAE standard 34.  As discussed in sections VII.B and VII.D.2 of the preamble, "Use conditions," and "Flammability," the results from the BAM testing are not relevant to conditions expected in MVAC.
Comment:  In late comments, one commenter remarked on the tests carried out by BAM, which were submitted to EPA during the public comment period (see documents EPA-HQ-OAR-2008-0664-0053.1 and EPA-HQ-OAR-2008-0664-0053.2).
 * The commenter stated that it does not doubt the accuracy of the measured results but rather whether they are relevant to practical applications. 
 * The commenter stated that ethane concentrations used during the ignition tests are above 2.5 percent of the LFL of ethane, and if these concentrations were realistic, the engine compartment and passenger compartment, even if equipped with an HFC-134a or R-744 AC system, would have to be certified as hazardous areas. The commenter further stated that if the internal refrigerant circuit is excluded as a source of ethane or HC emissions, this would also apply to vehicles not equipped with an AC system. 
 * Regarding a situation where mixing gases results in the mixture igniting at a concentration below the lower flammability limit of one of the gases, the commenter stated that the likelihood of this type of situation occurring in a vehicle is no higher than the probabilities of the occurrence of relevant refrigerant concentrations investigated during the risk assessment. The commenter explained that this is primarily attributable to the fact that the processes involved are highly dynamic (high impulse of refrigerant during a leak, air movement in the engine compartment etc.) and therefore impede the formation of the necessary homogeneous mixture. 
 * The commenter also stated that at high thermal loads, the PAG oil in the refrigerant circuit may lead to traces of propene and isobutene, which are emitted along with the refrigerant in the event of leakage, but that these traces are within the ppb or low ppm range. 
Response:  As discussed in sections VII.B and VII.D.2 of the preamble, "Use conditions," and "Flammability," the results from the BAM testing are not relevant to conditions expected in MVACs.
Generation of Hydrogen Fluoride (HF) 
[Refer also to section 3.3.1 for additional discussion on mitigation strategies and the implications on risk.]
Comment:  Two commenters stated that there is low risk due to exposure to HF. One of these commenter stated that (1) for vehicles that do not discontinue the use of the blower after collision, the risk due to exposure to HF when using HFO-1234yf is approximately twice the risk of the current use of HFC-134a, and (2) for vehicles that discontinue the use of blower after collision, the risk due to exposure to HF from use of HFO-1234yf is approximately the same as that with the current use of HFC-134a (on order of 10[-12] occurrences per operating hour, or one in one trillion). The second commenter stated that there is no need for concentration limits to protect against exposure to HF because the risks from exposure to HF from HFO-1234yf are similar to what would be experienced with HFC-134a 
One commenter also stated that concentrations of HF as low as 0.3 ppm cause a sensation of irritation. The commenter stated that this characteristic would deter someone from remaining exposed to excessive concentrations from an open hood. 
Other commenters stated that there is a high probability of HF generation in cars from HFO-1234yf. One commenter stated that the flammability of HFO-1234yf makes the production of HF more likely and increases the risk of HF exposure to vehicle passengers, workers at chemical facilities, automotive manufacturing facilities, vehicle servicing facilities, and to the general public. Two commenters stated that various health and safety concerns related to HF generation and its toxicity are well studied and documented, and three commenters stated use of HFO-1234yf is unacceptable as there is increased potential for HF exposure and related casualties. 
Response:  See section VII.D.3 in the preamble, "Toxicity of Hydrogen Fluoride," for our response to these comments.
Comment:  One commenter stated that testing with HFOs commissioned by the environmental organization Greenpeace in 2001 hinted at a multitude of decomposition products with high reactivity.  The commenter stated that apparently, even lubricants (polyalkylene glycol -  PAG) break down to HF when in contact with HFO-1234yf in a MVAC system.  The commenter further expressed that BAM testing showed that burning HFO -1234yf resulted in concentrations of HF greater than 90 ppm in the engine compartment. The commenter concluded that the tests prove that in a standard system with standard charge (900 grams) and oil, the risk for humans would be incalculable.
Response:  See section VII.D.3 in the preamble, "Toxicity of Hydrogen Fluoride," for our response to these comments.
Comment:  A commenter provided results from a test by IBExU on the decomposition of HFO-1234yf under heat (EPA-HQ-OAR-2008-0664-0053.3).  This commenter strongly warned against a decision in favor of HFO-1234yf because it would form highly toxic HF when burning.  Three commenters disagreed that the results of the IBExU testing were relevant because test conditions did not represent realistic conditions.  One commenter said that the SAE risk assessment, which used actual vehicle test data for HF formation, found that actual HF formation rates are far below the levels [from the IBExU test results] cited by the first commenter, the Federal Environmental Agency (Umweltbundesamt -- UBA).
Response:  See section VII.D.3 in the preamble, "Toxicity of Hydrogen Fluoride," for our response to these comments.
Comment:  Another test from BAM reported by UBA examined HF formation from HFO-1234yf and from HFC-134a (EPA-HQ-OAR-2008-0664-0080.1).  Fifty grams of refrigerant was streamed through a hole of 2 mm diameter onto a hot metal surface.  The study found that pure HFO-1234yf exploded on the hot surface whereas pure HFC-134a did not.  The study also found that when HFO-1234yf was mixed with 3% oil, it exploded at 600 °C.  The commenter stated that handling of HFO-1234yf in the presence of hot metal surfaces results in HF formation in concentrations far above allowed workplace concentrations.
Response:  See section VII.D.3 in the preamble, "Toxicity of Hydrogen Fluoride," for our response to these comments.
Comment:  One commenter stated that handling of HFO-1234yf in the presence of hot metal surfaces results in HF formation in concentrations far above allowed workplace conditions. 
Response:  EPA assumes that by "allowed workplace conditions," the commenter means long-term workplace exposure limits for HF.  Most workplace exposure limits assume that an individual could be exposed to a chemical continually over the course of working for 8 hours a day for 5 days per week for up to 20 years.  We do not find this relevant to assessing the risks of exposure to HF from HFO-1234yf.  We expect that such exposure would occur in an emergency situation where there is a large leak, perhaps due to a collision, that results in either combustion of the refrigerant or release onto a hot surface.  Also see section V and VII.D3 in the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and "Toxicity of Hydrogen Fluoride."
Comment:  In late comments, one commenter stated that the results of the laboratory tests conducted by the BAM and IBExU do not show any unexpected results and are also consistent with and can be explained by the SAE CRP investigations. The commenter questioned the practical relevance of the BAM testing given unrealistic vehicle conditions. The commenter stated that CRP investigations have shown that the test results obtained under laboratory conditions can only be applied to the vehicle to a limited extent. 
 * The commenter pointed out that tests conducted as part of the SAE CRP at Hughes and Ineris investigated whether the "worst-case-scenario" could lead to safety relevant situations.  The commenter stated that Hughes laboratory results regarding hot components in the engine compartment, in the absence of ignition at temperatures up to 700°C, only showed HF concentrations in the low single-digit ppm range, although 120 ppm was measured in one case.  The commenter also stated that Ineris laboratory tests showed that the formation of HF on hot components is a function of time, refrigerant concentration, temperature and the size of the hot surface. The commenter further stated that in realistic vehicle conditions, the length of time that leaking refrigerant remains on a hot surface is too short to allow the refrigerant to reach the relevant temperature. 
Response:  See sections V and VII.D.3 in the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions?" and "Toxicity of Hydrogen Fluoride."
Comment:  A commenter recommended EPA adopt the Acute Exposure Guideline Limit-2 (AEGL-2) as the governing guideline for exposures to HF in passenger vehicles. The commenter also stated that the OSHA Permissible Exposure Limit is not an appropriate benchmark for short-term exposure because it is designed for chronic occupational exposure, not rare acute exposures such as might occur from the decomposition products of HFO-1234yf.  
Response:  EPA considered the SAE CRP's approach to evaluating health risks from HF as a decomposition or combustion product from HFO-1234yf.  We agree that the use of AEGLs is appropriate for considering risks to consumers from HF.  In particular, we agree that the AEGL-2 over 10 minutes is an appropriate guideline to evaluate consumer health risks resulting from an emergency such as a collision that results in release of most or all  the refrigerant from the MVAC system.  First, we agree that such exposure is short-term (acute) and not long-term or chronic, and thus, an Acute Exposure Guideline Limit is more appropriate than an occupational exposure limit that considers long-term exposure for 8 hours a day, 5 days a week, over years.  Second, we agree that it will be rare, and likely a once-in-a-lifetime event, that someone would be exposed to HF through decomposition or combustion of HFO-1234yf.  Thus, it is sufficient to use the AEGL-2, which protects against permanent injury, but does not protect against short-term irritation as would the AEGL-1.  EPA also believes that the more conservative AEGL-2 is more appropriately protective than the AEGL-3, which protects against life-threatening exposures but does not protect against irreversible health effects.  Finally, we agree that a 10 minute averaging period for HF exposure is more appropriate for a limit than a 30 minute averaging period in case of an emergency, because people will likely be trying to escape quickly from a hazardous situation.
Retrofits of MVAC Systems
Use of HFO-1234yf as a Retrofit
Comment:  Several commenters stated that HFO-1234yf should be allowed initially in new vehicles but should not be used to retrofit vehicles using HFC-134a, or at least not unless there are industry standards to guide such a process.  One commenter stated that they do not recommend the use of flammable refrigerants in systems that were not designed with flammable refrigerants in mind.  Other commenters stated that it is critical to allow a natural phase-out of the fleet of cars using HFC-134a as the refrigerant, rather than requiring retrofitting existing cars with HFO-1234yf.  A commenter expressed concern that retrofitting of HFC-134a MVAC systems with HFO-1234yf would result in cases of cross-contamination of refrigerant, while another commenter contested this statement and found it unsupported.  
Other commenters opposed obstacles that would prevent older MVACs from being retrofitted to the new refrigerant.  These commenters mentioned the potential for greenhouse gas benefits when retrofitting systems currently using HFC-134a with HFO-1234yf.  
Response:  See section VII.E of the preamble, "Retrofit Usage."  
Comment:  One commenter requested justification for not using HFO-1234yf as a retrofit in existing MVAC systems.  
Response:  See section VII.E of the preamble, "Retrofit Usage."  Industry standard-making organizations and the manufacturer's submission have addressed the risks that could be posed by HFO01234yf only for new vehicles.  EPA has not received a SNAP submission requesting evaluation for retrofitting vehicles and is not aware of any analyses that have been performed to evaluate the risk. Before EPA could begin a rulemaking process to determine whether to find HFO-1234yf acceptable for use as a retrofit, we would need sufficient analyses of the risks.  
Comment:  One commenter stated that most of the use conditions imposed by the proposed rule seem designed to prevent retrofits using HFO-1234yf.  
Response:  The proposed use conditions were intended to address risks from the use of HFO-1234yf in new vehicles and were not designed to prevent retrofits using HFO-1234yf.  The final listing applies specifically to use of HFO-1234yf for new equipment.  The final use conditions are consistent with industry standards, including SAE J1739 (2009), SAE J639 (2011), and SAE J2844 (2011).
Use of Other Alternative Refrigerants as Retrofits in HFO-1234yf MVAC Systems
Comment:  Three commenters stated that they do not support the use of other refrigerants in HFO-1234yf systems. Two commenters stated that the use of retrofit refrigerant in an HFO-1234yf system could lead to several problems, including system contamination and failures, material compatibility, and safety concerns associated with the use of hydrocarbons or HFC-152a in HFO-1234yf systems not intended for highly flammable liquids. One commenter further recommended that EPA change the current SNAP and Section 609 rules, which allow many listed refrigerants to be installed in new MVAC systems and retrofitted in any type of MVAC refrigerant system.  
Two commenters commented that other refrigerants will likely be used in HFO-1234yf systems unless, as one commenter noted, such use is ruled illegal.  Both commenters also stated that the high anticipated cost of HFO-1234yf will likely lead to system retrofits, which one commenter stated could reverse climate benefits, jeopardize safety, and contaminate refrigerant recycling infrastructure. 
Response:  First, we note that "topping off" a system containing one refrigerant with a different refrigerant is illegal under existing SNAP program regulations in appendix D to subpart G of 40 CFR part 82.  In order to retrofit a system, it is necessary to recover the existing refrigerant and to replace it using Section 609 certified refrigerant-recovery equipment.  Also see section VI.F of the preamble, "Use by `do-it-yourselfers.'"  We note that this rule does not address section 609 regulations nor does it revisit previous SNAP listings.
Comment:  A commenter stated that there should be specific justification for why other refrigerants should not be installed in HFO-1234yf systems.  
 Response:  We raised a number of potential issues with retrofitting HFO-1234yf MVAC systems to other alternative refrigerants in the proposed rule (64 FR 53451; October 19, 2009).  For example, there may be safety issues with trying to use a highly flammable hydrocarbon refrigerant in a system that is designed for the mildly flammable HFO-1234yf, and there may be system compatibility issues that result in greater refrigerant emissions if other refrigerants are more corrosive to seals, gaskets, and hoses than HFO-1234yf.  EPA has not received additional specific information in public comments that might allow us to address such issues.  
Comment:  A commenter questioned, regarding retrofits, whether HFO-1234yf will require new or specialized equipment to handle this refrigerant, as well as an environmentally protected storage area. 
Response:  It is not clear from the comment if the equipment that the commenter refers to is (1) equipment for performing a retrofit, (2) new or specialized MVAC equipment for use with HFO-1234yf, or (3) refrigerant-handling equipment for recovery and recycling of HFO-1234yf.  Under the first interpretation of the commenter's statement, we would want information on the type of equipment that would be used to perform retrofits and an analysis of risks related to retrofitted systems.  Under the second interpretation of the commenter's statement, we do not have sufficient information on retrofit of existing equipment but we do have information showing that new MVAC equipment is acceptable when using HFO-1234yf.  Under the third interpretation of the commenter's statement, the "equipment" is refrigerant-handling equipment such as that required currently for CFC-12 or HFC-134a for recovering and potentially reclaiming the refrigerant.  EPA will address the issue of whether new or specialized equipment will be required to handle HFO-1234yf under a future rulemaking under Section 609 of the Clean Air Act (CAA).  Industry standards to date do recommend new recovery equipment that is designed specifically for handling HFO-1234yf.  Employers of service technicians will need to meet OSHA requirements for handling of flammable materials.
Concerning the comment about whether HFO-1234yf will require an "environmentally-protected storage area," it is not clear what the commenter means by that term.  Storage would need to be consistent with OSHA and U.S. Department of Transportation (DOT) requirements, at a minimum.  Because HFO-1234yf is less stable in the presence of water than HFC-134a, it is appropriate to take step to prevent water entering storage containers.
Use by "do-it-yourselfers"
Comment:  Some commenters raised concerns about EPA's statements in the proposed rule about potential health effects that might occur without professional training and the use of CAA Section 609 certified equipment.  These commenters stated that the studies and testing in the docket support a finding that use of HFO-1234yf by non-professionals is safe and do not offer valid technical support for EPA's concerns.  
Response:  See section VII.F of the preamble, "Use by `do-it-yourselfers'" for our response to these comments.
Comment:  A commenter referenced the study done by Gradient (CRP, 2008), stated that there are errors in Gradient's assumptions, and concluded that the low flammability concentrations determined by Gradient  will be even lower in reality.  The commenter also stated the SNUR docket does not contain supportable facts for EPA's conclusion that DIYers servicing their vehicles with HFO-1234yf would be exposed to large quantities of that refrigerant or that small quantities of HFO-1234yf would create any danger to DIYers.  Another commenter further stated that it is concerned that SNAP and SNUR provisions will prevent DIYers from using refrigerant to recharge their own ACs, impacting low-income individuals. 
In response to another commenter's comments, one commenter clarified the assumptions made in the SAE Phase II risk assessment (CRP, 2008) and stated that the conservativeness of model assumptions should be considered when evaluating overall risk.  
Response:  See sections VII.D.1 and VII.F of the preamble, "Toxicity of HFO-1234yf" and "Use by `do-it-yourselfers'" for discussion of the Gradient report (CRP, 2008) and how EPA used those data in its risk assessment (EPA-HQ-OAR-2008-0664-0036).  Concerning the commenter's reference to a statement in the risk screen document (EPA-HQ-OAR-2008-0664-0038) that "because of the risks of exposure to large amounts of the substitute when it used in servicing activities by an untrained worker, it is recommended that the refrigerant be made available only to qualified personnel," we disagree with the commenter's statement that "'do-it-yourselfers' will not be exposed to large amounts of the substitute."  A car requires the same charge of refrigerant, no matter who services it.  Further, qualified personnel (i.e., Section 609 certified technicians) would use Section 609-certified equipment, which would result in much lower exposures than might occur when a do-it-yourselfer uses small can taps.  The issue is the amount of exposure, not the amount of refrigerant in its container. 
Concerning the statement that the "conservativeness of model assumptions should be considered when evaluating overall risk," in general, EPA agrees that this is a consideration.  However, it is also standard Agency practice to consider conservative assumptions in order to be protective.
Comment:  Some commenters supported prohibiting sale of HFO-1234yf in small containers.  Other commenters stated that only certified technicians should be allowed to purchase and use refrigerants, including HFC-134a and HFO-1234yf.  Other commenters found no data to support restrictions on the sale of HFO-1234yf to non-professionals.  
Response:  See section VII.F of the preamble, "Use by `do-it-yourselfers.'"
Comment:  One of the commenters supported limiting the sales of HFO-1234yf to HFC-134a-certified technicians, but only if EPA determines that HFO-1234yf poses unacceptable risks for DIYers. Another commenter supported prohibiting sale of HFC-134a and HFO-1234yf in small containers and also restricting sale of all types of additives that do not meet SAE standards.  
Response:  Under the Significant New Use Rule (40 CFR 721.10182), EPA ruled that a Significant New Use Notice  is required before HFO-1234yf may be distributed in commerce in products intended for use by a consumer for the purpose of servicing, maintenance, and disposal involving HFO-1234yf.  This is because of concerns about potential health risks to DIYers.  The final SNUR does not explicitly limit the sales of HFO-1234yf to HFC-134a technicians or prohibit the sale of small containers of HFO-1234yf, but the practical effect is similar.  
Concerning the prohibition on sale of HFC-134a or of HFO-1234yf for use in small containers, or restrictions on sale of additives that do not meet SAE standards, this is beyond the scope of this SNAP rule for HFO-1234yf.  This rule is for the review and listing of HFO-1234yf as an acceptable substitute, subject to use conditions, for use in MVAC systems.  Under the SNAP program, we regulate the use of a substitute, rather than the sale of a product.
See also section VII.F of the preamble, "Use by `do-it-yourselfers.'"
Comment:  A commenter stated that banning DIY use of HFO-1234yf will mean that car owners will be forced to have professionals perform service work on their AC systems at a significantly higher cost.  This commenter stated that millions of lower-income motorists may be forced to go without air conditioning each year or may seek out lower-cost alternatives such as propane or HFC-152a.
Response:  See section VII.F of the preamble, "Use by `do-it-yourselfers,'" for our response to these comments.
Comment:  A commenter stated that when using small cans, the majority of users (i.e., non-professionals and DIYers) would not have equipment for refrigerant recovery, resulting in venting to the atmosphere of an uncontrolled amount of refrigerant from every small can. Another, commenter stated that a lack of training or certification could lead to misuse of HFO-1234yf and added expenses, and asserted that this has been prevalent with the use of HFC-134a by DIYers.  The commenter further pointed out that DIYers often do not repair systems correctly and buy two to three times the amount of refrigerant HFC-134a that their vehicle holds when doing their own repairs.
In response to these comments, another commenter stated that these comments are not directed to the major issues addressed by the pending SNAP rule but instead are attempts to have all servicing of mobile air conditioning performed by MACS members
Response:  As an initial matter, we note that the action taken today applies only to use with large containers of HFO-1234yf, which typically will not be sold to DIYers.  Thus, these comments are not relevant for purposes of this final action.  As provided in more detail in sections V, VII.D.1, and VII.F of the preamble, before small cans may be sold and used, further action and review must occur under both the SNUR (75 FR 65987; October 27, 2010) and under the SNAP program.  EPA would require additional information on consumer risk and a set of unique fittings from the refrigerant manufacturer for use with small cans or containers of HFO-1234yf before we would be able to issue a revised rule that allows for consumer filling, servicing, or maintenance of MVAC systems with HFO-1234yf.  Finally, to the extent that the commenters have concerns about the venting and recovery of refrigerant, we note that Section 609 of the CAA regulates the servicing of MVACs but only where servicing is done for consideration.    
servicing issues 
Servicing Specifications
Comment:  A commenter representing automobile dealerships opposed mandatory requirements for recycling and containment of the refrigerant because of potential costs and minimal environmental benefits. 
Response:  See section VII.G of the preamble, "Servicing Issues" for our response to these comments.
Comment:  One commenter recommended only industry and SAE recognized refrigerants be available for use in MVAC systems, with additional requirements for proper service fittings and service equipment. The commenter also stated that cheaper SNAP-approved refrigerants will likely be used to service HFO-1234yf systems due to the higher cost of HFO-1234yf.  
Response:  Limiting the availability of refrigerants to only those recommended by industry and SAE goes beyond the scope of this rule.  This rule is for the review and listing of HFO-1234yf as an acceptable substitute, subject to use conditions, for use in MVAC systems.  Concerning the statement about cheaper SNAP-approved refrigerants, we note that under current EPA regulations in Appendix D to subpart G of 40 CFR part 82, it is not legal to top-off the refrigerant in an MVAC system with a different substitute refrigerant.  
Comment:  One commenter stated that EPA should examine whether cross-contamination and other inappropriate servicing of MVAC systems may be subject to Title II emissions tampering guidelines. 
Response:  The prohibition on tampering in Section 203 of the CAA refers to removing or rendering inoperative an emission control "installed on or in a motor vehicle...in compliance with regulations under this title [i.e. Title II]..."  This comment appears to apply to implementation of EPA's regulations under Title II, and it is beyond the scope of this rule under the SNAP program.  This rule is for the review and listing of HFO-1234yf as an acceptable substitute, subject to use conditions, for use in MVAC systems.  
Technician Certification Specification
Comment:  Several commenters stated that appropriate training and certification should be required to purchase HFO-1234yf for use in MVACs.  Four commenters also stated that the final regulation should include a provision requiring proof of certification in order to purchase HFO-1234yf, and recommended that current AC systems tests (i.e., for CAA Section 609 certification) be updated. 
Some commenters disagreed with EPA's statement that HFO-1234yf may cause serious health effects when used in servicing and maintaining MVACs without professional training. 
Another commenter stated that EPA is limiting productivity by only allowing dealerships to perform refrigerant maintenance, and that independent MVAC serviced shops should be allowed to be certified. The commenter also questioned who will monitor "certified" technicians employed by dealerships that may do work on the side. A commenter representing automobile dealerships specifically opposed mandatory requirements for certification of technicians because of potential costs and burden on small businesses.  
Response:  See section VII.G of the preamble, "Servicing Issues" for our response to these comments.
Comment:  Some commenters indicated that SAE International is developing standards for safety and servicing of alternative refrigerant HFO-1234yf MVAC systems.  Another commenter stated that there are appropriate mechanisms within the industry for training.  
One commenter representing automobile dealerships objected to mandatory Section 609 technician certification and training for use of HFO-1234yf, stating that because dealerships already train technicians on flammable substances in accordance with hazard communication standards of the Occupational Safety and Health Administration (OSHA), and since the risks associated with HFO-1234yf are similar to those that already exist in MVAC service facilities, mandatory training and proof of training is not necessary.  To enable training pursuant to the OSHA hazard communication standard, the commenter stated that MVAC system and refrigerant suppliers should provide dealerships with sufficient information on the hazards posed by HFO-1234yf. 
Response:  See section VII.G of the preamble, "Servicing Issues" for responses to these comments.

Required Servicing Equipment
Comment:  Six commenters supported requirements for approved refrigerant handling equipment, and four commenters further stated that proper equipment should be a prerequisite for the purchase of HFO-1234yf. According to one commenter, because HFO-1234yf is designed for professional use, allowing persons lacking the proper equipment to purchase HFO-1234yf is not in the best interest of the consumer. 
One commenter stated that manufacturers of refrigerant recovery equipment should be required to comply with SAE J2843 and J2851. The commenter also supported the appropriate application of SAE J2888, J2912, and J2913. 
One commenter expressed concern that potential costs of Section 609 requirements could fall disproportionately on small businesses, but that high HFO-1234yf prices could serve as an incentive for shops to purchase and use equipment designed to meet SAE J2843, SAE J2851, and SAE J2099. 
Response:  A separate rulemaking under CAA Section 609 will address practices required in the servicing of MVAC systems using HFO-1234yf, including recycling and recovery.  That would include consideration of SAE standards.  The commenters' suggestions go beyond the scope of this rule.  This rule is for the review and listing of HFO-1234yf as an acceptable substitute, subject to use conditions, for use in MVACs.
Comment:  One commenter recommended that EPA remove all current refrigerants from the listed replacements except HFC-134a since it has recovery/recycling equipment meeting CAA and SAE standards. 
Response:  We interpret this comment to mean that EPA should find unacceptable all refrigerants for MVAC that are currently listed as acceptable substitutes under SNAP, except for HFC-134a.  This comment goes beyond the scope of this rule.  This rule is for the review and listing of HFO-1234yf as an acceptable substitute, subject to use conditions, for use in MVACs.

TSCA Significant New Use Rule (SNUR)
Comment:  One commenter recommended that EPA regulate the use and servicing of HFO-1234yf for MVACs under Section 609 of the CAA rather than under TSCA.  The commenter stated that EPA's authority under Section 609 has not been found to be inadequate to address potential problems relating to serving MVACs using HFO-1234yf, and criteria for regulating HFO-1234yf under TSCA have not been met. 
Response:  EPA has authority to regulate use of HFO-1234yf in the servicing of motor vehicles under Section 609 of the CAA where the servicing is done  for consideration (i.e., receiving something of worth or value to perform service, whether in money, credit, goods, or services). As EPA notes in the preamble, we expect to take action under section 609 to address HFO-1234yf soon. However, another issue of concern involves servicing of MVACs for free (e.g., DIY servicing) and this issue has come up in the context of EPA's review of HFO-1234yf under TSCA.  EPA believes that the criteria for regulating HFO-1234yf under TSCA have been met, as discussed in the proposed and final SNUR (April 2, 2010, 75 FR 16706; October 27, 2010, 75 FR 65987).
Comment:  In late comments, one commenter stated that HFO-1234yf (1-Propene, 2,3,3,3-tetrafluoro- CAS No. 754 - 12 - 1) should not be subject to a significant new use rule (SNUR) under Section 5(a)(2) of the Toxic Substances Control Act (TSCA) and recommended that EPA remove the SNUR and associated reporting/documentation requirements. This recommendation is based on concerns raised by the commenter in their submitted comments, which include the following: 
 * The commenter does not agree that that HFO-1234yf potential release levels may cause health or environmental concerns in applications not covered by the HFO-1234yf PMN; 
 * Based on test data on HFO-1234yf, the commenter does not agree with EPA's finding that identified health concerns for developmental toxicity and lethality to workers and consumers if they were exposed to a significant amount of HFO-1234yf substance via inhalation; and 
 * In response to the SNUR rule under docket ID EPA-HQ-OPPT-2008-0918, the commenter does not agree that serious health effects may be caused by HFO-1234yf in the following uses: (1) use of HFO-1234yf other than as an MVAC refrigerant in new passenger cars and vehicles as defined in 40 CFR 82.32 (c) and (d), (2) initial charging of MVAC units with HFO-1234yf by any person other than CAA Section 609 certified technicians not using CAA Section 609 certified refrigerant handling equipment, (3) servicing, maintenance, and disposal involving HFO-1234yf by persons other than CAA Section 609 certified technicians not using CAA Section 609 certified refrigerant handling equipment, or (4) sale or distribution of HFO-1234yf in containers smaller than 20 - pounds (net weight).
Response:  These comments address EPA's authority for a separate rulemaking action that was issued by EPA on October 27, 2010 (65 FR 65987) and thus are beyond the scope of this rulemaking action.  This rule is for the review and listing of HFO-1234yf as an acceptable substitute, subject to use conditions, for use in MVACs.
End of Life Vehicle Recycling Concerns
Regulatory Impacts on End-of-Life Vehicle (ELV) Recyclers
Comment:  Two commenters stated that EPA needed to perform further analysis on the potential small business impacts and costs of EPA's regulations and the introduction of HFO-1234yf.  A commenter representing recyclers of automobiles and scrap metal expressed concern about the regulatory burden and costs that automotive recyclers are likely to incur if they must manage flammable refrigerants that are regulated as hazardous waste under EPA's regulations implementing the Resource Conservation and Recovery Act (RCRA).  The same commenter also suggests that the RCRA subtitle C regulations would need to be changed to alleviate the hazardous-waste management requirements for handling HFO-1234yf.  The other commenter mentioned the costs to service and repair shops, end-of-life vehicle (ELV) recyclers, and automobile dealerships, and stated that EPA needed to analyze costs to these small businesses under the Regulatory Flexibility Act.  This latter commenter stated that EPA should determine if a significant change in price and supply expectations would affect the way that these businesses handle and deal with automobile repairs and recycling. 
Response:  See section VII.H of the preamble, "Cost, Availability, and Small Business Impacts," for our response to these comments.
Comment: A commenter stated that docket reports #0005 and #0008 did not recognize the important differences between regulation of vehicle repair and servicing facilities and regulation of ELV recycling facilities under the CAA and RCRA. Additionally, the commenter stated that approval of HFO-1234yf as proposed, because of its flammability, would likely impose a new technician-certification requirement and additional cost burdens upon ELV recyclers, while no such additional costs would be imposed on vehicle repair and servicing facilities. 
The same commenter expressed concern that the Proposed Rule would allow automotive manufacturers to make unreviewable decisions to use HFO-1234yf in new MVAC systems in passenger cars and trucks, and that such unilateral decisions could impose regulatory burdens and costs on ELV recyclers and negatively affect ELV recycling. 
Response:  Docket reports EPA-HQ-OAR-2008-0664-0005 and -0008 did not focus on issues of ELV recyclers; however, EPA did consider the impact at vehicle end of life in the SNAP risk screen for HFO-1234yf, in the docket at EPA-HQ-OAR-2008-0664-0038.  EPA's Office of Air and Radiation has shared the commenters' concerns with EPA's Office of Solid Waste and Emergency Response for consideration.  Concerning the possible requirement for a new technician-certification requirement for ELV-recyclers, EPA could address any need for such requirements through regulations under section 608 of the Clean Air Act at 40 CFR part 82 subpart F.  It is not clear at this time if such a requirement is needed.  We also note that there is nothing in existing regulatory requirements at 40 CFR part 82 subpart F or in this SNAP rule that would impose a requirement for technician certification for ELV recyclers.  We also note that although there may be additional requirements and associated costs for recycling of vehicles containing HFO-1234yf, it is possible that recyclers will be able to pass on that additional cost to parties that provide them with a hazardous waste.
Section 612 and this rulemaking do not mandate the use of any particular substitute.  Automotive manufacturers may make decisions for use of their automotive refrigerant giving primary consideration to their own costs rather than to those of automobile recyclers.  We expect that manufacturers, when choosing which substitute to use, will likely consider the cost implications of that choice, including the ultimate cost of disposal, to the extent that those costs apply to automobile manufacturers and to their dealerships.
We believe the potential burden of complying with RCRA regulations placed on those recycling or recovering a substitute is generally not pertinent to a decision of whether HFO-1234yf should be found acceptable under SNAP.  This is because we see no reason why the costs of disposal or recycling at end-of-life would affect the environmental or human health risks of using HFO-1234yf in MVAC or the risks of disposal or recycling at vehicle end-of-life.  The commenter has provided no reason to believe that the burden of complying with RCRA regulations would affect these risks. However, we evaluated the potential risks to human health from disposal or recycling of vehicles at their end-of-life as part of our review, as discussed in section V of the preamble, "Why is EPA finding HFO-1234yf acceptable subject to use conditions." We concluded that disposal or recycling of HFO-1234yf is not expected to present a toxicity risk to workers.  From the standpoint of overall environmental and human health impacts, we find HFO-1234yf to be acceptable, subject to the use conditions specified in the final rule.  Also see section VII.H of the preamble, "Cost, Availability, and Small Business Impacts."                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
Comment:  One commenter expressed concern for the process of recycling HFO-1234yf at vehicle end of life, and specifically expressed concern for disposal specifications in the follow-on rulemaking and their costs to recyclers.  The commenter also submitted questions regarding whether or not HFO-1234yf can be recycled and the best practices for processing end of life vehicles containing HFO-1234yf. The commenter was also concerned about storing HFO-1234yf in containment bottles, and how long it can be stored before disposal. 
Response:  These are issues that EPA will consider in the context of a future rulemaking on servicing and reclamation of automotive refrigerant under Section 609 of the CAA and possibly a rulemaking on proper disposal of refrigerant under Section 608 of the CAA.  In this and other SNAP rulemakings, EPA considers the potential health and environmental impacts of servicing and disposal, but does not consider specific details covered under the Section 608 and 609 regulations, such as certification procedures for technicians and for refrigerant handling equipment.
Occupational Risks at End-of-Life Vehicle Recycling
Comment:  Three commenters expressed concerns related to occupational risks of HFO-1234yf exposure at end-of-life recycling. Two of the commenters further urged EPA to conduct additional research on HFO-1234yf and related occupational risks to ELV recyclers before acting on the Proposed Rule. 
One commenter stated that is appears as if EPA did not consider ELV recycling based on docket reports #0005 and #0008. The commenter further stated that it disagreed with assumptions in these reports as the reports did not consider how shredder facilities and automotive-dismantling facilities might be different than vehicle repair and servicing facilities with regard to occupational risks. 
Response:  EPA considered occupational risks to workers during ELV recycling in developing our proposal, as part of the discussion of "disposal" of the MVAC system and of refrigerant.  EPA evaluated the occupational risks at end-of-life in the risk screen for HFO-1234yf (EPA-HQ-OAR-2008-0664-0038), separately from docket items -0005 and -0008 cited by one commenter.  EPA's risk screen found that, considering trained individuals in both equipment manufacturing and end-of-life, the maximum short-term exposure would be less than 28 ppm and the maximum 8-hour time-weighted exposure would be less than 9 ppm.  Both values are considerably less than either the occupational exposure guideline EPA used (250 ppm, 8-hour average) or the lower flammability limit of HFO-1234yf (6.2% concentration by volume; i.e., 62,000 ppm), indicating there should not be significant occupational concerns with using this substance at end-of-life of a vehicle.  
We also note that the flammability risks of HFO-1234yf are considerably less than those of gasoline, motor oil, or a number of other flammable substances that may already be present in vehicles to be recycled.  The flammability risk is lower because HFO-1234yf has much higher minimum ignition energy and a lower burning velocity than that of gasoline or other flammable substances in vehicles (EPA-HQ-OAR-2008-0664-0007).  For example, the burning velocity of HFO-1234yf is 1.5 cm/s.  This is more than an order of magnitude less than the burning velocity of gasoline, which is approximately 42 cm/s (Ceviz and Yuksel, 2005).  The minimum ignition energy is greater than 5000 mJ for HFO-1234yf and is between 0.1 and 0.3 mJ for most combustible fuels, four orders of magnitude difference (Sect. 4.5 of Gas Explosion Handbook, undated). 
Cost of HFO-1234yF 
Comment:  Three commenters stated that the cost of HFO-1234yf will be higher than HFC-134a. One commenter specified that HFO-1234yf will cost approximately ten times more than HFC-134a, making HFO-1234yf a cost prohibitive option. Another commenter stated that the cost of HFO-1234yf will likely be more than HFC-134a because the HFO-1234yf manufacturing process requires more energy and more steps than HFC-134a. Two commenters further stated that a black market for HFCs or HFOs could be created due to higher costs of HFOs. These commenters also expressed concern that lower cost alternatives to HFO-1234yf will be used, reversing climate benefits and posing greater safety and environmental concerns. 
Response:  EPA's understanding as well is that HFO-1234yf would cost approximately ten times the current cost of HFC-134a per pound of refrigerant.  However, other industry estimates find that it would be less expensive to build new cars using HFO-1234yf than using CO2, another alternative refrigerant with low GWP under consideration by the automotive industry ($75/vehicle vs. $500/vehicle; MACS 2010).  Using HFO-1234yf may be a cost-effective means for automobile manufacturers to comply with EPA's greenhouse gas emission standards for light-duty vehicles (75 FR 25324; May 7, 2010), as well as compliance with European Union requirements limiting  new vehicles to using MVAC refrigerants with a GWP less than 150.  We also note that other costs of repairing an MVAC system besides the refrigerant are on the order of hundreds of dollars, such as labor costs or replacement of the condenser, compressor, or evaporator; thus, it is not clear if a change in cost for the consumer of approximately $200 as part of a one-time repair will lead to widespread switching to other refrigerants.  In addition existing EPA regulations prohibit topping off an MVAC system with other refrigerants other than the one that is currently installed (Appendix D to Subpart G of 40 CFR Part 82).  
Comment:  A commenter stated that banning DIY use of HFO-1234yf will mean that car owners will be forced to have professionals perform the service work on their MVAC system, resulting in significantly higher out-of-pocket expenses.  This commenter stated that millions of lower-income motorists may be forced to go without air conditioning each year or may seek out lower-cost alternatives such as propane or HFC-152a.  
Response:  See section VII.F of the preamble, "Use by `do-it-yourselfers,'" for our response to these comments.
Comment:  In late comments, a commenter stated that since they do not currently have any information regarding the cost of HFO-1234yf, it is difficult to anticipate how much more vehicle service will cost consumers should they be forced to go to a vehicle service facility. However, based on discussions with suppliers, the commenter anticipates the cost of HFO-1234yf to be significantly higher than HFC-134a. As the cost of HFO-1234yf is anticipated to be higher than HFC-134a, the commenter stated that it is likely that the impact on low-income Americans will be significantly more severe than a retail sales ban on HFC-134a had such a ban been put in place for HFC-134a.  
Response:  The final rule addresses service fittings on automobiles and on large containers of refrigerant, the latter of which is unlikely to be used by DIYers.  Until the refrigerant manufacturer provides EPA with fittings for small cans and EPA publishes those fitting dimensions, DIYers are effectively limited in their ability to use HFO-1234yf.  We require further information before we can conclude that DIYers may safely use HFO-1234yf, as well as requiring an appropriate fitting from the refrigerant manufacturer for small can taps for servicing that would be used by DIYers (as required by existing regulations at appendix D to subpart G of 40 CFR part 82). 
EPA believes that there is not yet sufficient information to compare how much it will cost for a consumer to pay a professional technician to repair and recharge his or her MVAC system with HFO-1234yf, versus attempting this himself or herself.  However, the relative cost is irrelevant to EPA's decision as to whether DIYers should be allowed to use HFO-1234yf; we base this decision on health impacts.  
EPA also finds unclear the commenter's statement that the "impact on low-income Americans will be significantly more severe than a retail sales ban on HFC-134a..."  One interpretation of this is that the commenter is concerned that the higher cost of HFO-1234yf relative to HFC-134a will exacerbate the difference between charges for a car owner to repair his or her own car's MVAC system and charges for repair by a vehicle service facility.  A higher differential could exist if vehicle service facilities charged more for the same amount of refrigerant compared to a small container used by a consumer and if DIYers also used a comparable or lesser amount of refrigerant in servicing.  It is not clear that service facilities would charge more for the same amount of refrigerant, since facilities likely would be purchasing a larger container of 20 lbs or larger with a lower price per ounce than the price for a small container of 12 oz or less.  Further, based on available information, a DIYer leaks more refrigerant in the process of servicing than professional personnel (CRP, 2008).  Therefore, it is possible that a car owner may pay more for refrigerant when repairing his or her own car, because of leaks and inefficient use of refrigerant during servicing, than when allowing a professional technician at a service facility to service the car's MVAC system.
Also see section VII.F of the preamble, "Use by `do-it-yourselfers.'"
Comment:  One late commenter stated that there was insufficient information in the record on the cost, terms of availability and anticipated market share of HFO-1234yf for EPA to make the required statutory findings that HFO-1234yf "reduces the overall risk to human health and the environment" by comparison to other alternatives that are already available.  The commenter stated that this information is necessary in order for EPA to assess anticipated environmental effects adequately.  The same commenter stated that EPA's environmental analysis is based on price assumptions that were not disclosed and are no longer valid, and thus, EPA should subpoena the information from the manufacturer and reopen the public comment period. Additionally, the commenter stated that it, and other interested parties, have not had the opportunity to submit analysis and comments to EPA on anticipated environmental effects of approving HFO-1234yf under a situation in which the producer may charge as yet undisclosed monopoly prices. 
Response:  See section VII.H of the preamble, "Cost, availability, and small business impacts," for our response to these comments.  
Comment:  A late commenter stated that the information in the record is insufficient for EPA to make a statutory finding that HFO-1234yf is "currently or potentially available."  The commenter stated that a previous decision by the DC Circuit Court (Honeywell International, Inc. V. EPA, 374 F.3d 1363 (D.C. Cir. 2004)) implied that an interpretation of the term "available" in CAA section 612(c)(2) could consider economic factors if EPA adopted such an approach as a reasonable interpretation of the statutory language.  The commenter states that EPA should obtain information as to the anticipated cost of HFO-1234yf if the manufacturer does not grant licenses to produce. 
Response:  See section VII.H of the preamble, "Cost, availability, and small business impacts," for our response to these comments  
Comment:  In late comments, a commenter stated that to comply with requirements of the Unfunded Mandates Reform Act (UMRA), EPA needed to perform further analysis on the potential costs of EPA's SNAP regulations for HFO-1234yf to determine if the rule would result in the expenditure of $100 million or more per year by the private sector.  In particular, the commenter stated that EPA must obtain more information on pricing and the effect of the manufacturer's patent to determine whether the rule will exceed the $100 million threshold. 
Response:  See section VII.H of the preamble, "Cost, availability, and small business impacts," for our response to these comments.  
Comment:  In late comments, a commenter requests EPA to keep the comment period open until at least 30 days after EPA determines, and notifies the public, that it believes that it has obtained and made available in the docket "sufficient information" as directed by Congress to adequately assess the probable effects of approving HFO-1234yf as a substitute. 
Response:  EPA believes that there was already sufficient information in the public docket at the time of proposal to assess the health and environmental effects of finding HFO-1234yf acceptable as a substitute.  Further, we reopened the public comment period twice to allow the public to comment on additional information and on the interaction between the SNAP rule and the SNUR.  Therefore, we find no need to open the public comment period for a fourth time.  Also see response letter dated November 22, 2010 from Gina McCarthy, Assistant Administrator for Air and Radiation to Donald Elliot, Attorney for Arkema, Willkie Farr & Gallagher LLP in Docket EPA-HQ-OAR-2008-0664.
Timely Completion of the Rule
Comment:  Four commenters urged EPA to approve the use of HFO-1234yf in a timely manner. One commenter urged EPA to do everything possible to move the approval of HFO-1234yf in new vehicles forward. Three commenters urged EPA to approve the use of HFO-1234yf in a timely manner so that manufacturers in the European and American markets have a clear understanding of both EU and U.S. requirements impacting vehicle design for use of HFO-1234yf, and have sufficient time to design and produce vehicles complying with such requirements. One commenter also emphasized that EPA needs to remove any obstacles to commercially available alternative refrigerants for the 2012 model year as 2012 models are typically introduced early in the 2011 calendar year.  
Response:  EPA has prepared this final rule as expeditiously as possible.  It is complete prior to the introduction of the 2012 model year and prior to completion of the world's first plant dedicated to producing HFO-1234yf. 
Comment:  Some commenters stated that further research on TFA is necessary.  Two commenters stated that approval of HFO-1234yf should not be delayed due to concerns regarding atmospheric and ecological impacts and concerns raised by other commenters. One commenter further stated that sufficient information is currently available on the atmospheric and ecological impacts of HFO-1234yf, and EPA should not delay SNAP approval of HFO-1234yf to collect additional data on these issues. 
Response:  EPA has considered additional studies submitted during the public comment period (Luecken et al., 2009; Kajihara et al., 2010) and has performed further research on this issue.  We do not find that it is necessary to delay this rulemaking further in order to perform further research.  Also see section VII.C.5 of the preamble, "Formation of Trifluoroacetic Acid and Ecosystem Impacts."
Comment:  One commenter stated that issues raised by ARPI and AAIA  (regarding the conservative nature of the SAE CRP risk assessment for HFO-1234yf (CRP, 2008)) and EPA's use of that information for risk assessment) can be adequately addressed through the separate SNUR and Section 609 rulemakings.  This commenter stated EPA should not delay the SNAP approval that is urgently needed by automobile manufacturers. A different commenter stated that additional research and review of the available information regarding toxicity of HFO-1234yf needs to be conducted. 
Response:  As provided previously, we believe our toxicity assessments to date are sufficient to support this action.  See section VII.D.1 of the preamble, "Toxicity of HFO-1234yf."  
Other
Comment:  One commenter requested EPA to include the following requirement in the regulation: "HFO-1234yf or any SNAP listed refrigerant shall not be used as a delivery agent, or propellant, to introduce any chemical substance into mobile air conditioning systems."  
In response to that comment, another commenter stated in late comments that they find it advantageous to allow the use of HFO-1234yf as a transfer agent to introduce certain chemicals into HFO-1234yf MVAC systems. The commenter stated that certain non-refrigerant chemicals such as UV dyes, flush products, and other additives such as lubricants have no known health effects.  Furthermore, the commenter stated that vehicle manufacturers validate the material compatibility of these fluids for use in their MVAC systems and that SAE International has established standards for the stability and compatibility of dyes, flush materials, and additives (i.e., J2297 and J2670).  
Response:  EPA has not received sufficient information to support adding such a statement as a use condition in the final rule.  However, if a company wanted to introduce HFO-1234yf or any other listed refrigerant as a delivery agent or propellant, it would first be necessary to submit a SNAP application to EPA for an aerosol propellant. It would be necessary to provide EPA with further information at least 90 days before trying to sell HFO-1234yf as a propellant. There may also be obligations under other statutes, such as TSCA.
Comment:  One commenter urged better communication among OAR, ORCR, OPPT, and other EPA offices on regulations affecting multiple offices to ensure regulations encompass a wider array of environmental considerations. 
Response:  EPA's Offices of Air and Radiation and Pollution Prevention and Toxics have worked together extensively on issues of risk assessment for HFO-1234yf.  OAR's risk assessment considered the issues concerning risk at vehicle end of life (called "disposal" in EPA's risk screen, EPA-HQ-OAR-2008-0664-0038).  OAR also used the risk assessment from the Office of Pollution Prevention and Toxics in developing this rule (EPA-HQ-OAR-2008-0664-0036).  OAR has also consulted with the Office of Resource Conservation and Recovery concerning the issues raised by commenters about end-of-life recycling of vehicles.
Comment:  One commenter expressed concern that approval of HFO-1234yf as proposed is already a foregone conclusion, and requested clarification of EPA's intent and whether it will seriously consider comments submitted.  
Response:  EPA has taken seriously all comments submitted and, in fact, has made several changes to the rule in response to public comments.  
Comment:  In late comments, a commenter stated that its company is ready to work with EPA to develop an alternative program that will help improve customer education on the proper use of HFO-1234yf that could further minimize any adverse health or environmental impacts. The commenter also pledged to work with its suppliers to implement any can improvements that could further reduce refrigerant venting during charging. 
Response:  A program for customer education and for can improvements to reduce refrigerant emissions during charging would be welcome.  These would be appropriate for inclusion in a supplemental submission to SNAP and in a SNUN for the use of HFO-1234yf in consumer products for servicing, maintenance, or disposal of HFO-1234yf. 
Comment: In late comments, a commenter stated that Honeywell did not disclose to the Society of Automotive Engineers (SAE) its patents covering HFO-1234yf until April 9, 2010, and has now made clear that it does not consider itself as having any obligation to license its patents on fair, reasonable and non-discriminatory (FRAND) terms, and has refused to issue a license to the commenter on FRAND terms. The commenter further commented that the SAE Motor Vehicle Committee is currently delaying indefinitely the approval of HFO-1234yf standards, upon which the proposal heavily relies.  The commenter suggests that EPA should therefore re-open the record. 
Response:  One of the two SAE standards for HFO-1234yf cited in the proposal, SAE J1739, was already final at the time of proposal.  The second standard, SAE J639, was drafted at the time of proposal and was finalized in February, 2011.  However, the essential provisions of the revised SAE J639 standard were discussed in the preamble to the proposed rule and in documents in the public docket at the time of proposal (e.g., EPA-HQ-OAR-2008-0664-0012).  Those essential provisions were not changed in the 2011 final SAE J639 standard, which we reference in the use conditions.  Thus, we do not find it necessary to re-open the record.
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