Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for CFC-12 in Motor Vehicle Air Conditioning.

Substitute: HFO-1234yf

This risk screen does not contain Clean Air Act (CAA) Confidential
Business Information (CBI) and, therefore, may be disclosed to the
public.

INTRODUCTION

Ozone-depleting substances (ODS) are being phased out of production in
response to a series of diplomatic and legislative efforts that have
taken place over the past decade, including the Montreal Protocol and
the Clean Air Act Amendments of 1990 (CAAA).  The U.S. Environmental
Protection Agency (EPA), as authorized by Section 612 of the CAAA, is
developing a program to evaluate the human health and environmental
risks posed by alternatives to ODS.  The main purpose of EPA's program,
called the Significant New Alternatives Policy (SNAP) Program, is to
identify acceptable and unacceptable substitutes for ODS in specific end
uses.  

EPA’s decision on the acceptability of a substitute is based largely
on the findings of a screening assessment of potential human health and
environmental risks posed by the substitute in specific applications. 
EPA has already screened a large number of substitutes in many end uses
within all of the major ODS-using sectors, including refrigeration and
air conditioning, solvent cleaning, foam blowing, aerosols, fire
suppression, adhesives, coatings and inks, and sterilization. The
results of these risk screens are presented in a series of Background
Documents that are available in EPA's docket.

The purpose of this report is to supplement EPA’s Background Document
on the refrigeration and air conditioning sector (U.S. EPA 1994)
(hereinafter referred to as the Background Document) by adding to the
list of potential substitutes for CFC-12 as a motor vehicle air
conditioning (MVAC) refrigerant.  The specific proposed CFC-12
substitute examined in this report is 2,3,3,3-Tetrafluoropropene, or
“HFO-1234yf.” 

The potential risks associated with use of substitutes as MVAC
refrigerants have been examined at length in the Background Document. 
The reader is referred to this reference for a detailed discussion of
the methodologies used to conduct this risk screen.  In this risk
screen, reasonable worst-case occupational and consumer exposure
analyses were performed to ensure that use of HFO-1234yf as an MVAC
refrigerant will not pose unacceptable risks to workers or consumers. 
General population analyses were not conducted as chronic exposures are
not expected for the general public.

Section 2 of this report summarizes the results of the risk screen for
the proposed substitute.  The remainder of the report is organized into
the following sections:

Section 3: Atmospheric Assessment

Section 4: Flammability Assessment

Section 5: Asphyxiation Assessment

Section 6: Toxicity Assessment

Section 7: Volatile Organic Compound Assessment 

Section 8: Additional Environmental Impacts Analysis

Section 9: References

SUMMARY OF RESULTS						

HFO-1234yf is recommended for SNAP approval as an MVAC refrigerant so
long as all HFO-1234yf MVAC systems are designed to avoid occupant
exposure to concentrations of HFO-1234yf above 6.5% in the passenger
compartment for more than 15 seconds, even if in the event of the leak.

EPA's risk screen indicates that the use of the proposed substitute will
be less harmful to the atmosphere than the continued use of CFC-12.   No
significant toxicity risks to workers or vehicle passengers are expected
according to occupational and consumer modeling.  However, because of
the risk of exposure to large quantities of the substitute when it is
used in servicing activities by an untrained worker, it is recommended
that the refrigerant only be made available to qualified personnel. 
HFO-1234yf should not be made available for “do-it-yourself”
workers. Flammability models indicate that risks of fire or explosion in
the passenger compartment of a vehicle may be small for average sized
cars, but could be more significant for cars with a high ratio of
refrigerant charge to passenger compartment volume.  To protect against
the risk of fire or explosion, systems using HFO-1234yf should be
designed so that passenger exposures will not exceed the lower
flammability limit of the refrigerant (6.5% by volume in air) for more
than 15 seconds, even if a leak occurs.  Additionally, to protect
against flammability risks during servicing, systems should also be
designed to prevent refrigerant leaks into the engine compartment and
vehicle electric power source storage areas.  Appropriate design
features might include using a secondary refrigerant containment shell
around the refrigerant circuit, for example.  Further, systems should
also be engineered so that potential ignition sources are isolated from
the refrigerant circuit and any areas into which the refrigerant might
leak (should a leak occur).  Caution must be used in manufacturing
facilities and by refrigeration technicians to minimize fire and
explosion risk while in the presence of large quantities of the
substitute.  This includes installation of proper safety equipment
during manufacturing, transportation, and storage and providing proper
training and certification to technicians.  EPA recommends that American
Society of Heating, Refrigerating and Air-Conditioning Engineers
(ASHRAE) Standard 34 be followed.  

ATMOSPHERIC MODELING

This section presents an assessment of the potential risks to
atmospheric integrity posed by the use of HFO-1234yf as an MVAC
refrigerant.  The ODP, GWP, and atmospheric lifetime (ALT) of the
proposed substitute are presented in   REF _Ref175036149 \h  \*
MERGEFORMAT  Table 1 .	

The environmental impacts resulting from use of HFO-1234yf are generally
in the range of those predicted for other substitutes examined in the
Background Document.  The substitute is substantially less harmful to
the ozone layer, has less climate impact, and a shorter atmospheric
lifetime compared to CFC-12.

Table   SEQ Table \* ARABIC  1 .  Atmospheric Impacts of HFO-1234yf
Compared to CFC-12.

Refrigerant	Ozone Depleting Potential (ODP)	Global Warming Potential
(GWP)	Atmospheric Lifetime years (ALT)

HFO-1234yf	0 a	4a	<1b

CFC-12	1c	8,100d	100c

a HFO-1234yf SNAP Submission (Honeywell 2007).

b Atmospheric lifetime (ALT) is 11 days (Honeywell 2007).

c Available at: http://www.epa.gov/ozone/ods.html.

d IPCC, Second Assessment Report (1996).

FLAMMABILITY ANALYSIS

HFO-1234yf is flammable when its concentration in air is in the range of
6.5%-12.3% by volume (this is equal to 65,000 ppm to 123,000 ppm).  In
the presence of an ignition source (e.g., static electricity, a spark,
or a cigarette), an explosion or a fire could occur when the
concentration of HFO-1234yf is within these flammability limits.  The
remainder of this section addresses the potential for flammability risks
at the end-use, and during manufacture and servicing and provides a
discussion of measures to be taken to ensure safe use. 

Flammability Risks at the End-Use

To determine whether flammability would be a concern for vehicle
passengers, a reasonable worst-case scenario analysis was performed to
model catastrophic release of the refrigerant into a vehicle.  Two key
inputs to the model were passenger compartment volume (i.e., the space
into which the refrigerant would leak) and the refrigerant charge size. 
Because passenger compartment volumes and refrigerant charge sizes can
vary widely from model to model, the vehicle in each vehicle class with
the highest ratio of charge size to compartment volume was identified
(ICF 2008) and used in the model.    REF _Ref225232240 \h  \*
MERGEFORMAT  Table 2  presents the compartment volume and charge size of
the vehicles used in this analysis.

Table   SEQ Table \* ARABIC  2 .  Vehicles with the Highest Ratio of
Refrigerant Charge to Passenger Compartment Volume in each Vehicle Class

Class	Passenger Compartment Size (m3) a	MVAC Charge Size (g) HFC-134a b
Ratio of HFC-134a Charge to Compartment Volume (g/m3)	Manufacturer	Model
c



TWO SEATERS	1.42	907.2	640.75	MERCEDES-BENZ	SL65 AMG (MY 2007)

SMALL PICKUP TRUCKS	1.48	940	633.27	FORD	RANGER

S.U.V.	3.01	1250	414.96	MERCURY	MOUNTAINEER (w/ Aux Heat)

STANDARD PICKUP TRUCKS	1.59	632	397.84	TOYOTA	TOYOTA TACOMA PRERUNNER
REG CAB

COMPACT CARS	2.63	935.55	355.25	MERCEDES-BENZ	CLS Class (MY 2007)

SUBCOMPACT CARS	2.29	793.8	346.08	BMW	650i and M6 (MY 2007)

MINICOMPACT CARS	2.10	725	345.99	JAGUAR	JAGUAR XKR

MIDSIZE CARS	2.72	935.55	343.44	MERCEDES-BENZ	E Class (MY 2007)

LARGE CARS	2.94	793.8	269.55	BMW	750i (MY 2007)

SMALL STATION WAGONS	2.66	670	251.71	PONTIAC	VIBE

MINIVAN	4.42	1100	248.85	DODGE	GRAND CARAVAN SXT WAGON

VANS	8.20	1600	195.08	CHEVROLET	EXPRESS VAN (Passenger/Cargo)

MIDSIZE STATION WAGONS d	3.06	475	155.32	KIA	RONDO

a Source: FuelEconomy.gov, and if not available there, BlackBookUSA.com.
2008 New Car Cost Guide.  When volume unavailable, value was estimated
using BlackBook data and methods at 40 CFR 600, Subpart D.

b Source: Motor Information Systems database.

c Model Year (MY) 2008, unless otherwise indicated.

d Data were available for only 1 vehicle in this class.  By default it
has the ‘highest’ ratio.

In the analysis, the full charge of the MVAC unit is assumed to be
emitted within 140 seconds (Blackwell et al. 2006) and the vehicles are
assumed to have an air flow rate of 0.3 air exchanges per hour
(Blackwell et al. 2006).  Horizontal stratification is also assumed
since HFO-1234yf is denser than air and will settle in higher
concentrations closer to the bottom of the passenger compartment.  These
assumptions are reasonable, but very conservative; therefore the assumed
worst-case scenario has a low probability of occurring. 

In addition to this worst-case scenario analysis, which employed a
simple box-model, modeling was also conducted by an industry consortium
(Gradient 2008).  The consortium’s model used computational fluid
dynamics (CFD) to more realistically represent the behavior of the
leaked refrigerant in a vehicle (specifically, a Crown Victoria).  As
reported in the industry consortium’s report, Honeywell also conducted
CFD modeling; however Honeywell examined releases into a smaller vehicle
(i.e., a vehicle with a smaller passenger compartment volume). Finally,
the consortium also conducted field tests in which HFO-1234yf was
released into an actual vehicle.    REF _Ref225232686 \h  \* MERGEFORMAT
 Table 3  presents the results of all four analyses.  

Table   SEQ Table \* ARABIC  3 .  Results of Flammability Modeling

Flammability Model	Maximum Instantaneous Concentration of HFO-1234yf
(ppm)	Situation under which Maximum Concentration was Measured	Minimum
Instantaneous Concentration of HFO-1234yf (ppm)	Situation under which
Minimum Concentration was Measured

Worst-Case Scenario Box-model	291,193	Passenger compartment volume 1.42
m3 

Catastrophic release of total charge; all windows and doors closed;
stationary vehicle.	70,752	Passenger compartment volume 3.06 m3

Catastrophic release of total charge; all windows and doors closed;
stationary vehicle.

Industry Consortium CFD Model

(Gradient 2008)	65,000 a	Passenger compartment volume 3.1 m3 

Vehicle idling, low fan, large leak (0.5 mm orifice), recirculation
mode.	34,000a	Passenger compartment volume 3.1 m3 

Vehicle idling, low fan, large leak (0.5 mm orifice), outside air mode.

Honeywell

CFD Model	53,000	Passenger compartment volume 2.5 m3 

Large leak (0.5 mm orifice).	Not available.	Not available.

Industry Consortium Field Test	29,774	Passenger compartment volume 3.1
m3 

Vehicle shielded from wind; six mannequins placed in car to simulate
vehicle occupants; large leak (0.5 mm orifice); full charge released;
low fan.	Not available.	Not available.

a Only concentrations for the ‘worst-case scenarios’ (i.e., the
large leaks occurring under the conditions noted in the table) were
provided by Gradient (2008).  Concentrations resulting from smaller
leaks occurring under the conditions noted in the table are expected to
be less than the concentrations reported in the table.

The worst-case scenario box-model produced concentrations above the LFL
(65,000 ppm) in the passenger compartment for all vehicles; however CFD
modeling conducted by the industry consortium and the submitter produced
concentrations at or below the LFL.  Actual field testing of an
HFO-1234yf release found concentrations equal to about 46% of the LFL in
the passenger compartment.

 

To prevent against the risk of fire or explosion, especially in cars
which currently have high refrigerant charge to compartment volume
ratios, it is recommended that all HFO-1234yf systems be designed to
avoid occupant exposure to concentrations of HFO-1234yf above 6.5% in
the passenger compartment for more than 15 seconds, even if in the event
of the leak. 

Flammability Risks During Manufacture and Servicing

Catastrophic releases of large quantities of refrigerant during
manufacturing and servicing, especially in areas where large amounts of
refrigerant are stored, could cause an explosion.  For this reason, it
is important that only properly trained and certified refrigerant
technicians handle HFO-1234yf; the refrigerant should not be made
available to unqualified personnel or “do-it-yourself” users.  Also,
to protect against the risk of fire during servicing, HFO-1234yf MVAC
systems should be designed to prevent refrigerant leaks into the engine
compartment and vehicle electric power source storage areas. 
Appropriate design features might include using a secondary refrigerant
containment shell around the refrigerant circuit, for example.  Systems
should also be engineered so that potential ignition sources are
isolated from the refrigerant circuit and any areas into which the
refrigerant might leak (should a leak occur).  As a further precaution,
HFO-1234yf storage and transport equipment should be installed with
safety devices that minimize the likelihood of catastrophic releases. 
For example, NFPA 58 Liquefied Petroleum Gas Code (NFPA 2008) requires
the use of overfill protection devices (OPD) on cylinders to minimize
the likelihood of leaks.  The NPFA 58 Code also contains storage and
transportation requirements/guidelines.  Similar equipment safety and
procedural requirements should be implemented for this substitute.  

It is important that the strictest standards be followed during
manufacturing.  It is recommended that refrigerants be properly stored
and caution used within manufacturing facilities to minimize explosion
risk and that workers adhere to the requirements set by OSHA under 29
CFR 1910.  OSHA requirements include proper ventilation and storage
practices within manufacturing facilities to prevent fire and explosion.
 Proper ventilation should be maintained at all times during the
manufacture of equipment containing HFO-1234yf through adherence to good
manufacturing practices. If refrigerant levels in the air surrounding
the equipment rise above one-fourth of the lower flammability limit, the
space should be evacuated and re-entry should only occur after the space
has been properly ventilated.  Ventilation is also of the utmost
importance to mitigate the risk of fire or explosion when servicing
vehicles using HFO-1234yf. 

ASPHYXIATION ANALYSIS

The risk of asphyxiation in a vehicle following release of HFO-1234yf
for a reasonable worst-case scenario was investigated.  This analysis
does not consider conditions that are likely to occur that would reduce
the levels to which individuals would be exposed, such as open doors or
windows, fans operating, or conditioned airflow (either heated or
cooled). 

To determine if release of HFO-1234yf would present a risk of
asphyxiation, the charge of HFO-1234yf required to reduce oxygen levels
to the No Observed Adverse Effect Level (NOAEL) for hypoxia in each of
the cars presented in   REF _Ref225232240 \h  \* MERGEFORMAT  Table 2 
was calculated.  These charge sizes were then compared to the actual
charge size for each car.  If the actual charge for a car exceeded the
charge required to reduce oxygen levels to the NOAEL, there could be
risk of asphyxiation in the car under a worst-case refrigerant release
scenario.    REF _Ref175044517 \h  \* MERGEFORMAT  Table 4  presents the
results of the asphyxiation analysis.

Table   SEQ Table \* ARABIC  4 .  Reasonable Worst-Case Asphyxiation
Assessmenta

Car Class	Charge Required to Cause Impairment (g) b	Charge Size (g)b	May
Charge Cause Impairment?

TWO SEATERS	6,584	907	No

SMALL PICKUP TRUCKS	6,862	940	No

S.U.V.	13,956	1,250	No

STANDARD PICKUP TRUCKS	7,372	632	No

COMPACT CARS	12,194	936	No

SUBCOMPACT CARS	10,618	794	No

MINICOMPACT CARS	9,737	725	No

MIDSIZE CARS	12,612	936	No

LARGE CARS	13,632	794	No

SMALL STATION WAGONS	12,334	670	No

MINIVAN	20,494	1,100	No

VANS	38,021	1,600	No

MIDSIZE STATION WAGONS	14,188	475	No

a This analysis only includes those vehicles identified as having the
highest “refrigerant charge to compartment volume ratio” in each
vehicle class.

b Values provided in these columns refer to the charge required to cause
impairment based on concentrations of the substitute in the occupants’
breathing area (i.e., the ‘upper stratum’ of the car).  These data
assume 5% of the refrigerant is in the upper stratum.  Concentrations in
the lower stratum of the car are not considered in this analysis as
vehicle occupants are not expected to be in the foot well of the car.  

Based on the results of the worst-case scenario analysis, use of
HFO-1234yf in this end-use should not pose a significant risk of
asphyxiation or impaired coordination to vehicle occupants.  Further, as
the NOAEL for hypoxia (120,000 ppm) is greater than HFO-1234yf’s lower
flammability limit (65,000 ppm), the recommendation at the end of
Section   REF _Ref225244124 \r \h  \* MERGEFORMAT  4.1  (which ensures
concentrations of refrigerant will not exceed the LFL in the passenger
compartment) will further protect against the limited risk of
asphyxiation.

TOXICITY ANALYSIS

To assess potential health risks from exposure to this substitute when
used as an MVAC refrigerant, EPA identified the relevant toxicity
threshold values for comparison to modeled exposure concentrations for
different scenarios.  For the occupational exposure analysis, potential
risks from chronic and acute worker exposure were evaluated by comparing
exposure concentrations to available occupational exposure limits. 
Occupational exposure limits are typically established for either an
eight-hour or ten-hour time period for long-term exposure or for a 10 to
30-minute period for short-term exposure, as shown in   REF
_Ref225245311 \h  \* MERGEFORMAT  Table 5 .  To assess short-term
consumer (i.e., vehicle passenger) exposures, ICF conducted an analysis
based on modeling of stratified exposure concentrations within the
compartment of several different vehicles (ICF’s analysis is included
as Appendix A).  Chronic general public exposures are not expected, so a
reference concentration (RfC) was not determined.  A list of the
relevant toxicity limits is shown in   REF _Ref225245311 \h  \*
MERGEFORMAT  Table 5 .    REF _Ref225245434 \h  \* MERGEFORMAT  Table 6 
provides definitions of the acronyms used in   REF _Ref225245311 \h  \*
MERGEFORMAT  Table 5 .  EPA’s approach for identifying or developing
these values is discussed in Chapter 3 of the Background Document. 

Table   SEQ Table \* ARABIC  5 .  Toxicity Levels of HFO-1234yf

	Occupational

Long-term Exposure

ppm	Occupational

Short-term Exposure

ppm	Consumer 

Short-term Exposure

ppm

HFO-1234yf	250a	NA	See Appendix A

NA  = Not Available

a US EPA (2009).

Table   SEQ Table \* ARABIC  6 .  Explanation of Toxicity-Related
Acronyms

Exposure Limit	Definition	Explanation

LC50	Lethal Concentration	“The concentration of the chemical in air
that kills 50% of the test animals in a given time” a 

NOAEL	No Observed Adverse Effect Limit	“The highest exposure level at
which there are no biologically significant increases in the frequency
or severity of adverse effect between the exposed population and its
appropriate control; some effects may be produced at this level, but
they are not considered adverse or precursors of adverse effects.”b

RfC	Reference Concentration	A concentration “designed to protect the
general population against adverse systemic (i.e., noncancer)
effects.” c

a From http://www.ccohs.ca/oshanswers/chemicals/ld50.html

b From   HYPERLINK "http://www.epa.gov/riskassessment/glossary.htm#n" 
http://www.epa.gov/riskassessment/glossary.htm#n 

c U.S. EPA (1994)

Occupational Exposure 

Occupational exposure modeling was performed for the proposed substitute
to ensure that use of the substitute does not pose an unacceptable risk
to workers.  The methodology used for this screening assessment is based
on the one used in the occupational exposure and hazard analysis
described in Chapter 5 of the Background Document. A box-model approach
was used to evaluate potential worker exposure to alternative
refrigerants.   This approach has been widely used for many years to
estimate probable worker exposures to hazardous airborne materials and
has been described in detail by the National Institute for Occupational
Safety and Health (NIOSH).  This model takes into consideration the
duration and magnitude of the resulting exposure which is influenced by
1) duration and intensity of the release, 2) rate at which contaminated
air is diluted with uncontaminated air, 3) proximity of the worker to
the source of the release, and 4) the length of time the worker remains
in the affected space.  

Estimates of refrigerant release per event for various release scenarios
and data on number of events were obtained from the Vintaging Model.  
The release per event was conservatively assumed to be 5 percent of the
equipment charge during manufacturing and 3 percent of the equipment
charge during disposal.  The release rate per event was multiplied by
the number of events estimated to occur over a workday.  For equipment
manufacturing, the number of events per workday was assumed to equal the
number of units containing the substitute produced per plant per year
divided by 365 workdays per year.  For the purposes of this model, it is
assumed that HFO-1234yf will have a market penetration rate of 0.2% and
that one production facility will be in operation.  These assumptions
result in approximately 9 events/manufacturing facility/day.  For
disposal, it was conservatively assumed that 100 units are disposed
during an 8-hour work day.  

The maximum time weighted average (TWA) exposure was estimated for each
exposure scenario and these values were compared to the occupational
long-term exposure limit for HFO-1234yf.  The results are presented in  
REF _Ref175122161 \h  \* MERGEFORMAT  Table 7 .  

Table   SEQ Table \* ARABIC  7 .  Occupational Risk Assessment

	Maximum 15-minute TWA Exposure Levels 

Box-Model

(ppm)	Maximum 8-hr TWA Exposure Levels 

Box-Model

(ppm)	Occupational Long-Term Exposure Limit 

(ppm)	Workplace Guidance Levels Time Period

HFO-1234yf	27.76	8.5	250	8-hr TWA



The modeling results indicate that both the short-term (15-minute) and
long-term (8-hour) worker exposure concentrations at no point exceed 12
percent of the occupational long-term exposure limit.  Even the maximum
estimated short-term occupational level (i.e., maximum 15-minute TWA
exposure) is significantly lower than the 8-hour long-term exposure
limit and therefore occupational exposure to HFO-1234yf is not
considered a toxicity threat for trained professionals.

Gradient (2008) found that those consumers undertaking
“do-it-yourself” car repair could be exposed to concentrations of
HFO-1234yf ranging from 32,800 ppm (30-minute TWA) to 38,900 ppm
(maximum instantaneous concentrations).  These concentrations are
significantly higher than the occupational exposure limit; therefore it
is recommended that HFO-1234yf not be made available to untrained
workers, including for “do-it-yourself” car repair.

Consumer Exposure	

This section presents estimates of potential consumer exposures to
HFO-1234yf in motor vehicles.  A consumer exposure analysis was
performed to examine potential catastrophic release of the substitute
under a reasonable worst-case scenario.  The analysis was undertaken to
determine the 15- and 30-minute TWA for the substitute, which were then
compared to the short-term consumer toxicity limit presented in   REF
_Ref225245311 \h  \* MERGEFORMAT  Table 5  to assess the risk to
consumers.  However, the TWA values are fairly conservative as the
analysis does not consider opened windows, conditioned airflow (either
heated or cooled) and other variables that would reduce the levels to
which individuals would be exposed.

The model involves a refrigerant leak from an MVAC into an enclosed
vehicle.  The same set of vehicles used in the flammability and
asphyxiation analyses (i.e., those vehicles identified by ICF (2008) as
having the highest refrigerant charge to compartment volume ratios in
each vehicle class) are used in this model. The model assumes that the
individual is present at the start of the leak and the individual
remains in the car while the refrigerant is released. It is also assumed
that horizontal stratification causes most of the refrigerant to settle
in higher concentrations closer to the bottom of the passenger
compartment.  The full charge of the MVAC unit is assumed to be emitted
within 140 seconds (Blackwell et al. 2006) and the vehicles are assumed
to have an air flow rate of 0.3 air exchanges per hour (Blackwell et al.
2006).  Exposure concentrations were calculated using the box-model
described in the Background Document, which was adapted to estimate
concentrations on a minute-by-minute basis.  Concentrations in the
occupants’ breathing area (i.e., the upper stratum of the car) were
used for comparison to the toxicity limit.  Vehicle occupants are not
expected to be in the foot well (i.e., the lower stratum) of the car. 

The calculated levels of consumer exposure for the “worst-case”
vehicle in each vehicle class are presented in   REF _Ref225312255 \h 
\* MERGEFORMAT  Table 8  below.

Table   SEQ Table \* ARABIC  8 .  Reasonable Worst-Case Consumer
Exposure Assessment

Car Type	15-minute TWA Consumer Exposure (ppm)	30-minute TWA Consumer
Exposure (ppm)

TWO SEATERS	                      11,664 	                      11,282 

SMALL PICKUP TRUCKS	                      11,595 	                     
11,216 

S.U.V.	                        7,582 	                        7,334 

STANDARD PICKUP TRUCKS	                        7,257 	                  
     7,020 

COMPACT CARS	                        6,494 	                       
6,282 

SUBCOMPACT CARS	                        6,328 	                       
6,122 

MINICOMPACT CARS	                        6,303 	                       
6,097 

MIDSIZE CARS	                        6,279 	                       
6,074 

LARGE CARS	                        4,929 	                        4,768 

SMALL STATION WAGONS	                        4,598 	                    
   4,448 

MINIVAN	                        4,543 	                        4,395 

VANS	                        3,562 	                        3,446 

MIDSIZE STATION WAGONS	                        2,834 	                  
     2,741 



ICF analysed the maximum concentration in   REF _Ref175045524 \h  \*
MERGEFORMAT  Table 8  to determine if consumer exposures to HFO-1234yf
under a reasonable worst-case scenario may pose a toxicity threat.  ICF
concluded that human exposure to HFO-1234yf following the accidental
release of an MVAC refrigerant charge should not pose a toxicological
concern (see Appendix A for the full analysis).

General Population Exposure

Chronic exposures to the substitute are not expected for the general
population.

VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS

To determine if emissions of HFO-1234yf may adversely affect local air
quality by increasing levels of ground-level ozone, ICF (2009) modeled
potential emissions of HFO-1234yf and examined the affects of these
potential emissions on air quality in two regions where high levels of
ground-level ozone are a chronic problem. ICF (2009) concluded that
while there is a level of uncertainty surrounding the impacts of
HFO-1234yf emissions on air quality, “non-attainment resulting from
HFO-1234yf emissions is not likely to be a major concern for local air
quality in most locations.”

ADDITIONAL ENVIRONMENTAL IMPACTS ANALYSIS

The production of trifluoroacetic acid (TFA) occurs during the
atmospheric breakdown of many fluorocarbons, including HFO-1234yf.  TFA
can be wet- or dry-deposited to the earth’s surface and is highly
soluble and very persistent in aquatic environments (ICF 2009).  As TFA
is also mildly phytotoxic, ICF completed an analysis to determine if
emissions of HFO-1234yf could pose a significant risk of ecotoxicity. 
ICF (2009) concluded that “TFA production resulting from HFO-1234yf
emissions is not expected to pose significant harm to aquatic
communities.” 

REFERENCES

Blackwell, N., L. Bendixen and E. Birgfeld. 2006. Risk Analysis for
Alternative Refrigerant in Motor Vehicle Air Conditioning. September.

Honeywell.  2007. Significant New Alternatives Policy Program Submission
to the United States Environmental Protection Agency for HFO-1234yf.
October. 

Gradient.  2008.  Risk Assessment for Alternative Refrigerant
HFO-1234yf.  Confidential report prepared for SAE International
Cooperative Research Program 1234.  February.

ICF.  2008. Air Conditioning Refrigerant Charge Size to Passenger
Compartment Volume Ratio Analysis.  Confidential Memorandum prepared for
the U.S. Environmental Protection Agency.  August.

ICF.  2009.  Revised Final Draft Assessment of the Potential Impacts of
HFO-1234yf and the Associated Production of TFA on Aquatic Communities
and Local Air Quality.  Prepared for the U.S. Environmental Protection
Agency.  August.

ICF. 1997. Physiological Effects of Alternative Fire Protection Agents -
Hypoxic Atmospheres Conference. Stephanie Skaggs prepared the
proceedings of the conference held May 22, 1997 in New London, CT.

Kataoka.  1999.  “Allowable Charge Limit of Flammable Refrigerants and
Ventilation Requirements.”  Draft Proposal.  O. Kataoka/Daikin/Japan.
June.

NFPA.  2008.  NFPA 58: Liquefied Petroleum Gas Code.  National Fire
Protection Agency.

U.S. Department of Energy (DOE) and U.S. Environmental Protection Agency
(EPA). 2009.  FuelEconomy.gov Frequently Asked Questions.  Available
online at: <http://fueleconomy.gov/feg/info.shtml#sizeclasses>.

U.S. Department of Transportation (DOT).  2007.  Bureau of
Transportation Statistics Special Report: Trends in Personal Income and
Passenger Vehicle Miles.  October 2007.  Available online at: <
http://www.bts.gov/publications/bts_special_report/2007_10_03/>.

U.S. EPA. 1994.  Significant New Alternatives Policy Technical
Background Document:  Risk Screen on the Use of Substitutes for Class I
Ozone-depleting Substances: Refrigeration and Air Conditioning. 
Stratospheric Protection Division.  March.

U.S. EPA.  2008.  Guidance on Retrofitting to HFC-134a.  R-134a
Refrigerant – How Much to Charge into the System.  Last updated
December 17, 2008.  Available online at:
<http://www.epa.gov/ozone/title6/609/technicians/retrguid.html#134a>.

U.S. EPA.  2009.  “Risk Assessment: PMN 07-0601.  Reflecting
Deliberations And Decisions From the 03/04/09 RAD [Risk Assessment
Division] Disposition Meeting



Appendix A

Evaluation of accidental refrigerant release of HFO-1234yf in a motor
vehicle

Background

ICF evaluated the accidental release of a refrigerant charge of
HFO-1234yf into the passenger compartment of a motor vehicle.  The
evaluation included modeling of stratified exposure concentrations
within the compartment of several different vehicles. It is important to
note that exposure to the whole refrigerant charge would result from a
catastrophic event in the automobile (such as a car accident).  In this
event, exposure to car refrigerant is unlikely to be the primary risk to
the car’s driver or passengers.

We have not analyzed other scenarios in detail in the risk screen for
HFO-1234yf.  This is because as shown in the analysis below, there is no
risk to human health from accidental release of an entire refrigerant
charge resulting from a car crash. Exposures to consumers undertaking
“do-it-yourself” car repair will be prevented (as HFO-1234yf is not
to be made available to them), so other scenarios were not considered.
This analysis focuses on a worst case scenario.

Refrigerant Release Scenarios and Resulting Concentrations  

Based on the modeling, the most conservative scenario involves a small
Mercedes sedan with a high charge size to compartment volume ratio
(640.75 g/m3).  The highest concentration of HFO-1234yf was estimated in
the area of the floorboards at 282,000 ppm.  At the breathing zone,
however, the estimated concentration is approximately 11,700 ppm (Table
1).  

Table   SEQ Table \* ARABIC  1 : Worst-case scenario and resulting
concentrations

Car type	Passenger Compartment Size (m3)a	MAC Charge Size (grams)
HFC-134ab,c	Ratio of  HFC-134a Charge to Compartment Volume (g/m3)
Maximum 15-Minute TWA Exposure (ppm)	Manufacturer

Model





Lower compartment	Upper compartment

	TWO SEATERS	1.42	907.2	640.75	282,205	11,664	MERCEDES-BENZ

SL65 AMG (MY 2007)

aSource: FuelEconomy.gov, and if not available there, BlackBookUSA.com.
2008 New Car Cost Guide.  When volume was unavailable, the value was
estimated using BlackBook data and methods at 40 CFR 600, Subpart D.

bSource: Motor Information Systems database.

cAssuming a one-to-one replacement ratio for HFO-1234yf substituting for
HFC-134a.

Toxicity Evaluation for Reasonable Worst Case Scenario

This study considers the 11,700 ppm concentration for the purposes of
toxicity evaluation.  An accidental release of car refrigerant due to a
car crash is a very low probability event involving acute exposure only.
 Most toxicity studies involve exposures lasting several hours per day
for several days (e.g., 6 hours/day, 5 days/week for 3 months for
sub-chronic studies).  Acute toxicity studies are the most appropriate
for comparison to modeled human exposure under these conditions.  The
acute (4-hour) Lowest Observed Adverse Effect Level (LOAEL) value for
single inhalation exposure to HFO-1234yf in rats is 201,600 ppm.  

When the worst-case breathing zone exposure concentration following a
catastrophic release of HFO-1234yf (11,700 ppm) is compared to the acute
LOAEL value for the compound in rats (201,600 ppm), it is apparent that
even the worst case exposure concentration is more than one order of
magnitude lower (about 17 times lower).  This indicates that acute
toxicity is not a risk in this low-probability event.

Conclusion

ICF believes that the most appropriate toxicity study to use as a
comparison for acute exposures in humans is the 4-hour acute inhalation
study in rats, which had a LOAEL of 201,600 ppm.  The most conservative
modeled breathing-zone exposure concentration resulting from an
accidental complete discharge of the car’s refrigerant is 11,700 ppm,
much lower than the top exposure concentration to which rats were
exposed for 4 hours. Therefore, acute exposure to elevated
concentrations of HFO-1234yf is not expected to be a toxicological
concern in humans who are exposed following a worst-case, accidental
release of a car refrigerant charge.

 Vehicle classes used are those defined by the U.S. DOE and EPA at the
Fuel Economy.gov website (U.S. DOE and EPA 2009).

 All analyses conducted in this risk screen assume a 1:1 HFC-134a to
HFO-1234yf replacement ratio.  The HFO-1234yf submission (Honeywell
2007) indicates the refrigerant would replace CFC-12 at a rate of
approximately 87% and HFC-134a replaces CFC-12 at a rate of 80-90% (U.S.
EPA 2008).  As HFC-134a and HFO-1234yf have similar CFC-12 replacement
ratios, it was assumed that HFO-1234yf would replace HFC-134a at a 1:1
rate.  

 In order to simulate the horizontal concentration gradient that will
occur because of the weight differential between the refrigerant and
air, it is assumed that 95 percent of the leaked refrigerant mixes
evenly into the bottom 0.4 meter of the car, and the rest of the
refrigerant mixes evenly in the remaining volume (Kataoka 1999).

 The Crown Victoria was used by the industry consortium as it was the
vehicle used in the risk assessment of HFC-152a and CO2 (Blackwell et
al. 2006) as well as in another SAE Cooperative Research Program
Analysis.   The Crown Victoria was chosen by Blackwell et al. (2006) as
it represented a “possible worst-case scenario.”

 OSHA regulation 29 CFR 1910.110 considers ventilation adequate “when
the concentration of the gas in a gas-air mixture does not exceed 25
percent of the lower flammable limit.”

 Twelve percent oxygen in air (i.e., 120,000 ppm) is the NOAEL for
hypoxia (ICF 1997).

 ICF International maintains the Vintaging Model for EPA in order to
simulate the aggregate impacts of the ODS phaseout on the use and
emissions of various fluorocarbons and their substitutes over a period
of several years across more than 40 different applications.  The model
tracks the use and emissions of various compounds for the annual
vintages of new equipment that enter service in each end-use.  The
vintage of each type of equipment determines such factors as leak rate,
charge size, number of units in operation, and the initial ODS substance
that the equipment contained.    

 During disposal it is assumed that only 90 percent of the refrigerant
charge remains in the unit. 

 Acute exposure due to a catastrophic leak was selected as the
‘worst-case scenario,’ rather than chronic exposure to a long, slow
leak because chronic exposures are not expected for vehicle passengers. 
In the chronic exposure toxicity study conducted for this substitute,
rabbits were exposed to HFO-1234yf for 6 hours a day, for 28 gestation
days.  These sorts of exposures are not expected for vehicle occupants
as the average trip length in the U.S. is 10 miles (U.S. DOT 2007).

 In order to simulate the horizontal concentration gradient that will
occur because of the weight differential between the refrigerant and
air, it is assumed that 95 percent of the leaked refrigerant mixes
evenly into the bottom 0.4 meter of the car, and the rest of the
refrigerant mixes evenly in the remaining volume (Kataoka 1999).  

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Evaluation of accidental refrigerant release of HFO-1234yf in a motor
vehicle

Non-CBI Version 

September 28, 2009

Page   PAGE  2 

