HFO - 1234yf Non - CBI Risk Screen Page 1 October 13, 2009 

## 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 Busine ss Information (CBI) and, therefore, may be disclosed to the public. 

### 1. 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 subs titute 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 maj or 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 D ocuments 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 substitute s 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 occup ational 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 : ReferencesHFO - 1234yf Non - CBI Risk Screen Page 2 October 13, 2009 

### 2. SUMMARY OF RESULTS HFO - 1234 yf 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 u se of CFC - 12. No signi ficant toxicity risks to workers or vehicle passengers are expected according to occupational and consumer mod eling. H owever, b ecause 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 ma de 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 mo re than 15 seconds, even if a leak occurs. Additionally, to protect against flammability risks during servicing, s ystems should also be designed to prevent refrigerant leaks into the engine compartment and vehicle elec tric power source storage areas . Appropriate design features might include using a secondary refrigerant containment shell around the refrigerant circuit , for example . Further , s ystems 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 use d in manufacturing facilities and by refrigeration technic ians to minimize fire and explosion risk while in the presence of large quantities of the substitute. Thi s 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 Engine ers (ASHRAE) Standard 34 be followed. 

### 3. 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 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 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 4 a <1 b CFC - 12 1 c 8,100 d 100 c a HFO - 1234 yf SNAP Submission ( Honeywell 200 7 ) . 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). 

### 4. FLAMMABILITY ANALYSIS HFO - 1234 yf 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, aHFO - 1234yf Non - CBI Risk Screen Page 3 October 13, 2009 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.



### 4.1. Flammability Risks at the End - Use To determine whether flammability would be a concern for vehicle passengers , a reasonable worst - case scenario analys i s 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. Becau se passenger compartment volumes and refrigerant charge sizes can vary widely from model to model, the vehicle in each vehicle class 1 with the highest ratio of charge size to compartment volume was identifi ed (ICF 2008) and used in the model. Table 2 presents the compartment volume and charge size of the vehicles used in this analysis . 2 Table 2 . Vehicles with the Highest Ratio of Refrigerant Charge to Passenger Compartment Volume in each Ve hicle Class C lass Passenger Compartment Size (m 3 ) a M V

AC Charge Size (g) HFC 134a b Ratio of HFC 134a Charge to Compartment Volume (g/m 3 ) Manufacturer Model c

TWO SEATERS 1.42 907.2 640.75 MERCEDES - BENZ SL65 AMG (MY 2007) SMALL PICKUP TRUCKS 1.48 940 63 3.27 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 4.4 2 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. 1 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). 2 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.HFO - 1234yf Non - CBI Risk Screen Page 4 October 13, 2009 c Model Year (MY) 2008, unless otherwise indicated. d Data were available for only 1 vehicle in this cl ass. 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 (Blackwel l 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. 3 These assumptions are reasonable, but very conservative ; the refore the assumed worst - case scenario has a low probability of occurring . In addition to this worst - case scenario analysis , which employed a simple box - mo del, modeling was also conducted by an industry consortium ( Gradient 2008 ) . The consortium’s model used co mputational fluid dynamics (CFD) to more realistically represent the behavior of the leaked refrigerant in a vehicle (specifically, a Crown Victoria4 ) . As reported in the industry consortium’s report, Honeywell also conducted CFD modeling; however Honeywe ll 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. Table 3 presents the results of all four analyses. 

### Table 3 . Results of Flammability Modeling Flammability Model Maximum

Instantaneous Concentration of HFO - 1234yf (ppm) Situation under which

Maximum Concentration was Measured Mi nimum Instantaneous Concentration of HFO - 1234yf (ppm) Situation under which

Minimum Concentration was Measured Worst - Case Scenario Boxmodel 291,193 Passenger compartment volume 1.42 m 3 Catastrophic release of total charge; all windows and doors closed; stationary vehicle. 70,752 Passenger compartment volume 3.06 m 3 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 m 3 Vehicle idl ing, low fan, large leak (0.5 mm orifice ) , recirculation mode . 34,000 a Passenger compartment volume 3.1 m 3 Vehicle idling, low fan, large leak (0.5 mm orifice), outside air mode . Honeywell CFD Model 53,000 Passenger compartment volume 2.5 m 3 Large leak (0.5 mm orifice ) . Not available . Not available . Industry Consortium Field Test 29,774 Passenger compartment volume 3.1 m 3 Vehicle shielded from wind; six mannequins placed in car to simulate vehicle occupants; large leak (0.5 mm orifice); full charge rel eased; 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 occ urring under the conditions noted in the table a re expected to be less than the concentrations reported in the table. T he worst - case scenario box - model produced concentrations above the LFL (65,000 ppm) in the 3 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 re frigerant 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). 4 The Crown Victoria was used by the industry consortium as it was the vehicle used in the risk assessment of HFC - 152a and CO 2 (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.”HFO - 1234yf Non - CBI Risk Screen Page 5 October 13, 2009 passenger compartment for all vehicles ; howeve r 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.



### 4.2. 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 p ersonnel 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 Liqu e fied Petroleum Gas C ode (NFPA 200 8 ) 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 worker s 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 maint ained at all ti mes during the manufacture of equipment containing HFO - 1234yf through adherence to g ood manufacturing p ractices . If refrigerant levels in the air surrounding the equipment rise above one - fourth of the lower flammability limit , 5 the space sho uld be evacuated and re - entry should only occur after the space has been properly ventilated. 

### V entilation is also of the utmost importance to mitigate the risk of fire or explosion when servicing vehicles using HFO 1234yf . 

### 5. 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, suc h as open doors or windows, fans operating, or conditioned airflow (e ither 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 hypoxia6 in each of the cars presented in 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
5 OSHA regulation 29 CFR 1910.110 consi ders ventilation adequate “when the concentration of the gas in a gas - air mixture does not exceed 25 percent of the lower flammable limit.” 6 Twelve percent oxygen in air (i.e., 120,000 ppm) is the NOAEL for hypoxia (ICF 1997).HFO - 1234yf Non - CBI Risk Screen Page 6 October 13, 2009 levels to the NOAEL, there could be risk of asphyxiation in the car under a worst - case refrigerant release scenario. Tab le 4 presents the results of the asphyxiation analysis.

Tab le 4 . Reasonable Worst - Case Asphyxiation Assessment a Car Class Charge Required to Cause Impairment (g) b Charge Size (g) b May C harge 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 93 6 No SUBCOMPACT CARS 10,618 79 4 No MINICOMPACT CARS 9,737 725 No MIDSIZE CARS 12,612 93 6 No LARGE CARS 13,632 79 4 No SMALL STATION WAGONS 12,334 670 No MINIVAN 20,494 1 , 100 No VANS 38,0 21 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 requ ired to cause impairment based on concentrations of the substitute i n 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 ca r 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 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 . 

### 6. TOXICITY ANALYSIS To assess potential health risks from exposure to this substitute when use d a s 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 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 s everal 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 Table 5 . Table 6 provides definitions of the acronyms used in Table 5 . EPA’s approach for identifying or developing these values is discussed in Chapter 3 of the Background Document.HFO - 1234yf Non - CBI Risk Screen Page 7 October 13, 2009 Table 5 . Toxicity Levels of HFO - 1234yf Occupational Long - term Exposure ppm Occupational

Short - term Exposure ppm Consumer

Short - term Exposure ppm HFO - 1234yf 250 a NA See Appendix A NA = Not Available a US EPA (2009) .

Table 6 . Explanation of Toxicity- Related Acronyms Exposure Limit Definition Explanation LC50 Lethal Concentration “ T he concentration of the chemical in air that kills 50 % of the test animals in a given time ” a NOAEL No Observed Adverse Effect Limit “ T he 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 prod uced 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.c cohs.ca/oshanswers/chemicals/ld50.html b From http://www.epa.gov/riskassessment/glossary.htm#n c U.S. EPA (1994 ) 

### 6.1. O ccupational E xposure 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 t

he 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. 7 T he 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. 8 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

7 ICF International maintain s 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 track s 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. 8 During disposal it is assumed that only 90 percent of the refrigerant charge remains in the unit.HFO - 1234yf Non - CBI Risk Screen Page 8 October 13, 2009 events/manufacturing faci lity/day. For disp osal, 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 th ese value s were compared to the o ccupational l o ng -term exposure limit for HFO - 1234yf . T he results are presented in Table 7 . Table 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 b oth the short -term (15 - minute) and long -term (8 -hour) worker exp osure concentrations at no po int exceed 12 percent of the occupational long -term exposure limit . Even the maximum estimate d short -term occupational level (i.e., maximum 15 - mi nute TWA exposure) is significantly lower than the 8 -hour long -term exposure limi t 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 - yours elf ” 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 worker s, including for “do - it - yourself” car repair .



### 6.2. C onsumer 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 s ubstitute under a reasonable worst - case scenario . 9 The analy sis 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 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 individ uals 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 identif ied by ICF (2008) as having the highest refrigerant charge to compartment volume ratios in each vehicle class ) are used in this model . The model assume s 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 . 10 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). 9 Acute exposure due to a catastrophic leak was selected as the ‘worst - case scenario,’ rather than chroni c 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 so rts of exposures are not expected for vehicle occupants as the average trip length in the U.S. is 10 miles (U.S. DOT 2007). 10 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).HFO - 1234yf Non - CBI Risk Screen Page 9 October 13, 2009 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. C oncentrations 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 Table 8 below.

Table 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 4,76 8 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 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 ).



### 6.3. G eneral P opulation Exposure Chronic exposures to the substitute are not expected for the general population. 

### 7. 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 , I CF (200 9 ) modeled potential emission s 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. 11 ICF (200 9 ) 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.” 

### 8. 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 e arth’s surface and is highly soluble and very persistent in aquatic environments (ICF 200 9 ) . As TFA i s also mildly phytotoxic, ICF completed an analysis to determine if emissions of HFO - 1234yf could pose a significant risk of 11 These regions are the Houston - Galveston region and the South Coast Air Basin in California.HFO - 1234yf Non - CBI Risk Screen Page 10 October 13, 2009 ecotoxicity. ICF (200 9 ) concluded that “TFA production resulting from HFO - 1234yf emissions is not expected to pose significant harm to aquatic communities . ” 

### 9. RE FERENCES Blackwell, N., L. Bendixen and E. Birgfeld. 2006. Risk Analysis for Alternative Refrigerant in Motor Vehicle Air Conditioning. September. Honeywell . 200 7 . 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 Pro duction 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 prepare d 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 P etroleum 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#sizeclasse s>. 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_1 0_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. “ Ri sk Assessment: PMN 07 - 0601. Reflecting Deliberations And Decisions From the 03/04/09 RAD [Risk Assessment Division] Disposition MeetingEvaluation of accidental refrigerant release of HFO - 1234yf in a motor vehicle Non - CBI Version September 28, 2009 Page 1 

## 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. 12 The evaluation included modeling of stratified exposure concentrations within the compartment of several different vehicles. Itis important t o 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 c onsumers 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 Conc entrations Based on the modeling, the most conservative scenario involves a small Mercedes sedan with a high charge size to compartment vo lume ratio (640.75 g/m3 ). The highest concentration of HFO - 1234yf was estimated in the area of the floorboards at 2 82,000 ppm. At the breathing zone, however, the estimated concentration is approximately 11,700 ppm (Table 1).

Table 9 : Worst- case scenario and resulting concentrations Car type Passenger

Compartment Size (m 3 ) a MAC Charge

Size (g rams) HFC - 134a b,c Ratio of HFC 134a Charge to Compartment Volume (g/m 3 ) 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) a Source: 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. b Source: 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 cons iders the 11,700 ppm concentration for the purposes of toxicity evaluation. An accidental release of car ref

rigerant 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 - 12 This modeling and related assumptions are discussed in detail in the risk screen for HFO - 1234yf. The most conservative scenario is discussed here.Evaluation of accidental refrigerant release of HFO - 1234yf in a motor vehicle Non - CBI Version September 28, 2009 Page 2 1 234yf (11, 7 00 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 ref

rigerant is 11,700 ppm, much lower tha n 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 o f a car refrigerant charge.