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
2

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
3

6.1 Use of HFO-1234yf as a Retrofit.............................................................................. 31

6.2 Use of Other Alternative Refrigerants as Retrofits in HFO-1234yf MVAC Systems32

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............................................................................................. 44
4

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 
5

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
6

1. 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
7

Count Document ID No. Commenter Name Organization

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 Honeywellc, d

59 EPA-HQ-OAR-2008-0664-0135.1c 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.
8

2. ACCEPTABILITY DECISION

2.1 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).

2.2 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.
9

3. USE CONDITIONS FOR HFO-1234YF

3.1 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 HFO1234yf 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 HFO1234yf 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 HFO1234yf 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 airconditioning 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 
10

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 HFO1234yf 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 HFO1234yf. 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.
11

3.2 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.
12

3.3 Concentration in Passenger Compartment

Comment: Regarding the first proposed use condition that would limit the concentration of HFO1234yf 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. 
13

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. 

3.3.1 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.” 
14

3.3.2 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.

3.3.3 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 
15

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.

3.4 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 HFO1234yf 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.”
16

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.

3.5 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 
17

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.”

3.6 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.

3.7 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.

3.8 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.

3.9 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 HFC152a 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 
18

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.

3.10 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.

4. ENVIRONMENTAL IMPACTS OF HFO-1234YF

4.1 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 HFO1234yf, 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. 
19

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 HFO1234yf 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 HFO1234yf. 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).

4.3 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 HFO1234yf. Other commenters stated that HFO-1234yf will not contribute significantly to groundlevel 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.” 
20

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 HFO1234yf 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. 
21

4.4 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 HFO1234yf 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 1/80th 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. 
22

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.

4.5 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 
23

Papasavva et al. (2009).1 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.”

5. HEALTH AND SAFETY CONCERNS

5.1 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,2adverse 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-OAR2008-0664-0135.2 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 HFO1234yf 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.

 

1

Papasavva et al. (2009) includes several sources of emissions of automobile refrigerant, including regular leaks 

through hoses, irregular leaks, refrigerant loss during servicing, and refrigerant loss at end of vehicle life.

2

The risk assessment conducted by the commenter specifically focuses on the potential single, short-duration exposure scenarios 

associated with vehicle leaks to passengers and with can charging of Mobile Air Conditioning (MAC) systems by servicing 

personnel and do-it yourself individuals (DIYers). It does not address exposures to workers in an industrial setting, nor does it 

assess ignition risk for car passengers or vehicle repair workers.
24

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-OAR2008-0664-0036. 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. 
25

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. 
26

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-HQOAR-2008-0064-0038, is discussed in section V of the preamble, “Why is EPA finding HFO1234yf 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.’”

5.2 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/m3at 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.
27

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.”
28

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.

5.3 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, 
29

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 HFO1234yf. 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 HFO1234yf 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 
30

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 longterm 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)

3

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 shortterm exposure because it is designed for chronic occupational exposure, not rare acute exposures 

such as might occur from the decomposition products of HFO-1234yf. 

 

3 An AEGL-2 is intended to apply to an emergency situation where someone would try to move away from the 

hazard in a short period of time and may suffer some temporary irritation, but no permanent health damage. 
31

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.

6. RETROFITS OF MVAC SYSTEMS

6.1 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. 
32

Response: The proposed use conditions were intended to address risks from the use of HFO1234yf 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).

6.2 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 HFO1234yf 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 HFO1234yf 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 HFO1234yf, 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 
33

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 HFO1234yf 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.

7. 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, 
34

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-134acertified 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., nonprofessionals 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. 
35

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. 

8. SERVICING ISSUES

8.1 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 
36

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. 

8.2 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 HFO1234yf, 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 HFO1234yf. 

Response: See section VII.G of the preamble, “Servicing Issues” for responses to these 

comments.

8.3 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. 
37

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 HFO1234yf as an acceptable substitute, subject to use conditions, for use in MVACs.

9. TSCA SIGNIFICANT NEW USE RULE (SNUR)

Comment: One commenter recommended that EPA regulate the use and servicing of HFO1234yf 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: 
38

 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.

10. END OF LIFE VEHICLE RECYCLING CONCERNS

10.1 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. 
39

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 HFO1234yf 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 
40

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.

10.2 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-OAR2008-0664-0038), 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 endof-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). 

11. 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 HFC134a, 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 
41

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 lightduty 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 lowerincome motorists may be forced to go without air conditioning each year or may seek out lowercost 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 
42

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 
43

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.

12. 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 HFO1234yf, 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 
44

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.” 

13. 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.
45

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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