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EO12866_SNAP HFO-1234yf MVAC_RIN 2060-AP11_Final_Rule_20101214.doc

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 82

[EPA-HQ-OAR-2008-0664; FRL-xxxx-x]

RIN 2060-AP11

Protection of Stratospheric Ozone: New Substitute in the Motor Vehicle Air Conditioning 

Sector under the Significant New Alternatives Policy (SNAP) Program

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final Rule.

_______________________________________________________________________

SUMMARY: The Environmental Protection Agency’s (EPA) Significant New 

Alternatives Policy (SNAP) program is expanding the list of acceptable substitutes for

use in the motor vehicle air conditioning end-use as a replacement for ozone-depleting 

substances. The Clean Air Act requires EPA to review alternatives for ozone-depleting 

substances and to disapprove substitutes that present overall risks to human health and 

the environment more significant than those presented by other alternatives that are 

available or potentially available. The substitute addressed in this final rule is for use in 

new passenger cars and light-duty trucks in the motor vehicle air conditioning end-use 

within the refrigeration and air conditioning sector. EPA finds hydrofluoroolefin (HFO)-

1234yf acceptable, subject to use conditions, as a substitute for chlorofluorocarbon 

(CFC)-12 in motor vehicle air conditioning for new passenger cars and light-duty trucks. 

The substitute is a non-ozone-depleting gas and consequently does not contribute to 

stratospheric ozone depletion.

DATES: This final rule is effective on [insert date 60 days after publication]. 
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ADDRESSES: EPA has established a docket for this action under Docket ID No. EPAHQ-OAR-2008-0664. All documents in the docket are listed on the 

www.regulations.gov web site. Although listed in the index, some information is not 

publicly available, e.g., confidential business information (CBI) or other information 

whose disclosure is restricted by statute. Certain other material, such as copyrighted 

material, is not placed on the Internet and will be publicly available only in hard copy

form. Publicly available docket materials are available either electronically through 

www.regulations.gov or in hard copy at the Air Docket, EPA/DC, EPA West, Room 

3334, 1301 Constitution Ave., NW, Washington, DC. This Docket Facility is open from 

8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone 

number for the Public Reading Room is (202) 566-1744, and the telephone number for 

the Air Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Margaret Sheppard, Stratospheric 

Protection Division, Office of Atmospheric Programs; Environmental Protection Agency, 

Mail Code 6205J, 1200 Pennsylvania Avenue NW., Washington DC 20460; telephone 

number (202) 343-9163, fax number, (202) 343-2338; e-mail address at 

sheppard.margaret@epa.gov. 

Notices and rulemakings under the SNAP program are available on EPA's Stratospheric 

Ozone Web site at http://www.epa.gov/ozone/snap/regulations.html. The full list of 

SNAP decisions in all industrial sectors is available at http://www.epa.gov/ozone/snap.

SUPPLEMENTARY INFORMATION: 

This final rule provides motor vehicle manufacturers and their suppliers an additional 

refrigerant option for motor vehicle air conditioning (MVAC) systems in new passenger 
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cars and light-duty trucks. HFO-1234yf (2,3,3,3-tetrafluoroprop-1-ene), the refrigerant 

discussed in this final action, is a non-ozone-depleting substance.

Table of Contents

I. Does this action apply to me?

II. What abbreviations and acronyms are used in this action?

III. What is EPA’s final decision for HFO-1234yf for motor vehicle air conditioning 

(MVAC)?

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?

VI. What is the relationship between this SNAP rule and other EPA rules?

A. Significant New Use Rule

B. Rules under Sections 609 and 608 of the Clean Air Act

VII. What is EPA’s response to public comments on the proposal?

A. Acceptability decision

B. Use conditions

C. Environmental impacts

D. Health and safety impacts

E. Retrofit usage

F. Use by “do-it-yourselfers”

G. Servicing issues

H. Cost, availability, and small business impacts
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VIII. How does the SNAP program work?

A. What are the statutory requirements and authority for the SNAP program?

 B. What are EPA's regulations implementing section 612?

C. How do the regulations for the SNAP program work?

D. Where can I get additional information about the SNAP program?

IX. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination with Indian Tribal 

Governments

G. Executive Order 13045: Protection of Children from Environmental Health 

and Safety Risks

H. Executive Order 13211: Actions that Significantly Affect Energy Supply, 

Distribution, or Use

I. National Technology Transfer and Advancement Act

J. Executive Order 12898: Federal Actions to Address Environmental Justice in 

Minority Populations and Low-Income Populations

K. Congressional Review Act
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X. References

I. Does this Action Apply to Me?

This final rule regulates the use of the chemical HFO-1234yf (2,3,3,3-tetrafluoroprop1-ene, Chemical Abstracts Service Registry Number (CAS Reg. No. 754-12-1) as a 

refrigerant in new motor vehicle air conditioning (MVAC) systems in new passenger cars 

and light-duty trucks. Businesses in this end-use that might want to use HFO-1234yf in 

new MVAC systems in the future include:

 automobile manufacturers

 manufacturers of motor vehicle air conditioners

Regulated entities may include:

Table 1–Potentially Regulated Entities, 

by North American Industrial Classification System (NAICS) Code

Category NAICS code Description of regulated entities

Industry 336111 Automobile Manufacturing

Industry 336391 Motor Vehicle Air-Conditioning Manufacturing

This table is not intended to be exhaustive, but rather a guide regarding entities likely to 

be regulated by this action. If you have any questions about whether this action applies 

to a particular entity, consult the person listed in the preceding section, “FOR FURTHER 

INFORMATION CONTACT.”

II. What abbreviations and acronyms are used in this action?

100-yr-one-hundred year time horizon

AEGL-Acute Exposure Guideline Level
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AIST-the National Institute for Advanced Industrial Science and Technology of Japan

ASHRAE-American Society for Heating, Refrigerating, and Air-Conditioning Engineers

ATSDR-the U.S. Agency for Toxic Substances and Disease Registry

BAM-Bundesanstalt fuer Materialforschung und –pruefung (the German Federal Institute 

for Materials Research and Testing)

CAA-Clean Air Act

CAS Reg. No.-Chemical Abstracts Service Registry Number

CBI-Confidential Business Information

CFC-chlorofluorocarbon

CFC-12-the ozone-depleting chemical dichlorodifluoromethane, CAS Reg. No. 75-71-8

CFD-Computational Fluid Dynamics

CFR-Code of Federal Regulations

cm/s-centimeters per second

CO2-carbon dioxide, CAS Reg. No. 124-38-9

CRP-Cooperative Research Program

DIN-Deutsches Institut fuer Normung (designation for standards from the German 

Institute for Standards)

DIY-“do-it-yourself”

DOT-the United States Department of Transportation

EPA-the United States Environmental Protection Agency

EO-Executive Order

FMEA-Failure Mode and Effect Analysis

FR-Federal Register
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GWP-Global Warming Potential

HF-Hydrogen Fluoride, CAS Reg. No. 7664-39-3

HI-Hazard Index

HFC-hydrofluorocarbon

HFC-134a-the chemical 1,1,1,2-tetrafluoroethane, CAS Reg. No. 811-97-2

HFC-152a-the chemical 1,1-difluoroethane, CAS Reg. No. 75-37-6

HFO-hydrofluoroolefin

HFO-1234yf-the chemical 2,3,3,3-tetrafluoroprop-1-ene, CAS Reg. No. 754-12-1

ISO-International Organization for Standardization

JAMA-Japan Automobile Manufacturers Association

JAPIA-Japan Auto Parts Industries Association

LCA-Lifecycle Analysis

LCCP-Lifecycle Climate Performance

LFL-Lower Flammability Limit

LOAEL-Lowest Observed Adverse Effect Level

mg/L-milligram per liter

MIR-Maximum Incremental Reactivity

mJ-millijoule

mm-millimeter

MOE-Margin of Exposure

MPa-megapascal

MRL-Minimal Risk Level

MVAC-Motor Vehicle Air Conditioning
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NAICS-North American Industrial Classification System

ng/L-nanograms per liter

NHTSA-the U.S. National Highway Traffic Safety Administration

NOAEL-No Observed Adverse Effect Level

NOEC-No Observed Effect Concentration

NPRM-Notice of Proposed Rulemaking

NTTAA-National Technology Transfer and Advancement Act

ODP-Ozone Depletion Potential

ODS-Ozone-Depleting Substance

OEM-Original Equipment Manufacturer

OMB-Office of Management and Budget

OSHA-the United States Occupational Safety and Health Administration

PAG-Polyalkylene Glycol

PMN-Pre-Manufacture Notice

POCP-Photochemical Ozone Creation Potential

POD-Point of Departure

ppm-parts per million

ppt-parts per trillion

psig-pounds per square inch guage

R-1234yf-ASHRAE designation for refrigerant HFO-1234yf

R-134a-ASHRAE designation for refrigerant HFC-134a

R-152a-ASHRAE designation for refrigerant HFC-152a

R-744-ASHRAE designation for refrigerant CO2
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RCRA-the Resource Conservation and Recovery Act

RFA-Regulatory Flexibility Act

SAE-SAE International, formerly the Society of Automotive Engineers

SBA-the United States Small Business Administration

SIP-State Implementation Plan

SNAP-Significant New Alternatives Policy

SNUN-Significant New Use Notice

SNUR-Significant New Use Rule

SO2-sulfur dioxide, CAS Reg. No. 7446-09-5

TEWI-Total Equivalent Warming Impact

TFA-Trifluoroacetic acid, CF3COOH, also known as trifluoroethanoic acid, CAS Reg. No. 

76-05-1

TSCA-the Toxic Substances Control Act

TWA-Time-Weighted Average

UF-Uncertainty Factor

UMRA-Unfunded Mandates Reform Act

VDA-Verband der Automobilindustrie (German Association for the Automobile Industry)

VOC-Volatile Organic Compound

v/v-volume to volume

WEEL-Workplace Environmental Exposure Limit
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III. What is EPA’s final decision for HFO-1234yf for motor vehicle air 

conditioning (MVAC)?

In this final rule, EPA is finding HFO-1234yf acceptable, subject to use 

conditions, as a substitute for CFC-12 in new MVAC systems for passenger cars and 

light-duty trucks. This determination does not apply to the use of HFO-1234yf as a 

conversion or retrofit for existing MVAC systems. In addition, it does not apply to the 

use of HFO-1234yf in the air conditioning or refrigeration systems of heavy-duty trucks, 

refrigerated transport, or off-road vehicles such as agricultural or construction equipment. 

EPA is not mandating the use of HFO-1234yf or any other alternative for MVAC 

systems. This final rule is adding HFO-1234yf to the list of acceptable substitutes, 

subject to use conditions, in new MVAC systems. Automobile manufacturers have the 

option of using any refrigerant listed as acceptable for this end-use, so long as they meet 

any applicable use conditions. 

Under this decision, the following enforceable use conditions apply when HFO1234yf is used in a new MVAC system for passenger cars and light-duty trucks:

1. The high-pressure side of the MVAC system shall have a pressure relief 

device located in the high pressure side of the compressor or immediately 

adjacent to the compressor discharge fitting. The device shall release 

refrigerant only outside of the passenger, trunk, and storage compartments and 

MVAC air distribution system. These pressure relief devices shall be 

designed to minimize impingement of the refrigerant and oil on hot surfaces.
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2. The MVAC system high-pressure side relief device identified above in 1. shall 

be self-sealing. In no case shall the maximum release (blow-off) pressure be 

greater than the maximum refrigerant working pressure.

3. To prevent unnecessary discharge of refrigerant during operation, the system 

shall have a means to limit the compressor operation by cutting off 

transmission of power to the compressor before any component failure occurs 

and before activation of any pressure relief device (i.e., compressor cutoff 

switch).

4. In no case shall any high-pressure side refrigerant pressure relief valves (or 

burst disks) have an activation pressure greater than the maximum working 

pressure of 4.14 MPa. Gauge (600 psig). 

5. The maximum pressure on the low-pressure side of the MVAC system shall 

not exceed the saturation pressure of HFO-1234yf at 56oC.

6. HFO-1234yf refrigerant systems connections shall either be:

 Located outside the passenger compartment and outside the 

passenger cabin airflow path.

or

 Designed to prevent leakage if the connections are located inside 

the passenger cabin or in the passenger cabin airflow path. For 

safety reasons, individuals performing servicing shall follow the 

service and repair leakage recommendations (e.g., from 

manufacturer and in service shop manual), including any service 
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procedures established to prevent refrigerant from entering the 

cabin or airflow path.

7. High-side and low-side fittings shall be fitted with protective or sealing caps.

8. All MVAC system service fittings shall be located for ease of attachment of 

service hoses and shall be designed to minimize direct impingement of 

refrigerant on the service technician. Piping shall be of robust design to avoid 

damage or permanent deformation while connecting or disconnecting the 

service hose coupling(s) from factory charging and service equipment.

9. HFO-1234yf must be used with the following service fittings:

o For the low-side service port, use quick-connect fittings with an 

outside diameter of 14 + 0.2 mm (0.551 + 0.00787 inches). 

o For the high-side service port, use quick-connect fittings with an 

outside diameter of 17 + 0.2 mm (0.669 + 0.00787 inches).

o For connections with containers of 20 lbs or greater, use quickconnect fittings with an outside diameter of 14 + 0.2 mm (0.551 +

0.00787 inches).

o All fittings must be different from those for any other refrigerant.

10. A plainly legible and durable refrigerant label shall be mounted in a clearly

visible location under hood that does not require the removal of any parts or 

covers to be read. The label shall: identify the refrigerant; state the amount of

refrigerant charge in grams (or kilograms, to three decimal places); and 

identify the lubricant type (polyalkylene glycol [PAG] or polyolester [POE]). 

The label either shall include the chemical safety symbol for “flammable” or 
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shall state in text that the refrigerant is flammable in letters at least 3 mm in 

height that are red in color. The label shall contain the name or logo of the 

original equipment vehicle manufacturer or the refrigeration system 

manufacturer responsible for design compliance with this rule and with SAE 

standards. The label shall have a minimum size of 60 mm by 30 mm. It shall 

have text in bold-type letters at least 3 mm in height for identifying refrigerant, 

lubricant type and refrigerant amount. If the label contains text only and no 

symbols, the label shall also state the following:

“CAUTION SYSTEM CONTAINS REFRIGERANT R-1234yf UNDER HIGH 

PRESSURE-TO BE SERVICED ONLY BY QUALIFIED PERSONNEL” 

11. Manufacturers must conduct Failure Mode and Effect Analysis (FMEA) as 

provided in SAE J1739 (adopted 2009). Manufacturers must keep the FMEA 

on file for at least three years from the date of creation. 

Once the standard SAE J639 becomes final with provisions for HFO-1234yf, EPA will 

consider replacing use conditions 1 through 10 with a use condition requiring the safety 

provisions of SAE J639. 

IV. What are the final use conditions and why did EPA finalize these conditions?

Summary of the use conditions

This rule finalizes ten use conditions that were included in the draft SAE standard 

J639, which was available during the comment period on the proposed rule. The SAE 

standard has not yet been finalized. Thus, since EPA is unable to refer to the final SAE 

standard in the final rule, EPA instead is including in the use conditions the safety 
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requirements provided in the draft SAE standard1referred to in the proposed rule and 

included in the docket (EPA-HQ-OAR-2008-0664-0012). 

The eleventh use condition requires the manufacturer of MVAC systems and 

vehicles (i.e., the original equipment manufacturer [OEM]) to conduct and keep records 

of a risk assessment and failure Fault Mode and Effects Analysis (FMEA) for at least 

three years from the date of creation. There is an existing industry standard, SAE J1739, 

that gives guidance on how to do this. It is standard industry practice to perform the 

FMEA and to keep it on file while the vehicle is in production and for several years 

afterwards (US EPA, 2010a).

Reasons for revised use conditions

EPA proposed five use conditions in the Notice of Proposed Rulemaking (NPRM)

(October 19, 2009; 74 FR 53445). One use condition required manufacturers to meet all 

the safety requirements in the standard SAE J639, “Safety Standards for Motor Vehicle 

Refrigerant Vapor Compression Systems” and required use of unique servicing fittings

from that standard. Another use condition required automobile manufacturers to perform 

Fault Mode and Effect Analysis (FMEA) and to keep records of the FMEA.

The remaining three proposed use conditions specifically addressed risks of 

flammability of HFO-1234yf and indirectly addressed risks of generating hydrogen 

fluoride (HF) from combustion of HFO-1234yf. For the first of those proposed use 

conditions, which addressed the passenger compartment, the concentration of HFO1234yf was not to exceed the lower flammability limit (LFL) in the free space for more 

than 15 seconds. For the second proposed use condition, which addressed the engine 

 

1 The safety requirements cited here are from sections 5, 7, 9, 10, and 12 of the draft standard SAE J 639 

(System and Component Requirements; Service Port Fittings; Service Fitting Caps; Requirements for MAC 

System Labeling; and Refrigerant Line Routing and Refrigerant Connections). 
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compartment, the concentration of HFO-1234yf was not to exceed the LFL for any period 

of time. A third proposed use condition, which also addressed the engine compartment, 

would have required protective devices, isolation and/or ventilation techniques in areas 

where there is a potential to generate HFO-1234yf concentrations at or above 6.2% 

volume to volume (v/v) in proximity to exhaust manifold surfaces and hybrid or electric 

vehicle electric power sources. 

EPA based our determination of the appropriate use conditions to include in the 

final rule using information in the docket at the time of proposal, comments received on 

the proposed rule, and additional information we have received since the NPRM was 

published. We provided additional opportunities for comment on the public comments

and additional information we received with them when we re-opened the comment 

period on the proposed rule (74 FR 68558, December 28, 2009; 75 FR 6338, February 9, 

2010). First, SAE International’s Cooperative Research Program (hereafter called the 

SAE CRP) issued a new report on December 17, 2009 assessing risks of HFO-1234yf 

and carbon dioxide (CO2) as refrigerants for MVAC. This report found that the risks of 

HFO-1234yf were low overall, and somewhat less than risks for another potential 

alternative refrigerant (CO2, also know as R-744). The December 2009 CRP report 

found that the greatest risks from HFO-1234yf are likely to come from generation of HF, 

both from thermal decomposition and from ignition, rather than direct fire risks from 

ignition of HFO-1234yf (EPA-HQ-OAR-2006-0664-0056.2). (HF is a severe irritant to 

the skin, eyes, and respiratory system.) The SAE CRP estimates risks of excessive HF 

exposure at approximately 4.6 x 10-12 occurrences per vehicle operating hour and risks of 

ignition at approximately 9 x 10-14 occurrences per vehicle operating hour. These 
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correspond roughly to one occurrence in the entire US fleet of passenger vehicles over 2 

years for HF risks and one occurrence in the US vehicle fleet every 100 years for 

flammability risks.2 For comparison, the risk for excessive HF exposure is less than one 

ten-thousandth the risk of a highway vehicle fire and one fortieth or less of the risk of a 

fatality from deployment of an airbag during a vehicle collision (EPA-HQ-OAR-2008-

0664-0056.2). Even these estimates may be conservative because they assume that 

refrigerant could be released in a collision severe enough to rupture the evaporator (under 

the windshield) while the windshield and windows would remain intact and would 

prevent ventilation into the passenger cabin in case of a collision (EPA-HQ-OAR-2006-

0664-0056.2). 

Second, we received a number of public comments regarding the proposed use 

conditions. Some commenters claimed that the second use condition concerning 

concentrations in the engine compartment was infeasible because in the event of a leak, 

there would always be some small volume that would have a concentration over the LFL; 

these commenters further stated that exceeding the LFL would not necessarily create a 

risk of ignition, because one could have a leak that is not near a source of heat or flame 

(EPA-HQ-OAR-2006-0664-0116.2; EPA-HQ-OAR-2006-0664-0060). Some 

commenters stated that flammability was not a significant risk from use of HFO-1234yf, 

given the results of the SAE CRP risk assessment (December 17, 2009). These 

commenters stated that the use conditions limiting refrigerant concentrations were not 

necessary. These commenters also suggested a number of alternative ways of phrasing 

the use conditions in order to address risks from HF as well as flammability. Most of 

 

2 Assumes a fleet of approximately 250 million passenger vehicles and typical vehicle operation of 500 

hours per year. Sources: U.S. Census, http://www.census.gov/compendia/statab/2010/tables/10s1060.pdf;

SAE J2766, as cited in EPA-HQ-OAR-2008-0664-0056.2
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these comments suggested relying on the performance of a risk assessment and Fault 

Mode Effect Analysis (FMEA) consistent with SAE J1739 to determine appropriate 

protective strategies. Other commenters stated that the use conditions were not 

sufficiently protective as proposed because of other risks: (1) risks due to generation of 

HF from HFO-1234yf, both from thermal decomposition and from combustion; (2) risks 

from direct toxicity of HFO-1234yf; and (3) risks from flammability of HFO-1234yf 

because the LFL becomes lower than 6.2% at temperatures higher than 21oC (EPA-HQOAR-2006-0664-0088, -0054, -0089, -0097 and -0057).

After evaluating the comments and the additional information made available to 

the public through the re-opened comment period, we have decided not to include the 

three use conditions that directly address flammability in the final rule. We believe these 

use conditions are not necessary to ensure that overall risks to human health and the 

environment from HFO-1234yf will be similar to or less than those of other available or 

potentially available refrigerants that EPA has already listed or proposed as acceptable 

for MVAC. This is because of the low overall levels of risk identified for HFO-1234yf 

from flammability and from ignition of HF (EPA-HQ-OAR-2008-0664-0056.2). The 

highest risk identified for HFO-1234yf is potential consumer exposure to HF from 

decomposition and ignition, which is of the same order of magnitude of risks of HF from 

the current most common automotive refrigerant, hydrofluorocarbon (HFC)-134a3(order 

of magnitude of 10-12 events per vehicle operating hour). EPA previously found HFC134a acceptable for use in new and retrofit MVAC systems (59 FR 13044; March 18, 

1994; and 60 FR 31092, June 13, 1995), without use conditions addressing risks of HF. 

 

3 HFC-134a is also known as 1,1,1,2-tetrafluoroethane or, when used as a refrigerant, R-134a. The 

Chemical Abstracts Service Registry Number (CAS Reg. No.) is 811-97-2.
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Since that time, EPA has heard of no cases where someone has been injured due to 

exposure to HF from decomposition of HFC-134a from an MVAC system, and a risk 

assessment from the SAE CRP found no published reports in the medical literature of 

injuries to fire fighters or vehicle passengers from HF or other decomposition products of 

HFC-134a (EPA-HQ-OAR-2008-0664-0008). The direct risk of flammability from 

HFO-1234yf is extremely small. Further, the risks of HFO-1234yf are comparable to or 

less than the risks from other available or potentially alternatives in this end-use that EPA 

has already listed or proposed as acceptable (e.g., HFC-152a4, HFC-134a, and CO2) 

(EPA-HQ-OAR-2008-0664-0086.1).

We have concluded that the use conditions we are including in the final rule 

address the risks from both HF and flammability. Use conditions in the final rule that 

were taken from the draft industry standard SAE J639 provide for a pressure relief device 

designed to minimize direct impingement of the refrigerant and oil on hot surfaces and 

for design of the refrigerant circuit and connections to avoid refrigerant entering the 

passenger cabin. These conditions will mitigate risks of HF generation and ignition. The 

pressure release device ensures that pressure in the system will not reach an unsafe level 

that might cause an uncontrolled, explosive leak of refrigerant, such as if the air 

conditioning system is overcharged. The pressure release device will reduce the 

likelihood that refrigerant leaks would reach hot surfaces that might lead to either ignition 

or formation of HF. Designing the refrigerant circuit and connections to avoid refrigerant 

entering the passenger cabin ensures that if there is a leak, the refrigerant is unlikely to 

enter the passenger cabin. Keeping refrigerant out of the passenger cabin minimizes the 

 

4 HFC-152a is also known as 1,1-difluoroethane or, when used as a refrigerant, R-152a. The CAS Reg. No. 

is 75-37-6.
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possibility that there would sufficient levels of refrigerant to reach flammable 

concentrations or that HF would be formed and transported where passengers might be 

exposed. 

The last proposed use condition, requiring manufacturers to conduct and keep 

records of FMEA according to the standard SAE J1739 remains unchanged. 

The proposed use condition regarding conducting and keeping records of a Fault 

Mode and Effects Analysis according to the standard SAE J1739 remains unchanged. We 

have revised the remaining proposed use condition by replacing the reference to SAE 

J639 (adopted 2009) with specific language adopted from the 2010 draft version of the 

standard. This incorporates language from the most recent version of the standard, with 

new provisions designed specifically to address use of HFO-1234yf. In terms of 

substance, the final use conditions are essentially the same as a number of provisions that 

were under consideration by SAE and were made in the docket at the time of proposal 

(see EPA-HQ-OAR-2008-0664-0012 and the proposed use condition). 

V. Why is EPA finding HFO-1234yf acceptable subject to use conditions?

EPA is finding HFO-1234yf acceptable subject to use conditions because the use 

conditions are necessary to ensure that use of HFO-1234yf will not have a significantly 

greater overall impact on human health and the environment than other available or 

potentially available substitutes for CFC-12 in MVAC systems. Examples of other 

substitutes that EPA has already found acceptable subject to use conditions for use in 

MVAC include HFC-134a and HFC-152a. HFC-134a is the alternative most widely used 

in MVAC systems today. EPA has also proposed to find CO2 (R-744) acceptable subject 

to use conditions in MVAC (September 14, 2006; 71 FR 55140).
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All alternatives listed as acceptable for use in MVAC systems in passenger cars 

and light-duty trucks are required to have unique fittings under use conditions issued 

previously under the SNAP Program at 40 CFR part 82, appendix D to subpart G (61 FR 

54040, October 16, 1996). Thus, all substitutes for use in MVAC systems in passenger 

cars and light-duty trucks are subject to those use conditions, at a minimum, if found 

acceptable and thus are identified as acceptable subject to use conditions. For HFO1234yf, the unique fittings that must be used for MVAC systems are quick-connect 

fittings with an external diameter large enough that they will not connect with cars or 

refrigerant containers for HFC-134a or any other refrigerant, as described in the ninth use 

condition above in section II. The original submitter of HFO-1234yf to the SNAP 

program has provided EPA with a copy of and a diagram for these unique fittings. As 

described above, the fittings will be quick-connect fittings, different than those for any 

other refrigerant. The low-side service port and connections with containers of 20 lbs or 

greater will have an outside diameter of 14 mm (0.551 inches) and the high-side service 

port will have an outside diameter of 17 mm (0.669 inches), both accurate to within 2 mm. 

The submitter has not provided, and the draft SAE J639 standard does not include, unique 

fittings for use with small refrigerant containers or can taps.

5

 Thus, the final use 

conditions do not allow use of small containers for servicing MVAC systems.

In addition to the use conditions regarding unique fittings, which apply under 

appendix D to subpart G of 40 CFR part 82, EPA is requiring use conditions for the safe 

design of new MVAC systems using HFO-1234yf, consistent with standards of the 

 

5 The draft SAE J639 standard specifies unique fittings for high-side and low-side service ports and the 

manufacturer of HFO-1234yf supports these fittings. The unique fitting for large containers for use in 

servicing by professionals (e.g., 20 or 30 lbs) is the same as the fitting for the low-side service port in draft 

SAE J639 and is also specified in SAE J 2844, “R-1234yf New Refrigerant Purity and Container 

Requirements Used in Mobile Air-Conditioning Systems.” (US EPA, 2010b)
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automotive industry (e.g., SAE J1739, draft standard SAE J639). These use conditions 

are intended to ensure that new cars and light-duty trucks that have MVAC systems that 

use HFO-1234yf are specifically designed to minimize release of the refrigerant into the 

passenger cabin or onto hot surfaces that might result in ignition or in generation of HF. 

The industry standard SAE J1739 gives guidelines on designing vehicles to address these 

risks. 

Cost and Availability

EPA received initial estimates of the anticipated cost of HFO-1234yf from the 

manufacturer, claimed as confidential business information, as part of the initial SNAP 

submission (EPA-HQ-OAR-2008-0664-0013 and -0013.1). Initial publicly available 

estimates on the cost of HFO-1234yf were for approximately $40-60/pound (Weissler, 

2008). The first automobile manufacturer to announce its commitment to use HFO1234yf as a refrigerant has confirmed that the prices in its long-term purchase contracts 

are in the range that EPA considered at the time of proposal (Sciance, 2010).

In May 2010, two major chemical manufacturers, including the original submitter,

issued a press release, committing to building a “world-scale manufacturing facility” to 

produce HFO-1234yf (EPA-HQ-OAR-2008-0664-0128.1). The same manufacturers 

have committed to providing HFO-1234yf in time to meet requirements of a European 

Union directive to use only refrigerants with GWP less than 150 in new automobile 

designs starting in 2011. 

Environmental impacts

EPA finds that HFO-1234yf does not pose significantly greater risk to the 

environment than the other substitutes that are currently or potentially available. In at 
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least in one aspect, HFO-1234yf is significantly better for the environment than other 

alternatives currently found acceptable subject to use conditions. HFO-1234yf has a 

hundred-year time horizon (100-yr) global warming potential (GWP) of 4 (Nielsen et al., 

2007; Papadimitriou et al., 2007), compared to a GWP of 124 for HFC-152a, and a GWP 

of 1430 for HFC-134a (IPCC, 2007). CO2, another substitute currently under review in 

this end-use, has a GWP of 1, which is lower, but comparable to the GWP of HFO1234yf. A number of other refrigerant blends containing HFCs or HCFCs have been 

found acceptable subject to use conditions in MVAC that have higher GWPs in the range 

of 1000 to 2400, such as R-426A, R-414A, R-414B, R-416A, and R-420A. Further, 

HFO-1234yf has no ozone depletion potential (EPA-HQ-OAR-2008-0664-0013), 

comparable to CO2, HFC-152a, and HFC-134a, and has less risk of ozone depletion than 

all refrigerant blends containing HCFCs that EPA previously found acceptable subject to 

use conditions for MVAC systems.

EPA also considered the aggregate environmental impact of all anticipated 

emissions of HFO-1234yf, both for the proposed rule and for this final rule. We 

performed a conservative analysis that assumed widespread use of HFO-1234yf as the 

primary refrigerant for MVAC, as well as for other refrigeration and air conditioning uses

that were not included in the manufacturer’s original submission (ICF, 2009; ICF, 

2010a,b,c,e). Thus, we believe that actual environmental impacts are likely to be less 

than those we considered, either at the proposal or final stage.

Under Clean Air Act regulations (see 40 CFR 51.100(s)) addressing the 

development of state implementation plans (SIPs) to attain and maintain the national 

ambient air quality standards, HFO-1234yf is considered a volatile organic compound 
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(VOC). Available information indicates that HFO-1234yf has greater photochemical 

reactivity than HFC-134a, which is exempt from the definition of “VOC” in 40 CFR 

51.100(s). Some of the other acceptable substitutes in the MVAC end-use contain VOCs, 

such as R-406A, R-414A, R-414B, and R-426A. VOCs can contribute to ground-level 

ozone (smog) formation. For purposes of state plans to address ground-level ozone, EPA 

has exempted VOCs with negligible photochemical reactivity from regulation (40 CFR 

51.100(s)). The manufacturer of HFO-1234yf has submitted a petition to EPA requesting

that the chemical be exempted from regulation as a VOC, based on a claim that it has 

maximum incremental reactivity comparable to that of ethane (EPA-HQ-OAR-2008-

0664-0116.1). Separate from this action, EPA is reviewing that request and plans to issue 

a proposed rule shortly to address it. 

Regardless of whether EPA determines to exempt HFO-1234yf from regulation as 

a VOC for state planning purposes, other analyses available in the docket during the 

public comment period indicated that the additional contribution to ground-level ozone 

due to a widespread switch to HFO-1234yf is likely to be around 0.01% or less of all 

VOC emissions, based on the formation of reactive breakdown products such as OH-

(Luecken et al., 2009). Since issuing the NPRM, we performed an additional analysis 

that finds a worst-case increase in the Los Angeles region of 0.080 ppb, or a contribution 

of only 0.1% of the 1997 8-hour standard for ground-level ozone of 0.08 ppm (ICF, 

2010b). Our initial analysis at the proposal stage had estimated a maximum increase in 

ozone of 1.4 to 4.0% of the standard in the same region (ICF, 2009). The major 

difference between the 2009 and the 2010 versions of this analysis involved modeling of 

atmospheric chemistry. The 2010 study was based on the kinetics and decomposition 
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products predicted for HFO-1234yf, rather than using the oxidation of sulfur dioxide 

(SO2) as a proxy for decomposition of HFO-1234yf as was done in the 2009 study. The 

2010 analysis used updated baseline emission estimates that were 1.5% higher to 5.8%

lower than those in the 2009 analysis,

6

depending on the year analyzed (ICF, 2010e). We 

also evaluated environmental impacts based on alternative emissions estimates from a 

peer-reviewed journal article provided during the public comment period (Papasavva et 

al., 2009);7these values ranged from 26.3% to 51.1% lower than EPA’s estimates in the 

2009 analysis (ICF, 2009; ICF, 2010c). 

Another potential environmental impact of HFO-1234yf is its atmospheric 

decomposition to trifluoroacetic acid (TFA, CF3COOH). TFA is a strong acid that may

accumulate on soil, on plants, and in aquatic ecosystems over time and that may have the 

potential to adversely impact plants, animals, and ecosystems. Other fluorinated 

compounds also decompose into TFA, including HFC-134a. However, the amount of 

TFA produced from HFO-1234yf in MVAC is estimated to be at least double that of 

current natural and artificial sources of TFA in rainfall (Luecken et al., 2009). An initial 

analysis performed for EPA at the proposal stage found that, with highly conservative 

emission estimates, TFA concentrations in rainwater could be as high as 1.8 mg/L for the 

maximum monthly concentration for the Los Angeles area and would be no higher than 

0.23 mg/L on an annual basis, compared to a no observed adverse effect concentration of 

 

6 These changes in estimates reflect ongoing updates to EPA’s Vintaging Model, a model that considers 

industry trends in different end-uses that historically have used ODS.

7 Analyzed scenarios considered HFO-1234yf emissions from MVAC and from both MVAC systems and 

stationary air conditioning and refrigeration systems. The analysis also considered scenarios with typical 

emissions from MVAC systems during the entire year similar to those from current MVAC systems using 

HFC-134a and another scenario with reduced emissions of HFO-1234yf of approximately 50 g/yr per 

vehicle, in line with emissions estimates in a study by Papasavva et al. (2009) (EPA-HQ-OAR-2008-0664-

0114.1). Major differences between the data sources include assumptions of a lower leak rate (5.6% of 

charge vs. 8% of charge) and a lower annualized rate of leaks during servicing (3.2% of charge vs. 10% of 

charge) for the Papasavva et al. paper compared to assumptions in EPA’s Vintaging Model (ICF 2010a).
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1 mg/L for the most sensitive plant species (ICF, 2009). This analysis concluded, 

“Projected levels of TFA in rainwater should not result in a significant risk of 

ecotoxicity.” A more recent analysis by Luecken et al (2009) that became available 

during the initial public comment period reached the conclusion that emissions of HFO1234yf from MVAC could produce TFA concentrations in rainwater of 1/800th to 1/80th

the no-observed adverse effect level (NOAEL) for the most sensitive algae species

expected (Luecken et al., 2009). The conclusions in the Luecken study are supported by

additional analyses that have become available since we issued the proposed rule. A 

study from the National Institute of Advanced Industrial Science and Technology (AIST) 

in Japan, which became available during the re-opened comment period, estimated that 

concentrations of TFA in surface water would be approximately twice the level in 

rainwater (Kajihara et al., 2010). This study found that this higher level in surface water 

would be roughly 1/80th the NOAEL for the most sensitive algae species, even with 

assumptions of high emissions levels (i.e., assuming that all types of refrigeration and AC 

equipment currently using HFCs or HCFCs, not just MVAC systems, would use HFO1234yf). Kajihara et al. (2010) evaluated scenarios specific to Japan, with emissions of 

approximately 15,172 ton/yr in 2050, compared to a maximum of 64,324 metric tons/yr 

in 2050 in ICF, 2009 or a maximum of 24,715 metric tons/yr in 2017 in Luecken et al 

(2009). All three studies noted the potential for accumulation in closed aquatic systems.

As we developed the proposed rule, the data we relied on indicated that in the 

worst case, the highest monthly TFA concentrations in the area with the highest expected 

emissions, the Los Angeles area, could exceed the no observed adverse effect 

concentration for the most sensitive plant species, but annual values would never exceed 
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that value. Further, TFA concentrations would never approach levels of concern for 

aquatic animals (ICF, 2009). In a more recent analysis, ICF (2010a, b, c, e) performed

modeling for EPA using the kinetics and decomposition products predicted specifically 

for HFO-1234yf and considered revised emission estimates that were slightly lower than 

in a 2009 analysis (ICF, 2009). The revised analysis found a maximum projected 

concentration of TFA in rainwater of approximately 1,700 ng/L, roughly one-thousandth 

of the estimate from our 2009 analysis (ICF, 2010b). This maximum concentration is 

roughly 34% higher than the 1,264 ng/L reported by Luecken et al. (2009), reflecting the 

higher emission estimates we used (ICF, 2010b). A maximum concentration of 1700 

ng/L corresponds to roughly 1/600th of the NOAEL for the most sensitive algae species—

thus, it is not a level of concern. We find these additional analyses confirm that the 

projected maximum TFA concentration in rainwater and in surface waters should not 

result in a significant risk of aquatic toxicity, consistent with our original proposal.

Human health and safety impacts

Occupational risks could occur during the manufacture of the refrigerant, initial 

installation of the refrigerant into the MVAC system at the car assembly plant, servicing 

of the MVAC system, or final disposition of the MVAC system (i.e., recycling or 

disposal). Consumer risks could occur to drivers or riders in the passenger compartment. 

Risks of exposure to consumers could also occur if they purchase HFO-1234yf and 

attempt to install or service the MVAC system without proper training or use of 

refrigerant recovery equipment. In addition, members of the general public, consumers, 

and first-responders could face risks in the case of a vehicle accident that is severe 

enough to release the refrigerant.
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To evaluate these potential human health and safety impacts, we considered 

EPA’s own risk assessments (EPA-HQ-OAR-2008-0664-0036 and -0038), as well as 

detailed risk assessments with fault-tree analysis from the SAE CRP for HFO-1234yf and 

CO2 (EPA-HQ-OAR-2008-0664-0008 and -0056.2), and scientific data provided in 

public comments on the topics of health and safety risks.

8

 Health and safety risks that we 

evaluated included direct toxicity of HFO-1234yf, both long-term and short-term; 

toxicity of HF formed through thermal decomposition or combustion of HFO-1234yf; 

and flammability of HFO-1234yf. 

Occupational risks

For long-term occupational exposure to HFO-1234yf, EPA compared worker 

exposures to a workplace exposure limit of 250 ppm9over an 8-hour time-weighted 

average. For short-term occupational exposure to HFO-1234yf, we compared worker 

exposure to an acute exposure limit of 98,211 ppm, divided by a margin of exposure of 

30, for a value of 3270 ppm over 30 minutes.

10,11

 

8 On September 30, 2010, we received a final report from the German Federal Environment Agency (UBA) 

with additional information from testing of HFO-1234yf’s potential for flammability and for generating 

hydrogen fluoride. Although this comment was received too late in the rulemaking process for us to 

analyze it in depth, our preliminary review found that the procedures they used contain many unrealistic 

provisions that are not relevant to our decision and in some tests did not provide proper controls (e.g., 

lacking a comparison to HFC-134a under the same conditions). Concerning flammability risk, the results 

do not vary significantly from those we are relying on for the final rule. Thus, our preliminary review of the 

UBA test procedures and results does not suggest that we should re-evaluate our decision to find HFO1234yf acceptable subject to use conditions.

9 This was based on a NOAEL of 4000 ppm from the study, “An Inhalation Prenatal Developmental 

Toxicity Study of HFO-1234yf (2,3,3,3-Tetrafluoropropene) in Rabbits,” EPA-HQ-OAR-2008-0664-0041. 

We used a factor of 1.9 to account for differences in blood concentrations between animals and humans,

and a margin of exposure or collective uncertainty factor of 30. Uncertainty factors of 3 were assigned for 

animal to human extrapolation, and 10 for variability within the human population. The long-term 

workplace exposure limit was calculated as follows: 4000 ppm (animal exposure) x 1.9 (ratio of estimated 

human exposure/animal exposure) x 1/3 (UF for animal to human extrapolation) x 1/10 (UF for variability 

within the human population) exposure) = 250 ppm. This value was compared against 8-hour average 

concentrations. See EPA-HQ-OAR-2008-0664-0036 and EPA-HQ-OAR-2008-0664-0038.

10 This was based on a NOAEL of 51,690 ppm from the study, “Sub-acute (2-week) Inhalation Toxicity 

Study with HFO-1234yf in rats,” EPA-HQ-OAR-2008-0664-0020 through-0020.4, a factor of 1.9 to 
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Section 609 of the Clean Air Act requires technicians servicing MVAC systems 

for consideration (e.g., receiving money, credit, or services in exchange for their work) to 

use approved refrigerant recycling equipment properly and to have proper training and 

certification. Therefore, we expect that professional technicians have the proper 

equipment and knowledge to minimize their risks due to exposure to refrigerant from an 

MVAC system. Thus, we found that worker exposure would be low. Further, EPA 

intends to pursue a future rulemaking under Section 609 of the CAA to apply also to 

HFO-1234yf (e.g., servicing practices, certification requirements for recovery and 

recycling equipment intended for use with MVACs using HFO-1234yf, any potential 

changes to the rules for training and testing technicians, and recordkeeping requirements 

for service facilities and for refrigerant retailers). If workers service MVAC systems 

using certified refrigerant recovery equipment after receiving training and testing, 

exposure levels to HFO-1234yf are estimated to be on the order of 4 to 8.5 ppm on an 8-

hour time-weighted average (as compared with a 250 ppm workplace exposure limit) and

122 ppm on a 30-minute average (as compared with a short-term exposure level of 

98,211 ppm/[margin of exposure of 30] or 3270 ppm). (EPA-HQ-OAR-2008-0664-0036; 

 

account for differences in blood concentrations between animals and humans and a margin of exposure or 

collective uncertainty factor of 30. Uncertainty factors of 3 were assigned for animal to human 

extrapolation, and 10 for variability within the human population. The short-term workplace exposure 

value was calculated as follows: 51,690 ppm (animal exposure) x 1.9 (ratio of estimated human 

exposure/animal exposure)= 98,211 ppm This value was then divided by the expected exposure in each 

scenario, and compared against the target margin of exposure of 30. See EPA-HQ-OAR-2008-0664-0036 

and EPA-HQ-OAR-2008-0664-0038.

11 For comparison, the SAE CRP used exposure limits of 500 ppm over 8 hours and 115,000 ppm over 30 

minutes to evaluate risks for these same time periods. These are based on the 8-hr Workplace 

Environmental Exposure Limit (WEEL) for HFO-1234yf and for short-term exposure, assuming a NOAEL 

of approximately 405,800 ppm from the study, “Acute (4-hour) inhalation toxicity study with HFO-1234yf 

in rats.” Note that EPA disagrees with the finding that the acute inhalation toxicity study found a NOAEL. 

We consider this study to show adverse effects at all levels because of the presence of grey discoloration in 

the lungs of the test animals. In order to ensure sufficient protection, EPA’s risk assessment used a 

NOAEL from a subacute study instead of a LOAEL from an acute study.
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EPA-HQ-OAR-2008-0664-0038). We also analyzed exposure levels during manufacture 

and final disposition at vehicle end-of-life, and found that they would be no higher than 

28 ppm on a 15-minute average or 8.5 ppm on an 8-hour time-weighted average (EPAHQ-OAR-2008-0664-0038). Therefore, the manufacture, use, and disposal or recycling 

of HFO-1234yf are not expected to present a toxicity risk to workers.

We did not analyze the risk of generation of HF in the workplace. In its 

December 17, 2009 Risk Assessment for Alternative Refrigerants HFO-1234yf and R744 (CO2), the SAE CRP indicated that “service technicians will be knowledgeable about 

the potential for HF generation and will immediately move away from the area when they

perceive the irritancy of HF prior to being exposed above a health-based limit” (EPAHQ-OAR-2008-0664-0056.2). Since there is a similar potential to form HF from other 

MVAC refrigerants that have been used for years, such as CFC-12 or HFC-134a, it is 

reasonable to assume that service technicians, recyclers, and disposers will handle HFO1234yf similarly and that use of HFO-1234yf does not pose a significantly greater risk in 

the workplace with regard to HF generation than the use of those other refrigerants.

In that same report, the SAE CRP also discussed qualitatively the risks for 

emergency responders, such as firefighters or ambulance workers that respond in case of 

a vehicle fire or collision. With regard to risk of fire, the CRP report stated that “Due to 

the low burning velocity of HFO-1234yf, ignition of the refrigerant will not contribute 

substantially to a pre-existing fire” (EPA-HQ-OAR-2008-0664-0056.2). EPA considers 

this reasonable, given a burning velocity for HFO-1234yf of only 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). Concerning first responder exposure 
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to HF, the SAE CRP stated, “Professional first responders also have training in chemical 

hazards and possess appropriate gear which will prevent them from receiving HF 

exposures above health-based limits” (EPA-HQ-OAR-2008-0664-0056.2). We agree 

with this assessment. Other MVAC refrigerants containing fluorine such as CFC-12, 

which was historically used, and HFC-134a, which is the predominant refrigerant 

currently in use, also can produce HF due to thermal decomposition or combustion, and 

smoke and other toxic chemicals are likely to be present in case of an automotive fire

(CRP, 2008). Therefore, it is reasonable to expect that first responders are prepared for 

the presence of HF and other toxic chemicals when approaching a burning vehicle and 

that they will wear appropriate personal protective equipment.

EPA’s risk screen for HFO-1234yf evaluated flammability risks, including 

occupational risks. Modeling of concentrations of HFO-1234yf in workplace situations 

such as at equipment manufacture and during disposal or recycling at vehicle end-of-life 

found short-term, 15-minute concentrations of 28 ppm or less—far below the lower 

flammability limit (LFL) of 6.2% by volume (62,000 ppm) (EPA-HQ-OAR-2008-0664-

0038). The SAE CRP’s risk assessments evaluated flammability risks by comparing 

concentrations of HFO-1234yf with the LFL of 6.2%. The SAE CRP conducted 

Computational Fluid Dynamics (CFD) modeling of exposure levels in case of a leak in a 

system in a service shop. The SAE CRP’s earlier February 26, 2008 risk assessment 

found that a leaked concentration of HFO-1234yf exceeded the LFL only in the most 

conservative simulation, with the largest refrigerant leak and with all air being 

recirculated within the passenger cabin (EPA-HQ-OAR-2008-0664-0010). Updated CFD 

modeling performed for the December, 2010 SAE CRP risk assessment found that 
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concentrations of HFO-1234yf sometimes exceeded the LFL, but only within ten 

centimeters of the leak or less (EPA-HQ-OAR-2008-0664-0056.2). The risk assessment 

found the risk of this occupational exposure scenario to be on the order of 10-26cases per 

working hour. We note that HFO-1234yf is less flammable and results in a less energetic 

flame than a number of fluids that motor vehicle service technicians and recyclers or 

disposers deal with on a regular basis, such as oil, anti-freeze, transmission fluid, and 

gasoline. HFO-1234yf is also less flammable than HFC-152a, a substitute that we have 

already found acceptable for new MVAC systems subject to use conditions. Thus, EPA 

finds that the risks of flammability in the workplace from HFO-1234yf are similar to or 

lower than the risk posed by currently available substitutes when the use conditions are 

met.

Consumer exposure

EPA’s review of consumer risks from toxicity of HFO-1234yf indicated that 

potential consumer (passenger) exposure from a refrigerant leak into the passenger 

compartment of a vehicle is not expected to present an unreasonable risk (EPA-HQOAR-2008-0664-0036, EPA-HQ-OAR-2008-0664-0038). However, consumer exposure 

from filling, servicing, or maintaining MVAC systems may cause exposures at high 

enough concentrations to warrant concern. Specifically, this risk may be due to a lack of 

professional training and due to refrigerant handling or containment without the use of

refrigerant recovery equipment certified in accordance with the regulations promulgated 

under CAA Section 609 and codified at 40 CFR part 82, subpart B. Consumer filling, 

servicing, or maintaining of MVAC systems may cause exposures at high enough 

concentrations to warrant concern (EPA-HQ-OAR-2008-0664-0036). However, this rule 
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does not specifically allow for use of HFO-1234yf in consumer filling, servicing, or 

maintenance of MVAC systems. The manufacturer’s submission specifically addressed 

HFO-1234yf as a refrigerant for use by OEMs and by professional technicians (EPA-HQOAR-2008-0664-0013.1). 

The use conditions in this final rule provide for unique service fittings relevant to 

OEMs and to professional technicians (i.e., unique fittings for the high-pressure side and 

for the low-pressure side of the MVAC system and unique fittings for large cylinders of 

20 lb or more). 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.

EPA has issued a significant new use rule (SNUR) under the authority of TSCA. 

(October 27, 2010; 75 FR 65987). Under 40 CFR part 721, EPA may issue a SNUR 

where the Agency determines that activities other than those described in the 

premanufacture notice may result in significant changes in human exposures or 

environmental release levels and that concern exists about the substance’s health or 

environmental effects. Manufacturers, importers and processors of substances subject to 

a SNUR must notify EPA at least 90 days before beginning any designated significant 

new use through a significant new use notice (SNUN). EPA has 90 days from the date of 

submission of a SNUN to decide whether the new use "may present an unreasonable risk" 

to human health or the environment. If the Agency does not determine that the new use 

“may present an unreasonable risk,” the submitter would be allowed to engage in the use, 

with or without certain restrictions. The significant new uses identified in the SNUR for 
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HFO-1234yf are: (1) use other than as a refrigerant in motor vehicle air conditioning 

systems in new passenger cars and vehicles; (2) commercial use other than in new 

passenger cars and vehicles in which the charging of motor vehicle air conditioning 

systems with HFO-1234yf was done by the motor vehicle OEM; and (3) distribution in 

commerce of products intended for use by a consumer for the purposes of servicing, 

maintenance and disposal involving HFO-1234yf.

Under existing regulations in appendix D to subpart G of 40 CFR part 82, “A 

refrigerant may only be used with the fittings and can taps specifically intended for that 

refrigerant and designed by the manufacturer of the refrigerant. Using a refrigerant with 

a fitting designed by anyone else, even if it is different from fittings used with other 

refrigerants, is a violation of this use condition.” The manufacturer and submitter for 

HFO-1234yf has provided unique fittings for the high-pressure side and for the lowpressure side of the MVAC system and for large cylinders for professional use (typically 

20 lb or more12). Therefore, until the manufacturer provides unique fittings to EPA’s 

SNAP Program for use with can taps or other small containers for consumer use and until 

EPA publishes a final rule identifying such unique fittings, it would be a violation of the 

use condition in appendix D to use HFO-1234yf in small cans or containers for MVAC. 

Before issuing a rule allowing use of HFO-1234yf with fittings for small cans or 

containers for MVAC, we would first need to conclude through either review under 

 

12 EPA has issued lists of approved unique fittings for refrigerants in MVAC (see 

http://www.epa.gov/ozone/snap/refrigerants/fittlist.html). These have been issued for the high-side service 

port, low-side service port, 30-lb cylinders (that is, the most typical size container for use in professional 

servicing), and small cans (containers typically used by consumers). The label “30-lb cylinders” is not 

intended to restrict the existence of other container sizes that professional service technicians might use 

(e.g., 50 lb, 20 lb, 10 lb).
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TSCA or under the SNAP program that use of these smaller canisters would not pose an 

unreasonable risk to consumers. 

In our review of consumer risks from HFO-1234yf, we considered information 

concerning consumer exposure to HF from thermal decomposition or combustion of 

HFO-1234yf. EPA’s analysis at the time of the proposed rule focused on the 

flammability risk to consumers, which at the time we believed to be a significant risk in 

its own right, as well as a way to prevent consumer exposure to HF from combustion of 

HFO-1234yf. However, in preparing our proposal, we had available and did consider the 

SAE CRP’s 2008 evaluation of scenarios that might cause consumer or occupational 

exposure to HF (CRP, 2008). This report stated:

Decomposition of HFO-1234yf in a fire scenario might, in theory, pose a 

significant acute health risk to passengers or firemen. But in the event of a fire, 

other toxic chemicals will be produced by combustion of other automotive 

components and thus decomposition of the refrigerant may increase the risk for 

fire fighters and would not introduce an entirely new type of hazard. It is also 

anticipated that only a small portion of the refrigerant charge will be converted to 

these decomposition products. In U.S. EPA's assessment of risk of R-152a and 

CO2 (R-744), the agency cited a study by Southwestern Laboratories which 

indicated that a 100% R-134a atmosphere only produced an HF concentration of 

10 ppm when passed through a tube heated to 1,000 oF (Blackwell et al., 2006). A 

search of the medical literature also did not reveal any published reports of 

injuries to fire fighters or vehicle passengers resulting from exposures to COF2 or 

HF produced in fires involving refrigerants. (EPA-HQ-OAR-2008-0664-0008, p. 

67)

After the SAE CRP’s 2008 evaluation, SAE CRP members conducted tests to 

measure HF concentrations and to identify factors that were most likely to lead to HF 

formation (EPA-HQ-OAR-2008-0664-0056.2). One test on HF concentrations inside a 

car cabin found maximum concentrations were in the range of 0 to 35 ppm in trials both 

with HFO-1234yf and with HFC-134a, with concentrations dropping to 10 ppm or less 

after 10 minutes. In a second test of HF generated in the engine compartment, HF 
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concentrations from thermal decomposition of HFO-1234yf reached as high as 120 ppm 

in the engine compartment in the worst case, with interior passenger cabin values of 40 to 

80 ppm. Under the same extreme conditions (flash ignition, temperature of 700 °C, 

closed hood), HF concentrations from thermal decomposition of HFC-134a reached 36.1 

ppm in the engine compartment with interior passenger cabin values of 2 to 8 ppm. The 

other trials with less extreme conditions found HF concentrations from HFO-1234yf in 

the engine compartment of 0 to 8 ppm. 

The SAE CRP selected an Acute Exposure Guideline Limit (AEGL)-2 of 95 ppm 

over 10 minutes as its criterion for determining toxicity risk from HF.

13

 Thus, even 

assuming levels inside a passenger compartment reached the highest level that occurred 

during the tests – 80 ppm – a passenger inside a vehicle would at worst experience 

discomfort and irritation, rather than any permanent effects. HF levels that could result in 

similar effects were also observed for HFC-134a. The SAE CRP concluded that the 

probability of such a worst-case event is on the order of 10-12 occurrences per operating 

hour14 (EPA-HQ-OAR-2008-0664-0056.2). This level of risk is similar to the current 

level of risk of HF generated from HFC-134a (EPA-HQ-OAR-2008-0664-0086.1). To 

date, EPA is unaware of any reports of consumers affected by HF generated by HFC134a, which has been used in automobile MVAC systems across the industry since 1993. 

Thus, we do not expect there will be a significant risk of HF exposure to consumers from 

HFO-1234yf.

 

13 The AEGL-2 is defined as “the airborne concentration of a substance ...above which it is predicted that 

the general population, including susceptible individuals could experience irreversible or other serious, 

long lasting adverse effects or an impaired ability to escape.” 

http://www.epa.gov/oppt/aegl/pubs/define.htm

14 If we assume 250 million passenger vehicles in the US and typical driving times of 500 hours per year 

per vehicle, a risk of 4.6 x 10-12 per operating hour equates roughly to one event every 2 years for all 

drivers in the entire U.S.
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Depending on the charge size of an HFO-1234yf MVAC system, which may

range from as little as 400 grams to as much as 1600 grams (ICF, 2008), it is possible in a 

worst case scenario to reach a flammable concentration of HFO-1234yf inside the 

passenger compartment. This could occur in the case of a collision that ruptures the 

evaporator in the absence of a switch or other engineering mitigation device to prevent 

flow of high concentrations of the refrigerant into the passenger compartment, provided 

that the windows and windshield remain intact. As stated in the SAE CRP, ignition of 

the refrigerant once in the passenger cabin is unlikely (probability on the order of 10-14

occurrences per operating hour) because the only causes of ignition within the passenger 

cabin with sufficient energy to ignite the refrigerant would be use of a butane lighter

(EPA-OAR-2008-0664-0056.2). If a passenger were in a collision, or in an emergency

situation, it is unlikely that they would choose to operate a butane lighter in the passenger 

cabin. Additionally, it is unlikely ignition would occur from a flame from another part of 

the vehicle because automobiles are constructed to seal off the passenger compartment

with a firewall. If a collision breached the passenger compartment such that a flame from 

another part of the vehicle could reach it, that breach would also create ventilation that 

would lower the refrigerant concentration below the lower flammability limit. Similarly, 

if either a window or the windshield were broken in the collision, the ventilation created 

would lower the refrigerant concentration below the lower flammability limit. Therefore, 

EPA finds that flammability risks of HFO-1234yf to passengers inside a vehicle will be 

low. Further, these risks are likely to be less than those from HFC-152a, another 

flammable refrigerant that EPA has previously found acceptable subject to use 

conditions, because HFC-152a has a lower LFL and a lower minimum ignition energy
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than HFO-1234yf (EPA-HQ-OAR-2008-0664-0008, -0013.4, -0056.2).

Overall conclusion

EPA finds that the use of HFO-1234yf in new passenger vehicle and light-duty

truck MVAC systems, subject to the use conditions being adopted in the final rule, does 

not present a significantly greater risk to human health and the environment compared to 

the currently-approved MVAC alternatives or as compared to CO2, which has been 

proposed for approval in this end-use. 

VI. What is the relationship between this SNAP rule and other EPA rules?

A. Significant New Use Rule

Under the Toxics Substances Control Act, EPA has issued a Significant New Use 

Rule (75 FR 65987; October 27, 2010) for 1-propene, 2,3,3,3-tetrafluoro-, which is also 

known as HFO-1234yf. This rule requires persons who intend to manufacture, import, or 

process HFO-1234yf for a use that is designated as a significant new use in the final 

SNUR to submit a SNUN at least 90 days before such activity may occur. EPA has 90 

days from the date of submission of a SNUN to decide whether the new use "may present 

an unreasonable risk" to human health or the environment. If the Agency does not 

determine that the new use “may present an unreasonable risk,” the submitter would be 

allowed to engage in the use, with or without certain restrictions. The significant new 

uses identified in the final SNUR and subject to the SNUN requirement are: use other 

than as a refrigerant in motor vehicle air conditioning systems in new passenger cars and

vehicles; commercial use other than in new passenger cars or vehicles and in which the 

charging of motor vehicle air conditioning systems with HFO-1234yf was done by the 
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motor vehicle OEM; and distribution in commerce of products intended for use by a 

consumer for the purpose of servicing, maintenance and disposal involving HFO-1234yf. 

The health concerns expressed in the final SNUR are based primarily on potential 

inhalation exposures to consumers during “do-it-yourself” servicing, as well as a number 

of other relevant factors. 

B. Rules under Sections 609 and 608 of the Clean Air Act

Section 609 of the CAA establishes standards and requirements regarding 

servicing of MVAC systems. These requirements include training and certification of 

any person that services MVAC systems for consideration,15 as well as standards for 

certification of equipment for refrigerant recovery and recycling. EPA has issued 

regulations interpreting this statutory requirement and those regulations are codified at 40 

CFR part 82 subpart B. The statutory and regulatory provisions regarding MVAC 

servicing apply to any refrigerant alternative and are not limited to refrigerants that are 

also ODS. This final SNAP rule addresses the conditions for safe use of HFO-1234yf in 

new MVAC systems. Thus, the requirements in this rule apply primarily to OEMs, 

except for specific requirements for service fittings unique to HFO-1234yf. MVAC endof-life disposal and recycling specifications are covered under section 608 of the CAA 

and our regulations issued under that section of the Act.

VII. What is EPA’s response to public comments on the proposal?

This section of the preamble summarizes the major comments received on the 

October 19, 2009 proposed rule. Additional comments are addressed in a response to 

comments document in docket EPA-HQ-OAR-2008-0664.

 

15 Service for consideration means receiving something of worth or value to perform service, whether in 

money, credit, goods, or services.
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A. Acceptability decision

Comment: Several commenters supported EPA’s proposal to find HFO-1234yf 

an acceptable substitute for CFC-12 in 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 were 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, 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 were greater than those of other available alternatives, such as HFC134a, CO2, and hydrocarbons.

Response: For the reasons provided in more detail above, EPA has determined 

that HFO-1234yf, if used in accordance with the adopted use conditions, can be used 

safely in MVAC systems in new passenger vehicles and light-duty trucks. The use 

conditions established by this final rule ensure that the overall risks to human health and 

the environment are comparable to or less than those of other available or potentially

available substitutes, such as HFC-134a, HFC-152a, or CO2. EPA did not compare the 

risks to those posed by hydrocarbons since we have not yet received adequate 
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information for hydrocarbons that would allow us to make such a comparison for use in 

MVAC.

16

Comment: Some commenters suggested that EPA should consider other 

substitutes for CFC-12 in MVAC, 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: This rule only concerns EPA’s decision on the use of HFO-1234yf in 

new passenger vehicles and light-duty trucks. In a separate action, EPA has proposed to 

find CO2 acceptable subject to use conditions as a substitute for CFC-12 in MVAC 

systems for new motor vehicles (September 16, 2006; 71 FR 55140). We anticipate

taking final action on that proposal shortly. We currently have inadequate information on 

hydrocarbons to consider adding them to the list of substitutes for MVAC. We will 

review additional substitutes if they are submitted with complete and adequate data to 

allow an evaluation of whether such substitutes may be used safely within the meaning of 

section 612 of the CAA as compared with other existing or potential substitutes in the 

MVAC end-use. 

B. 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 

 

16 EPA previously reviewed two hydrocarbon blends for use in MVAC and found them unacceptable, 

stating “Flammability is a serious concern. Data have not been submitted to demonstrate that [the 

hydrocarbon blend] can be used safely in this end-use.” Appendixes A and B to subpart G of 40 CFR part 

82. 
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even impossible to meet and are not needed for safe usage. Some automobile 

manufacturers suggested relying upon established standards and practices, such as SAE 

protocols and standards, instead of use conditions. Some commenters suggested 

alternative language for use conditions. Other commenters expressed concern that the 

proposed use conditions limiting concentrations of HFO-1234yf would preclude the use 

of HFO-1234yf by any vehicle that is not initially designed to use this refrigerant.

Response: As described above, EPA agrees that the use conditions, as proposed, 

require modification. In this final rule, we have removed the first three proposed use 

conditions, which required design to keep refrigerant concentrations below the LFL. See 

section IV of the preamble, “What are the final use conditions and why did EPA finalize 

these conditions?” for our basis. With respect to the commenter who suggested that the 

proposed use conditions limiting concentrations of HFO-1234yf below the LFL would 

not allow use except in systems initially designed to use this refrigerant, we note that this

decision is limited to use in new motor vehicles and light-duty trucks. Further, the 

proposed use conditions limiting refrigerant concentration are not included in the final 

rule and thus do not have implications for a future decision concerning retrofits. 

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 
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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: We do not believe that the BAM testing of the flammability limits of 

mixtures of HFO-1234yf and ethane is relevant to assessing the risks of HFO-1234yf as a 

refrigerant in MVAC. Examples of flammable substances in the engine compartment 

may include compressor oil mixed with the refrigerant, motor oil, cleaners, anti-freeze, 

transmission fluid, brake fluid, and gasoline. These are typically liquid and there is no 

evidence that any vapors that might form would include significant amounts of ethane. 

These fluids typically contain larger molecules with higher boiling points than ethane 

(e.g., octane, polyalkalene glycol). It seems more likely, as one commenter suggested,

that these flammable fluids would ignite before breaking down into concentrations of 

ethane considered in the BAM testing. Further, the results of the testing are not 

surprising; based on a scientifically known chemical equilibrium principle known as Le 

Chatelier’s principle--the lower flammability limit of a mixture of two flammable 

substances falls between the lower flammability limit of the two individual substances. 

The range of flammable mixtures of ethane and refrigerants HFC-134a, HFO-1234yf, and 

CO2 is largest for CO2 and is similar for HFC-134a and HFO-1234yf (Besnard, 1996).
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A more relevant test to compare risks for HFO-1234yf and other alternative 

refrigerants in MVAC is to consider flammability of a mixture of compressor oil and 

refrigerant, as occurs in MVAC systems. Such testing, conducted as part of the SAE 

CRP, found that mixtures of HFO-1234yf and 5% oil and HFC-134a and 5% oil both 

ignited at temperatures higher than what usually occurs in a vehicle (730 oC or higher for 

HFO-1234yf and 800 oC or higher for HFC-134a). 

Furthermore, we note that the final use conditions do not rely on the lower 

flammability limit. As explained in more detail in sections IV and V of the preamble, 

“What are the final use conditions and why did EPA finalize these use conditions?” and

“Why is EPA finding HFO-1234yf acceptable subject to use conditions?”, we believe 

that the risks from HFO-1234yf and its decomposition products are very small and are 

comparable to or less than the risks from other acceptable alternatives available or 

potentially available for use in MVAC systems. The use conditions established in the 

final rule require manufacturers to design the system to prevent leakage from refrigerant 

system connections that might enter the passenger cabin, and to minimize impingement 

of refrigerant and oil onto hot surfaces. These use conditions will further reduce already 

low risks from flammability and HF generation. 

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: EPA agrees that the LFL decreases as temperature increases.

However, for the analysis relied on for the proposed rule, we considered an LFL relevant 

to the temperatures that might be expected in a collision or leak scenario and that would 
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not be so high as to be a higher risk factor than exposure to HF. The data provided by the 

commenter show an LFL of 5.7% at 60 oC (140 oF) and an LFL of 5.3% at 100 oC (212 

oF). If a passenger were exposed to temperatures this high in the passenger compartment 

for any extended period of time, he or she would suffer from the heat before there was a 

risk of the refrigerant igniting. However, after considering the available information, we 

find it is not necessary to require a concentration of HFO-1234yf below the LFL to 

address this refrigerant’s risks; rather, risks are sufficiently addressed with the final use 

conditions. As discussed above in section IV of the preamble, “What are the final use 

conditions and why did EPA finalize these conditions?”, we believe that the flammability

risks from HFO-1234yf are very small and overall risks from HFO-1234yf are 

comparable to or less than the risks from other acceptable alternatives used in MVAC. 

EPA finds that the use conditions in this final rule are sufficient to manage risks of injury

or adverse health effects caused by HFO-1234yf. 

Comment: Regarding the first proposed use condition that would limit the 

concentration of HFO-1234yf below the LFL in the passenger cabin, several commenters 

stated that the risks of refrigerant leaking into the passenger compartment and exceeding 

the LFL are very low. Some automobile manufacturers stated that it may not be possible 

to keep the concentration below the LFL in the event of a collision; however, the 

commenters said that even if concentrations in the passenger cabin exceeded the LFL, it 

would be extremely difficult to ignite the refrigerant. Some commenters stated that the 

engineering strategies that would be necessary to implement the proposed use condition 

would actually increase overall risk by increasing the risk of conveying smoke and fumes

from the engine compartment into the passenger compartment in the event of an accident. 
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Some commenters suggested alternative language for the use condition to give greater 

flexibility in engineering responses to allow for differences between vehicles. 

Response: As discussed above in section IV of the preamble, 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 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: As discussed above in section IV of the preamble, EPA is not 

including the proposed use condition and is not limiting the refrigerant concentration 

inside the passenger cabin or the engine compartment. 

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) standards in place of a specific 
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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 HFO1234yf 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: As discussed above in section IV of the preamble, EPA is not 

including the proposed use condition and is not requiring protective devices, isolation 

and/or ventilation techniques where levels of refrigerant concentration may exceed the 

LFL in proximity to exhaust manifold surfaces or near hybrid or electric vehicle power 

sources. As discussed above, we do not believe that the BAM testing of the flammability

limits of mixtures of HFO-1234yf and ethane is relevant to assessing the risks of HFO-
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1234yf as a refrigerant in MVAC. Based on information provided by OEMs that 

manufacture hybrid vehicles, we conclude that there will be sufficient protection against 

fire risk and generation of HF in the engine compartment for hybrid vehicles because

they have protective coverings on power sources that will prevent any sparks that might 

have enough energy to ignite refrigerant and engine surfaces will not be hotter than those 

in conventional vehicles (EPA-HQ-OAR-2008-0664-0081.1, -0081.2). Further, we agree 

that it is reasonable to assume that a collision severe enough to release refrigerant from 

the evaporator (under the windshield) would also release it in a location far enough away

from the battery pack to keep down refrigerant concentrations at the battery pack below 

the LFL. CFD modeling performed for the December, 2010 SAE CRP risk assessment 

found that concentrations of HFO-1234yf only exceeded the LFL within ten centimeters 

of the leak or less (EPA-HQ-OAR-2008-0664-0056.2), but the battery pack is typically 

placed more than ten centimeters away from the evaporator. EPA expects that OEMs 

will include assessment of risks from the exhaust manifold, hybrid power source, and 

electric vehicle power source as part of the FMEA required under one of the final use 

conditions in this rule. 

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 
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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: As discussed above in section IV of the preamble, EPA is not 

including the proposed use conditions that specified a refrigerant concentration not to be

exceeded. 

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: EPA is not including in the final rule the proposed use condition that 

sets a specific limit for refrigerant concentrations inside the engine compartment. See 

section IV of the preamble, “What are the final use conditions and why did EPA finalize 

these conditions?” for further rationale.

Comment: Several commenters agreed with EPA’s proposal to have 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: The use conditions referenced by the commenters were established in 

a separate final rule, promulgated in 1996, which applies to all refrigerants used in 

MVAC (see appendix D to subpart G of 40 CFR part 82). EPA has not proposed to 
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modify that existing rule for purposes of its acceptability determination for HFO-1234yf. 

These requirements indicate to technicians the refrigerant they are using and thus help 

reduce risks to the technician by ensuring that the technician will handle the refrigerant 

properly. In addition, these use conditions serve to prevent contamination of refrigerant 

supplies through unintended mixing of different refrigerants. For purposes of meeting 

that existing regulatory requirement, this final rule specifies use of fittings for the highpressure side service port, the low-pressure side service port, and for refrigerant 

containers of 20 pounds or greater. The submitter for HFO-1234yf has provided these 

fittings to the Agency and they are consistent with the draft SAE standard J639. In

addition, the final rule retains the requirement for a warning label identifying the 

refrigerant, consistent with both the current (2005) edition of SAE J639 and the current 

draft version.

Comment: Some commenters agreed with EPA’s proposal to have a highpressure compressor cut-off switch, as per SAE J639. Another commenter suggested that 

the compressor cut-off switch would be useful for all systems if the discharge pressure 

can reach the burst pressure, not just those systems with pressure relief devices.

Response: EPA is including as a final use condition the requirement that HFO1234yf MVAC systems must have a high-pressure compressor cut-off switch. The use 

condition requires a pressure relief device on the high-pressure side of the compressor for 

all MVAC systems using HFO-1234yf, and so the compressor cut-off switch will be 

required for all systems using HFO-1234yf, as suggested by the commenter.

Comment: Several commenters supported the requirement for vehicle makers to 

conduct and maintain FMEAs. Other automobile manufacturers stated that the final 
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SNAP rule finding HFC-152a acceptable as a substitute for CFC-12 in MVAC included 

this as a comment rather than as a use condition, and suggested that EPA do the same in 

the final rule for HFO-1234yf. Another commenter stated that FMEAs for each vehicle 

design are standard industry practice, and so no use condition is required; this commenter 

provided language for an alternate use condition should EPA choose to specify a use 

condition for vehicle design.

Response: EPA is retaining the requirement for FMEAs in the final rule as a use 

condition, rather than simply as an unenforceable comment. In an FMEA, vehicle 

designers analyze all the ways in which parts of the MVAC system could fail and identify

how they will address those risks in design of the system. In addition, keeping records of 

an FMEA is important to ensuring safe use because it documents that vehicle designers 

have complied with the safety requirements of this rule. We believe that it is necessary to 

retain this requirement as a use condition in order to ensure that OEMs are required to

analyze and address the risks and to document those efforts such that this analysis is 

available to demonstrate compliance to EPA in case of an EPA inspection. Information 

in the FMEAs complements the use conditions of this rule and is useful for demonstrating 

compliance. 

Comment: A commenter requested that EPA specifically allow manufacturers to 

perform FMEAs according to equivalent standards developed by organizations other than 

SAE (e.g., the International Organization for Standardization [ISO], the German Institute 

for Standards [DIN], or the Japan Automobile Manufacturers Association [JAMA]).

Response: We agree that standards from other standard-setting organizations may

provide equivalent assurance of safe use. However, we are not aware at this time of any
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standards that do so. In order to ensure safe use of HFO-1234yf, we would need to 

review any other standard to ensure that it provides equivalent assurances of safety before 

allowing its use in place of the SAE standard. An OEM, for example, could petition 

EPA’s SNAP program and provide copies of the other standard for consideration. If we 

agree that the other standard is equivalent, then we would add it to the use condition on 

FMEAs through a rulemaking.

Comment: A commenter expressed that EPA’s approach to setting use conditions 

impedes 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: As an initial matter, we note that the commenter does not point to any

specific legislative authority that supports his claim. Regardless, EPA disagrees with this 

commenter. Section 612 of the CAA provides that EPA may find substitutes for ODS 

acceptable if they present less risk to human health and the environment than other 

substitutes that are currently or potentially available. Congress did not establish any

limits on EPA’s authority for ensuring that substitutes are not more risky than other 

substitutes that are available and EPA has consistently interpreted this provision to allow 

the Agency to establish use conditions to ensure safe use of substitutes. In this case, we 

find that HFO-1234yf may be used safely, and with risks comparable to or less than those 

of other available substitutes for CFC-12 in the MVAC end-use, so long as it is used 

according to the use conditions established by this action. If the commenter were correct 

that the Department of Transportation (DOT) has sole authority to address fire risk from 
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MVAC systems, in the absence of such standards from DOT, EPA would need to 

determine that HFO-1234yf is unacceptable for use in MVACs. 

C. Environmental impacts

1. Ozone Depletion Potential

Comment: Several commenters agreed with EPA’s proposed finding that HFO1234yf would not contribute significantly to stratospheric ozone depletion, and that the 

ozone depletion potential (ODP) of HFO-1234yf is at or near zero. Two commenters 

claimed 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 HFO1234yf manufacturing process, or emissions of HFO-1234yf and its by-products from the 

manufacturing process 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: It is generally agreed among scientists that substances that contain 

chlorine, bromine or iodine may have an ozone depletion potential while those that 

contain only fluorine effectively have no ODP. In particular, this is because the CF3

radical produced from HFCs has negligible reactivity (Ravishankara et al., 1993); the 
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same radicals would be expected from HFO-1234yf. HFO-1234yf contains no chlorine, 

bromine, or iodine. Also, the atmospheric lifetime of HFO-1234yf is estimated at only 

11 to 12 days (Orkin et al., 1997; Papadimitrou et al., 2007), further reducing the amount 

of the chemical that could possibly reach the stratosphere. Unsaturated HFCs,such as 

HFO-1234yf, have at least one double bond or triple bond between two carbon atoms. 

Double bonds, like those in HFO-1234yf, are less stable than single bonds. A saturated 

HFC, such as HFC-134a, has only single bonds between atoms of carbon, and is thus 

more stable. Although HFO-1234yf may be more unstable than HFC-134a, EPA is not 

aware of any chemical reactions or decomposition pathways that would cause HFO1234yf or its breakdown products to lead to ozone depletion and the commenter has 

provided no technical or scientific support for their claims. For purposes of our 

determination, whether its ODP is zero or nearly zero, we expect HFO-1234yf to have

negligible impact on the ozone layer and we are listing it as acceptable, subject to use 

conditions.

2. Global Warming Potential

Comment: Several commenters agreed with EPA’s statement that HFO-1234yf 

has a global warming potential (GWP) of 4 over a 100-year time horizon. Some 

commenters noted the potential environmental benefits of having a lower GWP 

refrigerant available. Other commenters stated that HFO-1234yf would not be a solution 

to high global warming impacts because of environmental and health impacts of 

breakdown products, including HF, trifluoroacetic acid (TFA), and aldehydes. 

Response: EPA continues to believe that the 100-yr GWP of HFO-1234yf is 4, 

as supported by the commenters. We further agree with the commenters who state that 
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there will be an environmental benefit if car manufacturers switch to HFO-1234yf from 

HFC-134a, a refrigerant with a GWP of 1430 relative to CO2. 

We disagree with the commenters who claim that environmental and health 

impacts of breakdown products is a major cause for concern or will prevent HFO-1234yf 

from being a useful solution to high global warming impacts. One commenter 

mentioned concerns about HF in the atmosphere, but HFO-1234yf does not decompose 

to form significant amounts of HF in the atmosphere. In fact, HFC-134a and HFC-152a 

result in more HF in the atmosphere than HFO-1234yf because those two compounds 

decompose to form both COF2, carbonyl fluoride (and then HF and CO2) and CF3COF, 

trifluoroacetyl fluoride (and then TFA); in contrast, HFO-1234yf favors forming 

trifluoroacetyl fluoride (and then TFA) and does not decompose to carbonyl fluoride or 

to HF (ICF, 2010d). For a discussion on the potential human health impacts of HF, see 

sections V and VII.D.3, “Why is EPA finding HFO-1234yf acceptable subject to use 

conditions?“ and “Toxicity of Hydrogen Fluoride.” 

The fluorinated breakdown product that we have identified of greatest concern is 

TFA, because of its persistence and potential impacts on aquatic plants. As discussed 

above in section V and below in section VII.C.5, “Formation of Trifluoroacetic Acid and 

Ecosystem Impacts,” the projected concentrations of TFA, based on a conservative 

analysis, will be far below the level expected to cause any adverse impacts on aquatic 

life. 

EPA agrees that the breakdown products from the decomposition of HFO-1234yf 

will include aldehydes, but we disagree that this is a cause for concern. As part of the 

analysis of the atmospheric breakdown products of HFO-1234yf, we found that worst-
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case concentrations of formaldehyde would reach 6 to 8 parts per trillion (ppt) on a 

monthly basis or an average of 3 ppt on an annual average basis, compared to a healthbased limit of 8000 ppt,

17 i.e., a level that is roughly 1000 to 2600 times lower than the 

health-based limit (ICF, 2010d). Acetaldehyde levels would be even lower, with worstcase concentrations of 1.2 ppt and annual average concentrations of 0.23 ppt, compared 

to a health-based limit of 5000 ppt18 (ICF, 2010d). As discussed further below in section 

VII.D.1 of the preamble, “Toxicity of HFO-1234yf,” these concentrations are one to 

three orders of magnitude less than ambient concentrations of formaldehyde and 

acetaldehyde without the introduction of HFO-1234yf (ICF, 2010d). Thus, aldehydes 

that would be decomposition products of HFO-1234yf in the atmosphere would not 

contribute significantly to adverse health effects for people on earth’s surface. 

Other fluorinated alternatives that are acceptable in the MVAC end-use, HFC134a and HFC-152a, also create fluorinated breakdown products, and there is not 

evidence to show that those from HFO-1234yf create significantly more risk for human 

health or the environment than breakdown products from other alternatives. Thus, even 

assuming that risks from breakdown products would exist, based on use of HFO-1234yf 

in the MVAC end-use, we do not believe those risks are greater than the risks posed by

other acceptable alternatives. 

 

17 The Agency for Toxic Substances and Disease Registry (ATSDR) has established a chronic inhalation 

minimal risk level (MRL) of 0.008 ppm (8,000 ppt) for formaldehyde (ICF, 2010d). MRLs are available 

online at http://www.atsdr.cdc.gov/mrls/mrls_list.html.

18 EPA has established a Reference Concentration (RfC) of 0.005 ppm (5,000 ppt or 0.009 mg/m3

) for 

acetaldehyde (ICF, 2010d). A summary of EPA’s documentation for its risk assessment and RfC 

derivation for acetaldehyde is available online at http://www.epa.gov/ncea/iris/subst/0290.htm.
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3. 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: We note that EPA has chosen to use GWP as the primary metric for 

climate impact for the SNAP program, while also considering energy efficiency (March 

18, 1994; 59 FR 13044). We have not used specific lifecycle metrics such as Total 

Equivalent Warming Impact (TEWI), Lifecycle Analysis (LCA) or LCCP as metrics for 

climate impact, since it is not clear that there is agreement in all industrial sectors or enduses on which of these measures is most appropriate in which situations or how these 

metrics are to be calculated (SROC, 2005).

The available information on efficiency, LCCP and lifecycle emissions for 

MVAC does not raise concern that the indirect climate impacts from HFO-1234yf will 

cause significantly greater impacts on human health and the environment than other 

available alternatives. Looking at some of the information referenced by the commenters, 

we learned that:

 Bench testing for the Japan Automobile Manufacturers Association (JAMA) 

and the Japan Auto Parts Industry Association (JAPIA) found a system 
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efficiency (coefficient of performance) for HFO-1234yf that is roughly 96% 

of that for HFC-134a (JAMA-JAPIA, 2008)

 LCCP analysis conducted by JAMA found that indirect CO2 equivalent 

emissions from less efficient fuel usage due to use of the MVAC system were 

a few percent higher for HFO-1234yf and roughly 20 to 25% higher for CO2, 

compared to HFC-134a (JAMA, 2008)

 JAMA’s LCCP analysis found that when both direct emissions of refrigerant 

and indirect emissions from less efficient fuel usage are considered, HFC134a has higher total climate impact than either HFO-1234yf or CO2; in hotter 

climates like Phoenix, Arizona, HFC-134a has higher total climate impact 

than HFO-1234yf but slightly lower climate impact than CO2; and in all cases, 

HFO-1234yf had the lowest total climate impact of the three alternatives. 

(JAMA, 2008)

 MVAC systems can be designed to improve efficiency through steps such as 

changing the compressor, sealing the area around the air inlet, changing the 

thermal expansion valve, improving the efficiency of the internal heat 

exchanger, adding an oil separator to the compressor, and changing the design 

of the evaporator. Optimized new MVAC systems using either HFO-1234yf 

or CO2 can reduce fuel usage compared to current MVAC systems using 

HFC-134a. (Benouali et al., 2008; Meyer, 2008; Monforte et al., 2008)

EPA believes that there is good reason to expect that automobile manufacturers 

will choose to design new cars using more efficient MVAC components and systems than 

in the past because of recent regulations. The Department of Transportation has issued 
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new regulations raising the Corporate Average Fuel Economy standards for vehicles and 

EPA has issued new regulations restricting greenhouse gas emissions from light-duty

vehicles (75 FR 25324; May 7, 2010). Thus, in order to ensure that their fleets meet 

these standards, it is highly likely that automobile manufacturers will include MVAC 

systems optimized for efficiency in future models, regardless of the refrigerant used.

Comment: Concerning an appropriate rate of emissions for estimating 

environmental impacts of HFO-1234yf, three commenters recommended that EPA use 50 

g per vehicle per year total lifecycle emission rate. These commenters cited the work of

Wallington et al. (2008) and Papasavva et al. (2009).

19 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: EPA agrees that the permeability data indicate that regular leakage 

emissions of HFO-1234yf, which is released slowly through hoses, is likely to be lower 

than those from HFC-134a. However, this is only a portion of total emissions expected

because emissions may also come through irregular leaks due to damage to the MVAC 

system, refrigerant loss during servicing, and refrigerant loss at the end of vehicle life. In 

response to the commenters who suggested that we use an annual emission rate of 50 

g/vehicle/yr, we reexamined environmental impacts as part of our final environmental 

analysis (ICF, 2010c) using the recommended 50 g/vehicle/yr value and compared this to 

the impacts calculated assuming emissions are similar to those from HFC-134a in MVAC, 

as we did at the time of proposal (closer to 100 g/vehicle/yr). The emission values from 

using 50 g/vehicle/yr (i.e., values from the Pappasavva et al. (2009) study) were 26.3% to 

 

19 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.
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51.1% less than the emission estimates used in our analysis at the time of proposal (ICF, 

2009; ICF, 2010a; ICF, 2010c). In either case, as described more fully in section V

above and in sections VII.C.4 and VII.C.5, below, the overall environmental impacts on 

generation of ground-level ozone and of TFA were sufficiently low and the impacts of 

HFO-1234yf are not significantly greater than those of other available substitutes for 

MVAC. For further information, see the ICF analyses in the docket (ICF, 2010a,b,c,e).

4. Ground-Level Ozone Formation

Comment: Some commenters expressed concern about a potential increase in 

ground-level ozone of >1-4% calculated in EPA’s initial assessment (ICF, 2009) of 

environmental impacts of HFO-1234yf. Other commenters stated that HFO-1234yf will 

not contribute significantly to ground-level ozone. One commenter suggested that EPA 

provide an updated assessment of the potential contribution of HFO-1234yf to groundlevel ozone, considering the additional information provided in public comments (e.g., 

Luecken et al., 2009 and Wallington et al., 200920).

Response: We proposed that HFO-1234yf would be acceptable, even with a 

worst-case increase in ground-level ozone of >1 to 4%. In response to comments, EPA 

performed a new analysis that (1) used revised estimates of the expected emissions of 

HFO-1234yf; and (2) used reactions with ozone formation from hydroxyl radicals rather 

than using sulfur dioxide (SO2) as a surrogate for the hydroxyl radical, OH-, and rather 

than making assumptions about the relative reactivity of compounds. 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 

 

20 Prepublication version of Wallington et al., 2010 (Docket item EPA-HQ-OAR-2008-0664-0084.2)
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case, rather than an increase of 1.4 to 4% as determined in our initial analysis (ICF, 2009). 

This value also agrees with results from Kajihara et al., 2010 and Luecken et al., 2009. 

This revised analysis provides additional support that HFO-1234yf will not create 

significant impacts on ground level ozone formation or on local air quality.

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: Based on the comments received and additional studies, EPA believes 

that the initial assessment that assumed a POCP of 100 to 300 is overly conservative. We 

have revised our initial analysis to incorporate reaction kinetics specific to HFO-1234yf, 

consistent with Luecken et al., 2009, which avoids making an assumption of POCP. 

EPA’s revised analysis estimates worst-case increases in ground-level ozone formation of 

approximately 0.1% (ICF, 2010b). Compared to the uncertainty in the sources of 

emissions, the uncertainty in the measures that localities will take to meet the ozone 

standard, and the uncertainty in the analysis, a projected worst-case increase in ozone of 

0.1% is not significant for purposes of determining that HFO-1234yf poses substantially

greater human health or environmental risk than other alternatives. This provides further 

support for our proposed determination that the conditioned use of HFO-1234yf does not 

present a significantly larger risk to human health and the environment compared to 

HFC-134a, and in many cases likely poses less risk. For further information, see the 

analysis of environmental impacts in section V of the preamble, “Why is EPA finding 
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HFO-1234yf acceptable subject to use conditions?” and see the analysis in the docket 

(ICF, 2010b).

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 VOC. 

Response: (Note: EPA has previously found certain compounds exempt from the 

definition of “volatile organic compound”[VOC] for purposes of air regulations in State 

Implementation Plans, 40 CFR 51.100(s), if they have a MIR equal to or less than that of 

ethane on a mass basis. [69 FR 69298, November 29, 2004; 74 FR 29595, June 23, 2009; 

also see interim EPA guidance at 70 FR 54046, September 13, 2005]) In a separate 

rulemaking process, EPA is considering whether to list HFO-1234yf under 40 CFR 

51.100(s) as exempt from the definition of VOC for purposes of air regulations that 

States may adopt in State Implementation Plans. 

5. Formation of Trifluoroacetic Acid and Ecosystem Impacts

Comment: Several commenters agreed with EPA’s proposed finding that the 

projected maximum concentration of TFA in rainwater from degradation of HFO-1234yf 

does not pose a significant aquatic toxicity risk. Other commenters raised concern about 

the potential impacts of TFA on biodiversity, ecosystems, and human health. One 

commenter questioned the sustainability of HFO-1234yf, so long as there are questions 

remaining about its environmental fate and degradation. One commenter stated that 

artificial input of TFA into the environment should be avoided because of its toxicity and 

chemical properties. Another commenter stated that HFO-1234yf poses additional 
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environmental concerns compared to HFC-134a and advised against finding it acceptable

while the issue of TFA production is being further researched.

Response: We continue to conclude for purposes of our decision here that the 

degradation of HFO-1234yf into TFA does not pose a significant risk of aquatic toxicity

or ecosystem impacts. All available research indicates that, assuming emissions are no 

more than twice the current level of emissions from HFC-134a from MVAC, TFA 

concentrations in surface water and rainwater will be on the order of 1/800th to 1/80th of 

the no observed adverse effect level (NOAEL) for the most sensitive known alga

(Luecken et al., 2009; Kajihara et al., 2010). We have revised our analysis on TFA 

concentrations using the known reaction kinetics of HFO-1234yf. The revised estimate 

of the worst-case TFA concentration in rainwater is approximately 1700 ng/L, similar to 

the concentrations in Luecken et al. (2009) of 1260 ng/L and Kajihara et al. (2010) of 450

ng/L. We believe this provides a sufficient margin of protection to find that the use of 

HFO-1234yf in MVAC will not pose significantly greater risks than other available 

alternatives in this end-use. 

Comment: Some commenters stated that further research on TFA is necessary. 

Response: EPA has considered additional studies submitted during the public 

comment period (Luecken et al., 2009; Kajihara et al., 2010) and has performed further 

analysis on this issue. Luecken et al. (2009) predicted through modeling that in the U.S., 

HFO-1234yf used in MVAC would result in enough TFA to increase its concentration in 

rainwater to 1/80th to 1/800th of the NOAEL for the most sensitive plant species 

considered. Kajihara et al. (2010) predicted through modeling that in Japan, HFO-1234yf 

use in all potential refrigeration uses would increase the TFA concentration in surface 
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water to no more than 1/80th of the NOAEL for the most sensitive plant species 

considered. This study also found that surface water concentrations were roughly twice 

those in rainwater. Thus, even with highly conservative modeling that also considered 

accumulation in surface water, the concentrations of TFA are likely to be at least 80 times 

lower than a level expected to have no impact on the most sensitive aquatic species.

We also performed a further modeling analysis using refined assumptions on 

emissions and the mechanisms by which HFO-1234yf might break down. We found that 

the worst-case concentration of TFA would be approximately 1700 ng/L, similar to the 

concentrations in Luecken et al. (2009) of 1260 ng/L and Kajihara et al. (2010) of 450

ng/L (ICF, 2010b). These additional studies and analyses indicate even less risk than the 

studies available at the time of proposal and thus provide further support that TFA 

emissions from MVAC system will not pose a significant risk of aquatic toxicity or 

ecosystem impacts. 

We also note that EPA has an obligation to act on submissions in a timely manner 

under the Clean Air Act (§612(d)). Given that research to date has not indicated a 

significant risk, we disagree that the Agency should delay a final decision to await further 

studies that may be done in the future. If future studies indicate that HFO-1234yf poses a 

significantly greater environmental risk than we now believe, section 612(d) provides a 

process for an interested party to petition the Agency to change a listing decision.

Comment: Two commenters stated that EPA’s initial modeling (EPA-HQ-OAR2008-0664-0037) 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 
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overly conservative because a large portion of SO2 is in aerosol form, unlike for HFO1234yf. This commenter also referred to the impacts found in the peer-reviewed paper 

by Luecken et al. (2009).

Response: EPA agrees that the use of the oxidation of SO2 to SO3

-

as a proxy for 

the oxidation of HFO-1234yf likely results in overestimating TFA concentrations. This 

is because the sulfate particle is a condensation nuclei in the wet deposition process and it 

has a very high removal efficiency compared to the gas phase process for wet deposition 

that acts with HFO-1234yf and its decomposition products. Further, TFA forms more 

slowly from HFO-1234yf than sulfate forms from SO2 (ICF, 2010b). 

We have repeated the modeling using refined assumptions on emissions and the 

mechanisms by which HFO-1234yf might break down. This revised assessment (ICF, 

2010b) found TFA concentrations roughly one-thousandth those in the earlier assessment 

(1700 ng/L compared to 1,800,000 ng/L in ICF, 2009). This additional research provides 

stronger support for our conclusion that the degradation of HFO-1234yf into TFA does 

not pose a significant risk of aquatic toxicity or ecosystem impacts.

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. 
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Response: The statement from ICF, 2009 in context stated:

NOECs [No-observed effect concentrations] were compared to rainwater 

TFA concentrations because for most water bodies, it is difficult to predict what 

the actual TFA concentration will be. This is because concentrations of 

environmental contaminants in most fresh water bodies fluctuate widely due to 

varying inputs and outputs to most ponds, lakes, and streams. Comparison of 

NOECs to rainwater concentrations of TFA is actually more conservative because 

TFA is expected to be diluted in most freshwater bodies. The exception to this is 

vernal pools and similar seasonal water bodies that have no significant outflow 

capacity. (ICF, 2009)

We note that the “exception” described in the analysis is an exception to the 

expectation that TFA will be diluted more in freshwater bodies that in rainwater. We 

believe that the available evidence confirms that vernal pools do not dilute TFA as much 

as freshwater bodies with outflow capacity. Modeling by Kajihara et al., 2010 found 

surface water concentrations were roughly twice those in rainwater. However, even these 

concentrations were not high enough to be of significant concern for environmental 

impacts. As noted previously, even the highest levels of TFA concentrations were at 

least 80 times less that the NOAEL for the most sensitive aquatic species examined.

D. Health and safety impacts

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 
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present a developmental toxicity or lethality risk. Six 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: EPA continues to believe that HFO-1234yf, when used in new MVAC 

systems in accordance with the use conditions in this final rule, does not result in 

significantly greater risks to human health than the use of other available or potentially

available substitutes, such as HFC-134a or CO2. The results of most of the toxicity tests 

for HFO-1234yf either confirmed no observed adverse health effects, or found health 

effects at similar or higher exposure levels than for HFC-134a. For example, HFC-134a 

caused cardiac sensitization at 75,000 ppm but HFO-1234yf did not cause cardiac 

sensitization even at 120,000 ppm, the highest level in the study (NRC, 1996; WIL 2006). 

NOAELs from subacute exposure were higher for HFO-1234yf than for HFC-134a 

(NOAELs of 51,690 for HFO-1234yf with no effects seen in the study, compared to 

10,000 ppm for HFC-134a with lung lesions and reproductive effects seen at 50,000 ppm 

[NRC, 1996; TNO, 2005]). No adverse effects were seen at 50,000 ppm or any other 

level in subchronic (13-week) studies for both HFO-1234yf and HFC-134a (NRC, 1996; 

TNO, 2007a). 

In mutagenicity testing for HFO-1234yf, the two most sensitive of five strains of 

bacteria showed mutation; however, this screening test for carcinogenic potential is 

known to have only a weak correlation with carcinogenicity (Parodi et al., 198221; 

 

21 Predictive ability of the autoradiographic repair assay in rat liver cells compared with the Ames test ; S. 

Parodi; M. Taningher; C. Balbi; L. Santi Journal of Toxicology and Environmental Health, Vol. 10, Issue 

4 & 5 October 1982, pages 531 – 539.
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Kirkland et al., 200522), so a positive result in this test for the two most sensitive strains is 

not sufficient reason to consider HFO-1234yf to be a significant health risk. 

Mutagenicity testing for HFC-134a by the same test found no evidence of mutagenicity. 

Screening for carcinogenic potential in a genomics study did not identify HFO-1234yf as 

a likely carcinogen (Hamner Institutes, 2007). A two-year cancer assay for HFC-134a 

did not find evidence of carcinogenicity (NRC, 1996). 

EPA considers the results of developmental testing to date to be of some concern, 

but not a sufficient basis to find HFO-1234yf unacceptable for purposes of this action 

under the SNAP program. In a developmental study on rats, cases of wavy ribs were 

seen in some developing fetuses during exposure to HFO-1234yf (TNO 2007b); however, 

effects on bone formation were also seen for HFC-134a (NRC, 1996). It is not clear if 

this effect is reversible or not. Interim results from a two-generation reproductive study

did not find an association between exposure to HFO-1234yf and skeletal effects. This 

two-generation reproductive study for HFO-1234yf finds a NOAEL of 5000 ppm for 

delayed mean time to vaginal opening in F1 females (females in the first generation of 

offspring). A subacute (28-day) test for HFC-134a (single generation) found a NOAEL 

of 10,000 ppm for male reproductive effects (NRC, 1996). A developmental test on 

rabbits exposed to HFO-1234yf did not find effects on the developing fetus. However, 

some of the mother rabbits in this study died. The reason for the deaths is not known. 

The data on developmental effects are inconsistent depending on the test performed and 

the species tested. The development effects observed in the developmental study on rats 

are not significantly different from the developmental effects observed for HFC-134a. In 

 

22 Kirkland et al. (2005) Evaluation of a battery of three in vitro genotoxicity tests to determine rodent 

carcinogens and non-carcinogens. I. Sensitivity, specificity and relative predictivity, Mutation Research, 

584, 1-256.
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any case, as discussed above in section V and below in this section, our risk assessments 

found that HFO-1234yf would likely be used with exposure levels well below those of 

concern in the uses allowed under this rule. Thus, we do not find the observed 

developmental effects sufficient reason for finding HFO-1234yf unacceptable in this rule.

For purposes of this action, we prepared our risk assessment for long-term 

exposure using the level at which no deaths or other adverse health effects were seen in 

the rabbit developmental study—a “no observed adverse effect level” or NOAEL—to 

ensure that exposed people would be protected. The longer-term, repeated exposure in 

that study would be the exposure pattern (though not necessarily the exposure level) for a 

worker using HFO-1234yf on a regular basis or for a consumer exposed in a car due to a 

long, slow leak into the passenger compartment. Using the NOAEL concentration of 

4000 ppm as a starting point, we found no situations where we expect exposure to exceed 

the level that EPA considers safe for long-term or repeated exposure (EPA-HQ-OAR2008-0664-0036). Thus, we consider the potential toxicity risks of HFO-1234yf for those 

uses allowed under this action to be addressed sufficiently to list it as acceptable subject 

to use conditions.

Comment: Based on a risk assessment conducted by one commenter, the 

commenter concluded that if HFO-1234yf is used under the conditions specified in the 

commenter’s risk assessment, adverse health impacts would not be expected to car 

occupants, to servicing personnel, or to do-it-yourself (DIY) consumers. 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 hazard 
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index for HFO-1234yf was only one-half of the values predicted for HFC-134a, and in 

some cases, only one-third of the HFC-134a values, demonstrating from a health 

perspective that HFO-1234yf is a viable alternative to HFC-134a. 

Response: EPA agrees that adverse health impacts would not be expected to car 

occupants or to servicing personnel, so long as the use conditions of this rule are 

observed. However, EPA has issued a Significant New Use Rule under TSCA (October 

27, 2010; 75 FR 65987) that would require submission of additional information to EPA 

prior to the manufacture, import or processing of HFO-1234yf for certain uses, including 

distribution in commerce of products intended for use by a consumer for the purposes of 

servicing, maintenance and disposal involving HFO-1234yf (e.g., “do-it-yourself”

servicing of MVAC systems). 

Where available, it is EPA policy to use a NOAEL (No-Observed-Adverse-Effect 

Level) for the point of departure (POD) for risk assessment. This is the highest exposure 

level that did not cause an adverse health effect in a study. In this case, EPA selected the

POD from an animal (rat 2-week inhalation) study. Because animals may respond to 

different exposure levels than humans, there is some uncertainty when extrapolating from 

animals to humans. For this reason, an Uncertainty Factor (UF) is applied when 

extrapolating from animals to humans – typically a factor of 10 is used but, in this case, 

since there was a reasonable estimate of the pharmacokinetic component of the 

uncertainty, this UF was reduced to 3. An additional UF is applied to account for 

variation in the human population response to a chemical exposure – in this case, a UF of 

10 was used. The two UFs give a resultant UF of 30 to yield an acceptable level of health 

risk. As stated in the final SNUR, EPA’s policy for review of new chemicals under 
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TSCA is to divide the POD by the exposure level to obtain the MOE. For HFO-1234yf,

the “acceptable level of health risk” would be an MOE of 30 or greater

The commenter proposed dividing the estimated exposure to HFO-1234yf by the 

POD levels to obtain a HI. As a result, if the exposure is less than the POD, the HI is <1 

and the commenter considered this an “acceptable level of health risk.” The commenter’s 

approach to the hazard index does not factor in uncertainties about extrapolating from 

animal to human responses, nor does it address variability within the human population 

with regard to thresholds of response to chemical exposures. EPA has consistently

applied the margin of exposure (MOE) approach to evaluations of pre-manufacture 

notices (and for certain other risk assessments) in order to account for the uncertainties 

discussed above. The SNAP program considered work performed during evaluation of 

the pre-manufacture notice (EPA-HQ-OAR-2008-0664-0036), as well as a separate 

SNAP program risk screen (EPA-HQ-OAR-2008-0664-0038). SNAP program risk 

screens compare expected exposures to exposure limits that incorporate uncertainty 

factors based on EPA guidance, rather than calculating either a hazard index or a margin 

of exposure. Any of these approaches to risk assessment will come to a similar 

conclusion about whether there is a potential health concern when using the same point of 

departure, uncertainty factors, and exposure estimates. 

The Agency and the commenter disagree on all three of these inputs to the risk 

assessment and hence have reached different conclusions. Despite these differences, the 

assessments relied on by both the commenter and EPA show that there is low risk both to

car occupants and to service technicians. EPA’s risk assessment indicates a potential risk 
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to DIYers (EPA-HQ-OAR-2008-0664-0036). As stated previously in this action, this 

issue is further addressed through the Agency’s authority under TSCA. 

Comment: In response to EPA’s risk assessment (EPA-HQ-OAR-2008-0664-

0036), two commenters disagreed with the use of a 2-week study for evaluating 30 

minute exposures and stated that acute toxicity (4-hour test) or cardiac sensitization test 

results would be more appropriate for acute exposure evaluations. 

Response: Commenters have suggested that EPA use data from the 4-hour acute 

toxicity study or from the cardiac sensitization study as a starting point (“point of 

departure”) for assessing risks of short-term (acute) exposure. However, cardiac 

sensitization studies are for very short durations – on the order of 10 minutes – and they

only address cardiac sensitization. HFO-1234yf does not induce cardiac sensitization. 

EPA selected the point of departure for acute effects from a multiple-exposure 2-week 

(subacute) rat inhalation study on HFO-1234yf, reasoning that if no effects were seen in 

the duration of the study (6 hours per day, 5 days per week for 2 weeks), that no effects 

would be seen from a single exposure at a similar exposure level, either. Further, the 

subacute exposure rat study included more thorough pathology examinations than those 

included in a cardiac sensitization study.

The acute 4-hour exposure study in rats showed some lung effects at 

approximately 200,000 ppm, the lowest exposure level in the study. Thus EPA considers 

200,000 ppm to be a LOAEL (Low-Observed-Adverse-Effect Level). If a LOAEL were 

used in the risk assessment instead of a NOAEL, EPA would use an uncertainty factor to 

estimate a NOAEL, which would result in a lower POD than what was used. For 

example, if EPA had started with the LOAEL of 200,000 ppm, it would have required an 
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additional MOE of 10 to estimate a NOAEL from a LOAEL, for a total MOE of 300 

instead of 30. This would have resulted in a more conservative risk assessment than 

using the NOAEL from the 14-day subacute study. In the 4-hour acute toxicity study, 

some of the animals had grey, discolored lungs at all exposure levels in the study, and we 

considered this an adverse effect. Thus, EPA could only determine a lowest observed

adverse effect level (LOAEL) from the 4-hour acute study and could not determine a no 

observed adverse effect level (NOAEL). It is longstanding Agency policy to use the 

NOAEL where available instead of a LOAEL, because of greater assurance of a safe 

exposure level. EPA instead used the NOAEL for the next shortest study, the subacute 

14-day study, as the endpoint of concern for short term exposure because the LOAEL 

from the acute 4-hour study is an endpoint showing effects that may not result in safe 

exposure levels for humans. If we had used the value from the 4-hour acute toxicity

study, we would have had to consider additional uncertainty that would have resulted in a 

more conservative, more restrictive risk assessment than using the NOAEL from the 14-

day subacute study.

Further, EPA has uncertainties about using the available single exposure studies

on HFO-1234yf to determine the MOEs for different exposure scenarios. As a result of 

concerns with these studies, EPA calculated single exposure MOEs from the NOAEL in 

the 2-week inhalation toxicity study of HFO-1234yf in rats. There are some uncertainties 

in the single exposure (acute) assessments because of the observation of lethality in rabbit 

dams after multiple exposures to HFO-1234yf in a developmental study. For these

reasons, EPA recommended an acute inhalation toxicity study on rabbits in the proposed 
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SNUR to address the question of whether pregnant rabbits would die from a single 

exposure (April 2, 2010; 75 FR 16706). 

Comment: A commenter asserted that EPA’s methodology to estimate the 

exposure levels associated with the DIY use, using the SAE CRP (2008) Phase II Report, 

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 timeweighted average (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.
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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: 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 industrymodeled 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. These assumptions are 

conservative and protective, as intended. 

We considered the calculations provided by one commenter that assumed that the 

refrigerant fills a garage. However, this analysis assumes a longer-term, steady-state 

concentration after the refrigerant has diffused throughout the garage and uses a longterm, 8-hour time-weighted average exposure recommendation for comparison. EPA’s 

concerns about DIY consumer exposure focuses on short-term acute exposures, including 

peak exposures over a few minutes near the consumer’s mouth and nose because 

typically a DIY consumer will only need a short period of time to recharge a single 

MVAC system (Clodic, 2008). Thus, the commenter’s calculations do not address EPA’s 

concerns.

After reviewing the consumer DIY use exposure study from the SNAP/PMN 

submitter, EPA responded with a list of clarifying questions (US EPA, 2010c), to which 
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the submitter subsequently responded (Honeywell, 2010b). Although the submitter’s 

responses were helpful, EPA still has concerns about potential exposures to consumers 

during DIY use and the inherent toxicity of HFO-1234yf. However, since this 

acceptability determination is limited to use with fittings for large containers, which 

DIYers would not purchase, our concerns about potential health risk to DIY users need 

not be addressed in this action. We would plan to evaluate this issue further before 

taking a final action on a SNAP submission for unique fittings for small containers. We 

further note that the Agency would analyze this issue in the context of any SNUN filed 

pursuant to the recently issued SNUR (75 FR 65987). Although we do not reach any

conclusion in this final rule regarding safe use by DIYers, we make the following 

observations about the submitted study. With regards to exposure, the peak concentration 

values from the submitted study are as high as 3% by volume, equivalent to 30,000 ppm. 

These peaks appeared to occur in the first one or two minutes of each emission. 

Accordingly, EPA would need exposure data presented and averaged out over shorter 

Time Weighted Averages (TWAs) than the 30 minutes currently in the study, because it 

would appear that a number of these early exposure peaks could result in TWA values 

that would result in MOEs less than the acceptable Agency level of 30 described above in 

this section. This is important because the data on HFO-1234yf are insufficient to 

differentiate whether the toxicity is due to blood level alone from an acute exposure, is 

due to accumulated exposure over time (“area under the curve”), or is due to some 

combination of both. Since blood equilibrium levels are reached within minutes, a high 

level of exposure in a short duration could result in blood levels exceeding a threshold if 

the mode of action of the toxicity of HFO-1234yf is due to blood levels of the chemical. 
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EPA expects that exposure data with additional TWAs of 3, 5, and 10 minutes would 

help to resolve these issues of consumer exposure.

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 formed as breakdown products would be higher than 

that of carbonic acids. 

Response: EPA agrees that the breakdown products from the decomposition of 

HFO-1234yf will include aldehydes, but we disagree that this is a cause for concern. The 

aldehydes that would be produced as atmospheric breakdown products of HFO-1234yf 

are formaldehyde and acetaldehyde (ICF, 2010d). Their health effects include respiratory

effects; irritation of the eyes, nose, and throat; and corrosion of the gastrointestinal tract. 

EPA also considers formaldehyde and acetaldehyde to be probable human carcinogens 

(US EPA, 2000; ICF, 2010d). The decomposition products of HFO-1234yf are not noted 

for causing neurotoxic effects, and toxicity tests for HFO-1234yf did not identify this as 

an effect. 

As part of analysis of the atmospheric breakdown products of HFO-1234yf, we 

found that worst-case concentrations of formaldehyde would reach 6 to 8 parts per trillion 

(ppt) on a monthly basis or an average of 3 ppt on an annual average basis, compared to a 

health-based limit of 8000 ppt23—i.e., a level that is roughly 1000 to 2600 times lower 

than the health-based limit (ICF, 2010d). Acetaldehyde levels would be even lower, with 

worst-case concentrations of 1.2 ppt and annual average concentrations of 0.23 ppt, 

 

23 The Agency for Toxic Substances and Disease Registry (ATSDR) has established a chronic inhalation 

minimal risk level (MRL) of 0.008 ppm (8,000 ppt) for formaldehyde (ICF, 2010d). MRLs are available at 

http://www.atsdr.cdc.gov/mrls/mrls_list.html.
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compared to a health-based limit of 5000 ppt24 (ICF, 2010d). Thus, aldehydes that would 

be decomposition products of HFO-1234yf in the atmosphere would not contribute 

significantly to adverse human health effects (ICF, 2010d). 

Aldehydes, including formaldehyde and acetaldehyde, are already present in the 

atmosphere in significant amounts from natural sources such as plants, from direct 

emissions, from combustion products, or from breakdown of other compounds such as 

hydrocarbons (NRC, 1981; Rhasa and Zellner, 1987). The current background level of 

formaldehyde in the atmosphere ranges from 80 ppt in pristine areas to approximately

3300 ppt in New York, NY—one to three orders of magnitude more than the worst-case 

generation of formaldehyde from HFO-1234yf (ICF, 2010d). The maximum incremental 

acetaldehyde concentration calculated due to use of HFO-1234yf was approximately

three orders of magnitude less than the average concentration of acetaldehyde in areas 

with pristine air quality (ICF, 2010d). Thus, the additional aldehydes created during 

decomposition of HFO-1234yf in the atmosphere are not likely to have a significant 

impact on human health.

Comment: Some commenters stated that additional research and review of the 

available information regarding toxicity of HFO-1234yf needs to be conducted.

Response: EPA has an obligation to act on submissions in a timely manner under 

the Act (§612(d)). Our risk assessments to date have found no significant risk for car 

passengers or drivers, professional servicing personnel, or workers disposing of or 

recycling vehicles containing HFO-1234yf. We believe these assessments are sufficient 

 

24 EPA has established a Reference Concentration (RfC) of 0.005 ppm (5,000 ppt or 0.009 mg/m3

) for 

acetaldehyde (ICF, 2010d). A summary of EPA’s documentation for its risk assessment and RfC 

derivation for acetaldehyde is available online at http://www.epa.gov/ncea/iris/subst/0290.htm.
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to support this action. We note that these assessments rely on somewhat conservative 

assumptions. 

We note that we expect there will be no toxicity risks to DIYers because EPA 

must receive and take regulatory action to allow unique fittings for use with small cans of 

refrigerant before DIYers could be exposed, as per appendix D to subpart G of 40 CFR 

part 82. Further, because HFO-1234yf is not expected to be introduced into any new cars

until late 2011 or later, we expect to have further information and to take further action 

before DIYer could be exposed. In addition, the final SNUR would not allow distribution 

in commerce of products intended for use by a consumer for the purposes of servicing, 

maintenance and disposal involving HFO-1234yf until at least 90 days after submission 

of a SNUN.

We recognize that more studies will be performed on HFO-1234yf, further 

addressing risk. EPA’s New Chemicals Program has recommended additional testing of 

acute exposure in rabbits, including pregnant rabbits (April 2, 2010; 75 FR 16706). In 

addition, the manufacturer is voluntarily conducting a multi-generation reproductive 

study. If these or other future studies call into question the basis for our decision today, 

section 612 allows citizens to petition EPA to change or modify a listing decision or EPA 

could determine on its own to reassess this decision. 

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 
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that information on new price levels and availability is needed to assess the effectiveness 

of the SNUR. 

Response: EPA’s final SNUR addresses potential risks to human health from 

exposure to HFO-1234yf. However, as discussed above in section V of the preamble, 

“Why is EPA listing HFO-1234yf as acceptable subject to use conditions?”, this final 

SNAP rule does not allow for the use of HFO-1234yf with small cans or containers (i.e., 

container sizes that would be purchased by DIY users, such as small cans and containers 

less than 5 lbs) because it does not contain specifications for unique fittings for can taps 

and for these smaller containers. Existing SNAP program regulations in appendix D to 

subpart G of 40 CFR part 82 require the use of unique fittings for specific purposes (e.g., 

high pressure-side service port, small can taps) for each MVAC refrigerant, as submitted 

by the refrigerant manufacturer. Before HFO-1234yf can be introduced in small 

containers typically used by DIYers, the manufacturer must submit unique fittings to 

EPA, we must conclude that they are unique, and we must issue new proposed and final 

rules specifying those fittings. In addition, the final SNUR would not allow distribution 

in commerce of products intended for use by a consumer for the purposes of servicing, 

maintenance and disposal involving HFO-1234yf until at least 90 days after submission 

of a SNUN. These and other requirements ensure – to the extent possible, with the 

information currently available to EPA – that HFO-1234yf has no greater risk overall for 

human health and the environment than other available refrigerants for MVAC.

Under the final SNUR, it is necessary for EPA to receive and complete its review 

of a significant new use notice (SNUN) with additional information on consumer 

exposure risks before – if the Agency so decides – HFO-1234yf may be manufactured, 
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imported or processed for the purpose of use in DIY servicing, with or without other 

restrictions. We would also consider information in the SNUN before issuing a final rule 

specifying unique fittings for use with small containers of refrigerant.

In comments EPA received on the proposed SNAP rule, the initial direct final 

SNUR that was withdrawn and the proposed SNUR, no commenters suggested making 

the provisions of the SNUR stricter or suggested adding use conditions under the SNAP 

program for addressing risks to consumers during DIY servicing. A number of 

commenters stated that no restrictions were needed to address risks to consumers during 

DIY servicing, while other commenters stated more broadly that EPA should find HFO1234yf unacceptable because of its toxicity risks. We provided an additional opportunity

for comment on the SNAP rule after the direct final SNUR was issued (February 1, 2010; 

75 FR 4083), in response to a request to reopen the public comment period (EPA-HQOAR-2008-0664-0077.1), in part to allow comment on the relationship between these 

two rulemakings that both address HFO-1234yf. However, we do not believe that the 

conditions of the final SNUR are necessary to the determination that we are making here. 

As noted above, this final rule does not allow for the servicing of HFO-1234yf from

container sizes that would be purchased by DIY users because of the lack of an approved 

unique fitting for smaller containers. Further rulemaking under SNAP will occur prior to 

such use and any risks can be addressed in that rulemaking package. At that time, we 

will be able to fully consider the impact of the final SNUR.

2. Flammability

Comment: Five commenters stated that HFO-1234yf has a low likelihood of

ignition, especially under the conditions encountered in an automotive application. One 
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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: The available evidence indicates that HFO-1234yf will not present a 

significant risk of flammability and that any risk it poses is not greater than the risk 

presented by other available alternatives. For example, because of its higher LFL, its 

considerably higher minimum ignition energy (5000 mJ to 10,000 mJ), and its slower 

flame speed (1.5 cm/s), HFO-1234yf is less flammable than HFC-152a, a substitute that 

EPA has already found acceptable subject to use conditions. 

Further, an analysis conducted for SAE International’s Cooperative Research 

Program by Gradient Corporation (CRP, 2009) found that there was a very low 

flammability risk (on order of 10-14 occurrences per operating hour or 1 occurrence in 100 

years across the entire U.S. fleet of passenger vehicles). This was due to the low 

probability of achieving a concentration of HFO-1234yf above the LFL at the same time 

as having a sufficiently high energy source to cause the refrigerant to ignite. Further, 

even that low probability of ignition of HFO-1234yf may be overstated, because it 

assumes that a vehicle collision severe enough to crack open the evaporator (located 

under the windshield and steering wheel) is not severe enough to crack the windshield or 

windows that would hold refrigerant in the passenger compartment. In a sensitivity
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analysis, the SAE CRP considered how the flammability risk would change if a 

refrigerant release into the passenger compartment only occurs in a collision causing 

damage to more than the MVAC system. That analysis estimated that the risk of 

exposure to an open flame would then be reduced by a factor of 23,000, to approximately

4 x 10-19 occurrences per vehicle operating hour (EPA-HQ-OAR-2008-0664-0056.2).

For the reasons provided above in sections IV and VII.B of the preamble, “What 

are the final use conditions and why did EPA finalize these use conditions?” and “Use 

conditions,” EPA does not believe it is necessary to establish a use condition limiting

refrigerant concentrations, whether at 6.2% or some other, lower value. We believe the 

final use conditions sufficiently address flammability risks.

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 its sale and use by the general public.

Response: The purpose of the use conditions is to ensure that HFO-1234yf will 

not pose a greater risk to human health or the environment than other available or 

potentially available substitutes. For all of the reasons provided in sections IV and V

above, EPA has determined that HFO-1234yf will not pose a greater risk than other 

substitutes for MVAC. As explained above, EPA proposed restricting concentrations of 

the refrigerant below the LFL of 6.2% as a use condition. Based on comments and 

additional analysis, EPA has concluded that it is not necessary to require use conditions 

limiting refrigerant concentrations to below the LFL; rather, the use conditions now 

specify design parameters for MVAC systems and require an FMEA. This will ensure 
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that systems are designed to minimize risk not only from flammability, but also from 

exposure to HF. 

We will address use by service personnel through a rulemaking under section 609 

of the CAA. Although these rules will further address issues of interest to service 

personnel and others that might handle HFO-1234yf used in MVAC systems, we note 

that our risk assessments of use of HFO-1234yf found that significant flammability risks 

do not exist for personnel installing the refrigerant at equipment manufacture, 

professional servicing personnel, and personnel working with automobiles at equipment 

end-of-life (EPA-HQ-OAR-2008-0664-0036 and -0038). Moreover, we note that an 

industry-sponsored analysis of risks found the risk of ignition of HFO-1234yf to a 

technician is extremely small, on the order of 10-26occurrences per working hour (EPAHQ-OAR-2008-0664-0056.2).

As we have explained above, this rule only addresses the use of large containers 

for professional use (typically 20 lbs or larger) and thus HFO-1234yf may not be used in 

small container sizes that would be the type purchased by the general public. We will 

address the issue of risk to DIY users through a future rulemaking under SNAP if we 

receive a request for unique fittings for smaller containers from the refrigerant 

manufacturer. We also are addressing risks to DIY users through the Significant New 

Use Rule under the Toxic Substances Control Act (October 27, 2010; 75 FR 65987). 

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 fuer Materialforschung und –pruefung, 

BAM). Other commenters disagreed with those flammability conclusions, finding the 
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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: As explained above in section VII.B, we do not believe that these tests 

are relevant for assessing the flammability risks of HFO-1234yf as used in MVAC 

systems because they evaluated flammability based on the presence of ethane, a 

substance that should not be present in any situation that might cause flammability risks 

for MVAC systems.

3. Toxicity of Hydrogen Fluoride (HF)

Comment: Two commenters stated that there is low risk of exposure to HF. One 

of these commenters stated that (1) for vehicles that do not discontinue the use of the 

blower after collision, the risk of exposure to HF from use of HFO-1234yf is 

approximately twice the risk with the current use of HFC-134a, and (2) for vehicles that 

discontinue the use of the blower after collision, the risk of implementing HFO-1234yf 

due to exposure to HF is approximately the same as that with the current use of HFC134a (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.
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Other commenters stated that that there is a high probability of HF generation in 

cars from HFO-1234yf. One commenter stated that the flammability of HFO-1234yf 

makes the production of HF more likely and increases the risk of HF exposure to vehicle 

passengers, to 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 that use of HFO-1234yf is unacceptable as 

there is increased potential for HF exposure and related casualties.

Response: EPA has considered the potential for generation of HF from HFO1234yf, including the SAE CRP’s evaluation of scenarios that might cause workplace and 

consumer exposure to HF (EPA-HQ-OAR-2008-0664-0056.2). SAE CRP members 

conducted tests to measure HF concentrations and to identify factors that were most 

likely to lead to HF formation. One set of tests conducted in a car found that HF 

measurements inside the passenger cabin were 35 ppm or less (EPA-HQ-OAR-2008-

0664-0056.2). This highest value occurred during release of the entire charge of 

refrigerant of 1000 g into the passenger cabin with ignition started by a butane lighter 

augmented with an additional spark—a highly conservative scenario. (A more typical 

charge would be 575 g, and it would be unlikely to have the amount of ignition energy

that occurred artificially in the experiment with use of both a butane lighter and an 

additional spark source.) A second set of tests focusing on HF in the engine compartment

tried to simulate a major rupture in the AC system that would release 12 g/s of refrigerant 

across 5 cm onto an artificial hot surface at temperatures of 450 oC (typical of the exhaust 

manifold) and 700 oC (most extreme case), with the car hood in various positions. This 
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testing found HF concentrations as high as 120 ppm at the hot surface in the engine 

compartment in the worst case, with interior passenger cabin values of 40 to 80 ppm in 

the worst case (EPA-HQ-OAR-2008-0664-0056.2). This test was conservative for the 

following reasons: the temperature was high, representing extreme conditions; the 

refrigerant was released extremely close to the hot surface; the hood was closed; and the 

refrigerant ignited briefly. The other test trials under less extreme conditions resulted in 

HF concentrations of a few ppm. The test trials also found somewhat lower 

concentrations of HF generated during testing of HFC-134a using the same procedures 

and apparatus, with maximum concentration of 36 ppm in the engine compartment and 

concentrations of less than 8 ppm in the passenger compartment in the worst case. The 

SAE CRP selected an Acute Exposure Guideline Limit (AEGL)-2

25 of 95 ppm over 10 

minutes as its criterion for determining excessive risk. This limit was developed to 

protect against irreversible health effects when exposure remains below the limit of 95 

ppm over 10 minutes, but short-term discomfort or irritation could still occur. Thus, even 

assuming a passenger inside a vehicle was exposed to HF at the highest level found in the 

test of 80 ppm, exposure at this level would at worst cause discomfort and irritation, 

rather than permanent or disabling health effects. 

For both HFO-1234yf and for HFC-134a, HF concentrations in the passenger 

compartment fell between the level that would protect against all adverse health effects 

(AEGL-1 of 1.0 ppm for 10 minutes to 8 hours) and the level that would protect against 

irreversible or disabling health effects (AEGL-2 of 95 ppm over 10 minutes) (NRC, 

 

25 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. Irreversible or disabling but non-fatal health effects could occur between the AEGL-2 and the 

higher AEGL-3.
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2004). The SAE CRP concluded that the probability of such a worst case event is on the 

order of 10-12 occurrences per operating hour (EPA-HQ-OAR-2008-0664-0056.2). 

Commenters provided information indicating that this level of risk for HF generation is 

the same order of magnitude for both HFC-134a and for HFO-1234yf. EPA considers 

the risk level presented by HFO-1234yf to be similar to that of the refrigerant currently 

being used by automobile manufacturers, HFC-134a. Therefore, there is no reason to 

regulate HFO-1234yf more stringently to protect against HF exposure than for HFC-134a.

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: The commenter has not provided sufficient information on the testing 

commissioned by Greenpeace in 2001 for the Agency to determine what the results were 

or whether the testing conditions are relevant to this action. Concerning the BAM testing, 

EPA has not seen a testing report or a detailed description of the experimental method 

that allows for a full evaluation. Based on the information provided by the commenter, 

the temperature of the released substance reached 600 0C and HF concentrations of over 

90 ppm were measured in the engine compartment. According to a risk assessment from 

an automobile manufacturer, such a high temperature is unlikely and could only be 
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achieved on the exhaust manifold under heavy engine loads such as when a vehicle is 

climbing a hill, and the temperature of the exhaust manifold would drop in a minute or so 

during deceleration (EPA-HQ-OAR-2008-0664-0081.1). It is not clear what the 

conditions were for the study mentioned by the commenter. For example, it is not clear if 

the refrigerant was mixed with compressor oil as it normally would be in an MVAC; 

inclusion of oil with a relatively low flashpoint would be expected to lead to ignition at 

lower temperatures (EPA-HQ-OAR-2008-0664-0056.2, EPA-HQ-OAR-2008-0664-

0118.1). It also is not clear if the compressor fan was operating during the test. During 

normal vehicle operation, the fan would cool down the compressor and the engine 

compartment, avoiding the temperature of 600 °C on hot surfaces in the engine. 

Other tests have found that HF concentrations in the engine compartment were

approximately 5 ppm or less and only in the worst case (hot surface temperature of 700 °

C, closed hood on engine compartment) did HF concentrations attain a value of 

approximately 120 ppm in the engine compartment (OAR-2008-0664-0056.2). This level 

is slightly higher than the AEGL-2 of 95 ppm on a 10-minute average and is lower than 

the AEGL-3 for HF of 170 ppm on a 10-minute average, the value that would protect 

against life-threatening exposure but would not necessarily prevent long-term health 

effects. However, we note that we do not anticipate any circumstance where a person 

would be exposed to these levels in an engine compartment because such conditions 

would not occur during vehicle servicing, but rather during vehicle operation. Further, in 

the case of a collision resulting in a fire, we would expect that professional first 

responders have training in chemical hazards and possess appropriate gear which would

prevent them from receiving HF exposures above health-based limits (EPA-HQ-OAR-
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2008-0664-0056.2) and an interested by-stander would quickly back away from a fire or 

from irritating HF vapors, thus preventing excessive HF exposure. The concentration

measured in the passenger compartment in the same worst-case situation was in the range 

of 40 to 80 ppm, less than the concentration in the engine compartment and less than the 

AEGL-2 intended to protect against long-term health effects. Thus, we disagree with the 

commenter’s assertion that HF exposures from thermal decomposition or combustion of 

refrigerant would be likely to results in fatalities. We further note that the HF 

concentrations found in the passenger compartment were lower than the health-based 

limit, the AEGL-2 of 95 ppm over 10 minutes.

We also note that the risks presented by HFO-1234yf are not significantly

different than the risk posed by HFC-134a, the refrigerant currently in use in MVAC 

systems. Mixtures of HFC-134a and compressor oil also combust and generate HF. 

Testing performed using HFC-134a under worst-case conditions in the engine 

compartment (hot surface temperature of 700 oC, closed hood on engine compartment) 

found HF concentrations as high as 36 ppm in the engine compartment and 2 to 8 ppm in 

the passenger compartment. The amount of HF generated from a typical charge of HFC134a, if it all burned or decomposed, could be even more than for the expected charge of 

HFO-1234yf because charge sizes using HFO-1234yf are expected to be smaller (EPAHQ-OAR-2008-0664-0056.2). The SAE CRP considered potential risks of HF exposure 

from both HFO-1234yf and from HFC-134a. Both presented potential risks on the order 

of 10-12 occurrences per operating hour (EPA-HQ-OAR-2008-0664-0056.2, -0096.1). 

This corresponds to less than one case per year across the entire fleet of motor vehicles in 

the U.S. Although there is no specific testing data on HF production from HFC-152a, 
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another acceptable refrigerant for MVAC, since this compound contains fluorine, it 

presents risks of HF generation as well. As discussed above in Section IV of the 

preamble, we are not requiring specific use conditions that regulate production of HF, 

either directly or indirectly, because of the low level of risk. However, the final use 

conditions in this rule address the risks of HF production, as well as risks of flammability, 

by requiring certain design safety features of MVAC systems using HFO-1234yf and by

requiring risk analysis for each car model through FMEAs.

Comment: A commenter provided results from a test by IBExU on the 

decomposition of HFO-1234yf under heat (EPA-HQ-OAR-2008-0664-0053.3). This 

commenter strongly warned against a decision in favor of HFO-1234yf because it would 

form highly toxic HF when burning. Three commenters disagreed that the results of the 

IBExU testing were relevant because test conditions did not represent realistic conditions. 

One commenter said that the SAE risk assessment, which used actual vehicle test data for 

HF formation, found that actual HF formation rates are far below the levels [from the 

IBExU test results] cited by the first commenter, the Federal Environmental Agency

(Umweltbundesamt—UBA).

Response: The IBExU testing of HF generation from HFO-1234yf is not relevant 

to assessing the risks of HFO-1234yf as a refrigerant in MVAC. Laboratory tests 

concerning the nature of HF generation on hot surfaces found that this depends on the 

contact time of reactants on the hot surface, the temperature of the hot surface and the 

movement of refrigerant in diluted concentrations due to airflow (EPA-HQ-OAR-2008-

0664-0056.2; EPA-HQ-OAR-2008-0664-0116.2). The IBExU testing involved heating 

the refrigerant steadily in a sealed flask. Thus, the contact time in that test was far greater 
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than would occur in an engine compartment and the movement of refrigerant in that test 

was essentially zero, unlike in an engine compartment where there would be constant air 

movement. 

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 HFC134a did not. The study also found that when HFO-1234yf was mixed with 3% oil, it 

exploded at 600 °C. The commenter stated that handling of HFO-1234yf in the presence 

of hot metal surfaces results in HF formation in concentrations far above allowed 

workplace concentrations.

Response: These results are not consistent with results from hot-plate tests 

conducted by an automobile manufacturer and by a chemical manufacturer for the SAE 

CRP (EPA-HQ-OAR-2008-0664-0056.2; EPA-HQ-OAR-2008-0664-0115.1). Those 

manufacturers found that neither HFO-1234yf nor HFC-134a alone ignited at 900 °C. 

One of these tests found that HFO-1234yf mixed with PAG oil combusted starting at 

730 °C, while HFC-134a mixed with PAG oil ignited at 800°C and above; the other test 

observed no ignition of a blend of each refrigerant with PAG oil at 800 °C, but both 

blends ignited at 900 °C. Based on the lack of reproducibility of the specific ignition 

temperature, it appears that the specific ignition temperature may depend on variables in 

the testing (e.g., flash point of the oil used, amount of mixture used, angle of application, 

and air flow available). This information also shows that mixtures of refrigerant with 

compressor oil can combust at lower temperatures than pure refrigerant and that mixtures 
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of HFO-1234yf and oil and mixtures of HFC-134a and oil present similar risks of ignition 

and HF generation. Thus, we concluded that the risks of toxicity from HF exposure due 

to combustion or decomposition of HFO-1234yf are comparable to those from HFC-134a. 

Further, the risks from toxicity of HF posed by both refrigerants are small. The 

SAE CRP estimates this risk on the order of 10-12 cases per operating hour (EPA-HQOAR-2008-0664-0086.1). This is equivalent to less than one event per year across the 

entire fleet of motor vehicles in the U.S. For comparison, this is less than one tenthousandth the risk of a highway vehicle fire and one fortieth or less of the risk of a 

fatality from deployment of an airbag during a vehicle collision (EPA-HQ-OAR-2008-

0664-0056.2). 

E. Retrofit usage

Comment: Several commenters stated that HFO-1234yf should be used 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. 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 HFO1234yf 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. 
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Response: The submitter did not request review of HFO-1234yf for retrofitting 

vehicles and thus EPA did not review HFO-1234yf as acceptable (or acceptable subject 

to use conditions) for retrofitting in MVAC in this rulemaking. Consistent with the 

request submitted to the Agency, we proposed to find HFO-1234yf acceptable for use 

subject to use conditions in new MVAC systems and evaluated its risks only for use in 

new systems. We will consider the retrofit use of HFO-1234yf in MVAC systems if we 

receive a submission that specifically addresses retrofitting and the risks that are unique 

to retrofitting. In response to the commenter who raised a concern about a “phase-out” of 

HFC-134a and the potential that we would “require” use of HFO-1234yf, we note that 

our rulemakings under SNAP do not require use of any specific substitute. Rather, under 

SNAP, we have established lists of substitutes that are acceptable for use in various enduses (such as for MVACs) and end-users are free to choose which substitute to use, but 

must do so consistent with any use conditions that apply. As stated in the rule 

establishing the SNAP program, “The Agency...does not want to intercede in the 

market’s choice of available substitutes, unless a substitute has been proposed or is being 

used that is clearly more harmful to human health and the environment than other 

alternatives.” 59 FR 13046, March 18, 1994. We further note that this rulemaking does 

not change the status of HFC-134a, which remains an acceptable substitute for use in 

MVACs, subject to use conditions.

F. 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 
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studies and testing in the docket support a finding that use of HFO-1234yf by nonprofessionals is safe and do not offer valid technical support for EPA’s concerns. 

Response: EPA’s risk assessment and risk screen both indicated that worst-case 

exposure levels expected during servicing by do-it-yourselfers are of potential concern 

(EPA-HQ-OAR-2008-0664-0036 and EPA-HQ-OAR-2008-0664-0038). In both 

documents, this was based upon estimated exposure levels from a 2008 risk assessment 

by Gradient Corporation for the SAE CRP (EPA-HQ-OAR-2008-0664-0008). In EPA’s 

risk assessment (EPA-HQ-OAR-2008-0664-0036), we found that the level that EPA 

determined did not cause health effects in laboratory animals might be only 2 to 3 times 

higher than the exposure predicted for that use (the “margin of exposure”). Our risk 

assessment indicated a higher, more protective margin of exposure of at least 30 was 

needed to account for uncertainty in the extrapolation from animals to humans and for 

variability in the human population. In other words, we found that based on worst-case 

assumptions, a do-it-yourselfer’s exposure could be 10 or more times the level that EPA 

considered safe. The margin of exposure was calculated using a conservative estimated 

exposure level of 45,000 ppm over 30 minutes and a human equivalent concentration of 

98,211 ppm from a no-observed adverse effect level that we selected as the point of 

departure for risk assessment (EPA-HQ-OAR-2008-0664-0036). 

However, under this final rule, unique fittings have only been submitted for 

servicing fittings for the high-side and low-side ports and for large containers of HFO1234yf and thus the acceptability listing is limited to use of HFO-1234yf with the unique 

fittings specified (e.g., for large containers of 20 pounds or more). We expect these 

containers would not be purchased by DIYers because of their expense ($800 or more per 
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container) and because they would contain enough refrigerant for 10 charges or more. 

We will continue to review the issue of safe use for DIYers if and when we are requested 

to review unique fittings for a smaller container size. In addition, EPA is further 

addressing the issue of risks to DIYers in the Significant New Use Rule for 1-propene2,3,3,3-tetrafluoro- (75 FR 65987, October 27, 2010). This SNUR requires submission of 

a SNUN at least 90 days before sale or distribution of products intended for use by a 

consumer for the purpose of servicing, maintenance and disposal involving HFO-1234yf. 

EPA’s proposed rule on the use of HFO-1234yf as a substitute for CFC-12 in new 

MVAC systems did not propose to establish use conditions for servicing vehicles by

certified professionals, but our analyses indicate that there is not significant risk to 

certified professionals, because HFC-134a, which is currently used in most MVAC 

systems, presents similar risks and professionals have the knowledge and equipment to 

mitigate any risks. We plan to further address servicing by professionals when we 

develop a new rule under section 609 of the Clean Air Act for servicing and maintenance 

of MVAC systems. 

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: As noted previously, the submission only addressed unique fittings for 

large containers (e.g., 20 lbs or larger) of HFO-1234yf. If anyone is interested in using 

HFO-1234yf in small cans or other small containers, they would need to contact the 

refrigerant manufacturer to submit unique fittings for approval under the SNAP program. 
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Thus, under this final rule, we believe that only certified technicians will purchase HFO1234yf because the larger containers are likely to be prohibitively expensive for 

individuals performing DIY servicing ($800 or more for a 20 lb cylinder) and are likely 

to be too large for most individuals to use, containing enough refrigerant for 10 or more 

charges.

We also note that in a separate final rule under the authority of TSCA (October 27, 

2010; 75 FR 65987), EPA requires among other things, that notice must be given to EPA 

90 days before (1) HFO-1234yf is used commercially other than in new passenger cars 

and vehicles in which the charging of motor vehicle air conditioning systems with HFO1234yf was done by the motor vehicle OEM or (2) sale or distribution of products 

intended for use by a consumer for the purpose of servicing, maintenance and disposal 

involving HFO-1234yf.

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 lowerincome 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: While this final rule effectively prohibits DIY use because the final 

use conditions do not include unique fittings allowing for use with small refrigerant 

containers, we are not making any final determination about whether HFO-1234yf may

be safely used by DIYers. As we noted above, we have not yet received a submission for 

DIY use or received unique fittings for small containers from the manufacturer, but 

would evaluate such submissions when we receive one. We note that because it is 
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unlikely that any cars will have MVAC systems with HFO-1234yf before the 2013 model 

year, we believe the availability of small containers for DIY use will not be of concern 

until such cars are sold and there is a need to recharge a new MVAC system on a model 

year 2013 vehicle. The separate final Significant New Use Rule that the Agency has 

issued under TSCA (75 FR 65987; October 27, 2010) requires submission of a 

Significant New Use Notice at least 90 days before sale or distribution of products 

intended for DIY use. 

With respect to the commenter who suggests that some people may seek lower 

cost alternatives, presumably to repair an existing MVAC, 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. 

G. Servicing issues

Comment: Several commenters stated that appropriate training and certification 

should be required to purchase HFO-1234yf for use in MVACs. Four commenters also 

stated that the final regulation should include a provision requiring proof of certification 

in order to purchase HFO-1234yf, and recommended that current AC systems tests (i.e., 

for CAA section 609 certification) be updated.

Some commenters disagreed with EPA’s statement that HFO-1234yf may cause 

serious health effects when used in servicing and maintaining MVACs without 

professional training. Another commenter stated that EPA is limiting productivity by

only allowing dealerships to perform refrigerant maintenance, and that independent 

MVAC serviced shops should be allowed to be certified. The commenter also questioned 

who will monitor “certified” technicians employed by dealerships that may do work on 
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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: As background for the public comments, we note that under EPA’s 

regulations implementing section 609, one must be a section 609 certified technician in 

order to purchase CFC-12 or other ODS for use in MVAC (40 CFR 82.34(b)). Section 

609(e) of the CAA itself specifically prohibits sale of small containers less than 20 

pounds with Class I or Class II substances suitable for use as a refrigerant in MVAC, 

except for individuals performing service for consideration in compliance with section 

609. However, there is no comparable restriction on the sale of HFC-134a or on other 

substitutes for MVAC that do not contain Class I or Class II ODS, such as HFO-1234yf.

In the NPRM (74 FR 53449), EPA stated that any specific training and 

certification requirements would be adopted through a rulemaking under the authority of 

CAA section 609 and would be codified in 40 CFR part 82 subpart B, which contains the 

regulations implementing section 609. We will address concerns regarding certification 

and training requirements during that separate rulemaking process. We note, however, 

that the CAA itself mandates that persons performing service for consideration that 

involve the refrigerant must be properly trained and certified. Furthermore, as noted 

previously, we believe that there is not a significant health risk to professionals from 

HFO-1234yf because they will have the knowledge and equipment to mitigate any risks. 

Also, because HFC-134a presents similar risks to HFO-1234yf, and the flammability

risks of HFO-1234yf are less than those for HFC-152a, the health risks of HFO-1234yf 

are not significantly greater than those of other available substitutes. 
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With regard to whether independent service shops could service MVACs with 

HFO-1234yf or whether service would be limited to “dealerships,” we note that neither 

this rule nor any other CAA regulation would limit servicing to dealerships. The 

comment may concern the withdrawn SNUR, 75 FR 4983 (February 1, 2010), which 

referred to the “original equipment manufacturer”; the commenter may have interpreted 

this term to mean an automobile dealership. The final SNUR (October 27, 2010; 75 FR 

65987) requires a significant new use notice to EPA at least 90 days before “commercial 

use other than in new passenger cars and vehicles in which the charging of motor vehicle 

air conditioning systems with the PMN substance [HFO-1234yf] was done by the motor 

vehicle original equipment manufacturer.” This requirement restricts commercial use of 

HFO-1234yf to use for vehicles that were initially charged with HFO-1234yf by the 

automobile’s manufacturer, as opposed to allowing commercial use of HFO-1234yf for 

vehicles initially charged with a different refrigerant. The term “original equipment 

manufacturer” refers to the automobile manufacturer, not to dealerships. 

Comment: 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 
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enable training pursuant to the OSHA hazard communication standard, the commenter 

stated that MVAC system and refrigerant suppliers should provide dealerships with 

sufficient information on the hazards posed by HFO-1234yf. 

Response: EPA is issuing use conditions in this final rule that reference relevant 

SAE technical standards on safety. This rule does not, however, include a use condition 

requiring technician training and does not refer to specific training standards. We agree 

with the commenter that current technician training generally should be sufficient to 

ensure that professional technicians will use HFO-1234yf safely. Although this SNAP 

determination does not contain a use condition regarding technician training, as noted 

above, section 609 of the CAA requires technician training for persons servicing for 

consideration. EPA will consider in a separate rulemaking under section 609, whether it 

is necessary to modify our existing regulations under section 609 to include additional 

specifications for HFO-1234yf. 

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: This rulemaking does not impose requirements for recycling or 

containment of the refrigerant. A separate rulemaking under CAA section 609 will 

address practices required in the servicing of MVAC systems using HFO-1234yf, 

including recycling and recovery. Further, EPA notes that Section 608 of the CAA 

prohibits the intentional release of any refrigerant during the maintenance, repair, service, 

or disposal of refrigeration and air conditioning equipment, unless the Administrator 
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determines through rulemaking that such release does not pose a threat to the 

environment. We have not made such a determination for HFO-1234yf.

H. Cost, availability, and small business impacts

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.

Response: EPA believes that there was sufficient information in the record at the 

time of proposal for us to complete a meaningful environmental analysis, even in the 

absence of definitive cost information. At the time of proposal, we had available both 

estimates from a trade magazine provided by the manufacturer (Weissler, 2008), as well 

as estimates of price provided in the initial submission from the manufacturer (EPA-HQOAR-2008-0664-0013). The estimates of price provided by the manufacturer were 

claimed as confidential business information and thus were not available in the record to 

the public. 

We typically use this type of information for purposes of determining market 

penetration for a particular substance, so that we can evaluate how much of the substitute 

will likely be used and thus the environmental risks it might pose. In this case, however, 
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because the automobile industry tends to prefer use of a single substitute, information on 

the cost of the substitute was not critical to our analysis. Thus, in conducting our 

environmental analysis, we took a conservative approach, assuming that all new MVAC 

systems began using HFO-1234yf by 2020 (i.e., full market penetration). We also 

considered an even more conservative scenario, in which HFO-1234yf would be the only

refrigerant used for stationary air conditioning and for refrigeration as of 2020, as well as 

for MVAC. Even with these highly conservative assumptions, we found that there would 

not be sufficient negative environmental impacts due to emissions of HFO-1234yf to 

warrant finding it unacceptable.

In the proposal, we mentioned a cost estimate for HFO-1234yf of $40-$60/lb 

(Weissler, 2008). More recently, the first automobile manufacturer announcing its 

intension to use HFO-1234yf confirmed that this range does not underestimate prices of 

HFO-1234yf and is consistent with the manufacturer’s long-term purchase contracts 

(Sciance, 2010). Thus, the most recent information shows costs to be similar to those we 

considered at the time of proposal. This data contradicts the late commenter’s assertion 

that the manufacturer’s effective monopoly would result in significantly different, higher 

costs that would invalidate EPA’s earlier analysis. In any event, assuming that costs were 

higher as suggested by the commenter, then we expect that use of HFO-1234yf would be 

less than assumed for our health and environmental risk analysis. As mentioned in the 

proposal, emissions, and thus the resulting environmental effects such as impacts on local 

air quality or on production of TFA, would be expected to be less under a scenario with 

higher prices and less use of HFO-1234yf. Our analysis assumes widespread use and 

thus its results would be protective.
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We note that where a new chemical is introduced, there is some uncertainty in the 

price. At best, the manufacturer can provide rough estimates of price and of market share 

before the chemical is produced in commercial quantities and becomes subject to supply

and demand pressures. EPA’s requirement for information on cost, anticipated 

availability in the market, and anticipated market share (40 CFR 82.178(a)(14) through 

(16)) should not be construed as requiring precise, detailed cost estimates based upon a 

well-defined methodology. As noted above, we use these numbers for the purposes of 

predicting market penetration and thus how much of a particular substitute may be used 

and thus pose an environmental risk. As we did for HFO-1234yf, we typically take a 

environmentally-protective approach to our evaluation, assuming use at least as high as 

that the cost and availability information may indicate.

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 United 

States Court of Appeals for the District of Columbia Circuit (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 potentially 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 HFO1234yf if the manufacturer does not grant licenses to produce.

Response: The CAA does not require that EPA find a substitute to be available or 

potentially available when finding it acceptable. Section 612(c) states:
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...It shall be unlawful to replace any class I or class II substance with any 

substitute substance which the Administrator determines may present adverse 

effects to human health or the environment, where the Administrator has 

identified an alternative to such replacement that—

(1) reduces the overall risk to human health and the 

environment; and

(2) is currently or potentially available....

(emphasis added.)

This section makes clear that it is not the substitute under review that must be 

available or potentially available, but rather alternative replacements for ODS that EPA 

determines pose less overall risk to human health and the environment than the substitute 

being reviewed. Thus, if there are alternatives to the substance under review that are 

currently or potentially available and that pose less risk, EPA cannot find the substitute 

under review acceptable. Section 612(c) establishes no requirement that EPA must 

determine that the substitute under review is “available.” See also 40 CFR 

82.180(b)(describing types of listing decisions EPA can make in reviewing substitutes26).

We note that even if EPA was required to determine that the substitute under 

review is available or potentially available before it could make an acceptability

determination, we believe that the available information supports that HFO-1234yf is 

 

26 The regulations for the SNAP program include cost and availability as one of the criteria for review as to 

whether a substitute is acceptable or unacceptable as a replacement for ozone depleting substances 

(82.180(a)(7)(vii)), along with a number of criteria for different aspects of health and environmental 

impacts. Cost and availability are included as criteria because they affect assumptions we may make about 

a substitute regarding its risks, i.e., we need to know its cost and availability so we can make assumptions 

about the risk it might pose. In this case, we assumed that HFO-1234yf would be used widely across the 

industry in new MVACs because widespread use of a single refrigerant in new car models has been the 

industry practice with MVAC systems. Thus, more detail on cost and availability of the substitute was not 

necessary in order to identify assumptions we should make for estimating risk. 
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potentially available. EPA’s definition of “potentially available” at 40 CFR 82.172 

provides:

Potentially available is defined as any alternative for which adequate health, 

safety, and environmental data, as required for the SNAP notification process, 

exist to make a determination of acceptability, and which the Agency reasonably

believes to be technically feasible, even if not all testing has yet been completed 

and the alternative is not yet produced or sold.

This definition makes explicit that it is not necessary to have perfect information on a 

substitute nor is it necessary for the substitute to be produced or sold in order for EPA to 

consider it “potentially available.” Instead, it is necessary for EPA to find the health, 

safety and environmental data adequate to make a determination of acceptability, and for 

the Agency to reasonably believe that the alternative is “technically feasible,” in order for 

the alternative to be potentially available. We believe the record contains adequate 

information showing that HFO-1234yf is potentially available. The manufacturer has 

submitted the information required under 40 CFR 82.178 (e.g., pre-manufacture notice 

form and TSCA/SNAP addendum form containing: name and description of the 

substitute, physical and chemical information, information on ODP and global warming 

impacts, toxicity data, data on environmental fate and transport, flammability, exposure, 

cost and estimated production). The submitter has also provided unique fittings as 

required under appendix D to subpart G of 40 CFR part 82. Thus, we believe that there is 

“adequate health, safety, and environmental data.” Even if the commenter were correct 

about claims that higher costs would result if the manufacturer does not grant licenses for 

production, as discussed above, this does not affect the adequacy of the health, safety, 

and environmental data for HFO-1234yf, because we have protectively assumed 

widespread use that would result in more emissions and greater environmental impacts. 
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In addition, based on the experimental work conducted by the automobile industry, we 

reasonably believe that HFO-1234yf is technically feasible as a refrigerant. Thus, HFO1234yf would still be “potentially available” under the SNAP program’s definition.

One commenter points to Honeywell International, Inc. v. EPA, 374 F.3d 1363 in 

urging EPA to explicitly include cost as a consideration in determining whether a 

substitute is “potentially available.” In that case, the court vacated and remanded a 

SNAP decision in which EPA listed a foam blowing substitute as acceptable subject to

“narrowed use limits” on the basis that for some niche foam blowing uses, the substitutes 

that were already listed as acceptable might not be available. Under the narrowed use 

limits, the end-user would need to demonstrate and document that other substitutes were 

not technically feasible for a particular use. The court vacated and remanded EPA’s rule 

on the basis that EPA had considered cost in concluding that already listed substitutes 

might not be available based on “technical” feasibility, and that EPA had not attempted to 

justify the rule on the ground that the statute allows it to consider economic factors in 

making its SNAP determinations. The court left open the question of whether EPA could 

attempt to interpret the term “available” in section 612(c) as allowing for consideration of 

costs. 

Again, we note that “available or potentially available” applies only to the 

substitutes against which the substitute at issue is being compared. The Agency has not 

decided whether consideration of the cost of other substitutes should be a factor to 

consider in determining whether they are available or potentially available and thus 

should (or should not) be used for comparison to a substitute under review. However, we 

note that for purposes of the substitute under review, the Agency firmly believes that cost 
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should not be the primary or sole basis for finding a substitute unacceptable. EPA’s role 

is to determine the health and environmental risk associated with the use of substitutes 

and the market should serve to address the issue of costs. Costs will necessarily be a 

factor considered by the automobile manufacturers in deciding which substitute to use.

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 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: The RFA applies only when there are small entities subject to the 

requirements of the proposed or final rule. 5 U.S.C. § 604(a)(3). 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. To the extent the commenters are suggesting 
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that we must evaluate such costs for purposes of the Regulatory Flexibility Act, we note 

that under the RFA we evaluate costs imposed by the enforceable regulations being 

promulgated. To the extent the costs referred to by the commenter are already imposed 

under RCRA, they would not be new costs, but costs associated with the relevant RCRA 

regulations. Moreover, under this SNAP final rule, EPA is not requiring the use of HFO1234yf, and thus the costs associated with its use are not due to enforceable regulatory

requirements under SNAP. To the extent there are enforceable requirements for those 

persons who choose to use this new substitute, those requirements (the “use conditions”) 

apply primarily to manufacturers of automobiles and MVAC systems, because they

concern design of MVAC systems. The one use condition of the rule that applies to 

servicing of MVAC systems, and thus, could apply to small businesses, is the 

requirement for specific unique service fittings. However, EPA’s existing SNAP 

regulations at appendix D to subpart G of 40 CFR part 82 already require unique service 

fittings as specified by the refrigerant manufacturer. Thus, the costs of purchasing new 

unique fittings for this refrigerant are imposed by the pre-existing regulation. This rule 

specifies the requirements for the type of unique fitting, in accordance with the fittings 

provided to EPA by the manufacturer. These fittings are proposed for adoption as part of 

the draft SAE J639 standard. It is not clear that there would be any cost differential 

between these specific unique fittings and others that the automotive industry could adopt 

instead. For these reasons, EPA is able to certify that this regulation will not create a 

significant impact on a significant number of small entities.
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EPA notes that there may be costs of servicing or of disposal (end-of-life) to small 

businesses under future regulations under section 609 or 608 of the CAA. We will 

conduct an analysis of such costs, as necessary, as part of those future rulemakings.

Comment: 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 analyze this.

Response: UMRA applies only to “enforceable duties” imposed on State, local, 

and tribal governments or on the private sector. The SNAP rule does not impose duties 

on governments. As we have noted previously, the SNAP program does not mandate the 

use of any specific substitute for ozone depleting substances. Rather, through this action, 

we are expanding the choices of MVAC refrigerants available to the private sector. The 

issue raised by the commenter concerning the cost of the refrigerant and the effect of the 

manufacturer’s patent on pricing is not related to any requirement of the rule, and thus, 

EPA is not required to consider that cost under UMRA. 

VIII. How does the SNAP program work?

A. What are the statutory requirements and authority for the SNAP program?

Section 612 of the Clean Air Act (CAA) requires EPA to develop a program for 

evaluating alternatives to ozone-depleting substances (ODS). EPA refers to this program 

as the Significant New Alternatives Policy (SNAP) program. The major provisions of 

section 612 are: 
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1. Rulemaking

Section 612(c) requires EPA to promulgate rules making it unlawful to replace 

any class I (i.e., chlorofluorocarbon, halon, carbon tetrachloride, methyl chloroform, 

methyl bromide, and hydrobromofluorocarbon) or class II (i.e., hydrochlorofluorocarbon) 

substance with any substitute that the Administrator determines may present adverse 

effects to human health or the environment where the Administrator has identified an 

alternative that (1) reduces the overall risk to human health and the environment, and (2) 

is currently or potentially available.

2. Listing of Unacceptable/Acceptable Substitutes

Section 612(c) requires EPA to publish a list of the substitutes unacceptable for 

specific uses and to publish a corresponding list of acceptable alternatives for specific 

uses. The list of acceptable substitutes is found at 

http://www.epa.gov/ozone/snap/lists/index.html and the lists of “unacceptable”, 

“acceptable subject to use conditions”, and “acceptable subject to narrowed use limits” 

substitutes are found at 40 CFR part 82 subpart G. 

3. Petition Process

Section 612(d) grants the right to any person to petition EPA to add a substance 

to, or delete a substance from, the lists published in accordance with section 612(c). The 

Agency has 90 days to grant or deny a petition. Where the Agency grants the petition, 

EPA must publish the revised lists within an additional six months.

4. 90-day Notification

Section 612(e) directs EPA to require any person who produces a chemical 

substitute for a class I substance to notify the Agency not less than 90 days before new or 
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existing chemicals are introduced into interstate commerce for significant new uses as 

substitutes for a class I substance. The producer must also provide the Agency with the 

producer's unpublished health and safety studies on such substitutes. 

5. Outreach

Section 612(b)(1) states that the Administrator shall seek to maximize the use of 

federal research facilities and resources to assist users of class I and II substances in 

identifying and developing alternatives to the use of such substances in key commercial 

applications.

6. Clearinghouse

Section 612(b)(4) requires the Agency to set up a public clearinghouse of 

alternative chemicals, product substitutes, and alternative manufacturing processes that 

are available for products and manufacturing processes which use class I and II 

substances.

B. What are EPA’s regulations implementing section 612?

On March 18, 1994, EPA published the original rulemaking (59 FR 13044) which 

established the process for administering the SNAP program and issued EPA's first lists 

identifying acceptable and unacceptable substitutes in the major industrial use sectors (40 

CFR part 82, subpart G). These sectors include: refrigeration and air conditioning; foam 

blowing; cleaning solvents; fire suppression and explosion protection; sterilants; aerosols; 

adhesives, coatings and inks; and tobacco expansion. These sectors compose the 

principal industrial sectors that historically consumed the largest volumes of ODS.
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Section 612 of the CAA requires EPA to list as acceptable only those substitutes 

that do not present a significantly greater risk to human health and the environment as 

compared with other substitutes that are currently or potentially available. 

C. How do the regulations for the SNAP program work?

Under the SNAP regulations, anyone who plans to market or produce a substitute 

to replace a class I or II ODS in one of the eight major industrial use sectors must provide 

notice to the Agency, including health and safety information on the substitute at least 90 

days before introducing it into interstate commerce for significant new use as an 

alternative. This requirement applies to the person planning to introduce the substitute 

into interstate commerce,27 typically chemical manufacturers, but may also include 

importers, formulators, equipment manufacturers, or end-users28 when they are 

responsible for introducing a substitute into commerce.

The Agency has identified four possible decision categories for substitutes: 

acceptable; acceptable subject to use conditions; acceptable subject to narrowed use 

limits; and unacceptable. Use conditions and narrowed use limits are both considered 

“use restrictions” and are explained below. Substitutes that are deemed acceptable with 

no use restrictions (no use conditions or narrowed use limits) can be used for all 

applications within the relevant end-uses within the sector. Substitutes that are 

acceptable subject to use restrictions may be used only in accordance with those 

 

27 As defined at 40 CFR 82.104 “interstate commerce” means the distribution or transportation of any 

product between one state, territory, possession or the District of Columbia, and another state, territory, 

possession or the District of Columbia, or the sale, use or manufacture of any product in more than one 

state, territory, possession or District of Columbia. The entry points for which a product is introduced into 

interstate commerce are the release of a product from the facility in which the product was manufactured, 

the entry into a warehouse from which the domestic manufacturer releases the product for sale or 

distribution, and at the site of United States Customs clearance.

28 As defined at 40 CFR 82.172 “end-use” means processes or classes of specific applications within major 

industrial sectors where a substitute is used to replace an ozone-depleting substance. 
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restrictions. It is illegal to replace an ODS with a substitute listed as unacceptable, unless 

certain exceptions (e.g., test marketing, research and development) provided by the 

regulation are met.

After reviewing a substitute, the Agency may determine that a substitute is 

acceptable only if certain conditions in the way that the substitute is used are met to 

minimize risks to human health and the environment. EPA describes such substitutes as 

"acceptable subject to use conditions." Entities that use these substitutes without meeting 

the associated use conditions are in violation of section 612 of the Clean Air Act and 

EPA’s SNAP regulations.

For some substitutes, the Agency may permit a narrowed range of use within an 

end-use or sector. For example, the Agency may limit the use of a substitute to certain 

end-uses or specific applications within an industry sector. The Agency requires a user 

of a narrowed use substitute to demonstrate that no other acceptable substitutes are 

available for their specific application by conducting comprehensive studies. EPA 

describes these substitutes as “acceptable subject to narrowed use limits.” A person using 

a substitute that is acceptable subject to narrowed use limits in applications and end-uses 

that are not consistent with the narrowed use limit, are using these substitutes in an 

unacceptable manner and are in violation of section 612 of the CAA and EPA’s SNAP 

regulations.

The Agency publishes its SNAP program decisions in the Federal Register (FR). 

EPA publishes decisions concerning substitutes that are deemed acceptable subject to use 

restrictions (use conditions and/or narrowed use limits), or for substitutes deemed 
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unacceptable, as proposed rulemakings to allow the public opportunity to comment, 

before publishing final decisions. 

In contrast, EPA publishes substitutes that are deemed acceptable with no 

restrictions in “notices of acceptability,” rather than as proposed and final rules. As 

described in the rule initially implementing the SNAP program (59 FR 13044), EPA does 

not believe that rulemaking procedures are necessary to list alternatives that are 

acceptable without restrictions because such listings neither impose any sanction nor 

prevent anyone from using a substitute.

Many SNAP listings include “comments” or “further information” to provide 

additional information on substitutes. Since this additional information is not part of the 

regulatory decision, these statements are not binding for use of the substitute under the 

SNAP program. However, regulatory requirements so listed are binding under other 

regulatory programs. The “further information” classification does not necessarily

include all other legal obligations pertaining to the use of the substitute. While the items 

listed are not legally binding under the SNAP program, EPA encourages users of

substitutes to apply all statements in the “further information” column in their use of 

these substitutes. In many instances, the information simply refers to sound operating 

practices that have already been identified in existing industry and/or building-codes or 

standards. Thus, many of the statements, if adopted, would not require the affected user 

to make significant changes in existing operating practices.

D. Where can I get additional information about the SNAP program?

For copies of the comprehensive SNAP lists of substitutes or additional 

information on SNAP, refer to EPA’s Ozone Depletion web site at 
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www.epa.gov/ozone/snap/index.html. For more information on the Agency's process for 

administering the SNAP program or criteria for evaluation of substitutes, refer to the 

SNAP final rulemaking published March 18, 1994 (59 FR 13044), codified at 40 CFR 

part 82, subpart G. A complete chronology of SNAP decisions and the appropriate 

citations are found at http://www.epa.gov/ozone/snap/chron.html.

IX. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

Under Executive Order (EO) 12866 (58 FR 51735, October 4, 1993), this action is 

a "significant regulatory action.” It raises novel legal or policy issues arising out of legal 

mandates, the President's priorities, or the principles set forth in the Executive Order. 

Accordingly, EPA submitted this action to the Office of Management and Budget 

(OMB) for review under EO 12866 and any changes made in response to OMB 

recommendations have been documented in the docket for this action.

B. Paperwork Reduction Act

This action does not impose any new information collection burden. Today's 

action is an Agency determination. It contains no new requirements for reporting. The 

only new recordkeeping requirement involves customary business practice. Today's rule 

requires minimal record-keeping of studies done to ensure that MVAC systems using 

HFO-1234yf meet the requirements set forth in this rule. Because it is customary

business practice that OEMs conduct and keep on file Failure Mode and Effect Analysis 

(FMEA) on any potentially hazardous part or system from the beginning of production of 

a car model until three or more years after production of the model ends, we believe this 

requirement will not impose an additional paperwork burden. However, the Office of 
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Management and Budget (OMB) has previously approved the information collection 

requirements contained in the existing regulations in subpart G of 40 CFR part 82 under 

the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. and has assigned 

OMB control numbers 2060-0226. The OMB control numbers for EPA's regulations are 

listed in 40 CFR Part 9.

C. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) generally requires an agency to prepare a 

regulatory flexibility analysis of any rule subject to notice and comment rulemaking 

requirements under the Administrative Procedure Act or any other statute unless the 

agency certifies that the rule will not have a significant economic impact on a substantial

number of small entities. Small entities include small businesses, small organizations, 

and small governmental jurisdictions.

For purposes of assessing the impacts of today's rule on small entities, small 

entity is defined as: (1) A small business as defined by the Small Business 

Administration's (SBA) regulations at 13 CFR 121.201; for NAICS code 336111 

(Automobile manufacturing), a small business has <1000 employees; for NAICS code 

336391 (Motor Vehicle Air-Conditioning Manufacturing), a small business has <750 

employees; (2) a small governmental jurisdiction that is a government of a city, county, 

town, school district or special district with a population of less than 50,000; and (3) a 

small organization that is any not-for-profit enterprise which is independently owned and 

operated and is not dominant in its field.

After considering the economic impacts of today's final rule on small entities, I

certify that this action will not have a significant adverse economic impact on a 
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substantial number of small entities. The only new requirement on small entities in this

final rule is a requirement specifying the type of unique service fittings required when 

servicing MVAC systems using the refrigerant HFO-1234yf. Existing regulations at 

appendix D to subpart G of 40 CFR part 82 already require that there be unique service 

fittings for each refrigerant used in MVAC systems. Thus, the costs of purchasing new 

unique fittings for this refrigerant have already been imposed by the pre-existing 

regulation. This rule specifies the requirements for which type of unique fitting, in 

accordance with the fittings provided to EPA by the manufacturer. These fittings are 

proposed for adoption as part of the draft SAE J639 standard. It is not clear that there 

would be any cost differential between these specific unique fittings and others that the 

automotive industry could adopt instead. Thus, cost impacts of this final rule on small

entities are expected to be small. This final rule is expected to relieve burden for some 

small entities, such as car repair shops, by allowing them the flexibility to use a new 

refrigerant that otherwise would have been prohibited under previous requirements at 

appendix B to subpart G, 40 CFR part 82 and by allowing them to use the easy-to-use 

“quick-connect” fittings for this refrigerant. Other final rule requirements apply to 

original equipment manufacturers, which are not small entities. These final rule 

requirements are the least burdensome option for regulation.

Original equipment manufacturers are not mandated to move to MVAC systems

using HFO-1234yf. EPA is simply listing HFO-1234yf as an acceptable alternative with 

use conditions in new MVAC systems. This rule allows the use of this alternative to 

ozone-depleting substances in the MVAC sector and outlines the conditions necessary for 

safe use. By approving this refrigerant under SNAP, EPA provides additional choice to 
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the automotive industry which, if adopted, would reduce the impact of MVACs on the 

global environment. This rulemaking does not mandate the use of HFO-1234yf as a

refrigerant in new MVACs.

D. Unfunded Mandates Reform Act

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public Law 

104-4, establishes requirements for Federal agencies to assess the effects of their 

regulatory actions on State, local, and tribal governments and the private sector. Under 

section 202 of the UMRA, EPA generally must prepare a written statement, including a 

cost-benefit analysis, for proposed and final rules with ``Federal mandates'' that may

result in expenditures to State, local, and tribal governments, in the aggregate, or to the 

private sector, of $100 million or more in any one year. Before promulgating an EPA 

rule for which a written statement is needed, section 205 of the UMRA generally requires 

EPA to identify and consider a reasonable number of regulatory alternatives and adopt

the least costly, most cost-effective or least burdensome alternative that achieves the 

objectives of the rule. The provisions of section 205 do not apply when they are 

inconsistent with applicable law. Moreover, section 205 allows EPA to adopt an 

alternative other than the least costly, most cost-effective or least burdensome alternative 

if the Administrator publishes with the final rule an explanation why that alternative was 

not adopted. Before EPA establishes any regulatory requirements that may significantly 

or uniquely affect small governments, including tribal governments, it must have 

developed under section 203 of the UMRA a small government agency plan. The plan 

must provide for notifying potentially affected small governments, enabling officials of 

affected small governments to have meaningful and timely input in the development of 
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EPA regulatory proposals with significant Federal intergovernmental mandates, and 

informing, educating, and advising small governments on compliance with the regulatory

requirements.

EPA has determined that this rule does not contain a Federal mandate that may

result in expenditures of $100 million or more for State, local, and tribal governments, in 

the aggregate, or the private sector in any one year. Today's rule does not affect State, 

local, or tribal governments. The enforceable requirements of today's rule related to 

system design and documentation of the safety of alternative MVAC systems affect only 

a small number of original equipment manufacturers. Further, those requirements are 

consistent with requirements that the automotive industry is proposing to adopt through 

consensus standards of SAE International. We expect that most manufacturers of 

automobiles and MVAC systems would attempt to meet those requirements or something 

very similar, even in the absence of EPA’s regulations. The only requirement that is 

applied more widely than for original equipment manufacturers is a requirement 

specifying the type of unique service fittings required when servicing MVAC systems 

using the refrigerant HFO-1234yf. Existing regulations at appendix D to subpart G of 40 

CFR part 82 already require that there be unique service fittings for each refrigerant used 

in MVAC systems. The fittings required in this final rule are proposed for adoption as 

part of the draft SAE J639 standard. Thus, the costs of this rule are consistent with 

standard industry practice and are expected to be much less than $100 million per year.

This action provides additional options allowing greater flexibility for industry in 

designing consumer products. The impact of this rule on the private sector will be less 

than $100 million per year. Thus, today's rule is not subject to the requirements of 
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sections 202 and 205 of the UMRA. EPA has determined that this rule contains no

regulatory requirements that might significantly or uniquely affect small governments. 

This regulation applies directly to facilities that use these substances and not to 

governmental entities. This rule does not mandate a switch to HFO-1234yf and the 

limited direct economic impact on entities from this rulemaking is less than $100 million 

annually.

E. Executive Order 13132: Federalism

Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August 10, 1999), 

requires EPA to develop an accountable process to ensure ``meaningful and timely input 

by State and local officials in the development of regulatory policies that have federalism 

implications.'' ``Policies that have federalism implications'' is defined in the Executive 

Order to include regulations that have ``substantial direct effects on the States, on the 

relationship between the national government and the States, or on the distribution of 

power and responsibilities among the various levels of government.''

This action does not have federalism implications. It will not have substantial 

direct effects on the States, on the relationship between the national government and the 

States, or on the distribution of power and responsibilities among the various levels of 

government, as specified in Executive Order 13132. This regulation applies directly to

facilities that use these substances and not to governmental entities. Thus, Executive 

Order 13132 does not apply to this rule.

F. Executive Order 13175: Consultation and Coordination with Indian Tribal 

Governments
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Executive Order 13175, entitled ``Consultation and Coordination with Indian 

Tribal Governments'' (59 FR 22951, November 6, 2000), requires EPA to develop an 

accountable process to ensure ``meaningful and timely input by tribal officials in the 

development of regulatory policies that have tribal implications.'' This final rule does not 

have tribal implications, as specified in Executive Order 13175. It does not significantly 

or uniquely affect the communities of Indian tribal governments, because this regulation 

applies directly to facilities that use these substances and not to governmental entities. 

Thus, Executive Order 13175 does not apply to this rule.

G. Executive Order 13045: Protection of Children from Environmental Health 

Risks and Safety Risks 

This action is not subject to EO 13045 (62 FR 19885, April 23, 1997) 

because it is not economically significant as defined in EO 12866, and because 

the Agency does not believe the environmental health or safety risks addressed by 

this action present a disproportionate risk to children. This action’s health and 

risk assessments are discussed in sections V and VII.D of the preamble and in 

documents EPA-HQ-OAR-2008-0664-0036 and HQ-OAR-2008-0664-0038 in 

the docket for this rulemaking. 

H. Executive Order 13211: Actions Concerning Regulations That Significantly 

Affect Energy Supply, Distribution, or Use

This action is not a “significant energy action” as defined in Executive Order 

13211 (66 FR 28355 (May 22, 2001)), because it is not likely to have a significant 

adverse effect on the supply, distribution, or use of energy. This action could impact 
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manufacturing and repair of MVAC systems using an alternative refrigerant. This rule 

does not mandate a switch to HFO-1234yf. Preliminary information indicates that these 

new systems are more energy efficient than currently available systems in some climates. 

Therefore, we conclude that this rule is not likely to have a significant adverse effect on 

energy supply, distribution or use.

I. National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of 1995 

(“NTTAA”), Public Law No. 104-113, 12(d) (15 U.S.C. 272 note) directs EPA to use 

voluntary consensus standards in its regulatory activities unless to do so would be 

inconsistent with applicable law or otherwise impractical. Voluntary consensus standards 

are technical standards (e.g., materials specifications, test methods, sampling procedures, 

and business practices) that are developed or adopted by voluntary consensus standards 

bodies. NTTAA directs EPA to provide Congress, through OMB, explanations when the 

Agency decides not to use available and applicable voluntary consensus standards. 

This rulemaking involves technical standards. EPA has decided to use SAE

International’s most recent version of the SAE J1739 standard. This standard can be 

obtained from http://www.sae.org/technical/standards/. This standard addresses safety

and reliability issues in motor vehicle design, including MVAC systems using alternative 

refrigerants.

J. Executive Order 12898: Federal Actions to Address Environmental 

Justice in Minority Populations and Low-Income Populations
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Executive Order (EO) 12898 (59 FR 7629 (Feb. 16, 1994)) establishes federal 

executive policy on environmental justice. Its main provision directs federal agencies, to 

the greatest extent practicable and permitted by law, to make environmental justice part 

of their mission by identifying and addressing, as appropriate, disproportionately high 

and adverse human health or environmental effects of their programs, policies, and 

activities on minority populations and low-income populations in the United States. 

EPA has determined that this final rule will not have disproportionately high and 

adverse human health or environmental effects on minority or low-income populations 

because it increases the level of environmental protection for all affected populations 

without having any disproportionately high and adverse human health or environmental 

effects on any population, including any minority or low-income population. HFO1234yf is a non ozone-depleting substance with a low GWP. Based on the toxicological 

and atmospheric work described earlier, HFO-1234yf will not have any

disproportionately high and adverse human health or environmental effects on any

population, including any minority or low-income population. This final rule requires

specific use conditions for MVAC systems, if car manufacturers chose to make MVAC 

systems using this low GWP refrigerant alternative.

K. Congressional Review Act

The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the Small 

Business Regulatory Enforcement Fairness Act of 1996, generally provides that before a 

rule may take effect, the agency promulgating the rule must submit a rule report, which 

includes a copy of the rule, to each House of the Congress and to the Comptroller 

General of the United States. EPA will submit a report containing this rule and other 

required information to the U.S. Senate, the U.S. House of Representatives, and the 
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Comptroller General of the United States prior to publication of the rule in the Federal 

Register. A Major rule cannot take effect until 60 days after it is published in the Federal

Register. This action is not a “major rule” as defined by 5 U.S.C. 804(2). This rule will 

be effective [insert date 60 days after publication].

XI. References

The documents below are referenced in the preamble. All documents are located 

in the Air Docket at the address listed in section titled ``ADDRESSES'' at the beginning 

of this document. Unless specified otherwise, all documents are available in Docket ID 

No. EPA-HQ-OAR-2008-0664 at http://www.regulations.gov.

Benesch et al., 2002. Investigation of Effects of Trifluoroacetate on Vernal Pool 

Ecosystems. Environ. Tox and Chem. Vol. 21, No. 3 pp. 640-647. 2002. 

Available online at 

http://www3.interscience.wiley.com/journal/122678081/abstract?CRETRY=1&S

RETRY=0

Benouali et al., 2008. “A/C System Control Strategies for Major Refrigerant Options” 

June 11, 2008, Alternative Refrigerant Systems Symposium Phoenix, AZ. 

Available online at 

http://www2.dupont.com/Refrigerants/en_US/assets/downloads/SmartAutoAC/20

08_SAE_ARSS_Valeo_Eval.pdf

Besnard, S., 1996. Full Flammability Test of Gases and Gas Mixtures in Air. CERN. 

European Organization for Nuclear Research. 1996. Available online at 

http://cdsweb.cern.ch/record/1217583/files/CM-P00055900.pdf

Boutonnet et al., 1999. Boutonnet, J.C., et al. "Environmental Risk Assessment of 

Trifluoroacetic Acid," Human and Ecological Risk Assessment, Feb. 1999. 

Available online at 

http://www.informaworld.com/smpp/content~db=all~content=a922749285~frm=

abslink. 

CARB, 2008. Technical Support Document “Staff Analysis on Emissions and Economic 

Impact of Proposed Regulation for Small Containers of Automotive Refrigerant.”

Appendix G to Certification Procedures for Small Containers of Automotive 

Refrigerant. California Air Resources Board, effective March 10, 2010. 

Document incorporated by reference in California Code of Regulations (CCR), 
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title 17, sections 95360 through 95370. Available online at 

http://www.arb.ca.gov/regact/2009/hfc09/hfc09.htm.

Carter, 2009. Investigation of Atmospheric Ozone Impacts of 2,3,3,3-Tetrafluoropropene. 

Final report to Honeywell Internationl Contract UCR-09010016. William Carter, 

University of California, Riverside CA. June 2, 2009. Available online at 

http://www.cert.ucr.edu/%7Ecarter/pubs/YFrept.pdf.

Ceviz and Yuksel, 2005. “Cyclic variations on LPG and gasoline-fuelled lean burn SI 

engine.” Renewable Energy. In press. Available online at http://www.pmkbase.com/articles/LPGsdarticle(8).pdf.

Clodic et al., 2008. Evaluation of the Potential Impact of Emissions of HFC-134a From 

Non Professional Servicing of Motor Vehicle Air Conditioning Systems. D. 

Clodic, A. Tremoulet, Y, Riachi, D. Sousa, L. Palandre, A. Garnier, S.Clodic and 

M. Lansard. Prepared under CARB Agreement No. 06-341. December, 2008. 

Available online at http://www.arb.ca.gov/research/apr/past/06-341.pdf.

CRP, 2008. Risk Assessment for Alternative Refrigerants HFO-1234yf Phase II. 

Prepared for SAE International Cooperative Research Program 1234 by Gradient 

Corporation. February 26, 2008. Docket number EPA-HQ-OAR-2008-0664-

0008

CRP, 2009. Risk Assessment for Alternative Refrigerants HFO-1234yf and R-744 (CO2) 

Phase III. Prepared for SAE International Cooperative Research Program 1234 by

T. Lewandowski, Gradient Corporation. December 17, 2009. Docket number 

EPA-HQ-OAR-2008-0664-0056.2

DuPont, 2008. DuPont internal testing. Cited in docket number EPA-HQ-OAR-2008-0664-

0052.1.

Hamner Institutes, 2007. Toxicogenomic assessment of the carcinogenic potential of

2,3,3,3-tetrafluoropropene. The Hamner Institutes for Health Sciences. January 5, 

2007. Docket numbers EPA-HQ-OAR-2008-0664-0030 through -0030.6.

Honeywell, 2010a. Comment on EPA Proposed Rule (simulated vehicle service leak 

testing and exposure study). Docket ID: EPA-HQ-OPPT-2008-0918-0088.

Honeywell, 2010b. Response to EPA questions. Docket ID: EPA-HQ-OPPT-2008-

0918-0096.

ICF, 2008. ICF International. 2008. Air Conditioning Refrigerant Charge Size to 

Passenger Compartment Volume Ratio Analysis. Docket number EPA-HQOAR-2008-0664-0003

ICF, 2009. ICF International. 2009. Revised Final Draft Assessment of the Potential 

Impacts of HFO-1234yf and the Associated Production of TFA on Aquatic 
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Communities and Local Air Quality. Docket number EPA-HQ-OAR-2008-0664-

0037

ICF, 2010a. ICF International. 2010. Summary of HFO-1234yf Emissions Assumptions.

ICF, 2010b. ICF International. 2010. Revised Assessment of the Potential Impacts of 

HFO-1234yf and the Associated Production of TFA on Aquatic Communities, 

Soil and Plants, and Local Air Quality.

ICF, 2010c. ICF International. 2010. Sensitivity Analysis CMAQ results on projected 

maximum TFA rainwater concentrations and maximum 8-hr ozone concentrations.

ICF, 2010d. ICF International. 2010. Analysis of Potential Impacts of Aldehydes as 

Breakdown Products from HFO-1234yf.

ICF, 2010e. ICF International. 2010. Summary of Updates to the Vintaging Model that 

Impacted HFO-1234yf Emissions Estimates.

IPCC, 2007. Contribution of Working Group I to the Fourth Assessment Report of the 

Intergovernmental Panel on Climate Change, 2007. Solomon, S., D. Qin, M. 

Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.). 

Cambridge University Press, Cambridge, United Kingdom and New York, NY, 

USA. Available online at 

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html .

JAMA, 2008. “LCCP Result from JAMA,” Japan Automobile Manufacturers 

Association , T. Ikegami; K. Inui; K. Aoki. VDA Alternative Refrigerant Winter 

Meeting, Saalfelden, Austria, February 13-14, 2008. Available online at 

http://www.vdawintermeeting.de/fileadmin/downloads2008/presentations/Tohru_Ikegami_Toyot

a_Kenta_Aoki_Nissan_JAMA.pdf (begins, p. 23)

JAMA-JAPIA, 2008. ”New Refrigerants Evaluation Results” Japan Automobile 

Manufacturers Association-Japan Auto Parts Industries Association Consortium. 

T. Ikegami, M. Iguchi, K. Aoki, K. Iijima; VDA Alternative Refrigerant Winter 

Meeting, Saalfelden, Austria, February 13-14, 2008. Available online at 

http://www.vdawintermeeting.de/fileadmin/downloads2008/presentations/Tohru_Ikegami_Toyot

a_Kenta_Aoki_Nissan_JAMA.pdf .

Kajihara et al., 2010. “Estimation of environmental concentrations and deposition fluxes 

of R-1234-YF and its decomposition products emistted from air conditioning 

equipment to atmosphere”. H. Kajihara, K. Inoue, K. Yoshida, R. Nagaosa. 

February 17-19, 2010. 2010 International Symposium on Next-generation Air 

Conditioning and Refrigeration Technology. Docket number EPA-HQ-OAR2008-0664-0114.1
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Kirkland et al. (2005) Evaluation of a battery of three in vitro genotoxicity tests to 

determine rodent carcinogens and non-carcinogens. I. Sensitivity, specificity and 

relative predictivity, Mutation Research, 584, 1-256. Available online at 

www.sciencedirect.com.

Luecken et al., 2009. Luecken, D.J., Waterland, R.L., Papasavva, S., Taddonio, K.N., 

Hutzell, W.T., Rugh, J.P., Andersen, S.O. 2009. Ozone and TFA Impacts in 

North America from the Degradation of 2,3,3,3-Tetrafluoropropene (HFO1234yf), A Potential Greenhouse Gas Replacement. Environ. Sci. Technol., 

submitted for publication. Docket number EPA-HQ-OAR-2008-0664-0112.3

Meyer, 2008. “R-1234yf System Enhancements and Comparison to R-134a.” 2008, 

Alternative Refrigerant Systems Symposium Phoenix, AZ Available online at 

http://www2.dupont.com/Refrigerants/en_US/assets/downloads/SmartAutoAC/20

08_SAE_ARSS_Visteon_Eval.pdf

Monforte et al., 2008 ”Updated situation about alternative refrigerant evaluation” June 

10-12, 2008, Alternative Refrigerant Systems Symposium Phoenix, AZ. 

http://www2.dupont.com/Refrigerants/en_US/assets/downloads/SmartAutoAC/20

08_SAE_ARSS_Renault_Fiat_PSA_Eval.pdf

Nielsen et al., 2007. Nielsen, O.J., Javadi, M.S., Sulbaek Andersen, M.P., Hurley, M.D., 

Wallington, T.J., Singh, R. 2007. Atmospheric chemistry of CF3CF=CH2: 

Kinetics and mechanisms of gas-phase reactions with Cl atoms, OH radicals, and 

O3. Chemical Physics Letters 439, 18-22. Available online at 

http://www.cogci.dk/network/OJN_174_CF3CF=CH2.pdf.

NRC, 1981. Atmosphere-Biosphere Interactions: Toward a Better Understanding of the 

Ecological Consequences of Fossil Fuel Combustion. Committee on the 

Atmosphere and the Biosphere, Board on Agriculture and Renewable Resources, 

Commission on Natural Resources, National Research Council. 1981. Available 

from NRC Press or online at http://www.nap.edu/catalog.php?record_id=135.

NRC, 1996. NRC Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and 

HCFC-123 (1996). Available online at 

http://www.nap.edu/openbook.php?record_id=9268&page=29.

NRC, 2004. Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 

4 (2004) Board on Environmental Studies and Toxicology. The National

Academies Press. Available online at 

http://www.nap.edu/openbook.php?record_id=10902&page=127#p2000a02f9960

127001.

Orkin et al., 1997. Rate constants for the reactions of OH with HFC-245cb (CH3CF2CF3) 

and some fluoroalkenes (CH2CHCF3, CH2CFCF3, CF2CFCF3, and CF2CF2), 
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Journal of Physical Chemistry A 101 (1997), pp.9118-9124. Available online at 

http://pubs.acs.org/doi/abs/10.1021/jp971994r.

Papadimitriou et al., 2007. CF3CF=CH2 and (Z)-CF3CF=CHF: temperature dependent 

OH rate coefficients and global warming potentials. V. Papadimitriou, R 

Talukdar, R. Portmann, A. Ravishankaraa and J. Burkholder. Phys. Chem. Chem. 

Phys., 2007, Vol. 9, p. 1–13. Docket number EPA-HQ-OAR-2008-0664-0002. 

Available online at 

http://pubs.rsc.org/en/Content/ArticleLanding/2008/CP/b714382f. 

Papasavva et al., 2009. Estimated 2017 Refrigerant Emissions of 2,3,3,3-

tetrafluoropropene (HFC-1234yf) in the United States Resulting from Automobile 

Air Conditioning. Environ. Sci. Technol. 2009. 43 pp. 9252-9259. Docket 

number EPA-HQ-OAR-2008-0664-0112.1. Available online at 

http://www.ncbi.nlm.nih.gov/pubmed/20000517.

Parodi et al., 1982. Predictive ability of the autoradiographic repair assay in rat liver cells 

compared with the Ames test ; S. Parodi; M. Taningher; C. Balbi ;L. Santi .

Journal of Toxicology and Environmental Health, Vol. 10, Issue 4 & 5 October 

1982 , pages 531 – 539. Available online at 

http://www.informaworld.com/smpp/content~db=all~content=a915968516.

Ravishankara et al., 1993. Do Hydrofluorocarbons Destroy Stratospheric Ozone? A. R. 

Ravishankara, Andrew A. Turnipseed, Niels R. Jensen, Stephen Barone, Michael 

Mills, Carleton J. Howard, and Susan Solomon. Science, Vol. 263. no. 5143, pp. 

71 – 75. January 4, 1994. Available online at 

http://www.sciencemag.org/cgi/content/abstract/263/5143/71.

Rhasa and Zellner, 1987. Atmospheric Oxidation of Hydrocarbons. Free Radical 

Research 1987, Vol. 3, No. 1-5: Pages 199-209. Available online at 

http://informahealthcare.com/doi/abs/10.3109/10715768709069785 .

Sciance, 2010. “General Motors R-1234yf Implementation,” Presentation by Fred 

Sciance, General Motors to EPA staff. October 28, 2010. Docket number EPAHQ-OAR-2008-0664-0xxx.

Spatz, 2008. Spatz, M and B. Minor 2008 “HFO-1234yf: A Low GWP Refrigerant for 

MAC”, VDA Winter meeting. Available online at 

http://www2.dupont.com/Refrigerants/en_US/assets/downloads/SmartAutoAC/M

AC_VDA08_HFO_1234yf.pdf. 

SROC, 2005. Chapter 3 from Safeguarding the Ozone Layer and the Global Climate 

System: Special Report of the Intergovernmental Panel on Climate Change. 

Edited by Bert Metz, Lambert Kuijpers, Susan Solomon, Stephen O. Anderson, 

Ogunlade Davidson, Jose Pons, David de Jager, Tahl Kestin, Martin Manning and 
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Page 129 of 134

Leo Meyer. Cambridge University Press. 2005. Available online at 

http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521682060.

TNO, 2005. Sub-acute (2-week) Inhalation Toxicity Study with HFO-1234yf in Rats. 

2005. Docket number EPA-HQ-OAR-2008-0664-0020 and attachments -0020.1 

through -0020.4.

TNO, 2007a. Sub-chronic (13-week) inhalation toxicity study with HFO-1234yf in rats. 

2007. Docket number EPA-HQ-OAR-2008-0664-0022 and attachments -0022.1 

through -0022.5.

TNO, 2007b. Prenatal Developmental Inhalation Toxicity Study with HFO-1234yf in 

Rats. 2007. Docket number EPA-HQ-OAR-2008-0664-0023 and attachments -

0023.1 through -0023.9.

US EPA, 1994. U.S. Environmental Protection Agency (US EPA). 1994. Methods for 

derivation of inhalation reference concentrations and application of inhalation 

dosimetry. EPA/600/8-90/066F. Office of Health and Environmental 

Assessment, Washington, DC. 1994. Available online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=71993

US EPA, 2000. Hazard Summary for Formaldehyde, CAS ID# 50-00-0. Revised 2000. 

Available online at http://www.epa.gov/ttn/atw/hlthef/formalde.html

US EPA, 2010a. Email from Yaidi Cancel, EPA. To William Hill and Ward Atkinson, 

SAE Interior Climate Control Committee re: Minimum recordkeeping on SAE 

J1739. August 16, 2010.

US EPA, 2010b. Email from Margaret Sheppard, EPA to Christopher Seeton and Kasia 

Bober, Honeywell re: Summary of our conference call on service fittings for 

HFO-1234yf. November 8, 2010.

US EPA, 2010c. Clarifying questions for Honeywell on Exposure Study. Docket 

number EPA-HQ-OPPT-2008-0918-0095.

Wallington et al., 2008. Emissions of CO2, CO, NOx, HC, PM, HFC-134a, N2O and CH4

from the Global Light Duty Vehicle Fleet. Meterolo. Z. 17. 109-116. Available 

online at http://www.schweizerbart.de/resources/downloads/paper_free/56618.pdf

Wallington et al., 2010. “Estimated Photochemical Ozone Creation Potentials (POCPs) 

of CF3CF=CH2 (HFO-1234yf) and Related Hydrofluoroolefins (HFOs).” T. 

Wallington, M. Andersen, O. Nielsen. Atmospheric Environment, in press 2010. 

Docket number EPA-HQ-OAR-2008-0664-0084.2. Available online at 

http://www.sciencedirect.com or at doi:10.1016/j.atmosenv.2010.01.040.

Weissler, P., 2008. “Consensus Building on Refrigerant Type.” Automotive Engineering 
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Protection of Stratospheric Ozone: New Substitute in the Motor Vehicle Air 

Conditioning Sector under the Significant New Alternatives Policy (SNAP) 

Program (Page 130 of 134)

International. 9: 30-32. Docket number EPA-HQ-OAR-2008-0664-0006.

WIL, 2006. Acute Cardiac Sensitization Study of [name redacted] and HFO-1234yf in 

Dogs. WIL Laboratories, 2006. Docket number EPA-HQ-OAR-2008-0664-0019 

and attachments -0019.1 through -0019.2.

List of Subjects in 40 CFR Part 82

Environmental protection, Administrative practice and procedure, 

Air pollution control, Reporting and recordkeeping requirements, Stratospheric ozone 

layer.

Dated: ______________________________________

_____________________________________________ 

Lisa P. Jackson,

Administrator.

For the reasons set out in the preamble, 40 CFR part 82 is amended as

follows:

PART 82--PROTECTION OF STRATOSPHERIC OZONE

1. The authority citation for part 82 continues to read as follows:

 Authority: 42 U.S.C. 7414, 7601, 7671-7671q.

Subpart G--Significant New Alternatives Policy Program
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2. The first table in Subpart G to Appendix B of Part 82 is amended by adding one new 

entry to the end of the table to read as follows:

Appendix B to Subpart G of Part 82 - Substitutes Subject to Use Restrictions and 

Unacceptable Substitutes

REFRIGERANTS-ACCEPTABLE SUBJECT TO USE CONDITIONS

Application Substitute Decision Conditions Comments

*****

CFC-12 

Automobile 

Motor 

Vehicle Air 

Conditioning 

(New

equipment in 

passenger 

cars and lightduty trucks 

only)

HFO-1234yf 

as a 

substitute 

for CFC-12

Acceptable 

subject to 

use 

conditions

1. The high-pressure side of the MVAC 

system shall have a pressure relief device 

located in the high pressure side of the 

compressor or immediately adjacent to the 

compressor discharge fitting. The device 

shall release refrigerant only outside of the 

passenger, trunk, and storage 

compartments and MVAC air distribution 

system. These pressure relief devices shall 

be designed to minimize impingement of 

the refrigerant and oil on hot surfaces.

2. The MVAC system high-pressure side 

relieve device identified above in 1 shall be 

self-sealing. In no case shall the maximum 

release (blow-off) pressure be greater than 

the maximum refrigerant working pressure.

3. To prevent unnecessary discharge of 

refrigerant during operation, the system 

shall have a means to limit the compressor 

operation by cutting off transmission of 

power to the compressor before any 

component failure occurs and before 

activation of any pressure relief device 

(i.e., compressor cutoff switch).

4. In no case shall any high-pressure side 

refrigerant pressure relief valves (or burst 

disks) have an activation pressure greater 

than the maximum working pressure of 

4.14 MPa. Gauge (600 psig). 

5. The maximum pressure on the lowpressure side of the MVAC system shall 

not exceed the saturation pressure of HFO1234yf at 56oC.

6. HFO-1234yf refrigerant systems 

connections shall either be:

 Located outside the passenger 

compartment and outside the 

passenger cabin airflow path.

or

 Designed to prevent leakage if the 

connections are located inside the 

Additional 

training for 

service 

technicians 

recommended.

Observe

requirements 

of Significant 

New Use Rule 

at 40 CFR 

721.10182.
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Page 132 of 134

passenger cabin or in the passenger 

cabin airflow path. For safety 

reasons, individuals performing 

servicing shall follow the service and 

repair leakage recommendations 

(e.g., from manufacturer and in 

service shop manual), including any 

service procedures established to 

prevent refrigerant from entering the 

cabin or airflow path.

7. High-side and low-side fittings shall be 

fitted with protective or sealing caps.

8. All MVAC system service fittings shall 

be located for ease of attachment of service 

hoses and shall be designed to minimize 

direct impingement of refrigerant on the 

service technician. Piping shall be of 

robust design to avoid damage or 

permanent deformation while connecting 

or disconnecting the service hose 

coupling(s) from factory charging and 

service equipment.

9. HFO-1234yf must be used with the 

following service fittings:

 For the low-side service port, use 

quick-connect fittings with an 

outside diameter of 14 + 0.2 mm 

(0.551 + 0.00787 inches). 

 For the high-side service port, use 

quick-connect fittings with an 

outside diameter of 17 + 0.2 mm 

(0.669 + 0.00787 inches).

 For connections with containers of 

20 lbs or greater, use quick-connect 

fittings with an outside diameter of 

14 + 0.2 mm (0.551 + 0.00787 

inches).

 All fittings must be different from 

those for any other refrigerant.

10. A plainly legible and durable 

refrigerant label shall be mounted in a 

clearly visible location under hood that 

does not require the removal of any parts 

or covers to be read. The label shall: 

identify the refrigerant; state the amount of 

refrigerant charge in grams (or kilograms, 

to three decimal places); and identify the 

lubricant type (polyalkylene glycol [PAG] 

or polyolester [POE]). The label either

shall include the chemical safety symbol 

for “flammable” or shall state in text that 

the refrigerant is flammable in letters at 

least 3 mm in height that are red in color. 

The label shall contain the name or logo of 

the original equipment vehicle 

manufacturer or the refrigeration system 
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Page 133 of 134

manufacturer responsible for design 

compliance with this rule and with SAE 

standards. The label shall have a minimum 

size of 60 mm by 30 mm. It shall have text 

in bold-type letters at least 3 mm in height 

for identifying refrigerant, lubricant type 

and refrigerant amount. If the label 

contains text only and no symbols, the 

label shall also state the following:

“CAUTION SYSTEM CONTAINS 

REFRIGERANT R-1234yf UNDER

HIGH PRESSURE-TO BE SERVICED 

ONLY BY QUALIFIED PERSONNEL” 

11. Manufacturers must conduct Failure 

Mode and Effect Analysis (FMEA) as 

provided in SAE J1739 (adopted 2009). 

Manufacturers must keep the FMEA on 

file for at least three years from the date of 

creation. 

3. Appendix B to Subpart G is amended by revising the entry for ``CFC-12 Motor 

Vehicle Air Conditioners (Retrofit and New Equipment/NIKs)'' in the table titled 

``Refrigerants--Unacceptable Substitutes'' to read as follows:

Refrigerants--Unacceptable Substitutes

 * * * * * 

End -use Substitute Decision Comments

CFC-12 Motor 

Vehicle Air 

Conditioners (Retrofit 

and New 

Equipment/NIKs)

R-405A....... Unacceptable. R-405A contains R-c318, a 

PFC, which has an 

extremely high GWP and 

lifetime. Other Substitutes 

exist which do not contain 

PFCs.

Hydrocarbon 

Blend B.... 

Unacceptable. Flammability is a serious 

concern. Data have not 

been submitted to 

demonstrate it can be used 

safely in this end-use. 

Flammable 

Substitutes, 

other than R152a or HFO1234yf in new 

Unacceptable. The risks associated with 

using flammable 

substitutes (except R-152a 

and HFO-1234yf) in this 

end-use have not been 
*** E.O. 12866 Review _ Draft _ Do Not Cite, Quote, or Release During Review ***

Page 134 of 134

equipment. addressed by a risk 

assessment. R-152a and 

HFO-1234yf may be used 

in new equipment with the 

use conditions in appendix 

B to this subpart. 

 

[FR Doc. ]

BILLING CODE 6560-50-P