FILENAME   \* MERGEFORMAT  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].

ADDRESSES:  EPA has established a docket for this action under Docket ID
No. EPA-HQ-OAR-2008-0664.  All documents in the docket are listed on the
  HYPERLINK "http://www.regulations.gov"  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
HYPERLINK "http://www.regulations.gov"  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<PHONE_NUMBER>, and the
telephone number for the Air Docket is<PHONE_NUMBER>.

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<PHONE_NUMBER>, fax number, (202)
343-2338; e-mail address at   HYPERLINK
<EMAIL_ADDRESS><EMAIL_ADDRESS>.

Notices and rulemakings under the SNAP program are available on EPA's
Stratospheric Ozone Web site at   HYPERLINK
"http://www.epa.gov/ozone/snap/regulations.html"
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 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

Does this action apply to me?

What abbreviations and acronyms are used in this action?

What is EPA’s final decision for HFO-1234yf for motor vehicle air
conditioning (MVAC)?

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

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

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

Significant New Use Rule

Rules under Sections 609 and 608 of the Clean Air Act

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

Acceptability decision

Use conditions

Environmental impacts

Health and safety impacts

Retrofit usage

Use by “do-it-yourselfers”

Servicing issues

Cost, availability, and small business impacts

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

Executive Order 12866: Regulatory Planning and Review

Paperwork Reduction Act

Regulatory Flexibility Act

Unfunded Mandates Reform Act

Executive Order 13132: Federalism

Executive Order 13175: Consultation and Coordination with Indian Tribal
Governments

Executive Order 13045: Protection of Children from Environmental Health
and Safety Risks

Executive Order 13211: Actions that Significantly Affect Energy Supply,
Distribution, or Use

National Technology Transfer and Advancement Act

Executive Order 12898: Federal Actions to Address Environmental Justice
in Minority Populations and Low-Income Populations

Congressional Review Act

X.	References

Does this Action Apply to Me?

	This final rule regulates the use of the chemical HFO-1234yf
(2,3,3,3-tetrafluoroprop-1-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

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

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

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

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

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
HFO-1234yf is used in a new MVAC system for passenger cars and
light-duty trucks:

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.

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.

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).

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).

The maximum pressure on the low-pressure side of the MVAC system shall
not exceed the saturation pressure of HFO-1234yf at 56oC.

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 procedures established to prevent
refrigerant from entering the cabin or airflow path.

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

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.

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.

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 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”

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.

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
requirements provided in the draft SAE standard referred 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 HFO-1234yf 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 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
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.  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 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-HQ-OAR-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)-134a (order of magnitude of 10-12
events per vehicle operating hour).  EPA previously found HFC-134a
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.  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-152a, 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 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).

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).

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 HFO-1234yf, 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.  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 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
HFO-1234yf 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 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 HFO-1234yf.  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 (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 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, 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);
these 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 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 HFO-1234yf 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 HFO-1234yf).  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 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.

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.  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 ppm over 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.,

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; 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
(EPA-HQ-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 R-744 (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”
(EPA-HQ-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 HFO-1234yf 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 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 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 10-26 cases 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-HQ-OAR-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 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-HQ-OAR-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 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 low-pressure side of the MVAC
system and for large cylinders for professional use (typically 20 lb or
more).  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 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
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.  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 hour
(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 HFC-134a, 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.

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 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?

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 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, 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 end-of-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.

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 HFC-134a, 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 information for hydrocarbons that would allow us to
make such a comparison for use in MVAC.

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.

 Use conditions

Comment:  Several commenters stated that the proposed use conditions
limiting concentrations of HFO-1234yf below the lower flammability limit
are overly stringent or even impossible to meet and are not needed for
safe usage.  Some automobile manufacturers suggested relying upon
established standards and practices, such as SAE protocols and
standards, instead of use conditions.  Some commenters suggested
alternative language for use conditions.  Other commenters expressed
concern that the proposed use conditions limiting concentrations of
HFO-1234yf would preclude the use of HFO-1234yf by any vehicle that is
not initially designed to use this refrigerant.

Response:  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 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).

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 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.  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 use condition.  One commenter stated that electric terminals on
hybrid vehicles are well protected to prevent fires and should not
ignite the refrigerant.  Another commenter stated that an accident
severe enough to cause refrigerant leakage would also result in damage
to the duct between the evaporator [in the MVAC system] and the battery
pack, preventing an increase in refrigerant concentrations at the
battery pack.  One commenter stated that it is difficult to establish
generic SNAP use conditions for hybrid vehicles, and individual
manufacturers need to understand particular design features of their
hybrid vehicles to ensure safe refrigerant application.

Three commenters expressed concern for using HFO-1234yf in hybrid and
electric vehicles and stated that the use condition is not conservative
enough.  One commenter stated that the maximum concentrations of
HFO-1234yf need to be far below the 6.2% LFL based on new tests done at
the Federal Institute for Materials Research and Testing (BAM) and that
they are unsure whether or not additional measures can effectively avoid
the risk of explosive mixtures.  Another commenter stated that
HFO-1234yf would raise concerns in the field of battery cooling needed
in electric vehicles because flammability and chemical reactions would
pose major risks, which could lead to legal consequences for OEMs.

Response:  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-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 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 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 high-pressure 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
high-pressure compressor cut-off switch, as per SAE J639.  Another
commenter suggested that the compressor cut-off switch would be useful
for all systems 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 HFO-1234yf 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 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 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 MVAC systems, in the absence of such standards
from DOT, EPA would need to determine that HFO-1234yf is unacceptable
for use in MVACs.

  Environmental impacts

Ozone Depletion Potential

Comment:  Several commenters agreed with EPA’s proposed finding that
HFO-1234yf 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 HFO-1234yf 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 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 HFO-1234yf 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.

  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 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-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 ppt, 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, compared to a
health-based limit of 5000 ppt (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,
HFC-134a 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.

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
end-uses 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
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, HFC-134a 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 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). 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 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).

  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 ground-level ozone,
considering the additional information provided in public comments
(e.g., Luecken et al., 2009 and Wallington et al., 2009).

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 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 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 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 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-OAR-2008-0664-0037) greatly overestimates the local deposition
of TFA from oxidation of HFO-1234yf.  In particular, one commenter
claimed that the modeling’s use of the oxidation of SO2 to sulfate
ion, SO3-, as a proxy for the oxidation of HFO-1234yf is overly
conservative because a large portion of SO2 is in aerosol form, unlike
for HFO-1234yf.  This commenter also referred to the impacts found in
the peer-reviewed paper by Luecken et al. (2009).

Response:  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.

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.

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 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., 1982; Kirkland et al., 2005), 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 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-OAR-2008-0664-0036).  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 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 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 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
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 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 time-weighted 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-OAR-2008-0664-0036.  The specific
exposure parameters that the commenters questioned were assumptions
regarding:

	• garage volume;

	• time the user spent under the hood during recharging operations;

	• the size of the space where any leaking gas would disperse;

	• the air exchange rate in a service area that should be
well-ventilated when the engine is running;

	• use of the refrigerant in a closed garage with no ventilation; and,

	• the amount of refrigerant used during recharge operations.

During the comment period for the proposed SNUR, the PMN and SNAP
submitter conducted a simulated vehicle service leak testing, using
HFC-134a as a surrogate, indicating that exposures from use of a 12-oz
can during consumer DIY use are below the Agency’s level of concern
for HFO-1234yf (Honeywell, 2010a).

Response:  Concerning exposure estimates for DIYers, the exposure values
in the EPA risk assessment (EPA-HQ-OAR-2008-0664-0036) are bounding
estimates of the maximum possible theoretical concentrations.  The EPA
assessment used the industry-modeled DIY scenarios and assumptions in a
2008 report by Gradient Corporation for the SAE CRP (CRP, 2008) as a
starting point for creating the bounding estimates.  To do so, EPA
assumed that the entire leakage mass of each industry-modeled scenario
was released to its corresponding volume with no air exchange.  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 long-term, 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 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.  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
ppt—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, compared to a health-based limit of 5000 ppt
(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