[Federal Register Volume 91, Number 65 (Monday, April 6, 2026)]
[Proposed Rules]
[Pages 17176-17186]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2026-06665]
=======================================================================
-----------------------------------------------------------------------
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 82
[EPA-HQ-OAR-2024-0503; FRL-12207-03-OAR]
RIN 2060-AW45
Protection of Stratospheric Ozone: Listing of Substitutes Under
the Significant New Alternatives Policy Program in Refrigeration and
Air Conditioning and Fire Suppression; Supplemental Notice of Proposed
Rulemaking
AGENCY: Environmental Protection Agency (EPA).
ACTION: Supplemental proposed rule.
-----------------------------------------------------------------------
SUMMARY: Pursuant to the U.S. Environmental Protection Agency's
Significant New Alternatives Policy program, this action proposes to
list the refrigerant 2,3,3,3-tetrafluoropropene, also known as HFO-
1234yf, as acceptable, subject to use conditions, in the motor vehicle
air conditioning end-use for retrofit of heavy-duty pickup trucks and
complete heavy-duty vans. This action supplements the Agency's November
10, 2025, proposal with respect to the proposed listings in the motor
vehicle air conditioning end-use for retrofit of heavy-duty pickup
trucks and heavy-duty vans (both complete and incomplete vans). The EPA
is also supplementing that proposal to clarify the intended scope of
that proposed rule. The EPA is providing an opportunity for public
comment on the additional listing and the clarification. The EPA is not
reopening the comment period for any portions of the November 10, 2025,
proposal which are not explicitly addressed in this supplemental
proposal.
DATES: Comments on this supplemental proposal must be received on or
before May 6, 2026 unless a public hearing is held. If a public hearing
is held, comments on this supplemental proposal must be received on or
before 30 days after the date of the public hearing. Public hearing:
Any party requesting a public hearing must notify the contact listed in
the FOR FURTHER INFORMATION CONTACT section, which is Emily Maruyama at
email address: [email protected] by 5 p.m. Eastern Daylight Time
on or before April 13, 2026. If a public hearing is held, it will take
place on or around April 21, 2026. Please refer to the SUPPLEMENTARY
INFORMATION section for additional information on the public hearing.
ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2024-0503 by any of the following methods:
Federal Rulemaking Portal: https://www.regulations.gov
(our preferred method). Follow the online instructions for submitting
comments.
Email: [email protected]. Include Docket ID No. EPA-
HQ-OAR-2024-0503 in the subject line of the message.
Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Air and Radiation Docket, Mail Code 28221T, 1200 Pennsylvania
Avenue NW, Washington, DC 20460.
Hand Delivery or Courier: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operations are 8:30 a.m. to 4:30 p.m.,
Monday-Friday (except Federal Holidays).
Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov, including personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the ``Public Participation''
heading of the SUPPLEMENTARY INFORMATION section of this document. For
information on EPA Docket Center services, please visit us online at
https://www.epa.gov/dockets.
If a public hearing is requested on or before April 13, 2026, the
EPA will post an update at https://www.epa.gov/snap. The EPA does not
intend to publish a document in the Federal Register announcing
updates. The public hearing will be held on or around April 21, 2026.
Information on the hearing including the time and URL will be posted on
the EPA's Stratospheric Ozone website at https://www.epa.gov/snap.
Refer to the section titled, Public Participation for additional
information.
FOR FURTHER INFORMATION CONTACT: For information about this proposed
rule, contact Emily Maruyama, Chemicals, Coatings, and Products
Division, Office of Clean Air Programs (Mail Code 6205A), Environmental
Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC 20460;
telephone
[[Page 17177]]
number: (202) 564-2809; email address: [email protected]. Notices
and rulemakings under the EPA's Significant New Alternatives Policy
program are available on the EPA's website at https://www.epa.gov/snap/snap-regulations.
SUPPLEMENTARY INFORMATION:
Preamble acronyms and abbreviations. Throughout this preamble the
use of ``we,'' ``us,'' or ``our'' is intended to refer to the EPA. We
use multiple acronyms and terms in this preamble. While this list may
not be exhaustive, to ease the reading of this preamble and for
reference purposes, the EPA defines the following terms and acronyms
here:
AC Air Conditioning
ANSI American National Standards Institute
ASHRAE American Society of Heating, Refrigerating and Air-
Conditioning Engineers
CAA Clean Air Act
CAS Reg. No. Chemical Abstracts Service Registry Identification
Number
CBI Confidential Business Information
CFC Chlorofluorocarbon
CFR Code of Federal Regulations
CO2 Carbon Dioxide
CRP Cooperative Research Program
DIY Do it yourself
EEAP Environmental Effects Assessment Panel
EPA United States Environmental Protection Agency
FR Federal Register
GVWRv Gross Vehicle Weight Rating
HCFC Hydrochlorofluorocarbon
HD Heavy-duty
HFC Hydrofluorocarbon
HFO Hydrofluoroolefin
ICF ICF International, Inc.
LD Light-duty
LFL Lower Flammability Limit
LMDV Light- and medium-Duty Vehicle
MD Medium-duty
mJ Millijoules
MVAC Motor Vehicle Air Conditioning or Motor Vehicle Air Conditioner
MY Model Year
NAAQS National Ambient Air Quality Standard
NAICS North American Industrial Classification System
NPRM Notice of Proposed Rulemaking
ODS Ozone-Depleting Substances
OEL Occupational Exposure Limit
OEM Original Equipment Manufacturer
OMB United States Office of Management and Budget
PBI Proprietary Business Information
PMN Pre-Manufacture Notice
ppm Parts Per Million
PRA Paperwork Reduction Act
RFA Regulatory Flexibility Act
SAE SAE International, previously known as the Society of Automotive
Engineers
SDS Safety Data Sheet
SIP State Implementation Plan
SNAP Significant New Alternatives Policy
SNUR Significant New Use Rule
TFA Trifluoroacetic Acid
TLV Threshold Limit Value
TWA Time Weighted Average
UMRA Unfunded Mandates Reform Act
VOC Volatile Organic Compounds
Table of Contents
I. Executive Summary
A. Purpose of the Regulatory Action
B. Summary of the Major Provisions of the Regulatory Action
II. Public Participation
A. Written Comments
B. Participation in Virtual Public Hearing
III. General Information
A. Does this action apply to me?
B. What action is the Agency proposing to take?
C. What is the Agency's authority for taking this action?
D. What are the guiding principles of the SNAP program and what
are the SNAP criteria for evaluating substitutes?
E. Children's Environmental Health
IV. Proposed Listing for Motor Vehicle Air Conditioning
A. What is the EPA proposing in this action?
B. Background on MVACs in HD Pickup Trucks and HD Vans
C. What are the ASHRAE classifications for refrigerant
flammability and toxicity?
D. What is refrigerant HFO-1234yf and how does it compare to
other refrigerants in this end-use?
E. What use conditions is the EPA proposing for HFO-1234yf for
retrofit of MVACs in this end-use and what existing requirements
apply to this refrigerant?
V. Clarification of Intended Scope of the 2025 NPRM and Other
Clarifications
VI. On which topics is the EPA specifically requesting comment?
VII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Executive Order 14192: Unleashing Prosperity Through
Deregulation
C. Paperwork Reduction Act (PRA)
D. Regulatory Flexibility Act (RFA)
E. Unfunded Mandates Reform Act (UMRA)
F. Executive Order 13132: Federalism
G. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
H. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
I. Executive Order 13211: Actions That Significantly Affect
Energy Supply, Distribution, or Use
J. National Technology Transfer and Advancement Act
VIII. References
I. Executive Summary
A. Purpose of the Regulatory Action
The EPA is proposing a new listing after our evaluation of human
health and environmental information for one substitute under Clean Air
Act (CAA) section 612, Significant New Alternatives Policy (SNAP)
program. The Agency is proposing this new listing in the refrigeration
and air conditioning (AC) sector based on the information the EPA
included in the docket. This supplemental notice of proposed
rulemaking, hereafter referred to as the ``supplemental proposal'' or
``supplemental action,'' would provide a new refrigerant option in
specific uses, thereby increasing flexibility for industry. The EPA is
also supplementing the Agency's November 10, 2025, Notice of Proposed
Rulemaking (NPRM), hereafter referred to as the ``2025 NPRM,'' to
clarify the intended scope of that proposal.\1\
---------------------------------------------------------------------------
\1\ See 90 FR 50766 (November 10, 2025).
---------------------------------------------------------------------------
B. Summary of the Major Provisions of the Regulatory Action
This action proposes to list 2,3,3,3-tetrafluoropropene,\2\ also
known as hydrofluoroolefin (HFO)-1234yf or R-1234yf, hereafter referred
to as ``HFO-1234yf,'' as acceptable, subject to use conditions, in the
motor vehicle air conditioning (MVAC) end-use for retrofit of heavy-
duty (HD) pickup trucks and complete HD vans. This proposal supplements
the 2025 NPRM with respect to the proposed listings in the MVAC end-use
for retrofit of HD pickup trucks and HD vans (both complete and
incomplete vans). In the 2025 NPRM, the EPA proposed to list three
other substitutes as acceptable, subject to use conditions, for similar
end-uses. The EPA is supplementing the 2025 NPRM to clarify the
intended scope of that proposal for R-444A as acceptable, subject to
use conditions, in the MVAC end-use. In the 2025 NPRM, the EPA proposed
a listing for R-444A in the MVAC end-use for retrofit of HD pickup
trucks and HD vans (both complete and incomplete). The Agency included
incomplete HD vans in error and is clarifying that we intended for this
proposed listing to apply to HD pickup trucks and complete HD vans
only. The scope of the proposals in the 2025 NPRM for the two other
substitutes proposed in this end-use, R-456A and R-480A, are not
affected by this supplemental proposal and thus remain unchanged.
---------------------------------------------------------------------------
\2\ CAS Reg. No. 754-12-1.
---------------------------------------------------------------------------
The proposed new listing for HFO-1234yf would appear as a change to
appendix B of 40 Code of Federal Regulations (CFR) part 82, subpart G,
within row 12 in the table titled ``Refrigerants--Acceptable Subject to
Use Conditions.'' The clarification of the intended scope of the 2025
NPRM listing for R-444A in the MVAC end-use
[[Page 17178]]
discussed in section V of this supplemental proposal would appear as a
change to appendix B of 40 CFR part 82, subpart G, within row 10 in the
same table titled ``Refrigerants--Acceptable Subject to Use
Conditions.'' In this supplemental proposal, the EPA is not proposing
changes beyond these. The specific proposed regulatory changes to
appendix B are available in a document in the docket under the title
``Proposed Changes to Appendix B for SNAP 27 Supplemental Proposal.''
\3\
---------------------------------------------------------------------------
\3\ To see the adjustments to the proposed regulatory text
discussed in this supplemental action in context with all the other
proposed changes and listings discussed in the 2025 NPRM, see the
document in the docket for this rulemaking under the title
``Proposed Regulatory Text for SNAP Rule 27--Supplemental
Proposal.''
---------------------------------------------------------------------------
II. Public Participation
A. Written Comments
Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2024-
0503 at https://www.regulations.gov (our preferred method), or the
other methods identified in the ADDRESSES section. Once submitted,
comments cannot be edited or removed from the docket. The EPA may
publish any comment received in the public docket. Do not submit to the
EPA's docket at https://www.regulations.gov any information you
consider to be Confidential Business Information (CBI), Proprietary
Business Information (PBI), or other information whose disclosure is
restricted by statute. Multimedia submissions (audio, video, etc.) must
be accompanied by a written comment. The written comment is considered
the official comment and should include discussion of all points you
wish to make. The EPA will generally not consider comments or comment
contents located outside of the primary submission (i.e., on the web,
cloud, or other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the
full EPA public comment policy; information about CBI, PBI, or
multimedia submissions; and general guidance on making effective
comments.
B. Participation in Virtual Public Hearing
The EPA may hold a virtual public hearing if the Agency receives a
request to hold one. Any party requesting a public hearing must notify
the contact listed in the FOR FURTHER INFORMATION CONTACT section,
which is Emily Maruyama at email address: [email protected] by 5
p.m. Eastern Daylight Time on or before April 13, 2026. If a virtual
public hearing is held, it will take place on or around April 21, 2026
and further information will be provided on the EPA's Stratospheric
Ozone website at https://www.epa.gov/snap.
The EPA will make every effort to follow the schedule as closely as
possible on the day of the hearing; however, please plan for the
hearings to run either ahead of schedule or behind schedule. Each
commenter will have three to five minutes to provide oral testimony.
The EPA encourages commenters to provide a copy of their oral testimony
electronically by emailing it to [email protected]. The EPA also
recommends submitting the text of your oral comments as written
comments to the rulemaking docket EPA-HQ-OAR-2024-0503. Written
statements and supporting information submitted during the comment
period will be considered with the same weight as oral comments and
supporting information presented at the public hearing. The EPA may ask
clarifying questions during the oral presentations but will not respond
to the presentations at that time.
Please note that any updates made to any aspect of the hearing will
be posted online at https://www.epa.gov/snap. While the EPA expects the
hearing to go forward as set forth above, please monitor our website or
contact Emily Maruyama, 202-564-2809, [email protected] to
determine if there are any updates. The EPA does not intend to publish
a document in the Federal Register (FR) announcing updates.
III. General Information
A. Does this action apply to me?
The following list identifies regulated entities that may be
affected by this rulemaking and their respective North American
Industrial Classification System (NAICS) codes:
All Other Basic Organic Chemical Manufacturing (325199).
Motor Vehicle Manufacturing (3361).
Motor Vehicle Parts Manufacturing (3363).
Recyclable Material Merchant Wholesalers (423930).
General Automotive Repair (811111).
This list is not intended to be exhaustive, but rather to provide a
guide for readers regarding entities likely to be affected by this
action. To determine whether your facility, company, business, or
organization could be affected by this action, you should carefully
examine the regulations at 40 CFR part 82, subpart G, and the proposed
revisions. If you have questions regarding the applicability of this
action to a particular entity, consult the person listed in the FOR
FURTHER INFORMATION CONTACT section.
B. What action is the Agency proposing to take?
The EPA is proposing to list HFO-1234yf as acceptable, subject to
use conditions, in the MVAC end-use for retrofit of HD pickup trucks
and complete HD vans. The EPA is also supplementing the 2025 NPRM to
clarify the intended scope of that proposal. Specifically, in the 2025
NPRM, the EPA proposed to list R-444A as acceptable, subject to use
conditions, in the MVAC end-use for retrofit of complete and incomplete
HD vans. This supplemental action is clarifying that the EPA intended
for this proposed listing to apply only to complete HD vans.
C. What is the Agency's authority for taking this action?
This proposal supplements the 2025 NPRM. See the 2025 NPRM for a
full discussion of the Agency's authority for taking this action.
D. What are the guiding principles of the SNAP program and what are the
SNAP criteria for evaluating substitutes?
This proposal supplements the 2025 NPRM. See the 2025 NPRM for a
full discussion of the guiding principles of the SNAP program and the
SNAP criteria for evaluating substitutes.
E. Children's Environmental Health
This action is subject to the EPA's Policy on Children's Health
(https://www.epa.gov/children/childrens-health-policy-and-plan) because
the rule has considerations for human health. Accordingly, we have
evaluated the environmental health effects of HFO-1234yf to general
population exposure.
In summary, the risk screen for the use of HFO-1234yf in the MVAC
end-use for retrofit of HD pickup trucks and complete HD vans found
that this substitute is not expected to cause a significant risk to
human health in the general population when manufactured for use and
used as a refrigerant in HD pickup truck and complete HD van AC
systems. Additionally, the EPA found that the toxicity risks of using
HFO-1234yf in the MVAC end-use for retrofit of HD pickup trucks and
complete HD vans are comparable to or lower than that of other
available substitutes in the same end-use. The risk screen found that
HFO-1234yf can be used without exceeding the recommended
[[Page 17179]]
occupational exposure limit (OEL) of 500 ppm (8-hr OEL); thus, the
toxicity risks of this refrigerant are comparable to those of other
acceptable substitutes in MVACs, which also are used without exceeding
their OELs. The risk screen also found that HFO-1234yf in HD pickup
trucks and complete HD vans does not pose a significant risk of end-use
exposure, provided systems are installed in appropriate spaces with
proper engineering controls, emergency response plans, and according to
guidelines from the manufacturer, standards, and the safety data sheet.
While the EPA has not conducted a separate analysis of risks to infants
and children associated with this rule, the rule does contain use
conditions that would reduce exposure risks to the general population,
with the reduction of exposure being most important to the most
sensitive individuals.
The results of this evaluation are contained in section IV.D. of
this preamble and in the risk screen titled ``Risk Screen on
Substitutes in Motor Vehicle Air Conditioning (Heavy-Duty Pickup Trucks
and Complete Heavy-Duty Vans) (Retrofit Equipment); Substitute: HFO-
1234yf (Solstice[supreg] yf or Solstice[supreg] 1234yf).'' A copy of
this document is available in the public docket for this action at
Docket ID No. EPA-HQ-OAR-2024-0503.
This action is consistent with the EPA's Policy on Children Health
because it provides an additional retrofit option and would not pose
additional adverse effects to human health when used in accordance with
existing and proposed requirements and as intended by the submitter.
Furthermore, Executive Order 13045 (``Protection of Children from
Environmental Health Risks and Safety Risks'') applies to this action.
Information on how this action is subject to this Executive Order is
available in a section of this preamble under the same name.
IV. Proposed Listing for Motor Vehicle Air Conditioning
A. What is the EPA proposing in this action?
The EPA is proposing to list HFO-1234yf as acceptable, subject to
use conditions, in the MVAC end-use for retrofit of HD pickup trucks
and complete HD vans. In the 2025 NPRM, the EPA proposed to list three
substitutes, R-444A, R-456A, and R-480A as acceptable, subject to use
conditions, in the MVAC end-use for retrofit of HD pickup trucks and
complete and incomplete HD vans. During the public comment period, the
EPA received comments and feedback from stakeholders highlighting that
the proposal did not include a listing of HFO-1234yf in the MVAC end-
use for retrofit of HD pickup trucks and HD vans. The EPA reviewed
these comments and agrees that the Agency should have included all four
refrigerants for this end-use consistent with other MVAC listings in
the 2025 NPRM and is issuing this supplemental proposal to add this
listing. To support this listing, the Agency has provided in the docket
the risk screen for HFO-1234yf for this end-use and proposes to find
HFO-1234yf acceptable, subject to use conditions, in the MVAC end-use
for retrofit of HD pickup trucks and complete HD vans.
The 2025 NPRM proposed to list HFO-1234yf as acceptable, subject to
use conditions, in the MVAC end-use for retrofit of light- and medium-
duty vehicles (LMDVs). HFO-1234yf has not otherwise been listed as
acceptable for other MVAC retrofit applications. The proposed listing
for HFO-1234yf in this supplemental action would allow for retrofits of
chlorofluorocarbon (CFC)-12 MVACs as well as for retrofits of MVACs
using any of the refrigerants the SNAP program lists as acceptable or
acceptable, subject to use conditions, in this end-use.
B. Background on MVACs in HD Pickup Trucks and HD Vans
The SNAP program uses the term MVAC broadly to describe a wide
variety of non-stationary AC systems that provide passenger comfort
cooling for LMDVs, HD vehicles, nonroad vehicles, buses, and trains.
The SNAP MVAC end-use includes systems that may also be subject to
other CAA regulatory programs, including for example, where those
systems fit within the regulatory definition of ``MVAC'' under 40 CFR
82.32,\4\ or the definition of an ``MVAC-like appliance'' \5\ or
``appliance'' under 40 CFR 82.152, or both.
---------------------------------------------------------------------------
\4\ As defined in 40 CFR 82.32, Motor vehicle air conditioners
mean mechanical vapor compression refrigeration equipment used to
cool the driver's or passenger's compartment of any motor vehicle.
This definition is not intended to encompass the hermetically sealed
refrigeration systems used on motor vehicles for refrigerated cargo
and the air conditioning systems on passenger buses using
hydrochlorofluorocarbon (HCFC)-22 refrigerant. See also 40 CFR
82.152 (defining MVAC to mean ``any appliance that is a motor
vehicle air conditioner as defined in subpart B of 40 CFR part
82'').
\5\ As defined in 40 CFR 82.152 MVAC-like appliance means a
mechanical vapor compression, open-drive compressor appliance with a
full charge of 20 pounds or less of refrigerant used to cool the
driver's or passenger's compartment of off-road vehicles or
equipment. This includes, but is not limited to, the air-
conditioning equipment found on agricultural or construction
vehicles. This definition is not intended to cover appliances using
R-22 refrigerant.
---------------------------------------------------------------------------
To appropriately evaluate human health and environmental risks, the
SNAP program considers the type of vehicle in which the proposed
alternative would be used. The vehicle types within the MVAC end-use
addressed in this supplemental proposal to list HFO-1234yf as
acceptable, subject to use conditions, include limited types of
vehicles, specifically, HD pickup trucks and complete HD vans (e.g.,
large passenger vehicles such as large pickup trucks or vans). In this
supplemental action, the EPA is not making any changes to the proposed
MVAC acceptability listings for HFO-1234yf included in the 2025 NPRM
(e.g., retrofit LMDVs, new HD on-highway vehicles, and new buses) and
is not reopening the comment period for those proposed listings.
HD vehicles are often subdivided by vehicle weight classifications,
as defined by the vehicle's gross vehicle weight rating (GVWR), which
is a measure of the combined curb (empty) weight and cargo carrying
capacity of the truck. HD vehicles have GVWRs above 8,500 pounds. HD
pickup trucks and HD vans are Class 2b and 3 vehicles with GVWRs
between 8,501 and 14,000 pounds.
The types of vehicles for which the EPA is proposing to list HFO-
1234yf for retrofit use as acceptable, subject to use conditions, in
this supplemental action, are in many ways more similar to light-duty
(LD) or medium-duty (MD) vehicles than they are to the HD vehicles with
a higher GVWR classification. These vehicle types are similar to LD
vehicles technologically and most are manufactured by companies with
major LD markets in the United States and in a similar manner to LD
vehicles.\6\ In many cases, these types of HD vehicles are versions of
their LD counterparts.\7\ The primary difference between HD pickup
trucks and HD vans and their LD counterpart vehicles is that HD pickup
trucks and HD vans are occupational or work vehicles that are designed
for much higher towing and payload capabilities than are LD pickup
trucks and LD vans. HD pickup trucks and HD vans share many design
similarities with their
[[Page 17180]]
lighter counterparts. For example, MVAC systems in HD pickup trucks and
HD vans generally have a similar configuration and use similar
components as their lighter counterparts. Differences may exist in
terms of cooling capacity (e.g., based on cabin volume), system layout
(e.g., the number of evaporators), and the durability requirements due
to longer truck life.\8\
---------------------------------------------------------------------------
\6\ This is more broadly true for HD pickup trucks than HD vans
because every manufacturer of HD pickup trucks also makes LD pickup
trucks, while only some HD van manufacturers also make LD vans (80
FR 40148; July 13, 2015).
\7\ ICF. (2026a). Technical Support Document for Motor Vehicle
Air Conditioning in Limited Heavy-Duty Applications.
\8\ ICF. (2026a).
---------------------------------------------------------------------------
All types of HD vehicles can be sold as ``complete'' or
``incomplete'' vehicles.\9\ Approximately 90 percent of HD pickup
trucks and HD vans are \3/4\-ton and 1-ton pickup trucks, 15-passenger
vans, and large work vans that are sold by vehicle manufacturers as
complete vehicles.\10\ Complete vehicles are sold by vehicle
manufacturers to end users with no secondary manufacturer making
substantial modifications prior to registration and use. Incomplete
vehicles are sold by vehicle manufacturers to secondary manufacturers
without the primary load-carrying device or container attached.\11\
---------------------------------------------------------------------------
\9\ See 76 FR 57259-60 (September 15, 2011).
\10\ ICF. (2026a).
\11\ Incomplete HD vehicles can also be sold to and modified by
tertiary or subsequent manufacturers. For the purposes of this
supplemental proposal, the discussion of modifications made by
secondary manufacturers also applies to modifications made by
tertiary or subsequent manufacturers.
---------------------------------------------------------------------------
Examples of modifications by secondary manufacturers to HD pickup
trucks are installing a flatbed platform or tool storage bins. The EPA
is not aware of any equipment added by a secondary manufacturer to an
incomplete HD pickup truck that would result in a secondary
manufacturer modifying or adjusting the already installed MVAC system
to provide cooling capacity.
Incomplete HD vans are typically sold with no enclosed cabin area
behind the driver's seat, and secondary manufacturer modifications
could include applications such as conversion to ambulances, shuttle
vans, and motor homes. Incomplete HD vans may include original
equipment manufacturer (OEM) MVACs that are identical to those
installed in the complete HD van on which the incomplete model is
based. In some cases, these systems are designed solely for cooling the
front driver area, while other systems are manufactured by the OEM with
additional capability to provide cooling behind the driver area to the
cabin after modification.
MVACs across all vehicle types are typically charged during vehicle
manufacture. Incomplete HD vehicles are modified by secondary
manufacturers and that modification may or may not involve the
installation of additional AC or refrigeration equipment.\12\ While
some secondary manufacturers use the OEM MVAC system with no
modification to the contained refrigerant system (hoses, connections,
heat exchangers, compressor, etc.), this is not a uniform practice. At
the time of this supplemental action, the EPA does not have sufficient
information on the potential for modifications to OEM-installed MVAC
systems of incomplete HD vans by secondary manufacturers and the impact
of those modifications on the safe use of HFO-1234yf. For this reason,
the EPA is not proposing to find HFO-1234yf acceptable, subject to use
conditions, in the MVAC end-use for retrofit of incomplete HD vans in
this supplemental proposal.
---------------------------------------------------------------------------
\12\ For example, AC for the rear compartment of an ambulance or
shuttle van.
---------------------------------------------------------------------------
Historically, the class I ozone-depleting substances (ODS)
refrigerant CFC-12 was the primary refrigerant used in MVACs for
passenger vehicles and trucks. In the initial 1994 SNAP rulemaking,
hydrofluorocarbon (HFC)-134a, amongst other substitutes, was listed as
acceptable for use in new and retrofit MVACs, including HD pickup
trucks and HD vans.\13\ Since then, the EPA has listed additional
alternatives for MVACs as acceptable, subject to use conditions, for
use in new HD pickup trucks and complete HD vans, including HFO-1234yf,
HFC-152a, and carbon dioxide (R-744).
---------------------------------------------------------------------------
\13\ See 59 FR 13044 (March 18, 1994).
---------------------------------------------------------------------------
The EPA previously listed HFO-1234yf as acceptable, subject to use
conditions, in newly manufactured HD pickup trucks and complete HD
vans.\14\ As of model year (MY) 2026, both HFO-1234yf and HFC-134a are
used in new HD pickup trucks that are manufactured and imported in the
United States. New complete HD vans continue to primarily use HFC-
134a.\15\
---------------------------------------------------------------------------
\14\ See 81 FR 86778 (December 1, 2016).
\15\ ICF. (2026a).
---------------------------------------------------------------------------
The EPA considers other relevant regulatory programs when
developing listing decisions and use conditions. For example, CAA
section 609 and implementing regulations in 40 CFR part 82, subpart B
address the repair and servicing of MVACs as well as technician
training and certification. CAA section 608 and implementing
regulations in 40 CFR part 82, subpart F restrict the sale of
refrigerant and address disposal and other activities involving MVACs
that are not regulated under CAA section 609.
By considering the regulatory requirements that already exist,
consistent with the SNAP program's guiding principles, the EPA has been
able to limit the use conditions the Agency would have otherwise
considered, particularly for retrofits. See the 2025 NPRM for a full
discussion of the EPA's regulatory approach under CAA sections 609 and
612 regarding the repair and servicing of MVACs and recovery,
recycling, and recharging equipment.
C. What are the ASHRAE classifications for refrigerant flammability and
toxicity?
American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE) Standard 34-2024 assigns a safety group for each
refrigerant, which consists of two to three alphanumeric characters
(e.g., A2L or B1).\16\ The initial character indicates the toxicity,
and the numeral, with or without suffix letter, denotes the
flammability. HFO-1234yf is in the A2L Safety Group. ASHRAE classifies
Class A refrigerants as refrigerants for which toxicity has not been
identified at concentrations less than or equal to 400 parts per
million (ppm) by volume, based on data used to determine threshold
limit value-time-weighted average (TLV-TWA) or consistent indices.
Throughout this document, refrigerants in the flammability class of
``2L'' are referred to as lower flammability refrigerants. See the 2025
NPRM for a full discussion of the ASHRAE classifications for
refrigerant flammability and toxicity.
---------------------------------------------------------------------------
\16\ ASHRAE. (2024). ANSI/ASHRAE Standard 34-2024: Designation
and Safety Classification of Refrigerants.
---------------------------------------------------------------------------
D. What is refrigerant HFO-1234yf and how does it compare to other
refrigerants in this end-use?
The EPA is proposing to list HFO-1234yf as acceptable, subject to
use conditions, in the MVAC end-use for retrofit of HD pickup trucks
and complete HD vans.
The redacted submission and supporting documentation for this
proposed refrigerant are in the docket.\17\ The EPA performed a risk
screening assessment to examine the human health and environmental
risks of this substitute, also available in the docket.\18\
[[Page 17181]]
The EPA notes that the environmental, flammability, and toxicity
information in this section is similar to the information provided in
the 2025 NPRM related to the proposed listing of HFO-1234yf in the MVAC
end-use for retrofit of LMDVs. As mentioned in the 2025 NPRM, the
environmental, flammability, and toxicity information about this
proposed substitute does not differ between LMDV MVACs and HD pickup
truck and complete HD van MVACs.
---------------------------------------------------------------------------
\17\ See Docket ID No. EPA-HQ-OAR-2024-0503.
\18\ ICF. (2026b). Risk Screen on Substitutes in Motor Vehicle
Air Conditioning (Heavy-Duty Pickup Trucks and Complete Heavy-Duty
Vans) (Retrofit Equipment); Substitute: HFO-1234yf (Solstice[supreg]
yf or Solstice[supreg] 1234yf). See Docket ID No. EPA-HQ-OAR-2024-
0503.
---------------------------------------------------------------------------
Environmental information: The specific atmospheric effects values
can be found in the risk screen developed for HFO-1234yf for the
proposed listing in this supplemental action. These were determined
consistent with the source information noted in section III.D. of the
2025 NPRM.
HFO-1234yf is excluded from the EPA's regulatory definition of
volatile organic compounds (VOCs), which is used for addressing the
development of state implementation plans (SIPs) to attain and maintain
the National Ambient Air Quality Standard (NAAQS).\19\
---------------------------------------------------------------------------
\19\ 40 CFR 51.100(s).
---------------------------------------------------------------------------
HFO-1234yf can break down into trifluoroacetic acid (TFA) in the
atmosphere. HFO-1234yf is almost completely transformed into TFA.\20\
For more information on TFA, see the response to comments section of
SNAP Rule 26.\21\
---------------------------------------------------------------------------
\20\ EEAP. (2023). Environmental Effects of Stratospheric Ozone
Depletion, UV Radiation, and Interactions with Climate Change. 2022
Assessment Report. UNEP, Environmental Effects Assessment Panel.
https://ozone.unep.org/system/files/documents/EEAP-2022-Assessment-Report-May2023.pdf.
\21\ See 88 FR 50457-8 (June 13, 2024).
---------------------------------------------------------------------------
Flammability information: HFO-1234yf is a lower flammability
refrigerant (ASHRAE flammability classification 2L). HFO-1234yf may
pose a greater flammability risk than nonflammable substitutes in the
MVAC end-use for retrofit of HD pickup trucks and complete HD vans. The
flammability risk, determined by the likelihood of exceeding the lower
flammability limit (LFL), is evaluated in the risk screen referenced in
this section. The EPA is proposing to determine that HFO-1234yf may be
used safely since flammability risk can be mitigated by use consistent
with the proposed labeling requirements in appendix D of 40 CFR part
82, subpart G, recommendations in the manufacturers' safety data sheet
(SDS), and other safety precautions common in the refrigeration and AC
industry. The flammability characteristics of HFO-1234yf make the risk
of ignition low. HFO-1234yf requires an open flame to ignite, such as a
match or lighter, because of its relatively high minimum ignition
energy of greater than 5,000 millijoules (mJ).\22\ HFO-1234yf has an
LFL of 62,000 ppm,\23\ and has a low burning velocity \24\ compared to
refrigerants with flammability classification of 2 such as HFC-152a
\25\ or with flammability classification of 3 such as hydrocarbon
refrigerants.\26\ As a result of these flammability characteristics,
HFO-1234yf is difficult to ignite, and is generally unable to propagate
a flame once ignited (i.e., flames resulting from HFO-1234yf put
themselves out).
---------------------------------------------------------------------------
\22\ Minor, B. et al. (2009). (111g) Flammability
Characteristics of Low GWP Refrigerant HFO-1234yf. AIChE 2009 Spring
Meeting & 5th Global Congress on Process Safety. https://proceedings.aiche.org/conferences/aiche-spring-meeting-and-global-congress-on-process-safety/2009/proceeding/paper/111g-flammability-characteristics-low-gwp-refrigerant-hfo-1234yf.
\23\ Manufacturer's Safety Data Sheet for HFO-1234yf. Honeywell
(May 23, 2019). See also Minor, B. et al. (2009).
\24\ A2L refrigerants have a burning velocity of less than 0.1
meters/second (m/s), per International Standards Organization 817
and ASHRAE 34-2024. HFO-1234yf has a burning velocity of 0.015m/s,
see Minor, B. et al. (2009).
\25\ The burning velocity of HFC-152a is measured at
approximately 0.236 m/s. Takizawa, K. et al. (2005). Burning
velocity measurement of fluorinated compounds by the spherical-
vessel method, Combustion and Flame, Volume 141, Issue 3, Pages 298-
307: https://doi.org/10.1016/j.combustflame.2005.01.009.
\26\ The burning velocity of R-290 is at least 0.4 m/s,
depending on temperature and pressure. Metghalchi, M. & Keck, J.C.
(1980). Laminar Burning Velocity of Propane-Air Mixtures at High
Temperature and Pressure. Combustion And Flame 38: 143-154 https://james-keck-memorial-collection.unibs.it/JCKeck-papers/MetghalchiKeck-CombustionFlame-38-143-1980.pdf.
---------------------------------------------------------------------------
Consistent with the other proposed listings in the 2025 NPRM, under
this supplemental action, HFO-1234yf could be used to retrofit MVACs
originally designed for an A1 refrigerant. The EPA considered if this
could create additional flammability risk distinct from its use in a
new MVAC that is specifically designed with mitigation measures to use
a flammable refrigerant. The original submission for HFO-1234yf in new
vehicles included analyses that evaluated the flammability and toxicity
risks of HFO-1234yf in MVACs that were originally designed for HFC-
134a. These analyses consist of reports published in 2008, 2009, and
2013 from the SAE International, previously known as the Society of
Automotive Engineers (SAE), Cooperative Research Program (CRP). The
vehicles in these analyses did not feature any design changes to
address potential flammability. In this way, MVACs used in the original
analyses were analogous to vehicles that would be retrofit under this
supplemental proposal, because they could be originally designed for an
A1 refrigerant.\27\ The 2008 report found that the increased
flammability risk of HFO-1234yf in a vehicle designed for use with HFC-
134a is well below those commonly accepted by the general public.\28\ A
revised 2009 report found that the risks of HFO-1234yf were low
overall, and somewhat less than the toxicity risks posed by R-744.\29\
The submitter of HFO-1234yf provided these analyses to the EPA to
support the Agency's original consideration of HFO-1234yf in new
vehicles, and the Agency based its listing of acceptability in part on
the findings of these analyses. The EPA concluded that the risks of
HFO-1234yf are comparable to or less than the risks from other
available or potentially available alternatives in this end-use that
the Agency had already listed or proposed as acceptable (e.g., HFC-
152a, HFC-134a, and R-744).\30\
---------------------------------------------------------------------------
\27\ Gradient Corporation. (2008). Risk Assessment for
Alternative Refrigerant HFO-1234yf. (Phase I) Prepared for the
Society of Automotive Engineers (SAE) Cooperative Research Project
150.
\28\ Gradient Corporation. (2008). Risk Assessment for
Alternative Refrigerant HFO-1234yf. Confidential report prepared for
SAE International Cooperative Research Program 1234.
\29\ Gradient Corporation. (2009). Risk Assessment for
Alternative Refrigerants HFO-1234yf and R-744 (CO2).
Confidential report prepared for SAE International Cooperative
Research Program 1234.
\30\ See 76 FR 17491 (March 29, 2011).
---------------------------------------------------------------------------
SAE revised its assessment of HFO-1234yf and released a
supplemental report in 2013 that contained two new fault tree analyses
that included additional ``worst-case scenarios.'' \31\ The report
revised the probability of a vehicle fire due to ignition of HFO-1234yf
in a system featuring no design changes compared to an HFC-134a system
to about 3 x 10-12 events per hour of vehicle operation.
---------------------------------------------------------------------------
\31\ Gradient Corporation. (2013a). Additional Risk Assessment
of Alternative Refrigerant R-1234yf. Confidential report prepared
for SAE International Cooperative Research Program 1234-4.
---------------------------------------------------------------------------
The submitter of HFO-1234yf in the MVAC end-use for retrofit of
LMDVs and HD pickup trucks and complete HD vans provided an updated
fault tree analysis that evaluated the additional risk associated with
use of HFO-1234yf specifically in retrofit applications and the EPA
considered this new analysis in our review of HFO-1234yf.\32\ The
analysis only considered scenarios that increased the flammability risk
in a retrofit (such as increased risk of mechanical fan failure and
electrical fires and less consistent presence and deployment of
airbags) and did not
[[Page 17182]]
consider scenarios that reduced the flammability risk in a retrofit
(such as the larger cabin size in older vehicles that would be
retrofit). The overall estimated risk was about 8 x 10-12
events per operating hour, which is similar to the risk of vehicle fire
due to HFO-1234yf ignition in new MVAC equipment (5 x 10-12
events per operating hour).\33\ The actual increased risk is likely
lower than this, as the evaluation only considered circumstances that
would increase the probability of a vehicle fire and did not consider
circumstances that would reduce the probability.
---------------------------------------------------------------------------
\32\ Gradient Corporation. (2023a). Retrofit Analysis Letter.
Prepared for Honeywell International.
\33\ Gradient Corporation. (2009).
---------------------------------------------------------------------------
The MVAC systems, vehicle designs, and the potential for exposure
for the HD vehicle types for which the EPA is proposing HFO-1234yf for
retrofit use as acceptable, subject to use conditions, in this
supplemental action are identical or very similar to those of LD
vehicles.\34\ In 2016, the EPA evaluated how the risks of using HFO-
1234yf in new HD pickup trucks and complete HD vans compare to the
risks of using HFO-1234yf in new LD vehicles.\35\ The EPA presented
information on the highest refrigerant charge to passenger compartment
volume ratios for different vehicle types and the highest ratio for all
HD pickup truck and HD van vehicle types was 410 g/m\3\ in HD pickup
trucks, which was less than the maximum ratio identified in the
analysis for HFO-1234yf in LD vehicles in two seaters, which was 641 g/
m\3\.\36\ The EPA concluded that the available assessments on the use
of HFO-1234yf in LD vehicles were sufficiently conservative to account
for all possible flammability risks from the use of HFO-1234yf in HD
pickup trucks and complete HD vans.\37\ Consistent with the approach
taken in SNAP Rule 21 when the EPA listed HFO-1234yf in new HD pickup
trucks and complete HD vans and relied on analysis for the use of HFO-
1234yf in LD vehicles, the EPA proposes to find it appropriate to rely
on the same analysis included in this section related to the use of
HFO-1234yf in LD vehicle types.\38\
---------------------------------------------------------------------------
\34\ See 81 FR 86778 (Dec. 1, 2016).
\35\ ICF. (2016b). Technical Support Document for Acceptability
Listing of HFO-1234yf for Motor Vehicle Air Conditioning in Limited
Heavy-Duty Applications.
\36\ ICF. (2016b).
\37\ See 81 FR 22810 (April 16, 2016).
\38\ See 81 FR 86778 (December 1, 2016).
---------------------------------------------------------------------------
The EPA conducted a risk screen in 2026 for HFO-1234yf in the MVAC
end-use for retrofit of HD pickup trucks and complete HD vans to
support the proposed listing in this supplemental action. The risk
screen found that concentrations of HFO-1234yf did exceed the LFL in
the passenger compartment of a HD pickup truck under the modeled worst-
case scenario. For the HD pickup truck and HD van vehicle types
evaluated in this risk screen, the highest refrigerant charge to
passenger compartment ratio was 390 g/m\3\ in HD pickup trucks.\39\
This ratio is substantially less than the maximum ratio identified for
many vehicle types mentioned in the risk screen for HFO-1234yf use in
retrofit LMDVs including two seaters (640.75 g/m\3\), small pickup
trucks (633.27 g/m\3\), sport utility vehicles (414.96 g/m\3\), and
standard pickup trucks (397.84 g/m\3\).\40\ The lower ratio indicates a
relatively lower risk.
---------------------------------------------------------------------------
\39\ ICF. (2026b).
\40\ ICF. (2025k). Risk Screen on Substitutes in Motor Vehicle
Air Conditioning (Light-Duty and Medium-Duty Vehicles) (Retrofit
Equipment); Substitute: HFO-1234yf (Solstice[supreg] yf or
Solstice[supreg] 1234yf).
---------------------------------------------------------------------------
As discussed in the 2025 NPRM, the risk screen for HFO-1234yf use
for retrofit of LMDVs found that concentrations of HFO-1234yf did
exceed the LFL in the passenger compartment under certain worst-case
scenarios but remained well below the LFL in more realistic industry
consortium field testing. For example, using a simple box model,
combining the highest ratio of refrigerant charge to observed passenger
compartment size with a catastrophic release of 60 percent of the
charge in 60 seconds, resulted in a maximum instantaneous charge of
172,000 ppm, compared to an LFL of 62,000 ppm. However, analysis using
the more accurate technique of computational fluid dynamics modeling
found the instantaneous concentration of HFO-1234yf to vary from 65,000
ppm to 34,000 ppm. The industry consortium field testing found a
maximum instantaneous concentration of HFO-1234yf of 29,774 ppm when a
vehicle's full charge was released.\41\
---------------------------------------------------------------------------
\41\ ICF. (2025k).
---------------------------------------------------------------------------
The EPA's original 2009 risk analysis of HFO-1234yf for use in new
LMDVs also identified scenarios in which concentrations exceeded the
LFL.\42\ The EPA listed HFO-1234yf as acceptable, subject to use
conditions, in new LMDVs leveraging this risk analysis. In the EPA's
original listing, the Agency stated that it found that the use of HFO-
1234yf in the MVAC end-use for new passenger vehicle and LD trucks,
subject to the use conditions adopted in that listing, does not present
a greater overall risk to human health and the environment compared to
the currently approved MVAC alternatives or as compared to R-744.\43\
The EPA has also subsequently listed R-744 as acceptable, subject to
use conditions, in new LMDVs. Finally, HFO-1234yf in new LMDVs has been
widely adopted since being listed in 2012. In MY2023, the share of new
LMDVs sold in the United States with HFO-1234yf reached 97 percent.\44\
HFO-1234yf has also been adopted for use in new HD pickup trucks and
complete HD vans. Even with its broad use, the EPA is not aware of any
real-world instances in which HFO-1234yf has ignited and caused a
vehicle fire, which further augments the record for this refrigerant.
---------------------------------------------------------------------------
\42\ ICF. (2009). Risk Screen on Substitutes for CFC-12 in Motor
Vehicle Air Conditioning: Substitute: HFO-1234yf.
\43\ See SNAP Rule 16, 76 FR 17488 (March 29, 2011).
\44\ U.S. Environmental Protection Agency. (2024). EPA
Automotive Trends Report: Greenhouse Gas Emissions, Fuel Economy,
and Technology since 1975: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P101CUU6.pdf.
---------------------------------------------------------------------------
SAE J1660 currently provides guidance on how to retrofit a vehicle
originally charged with CFC-12 to HFC-134a. The EPA anticipates that
SAE would develop an analogous standard or revise this standard for
retrofitting vehicles using newer refrigerants, including HFO-1234yf.
Following such standards may further reduce the flammability risk
associated with retrofitting MVACs, which is already expected to be
extremely small in magnitude.
Given the findings of the evaluation materials available in the
docket, that the environmental, flammability, and toxicity information
about HFO-1234yf does not differ between MVAC end-use for LMDVs and HD
pickup trucks and complete HD vans, that the MVACs used in the original
analysis for HFO-1234yf in new vehicles were analogous to vehicles that
would be retrofit, and the widespread adoption of HFO-1234yf without
documented flammability issues, the EPA is proposing that HFO-1234yf
may be safely used in the MVAC end-use for retrofit of HD pickup trucks
and complete HD vans.
Toxicity information: Toxicity risk, determined by the likelihood
of exceeding the exposure limits in these end-uses, are evaluated in
the previously referenced risk screen. HFO-1234yf is a lower toxicity
(ASHRAE toxicity group A) refrigerant. ASHRAE has adopted an OEL for
this refrigerant of 500 ppm. The toxicity risks of using HFO-1234yf in
the MVAC end-use for retrofit of HD pickup trucks and complete HD vans
are comparable to or lower than that of other available substitutes in
the same end-use,
[[Page 17183]]
including HFC-134a.\45\ Toxicity risks of the proposed refrigerant can
be mitigated by use consistent with applicable industry safety
standards, recommendations in the manufacturers' SDS, and other safety
precautions common in the refrigeration and AC industry.
---------------------------------------------------------------------------
\45\ See previous listing decisions for information regarding
the toxicity of other available alternatives. (https://www.epa.gov/snap/substitutes-motor-vehicle-air-conditioning).
---------------------------------------------------------------------------
HFO-1234yf is subject to a significant new use rule (SNUR) under 40
CFR 721.10182(a). Significant new uses under this requirement include:
use other than as a refrigerant: in MVAC systems in new passenger cars
and vehicles (as defined in 40 CFR 82.32(c) and (d)), in stationary and
transport refrigeration, or in stationary AC, commercial use other than
in passenger cars and vehicles in which the original charging of MVAC
systems with the pre-manufacture notice (PMN) substance was done by the
motor vehicle original equipment manufacturer (OEM), in stationary and
transport refrigeration, or in stationary AC., and use in consumer
products other than products used to recharge the MVAC systems in
passenger cars and vehicles in which the original charging of MVAC
systems with the PMN substance was done by the motor vehicle OEM.
Use in all MVAC end-uses, except for when originally charged with
HFO-1234yf, would fall under (B) or (C) as commercial or consumer use
to recharge an MVAC in which the original charging of the MVAC was with
a substance other than HFO-1234yf. The EPA considers retrofitting a
vehicle to use HFO-1234yf that was not originally charged by the OEM
with HFO-1234yf to be a significant new use of HFO-1234yf under this
SNUR. Significant new uses require the chemical producer to submit a
significant new use notice to the EPA for review of a substance before
introducing the substance into interstate commerce in the significant
new use.
Comparison to other substitutes in these end-uses: The Agency
understands that this substitute will be marketed as a retrofit option
for different refrigerants, including HFC-134a. HFC-134a is the only
available refrigerant listed as acceptable for retrofit of MVACs in HD
pickup trucks and complete HD vans.
The specific atmospheric effects values can be found in the
individual risk screen for HFO-1234yf. These were determined consistent
with the source information noted in section III.D. of the 2025 NPRM.
The atmospheric effects for HFO-1234yf are overall better than or
comparable to many of the substitutes currently listed as acceptable in
this end-use, such as HFC-134a. The EPA acknowledges that the
atmospheric effects of HFO-1234yf are relatively lower than the three
blends, R-444A, R-456A, and R-480A, that were proposed as acceptable,
subject use conditions, in the MVAC end-use for retrofit of HD pickup
trucks and HD vans in the 2025 NPRM. The EPA's analysis found that the
effects on human health and the environment associated with
retrofitting HD pickup trucks and complete HD vans with HFO-1234yf are
comparable to the other alternatives proposed for this use in the 2025
NPRM, and lower than that of HFC-134a.\46\
---------------------------------------------------------------------------
\46\ The EPA is aware that the submitter of HFO-1234yf is likely
to market this substitute to retrofit MVACs originally charged with
HFC-134a.
---------------------------------------------------------------------------
The EPA's risk screen for HFO-1234yf in the MVAC end-use for
retrofit of HD pickup trucks and complete HD vans found that this
substitute can be used without exceeding the recommended OEL of 500 ppm
(8-hr OEL); thus, the toxicity risks of this refrigerant are comparable
to those of other acceptable substitutes in MVACs, which also are used
without exceeding their OELs.\47\
---------------------------------------------------------------------------
\47\ ICF. (2026b).
---------------------------------------------------------------------------
The flammability of HFO-1234yf may be greater than that of other
available substitutes in the same end-use that have an ASHRAE
flammability classification of 1. The EPA's analysis of the
flammability risks of HFO-1234yf found that when used in accordance
with the proposed use conditions, this A2L refrigerant may be safely
used in this end-use without presenting additional adverse effects to
human health and the environment than other alternatives. HFO-1234yf
was listed as acceptable, subject to use conditions, in MVAC end-use
for new HD pickup trucks and complete HD vans in 2016. Since then, no
reports of harm or incidences of fire were recorded. We note that
flammability risk can be minimized by use consistent with applicable
industry safety standards as well as recommendations in the
manufacturers' SDS and other safety precautions common in the MVAC
industry and any difference in flammability can be addressed by the
existing labeling requirements in appendix D of 40 CFR part 82, subpart
G.\48\
---------------------------------------------------------------------------
\48\ Described in section IV.E of this supplemental proposal.
---------------------------------------------------------------------------
This proposed refrigerant provides an additional retrofit option
and would not pose additional adverse effects to human health or the
environment when used in accordance with existing and proposed
requirements and as intended by the submitter. To provide additional
options for the full range of MVACs, the EPA is proposing this listing
for HFO-1234yf as acceptable, subject to use conditions, in the MVAC
end-use for retrofit of HD pickup trucks and complete HD vans.
E. What use conditions is the EPA proposing for HFO-1234yf for retrofit
of MVACs in this end-use and what existing requirements apply to this
refrigerant?
The EPA is proposing the use condition that unique service port
fittings specific to HFO-1234yf must be used in retrofit applications
for this end-use. Service port fittings for HFO-1234yf were previously
established and are identified in appendix B of 40 CFR part 82, subpart
G.
Appendix D of 40 CFR part 82, subpart G specifies requirements for
unique fittings for new and retrofit MVAC listings and specifies
information that must appear on a new label when a retrofit is
performed, and outlines requirements for how the retrofit is completed
including specifications for how unique fittings must be applied when
performing a retrofit. The requirements for labeling, unique fittings,
and the performance of the retrofit would apply to this proposed
acceptability listing for MVAC retrofits. In the case of HFO-1234yf,
the requirement to include a label would mitigate risk by ensuring that
technicians are aware that the MVAC refrigerant is flammable. In the
2025 NPRM, the EPA proposed minor adjustments to these retrofit
specifications and labeling requirements that would also apply to the
proposed listing of HFO-1234yf in this supplemental action. The
existing requirements and proposed amendments are described fully in
section VIII.G. of the 2025 NPRM. While the proposed changes to section
VIII.G. of the 2025 NPRM are relevant to the proposed listing of HFO-
1234yf in this supplemental action, the EPA is not reopening comment on
the proposed changes since the changes are broadly applicable to all
MVAC retrofits, is not specific to this end-use, and is not specific to
the proposed listing of HFO-1234yf in this supplemental proposal.
In the 2025 NRPM, the EPA also proposed to amend appendix B of 40
CFR part 82, subpart G. This provision currently states that flammable
refrigerants in MVACs, both new and retrofit are unacceptable, except
for HFO-1234yf and HFC-152a when used in new MVAC equipment. The 2025
NPRM proposed to amend this provision so that unacceptability also
[[Page 17184]]
would not apply to HFO-1234yf used in retrofit MVACs. This proposed
amendment is described fully in section VIII.F. of the 2025 NPRM and
this supplemental proposal does not adjust or change those proposed
revisions. However, the proposed revisions are relevant to this listing
in that they would allow for use of HFO-1234yf in retrofits not only in
LMDVs but also in HD pickup trucks and complete HD vans.
The EPA's SNAP program has a longstanding approach of requiring
unique fittings for use with each refrigerant in MVACs. Appendix D of
40 CFR part 82, subpart G requires that each refrigerant be used with a
set of fittings that is unique to that refrigerant. This is intended to
prevent cross contamination of different refrigerants, preserve the
purity of recycled refrigerants, and ultimately to avoid venting of
refrigerant consistent with requirements under CAA section 608(c).\49\
In the 1996 SNAP Rule requiring the use of unique fittings on all
refrigerants submitted for use in MVACs, the EPA urged industry to
develop mechanisms to ensure that the venting prohibition under CAA
section 608(c) and the implementing regulations at 40 CFR 82.154 are
observed.\50\ The EPA has issued multiple SNAP rules requiring the use
of fittings unique to a refrigerant for use on ``containers of the
refrigerant, on can taps, on recover, recycle, and recharge equipment,
and on all [motor vehicle] air conditioning system service ports.''
\51\
---------------------------------------------------------------------------
\49\ Codified at 40 CFR 82.154(a).
\50\ See 61 FR 54032 (October 16, 1996).
\51\ See appendix D of 40 CFR part 82, subpart G.
---------------------------------------------------------------------------
The EPA expects that the companies selling refrigerants intended to
be used as retrofits would make appropriate unique fittings and
refrigerant labels available to certified technicians and do-it-
yourselfers (DIYers) to allow them to conduct a retrofit in a manner
that meets requirements under the CAA.
V. Clarification of Intended Scope of the 2025 NPRM and Other
Clarifications
The EPA is supplementing the 2025 NPRM to clarify the intended
scope of that proposal. In the 2025 NPRM, the EPA proposed a listing
for R-444A as acceptable, subject to use conditions, in the MVAC end-
use for retrofit of HD pickup trucks and HD vans (both complete and
incomplete). The Agency included incomplete HD vans in error and is
clarifying that we intended for this proposed listing to apply to HD
pickup trucks and complete HD vans only.
See sections VIII.B., VIII.D., and VIII.E. of the 2025 NPRM for a
full discussion of the EPA's basis for proposing to list R-444A in this
end-use. This discussion only provided a basis for the proposed listing
of R-444A in the MVAC end-use for retrofit of HD pickup trucks and
complete HD vans. The EPA's risk screen of R-444A was for HD pickup
trucks and complete HD vans. The risk screen did not include a scenario
for reviewing risk of R-444A in incomplete HD vans. The SNAP program
has thus far not listed any A2L refrigerant as acceptable for either
new or retrofit use in incomplete HD vans due to lack of sufficient
information on the appropriate risk scenarios for use of flammable
refrigerants in incomplete HD vans.
In 2016, when the EPA listed HFO-1234yf as acceptable, subject to
use conditions, in the MVAC end-use for new HD pickup trucks and
complete HD vans, the EPA did not finalize a listing for HFO-1234yf in
any incomplete HD vans, stating that we did not have sufficient
information on the potential for modifications to OEM-installed MVAC
systems of incomplete HD vans by secondary manufacturers and the impact
of those modifications on the safe use of HFO-1234yf. At the time of
the 2025 NPRM, the same limitation applied and the EPA did not have
sufficient information on the potential for modifications to OEM-
installed MVAC systems of incomplete HD vans by secondary manufacturers
and the impact of those modifications on the safe use of R-444A. For
this reason and to remain consistent with our previous approach in SNAP
Rule 21, the EPA is clarifying that the intended scope of the proposed
listing for R-444A does not include incomplete HD vans and is
requesting comment on the proposed listing as clarified.\52\ The Agency
will consider the comments received during the comment period for the
2025 NPRM on this proposed listing and will review any additional
comments regarding the clarification to the scope of the listing made
in this supplemental action.
---------------------------------------------------------------------------
\52\ See SNAP Rule 21, 81 FR 86778 (December 1, 2016).
---------------------------------------------------------------------------
The clarification in this supplemental action does not impact any
of the other MVAC end-uses in the 2025 NPRM where R-444A was proposed
as acceptable, subject to use conditions, including as a retrofit in
LMDVs, HD pickup trucks, and complete HD vans.
In this supplemental action, the EPA is also clarifying language in
the 2025 NPRM and associated proposed regulatory text document related
to HD pickup trucks. In the 2025 NPRM, the EPA proposed listings for R-
444A, R-456A, and R-480A in the MVAC end-use for retrofit of HD pickup
trucks (complete and incomplete). The Agency differentiated between
complete and incomplete HD pickup trucks in error and is clarifying
that we intended for the proposed listings for R-444A, R-456A, and R-
480A to apply to HD pickup trucks generally. In contrast to HD vans,
the EPA does not see complete and incomplete HD pickup trucks as two
separate applications with unique risk profiles and has previously
treated complete and incomplete HD pickup trucks the same. For purposes
of consistency, the EPA is clarifying the regulatory language for the
proposed listings of R-444A, R-456A, and R-480A to use the term ``HD
pickup trucks'' rather than HD pickup trucks (complete and incomplete).
From a practical perspective, this clarification does not change the
types of vehicles that the proposed listings apply to; it is simply a
clarification of terminology. The proposed regulatory text related to
the clarifications addressed in this section may be found in the docket
for this rulemaking.\53\
---------------------------------------------------------------------------
\53\ See Docket ID No. EPA-HQ-OAR-2024-0503 in documents titled
``Proposed Changes to Appendix B for SNAP 27 Supplemental Proposal''
and ``Proposed Regulatory Text for SNAP Rule 27--Supplemental
Proposal.''
---------------------------------------------------------------------------
VI. On which topics is the EPA specifically requesting comment?
1. The EPA is requesting comment on the proposed listing of HFO-
1234yf as acceptable, subject to use conditions, in the MVAC end-use
for retrofit of HD pickup trucks and complete HD vans. Specifically,
retrofitting MVACs designed for a nonflammable refrigerant such as HFC-
134a to use a flammable refrigerant may present new risks. The EPA
seeks comment on whether additional strategies to mitigate the
flammability risk of A2L refrigerants beyond those required by appendix
D to part 82, subpart G are necessary and suggestions of what those
strategies may be.
2. The EPA is requesting comment on the clarifications described in
section V. of this supplemental action, including the clarification of
the intended scope of the 2025 NPRM as it relates to the proposed
listing of R-444A in the MVAC end-use for retrofit of complete HD vans
and the clarification of terminology related to HD pickup trucks.
VII. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders
can be
[[Page 17185]]
found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is not a significant regulatory action and was
therefore not submitted to the Office of Management and Budget (OMB)
for review.
B. Executive Order 14192: Unleashing Prosperity Through Deregulation
This action is expected to be an Executive Order 14192 deregulatory
action. This proposed rule is expected to provide burden reduction by
proposing to list more alternatives that would be available for use by
industry.
C. Paperwork Reduction Act (PRA)
This action does not impose any new information collection burden
under the PRA. OMB has previously approved the information collection
activities contained in the existing regulations and has assigned OMB
control number 2060-0226. This rule contains no new requirements for
reporting or recordkeeping.
D. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. In
making this determination, the EPA concludes that the impact of concern
for this rule is any significant adverse economic impact on small
entities and that the Agency is certifying that this rule will not have
a significant economic impact on a substantial number of small entities
because the rule has no net burden on the small entities subject to the
rule. This action proposes to add the additional options under SNAP of
HFO-1234yf in the specified end-uses but does not mandate such use.
Thus, if the rule were finalized as proposed, it would not impose new
costs on small entities. We have therefore concluded that this action
will have no net regulatory burden for all directly regulated small
entities.
E. Unfunded Mandates Reform Act (UMRA)
This action does not contain an unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. The action imposes no enforceable duty on any state,
local or Tribal governments or the private sector.
F. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.
G. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have Tribal implications as specified in
Executive Order 13175. It will not have substantial direct effects on
Tribal governments, on the relationship between the Federal government
and Indian Tribes, or on the distribution of power and responsibilities
between the Federal government and Indian Tribes, as specified in
Executive Order 13175. Thus, Executive Order 13175 does not apply to
this action.
H. Executive Order 13045: Protection of Children From Environmental
Health and Safety Risks
Executive Order 13045 directs Federal agencies to include an
evaluation of the health and safety effects of the planned regulation
on children in Federal health and safety standards and explains why the
regulation is preferable to potentially effective and reasonably
feasible alternatives. This action is not subject to Executive Order
13045 because it is not a significant regulatory action under section
3(f)(1) of Executive Order 12866, and because the EPA does not believe
the environmental health or safety risks addressed by this action
present a disproportionate risk to children. While the EPA has not
conducted a separate analysis of risks to infants and children
associated with this rule, the rule does contain use conditions that
would reduce exposure risks to the general population, with the
reduction of exposure being most important to the most sensitive
individuals. This action's health and risk assessments are contained in
the comparison of toxicity for the proposed substitute in section IV.D.
of this supplemental action, as well as in the risk screen for the
substitute that is listed in this supplemental proposed rule. The risk
screen is in the docket under the title ``Risk Screen on Substitutes in
Motor Vehicle Air Conditioning (Heavy-Duty Pickup Trucks and Complete
Heavy-Duty Vans) (Retrofit Equipment); Substitute: HFO-1234yf
(Solstice[supreg] yf or Solstice[supreg] 1234yf),''at Docket ID No.
EPA-HQ-OAR-2024-0503. However, the EPA's Policy on Children's Health
applies to this action. Information on how the Policy was applied is
available under ``Children's Environmental Health'' in the General
Information section of this preamble.
I. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution, or Use
This action is not subject to Executive Order 13211, because it is
not a significant regulatory action under Executive Order 12866.
J. National Technology Transfer and Advancement Act
This supplemental rulemaking does not involve technical standards.
VIII. References
Unless specified otherwise, all documents are available
electronically at https://regulations.gov, docket number EPA-HQ-OAR-
2024-0503.
ASHRAE. (2024). ANSI/ASHRAE Standard 34-2024: Designation and Safety
Classification of Refrigerants.
EEAP. (2023). Environmental Effects of Stratospheric Ozone
Depletion, UV Radiation, and Interactions with Climate Change. 2022
Assessment Report. UNEP, Environmental Effects Assessment Panel.
https://ozone.unep.org/system/files/documents/EEAP-2022-Assessment-Report-May2023.pdf.
Gradient Corporation. (2008). Risk Assessment for Alternative
Refrigerant HFO-1234yf. Confidential report prepared for SAE
International Cooperative Research Program 1234.
Gradient Corporation. (2008). Risk Assessment For Alternative
Refrigerant HFO-1234yf. (Phase I) Prepared for the Society of
Automotive Engineers (SAE) Cooperative Research Project 150.
Gradient Corporation. (2009). Risk Assessment for Alternative
Refrigerants HFO-1234yf and R-744 (CO2). Confidential
report prepared for SAE International Cooperative Research Program
1234.
Gradient Corporation. (2013a). Additional Risk Assessment of
Alternative Refrigerant R-1234yf. Confidential report prepared for
SAE International Cooperative Research Program 1234-4.
Gradient Corporation. (2023a). Retrofit Analysis Letter. Prepared
for Honeywell International.
ICF. (2009). Risk Screen on Substitutes for CFC-12 in Motor Vehicle
Air Conditioning: Substitute: HFO-1234yf.
ICF. (2016b). Technical Support Document for Acceptability Listing
of HFO-1234yf for Motor Vehicle Air Conditioning in Limited Heavy-
Duty Applications.
ICF. (2025k). Risk Screen on Substitutes in Motor Vehicle Air
Conditioning (Light-Duty and Medium-Duty Vehicles) (Retrofit
Equipment); Substitute: HFO-1234yf (Solstice[supreg] yf or
Solstice[supreg] 1234yf).
[[Page 17186]]
ICF. (2026a). Technical Support Document for Motor Vehicle Air
Conditioning in Limited Heavy-Duty Applications.
ICF. (2026b). Risk Screen on Substitutes in Motor Vehicle Air
Conditioning (Heavy-Duty Pickup Trucks and Complete Heavy-Duty Vans)
(Retrofit Equipment); Substitute: HFO-1234yf (Solstice[supreg] yf or
Solstice[supreg] 1234yf).
Metghalchi, M. & Keck, J.C. (1980). Laminar Burning Velocity of
Propane-Air Mixtures at High Temperature and Pressure. Combustion
And Flame 38: 143-154: https://james-keck-memorial-collection.unibs.it/JCKeck-papers/MetghalchiKeck-CombustionFlame-38-143-1980.pdf.
Minor, B. et al. (2009). (111g) Flammability Characteristics of Low
GWP Refrigerant HFO-1234yf. AIChE 2009 Spring Meeting & 5th Global
Congress on Process Safety. https://proceedings.aiche.org/conferences/aiche-spring-meeting-and-global-congress-on-process-safety/2009/proceeding/paper/111g-flammability-characteristics-low-gwp-refrigerant-hfo-1234yf.
SAE. (2011). J1660 ``Fittings and Labels for Retrofit of CFC-12 (R-
12) Mobile Air-Conditioning Systems to HFC-134a (R-134a).''
Takizawa, K. et al. (2005). Burning velocity measurement of
fluorinated compounds by the spherical-vessel method, Combustion and
Flame, Volume 141, Issue 3, Pages 298-307: https://doi.org/10.1016/j.combustflame.2005.01.009.
U.S. Environmental Protection Agency. (2024). EPA Automotive Trends
Report: Greenhouse Gas Emissions, Fuel Economy, and Technology since
1975: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P101CUU6.pdf.
List of Subjects in 40 CFR Part 82
Environmental protection, Administrative practice and procedure,
Air pollution control, Chemicals.
Lee Zeldin,
Administrator.
[FR Doc. 2026-06665 Filed 4-3-26; 8:45 am]
BILLING CODE 6560-50-P