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Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for HCFC-22 in Residential and Light Commercial Air 

Conditioning and Heat Pumps

Substitute: HFC-32 (Difluoromethane)

This risk screen is restricted to residential and light commercial window air conditioner 

applications and other self-contained room air conditioners meeting the requirements of UL 

484: Room Air Conditioners.

This risk screen does not contain Clean Air Act (CAA) Confidential Business Information 

(CBI) and, therefore, may be disclosed to the public.

1. INTRODUCTION

Ozone-depleting substances (ODS) are being phased out of production in response to a series of 

diplomatic and legislative efforts that have taken place over the past two decades, including the Montreal 

Protocol and the Clean Air Act Amendments of 1990 (CAAA). The U.S. Environmental Protection 

Agency (EPA), as authorized by Section 612 of the CAAA, administers the Significant New Alternatives 

Policy (SNAP) Program, which identifies acceptable and unacceptable substitutes for ODS in specific 

end-uses based on assessment of their health and environmental impacts. 

EPA’s decision on the acceptability of a substitute is based on the findings of a screening assessment of 

potential human health and environmental risks posed by the substitute in specific applications. EPA has 

already screened a large number of substitutes in many end-use applications within all of the major ODSusing sectors, including refrigeration and air conditioning, solvent cleaning, foam blowing, aerosols, fire 

suppression, adhesives, coatings and inks, and sterilization. The results of these risk screens are presented 

in a series of Background Documents that are available in EPA's docket.

The purpose of this risk screen is to supplement EPA’s Background Document on the refrigeration and air 

conditioning sector (EPA 1994) (hereinafter referred to as the Background Document). This risk screen 

evaluates the potential use of HFC-32 as a substitute for HCFC-22 in the residential and light commercial 

air conditioning and heat pump end-use, specifically in room air-conditioning (AC) systems included

under Underwriters Laboratory (UL) Standard 484: Room Air Conditioners. These systems are limited to

packaged terminal air-conditioners (PTAC), packaged terminal heat pumps (PTHP), and other AC units

that include a hermetic refrigerant motor-compressor and are intended for installation in a window, 

through a wall, or as a console located in or adjacent to the space to be conditioned (e.g., portable AC

units), and hereinafter will be referred to collectively as “room AC systems.” The scope of UL 484 and 

this risk screen specifically excludes remote-condenser applications such as a mini-split ductless air 

conditioner. The proposed substitute, HFC-32, may contain minute quantities of impurities. Table 1 

details the composition of the substitute, including the maximum estimated concentration of impurities 

that may be present, as indicated by the submitter (allowable impurity levels per 40 CFR Part 82 or under 

AHRI Standard 7001 may be different).

 

1 AHRI Standard 700-2012: Specification for Fluorocarbon Refrigerants specifies acceptable levels of contaminants (i.e., purity 

requirements) for fluorocarbon refrigerants regardless of source and lists acceptable test methods.
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Table 1. Composition of HFC-32

Proposed Substitute Concentration

(Weight Percent)

HFC-32 99.909

Potential Impurities Maximum Concentration

(Weight Percent)

Section 2 of this risk screen summarizes the results of the risk screen for the proposed substitute listed in 

Table 1. The remainder of the risk screen is organized into the following sections:

 Section 3: Atmospheric Assessment

 Section 4: Volatile Organic Compound Assessment

 Section 5: Discussion of End-Use Scenarios Modeled

 Section 6: Potential Health Effects

 Section 7: Flammability Assessment

 Section 8: Asphyxiation Assessment

 Section 9: End-Use Exposure Assessment 

 Section 10: Occupational Exposure Assessment

 Section 11: General Population Assessment

 Section 12: References

2. SUMMARY OF RESULTS

HFC-32 is recommended for SNAP approval for residential and light commercial air conditioning and 

heat pump systems that comply with UL Standard 484: Room Air Conditioners. EPA's risk screen 

indicates that the use of the proposed substitute will be less harmful to the atmosphere than the continued 

use of HCFC-22. In addition, HFC-32 contributions to volatile organic compound (VOC) emissions are 

not significant, as HFC-32 is exempt under CAA regulations (40 CFR § 51.100(s)). No significant 

asphyxiation risks to consumers or toxicity risks to workers, consumers, or the general population are 

expected. Because units are to be installed in locations with adequate space or ventilation in accordance 

with the AC maintenance manual for HFC-32, as discussed in greater detail in Section 9, significant 

toxicity or flammability risk to consumers is unlikely. Given that the MSDS for HFC-32 and good 

manufacturing practices will be adhered to, and that the appropriate safety and personal protective 

equipment (PPE) (e.g., protective gloves, tightly sealed goggles, protective work clothing, and suitable 

respiratory protection in case of leakage or insufficient ventilation) consistent with Occupational Safety 

and Health Administration (OSHA) guidelines will be used during manufacture, installation, servicing, 

and disposal of room AC systems using HFC-32, worker exposure to HFC-32 will be unlikely. Additional 

safeguards, including specified refrigerant concentration limits (RCL) for HFC-32, are also provided by 

adherence to industry standards including American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) Standards 15,2

34,3and 62,

4

and UL Standard 484.5

 

2

Safety Standard for Refrigeration Systems ASHRAE Standard 15 establishes safeguards for life, limb, health, and property and 

prescribes safety requirements.

3 Designation and Safety Classification of Refrigerants ASHRAE Standard 34 is establishes a uniform system for assigning 

reference numbers, safety classifications, and refrigerant concentration limits to refrigerants. Safety classifications based on 

toxicity and flammability data are included.

4 Ventilation for Acceptable Indoor Air Quality ASHRAE Standard 62 establishes minimum ventilation rates and other measures 

intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects.

5 UL 484 Standard for Safety: Room Air Conditioners establishes safety requirements for room air conditioners that are designed 
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3. ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to the atmosphere posed by the use of HFC-32

in the residential and light commercial air conditioning and heat pumps sector. The ozone depletion 

potential (ODP), global warming potential (GWP), and atmospheric lifetime (ALT) of the proposed 

substitute are presented in Table 2. As compared to HCFC-22, the proposed substitute is substantially 

less harmful to the ozone layer, has less climate impact, and has a shorter atmospheric lifetime. HFC-32 

does however, have a non-zero GWP, but at 675, this value is generally in the range of or lower than 

those predicted for other substitutes examined in the Background Document, as well as a commonly

utilized substitute, R-410A. Thus, EPA believes that use of HFC-32 would result in substantially less 

harm to the climate and ozone layer than the continued use of ODS and commonly used ODS substitutes, 

such as R-410A.

Table 2. Atmospheric Impacts of HFC-32 Compared to HCFC-22 and R-410A

Refrigerant ODP GWP ALT (years)

HFC-32 0

a 675b 4.9b

HCFC-22 0.04

c 1,810b 12b

R-410Ad 0 2,088b NAe

a HFC-32 SNAP Submission (Daikin 2011)

b

IPCC 4th Assessment Report (Forster et al. 2007)

cWMO (2011)

d R-410A is a blend of 50% HFC-32 and 50% HFC-125

e Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-32 is 4.9 years, and 

the ALT for HFC-125 is 29 years (IPCC 4th Assessment Report [Forster et al. 2007]).

NA = not applicable

4. VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT

HFC-32 is exempt from the definition of volatile organic compound (VOC) under CAA regulations (40 

CFR § 51.100(s)). Therefore, environmental impacts from the release of HFC-32 as a VOC are not a 

significant concern. 

5. DISCUSSION OF END-USE SCENARIOS MODELED

HFC-32 has been proposed for use in residential and light commercial air conditioners and heat pumps, 

including PTACs, PTHPs, and other room AC units that employ hermetic refrigerant motor-compressors 

and are intended for installation in a window, through a wall, or as a console located in or adjacent to the 

space to be conditioned. The remainder of this risk screen assesses the risk of PTAC/PTHP systems, 

which represent a reasonable worst-case scenario for room air conditioning systems (as included under 

UL 484). These systems consist of a separate, un-encased combination of heating and cooling assemblies 

mounted through a wall. There is forced ventilation as well as separable outdoor horizontal slats 

providing air circulation. Models can be designated as “cooling only” or heating can be provided by hot 

water, steam, or electrical resistance heat (Daikin 2013). In addition, PTAC and PTHP systems are 

classified as “high probability systems” by ASHRAE Standard 15; if a leak occurs, the entire refrigerant 

charge of the system has the potential to be released into one room connected to the unit (ASHRAE 

2010a). 

For the reasonable worst-case scenario, it was assumed that a PTAC is installed in a small, enclosed 

dormitory room of 41 m

3

(1,450 ft3) and is used to cool only that room. HFC-32 is also proposed for other 

residential and light commercial uses, including hotel and motel guest rooms, hospitals and assisted living 

facilities, apartments and military barracks, and offices and similar spaces in a variety of building types 

 

to provide delivery of conditioned air to an enclosed space, room, or zone. 
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and for use in PTHP systems. However, because these spaces are typically larger than small dormitory 

rooms and have higher ventilation rates,6these room types were considered to be less conservative and 

thus not modeled in this risk screen. PTAC and PTHP systems have the same charge sizes and operate in 

the same way, except that PTAC systems provide cooling only while PTHP systems provide heating and 

cooling. The conservative results of this analysis can be used to assess the use of HFC-32 in PTAC or 

PTHP systems in all proposed end-use applications. 

Under EPA’s proposed charge size limits, for a room AC unit installed in a room of 41 m

3

(with a 

capacity of 6,500 BTU/hour), the maximum HFC-32 refrigerant charge allowed is 5,350 grams, and 7,960 

g is the maximum charge allowed for a room AC installed in any room size. EPA’s proposed charge size 

limits will also restrict the charge size for a PTAC unit installed in a 41 m

3

room (with a capacity of 6,500 

BTU/hour) to 1,460 grams, and the maximum charge size for a PTAC in any room size would be 4,650 g. 

However, the submission states that PTAC and PTHP units will be produced with charge sizes up to 

8,500 grams (Daikin 2013). Therefore, this risk screen conservatively evaluates the risk associated with 

the maximum charge size for a PTAC indicated by the submitter (i.e., 8,500 grams), the maximum charge 

size for a room AC proposed by EPA (i.e., 7,960 grams), and the maximum charge size for a PTAC

proposed by EPA in a small, enclosed dormitory room of 41 m

3

(i.e., 1,460 grams). Under the worst-case 

scenario, the full charge of the unit is assumed to be emitted over the course of one minute into the 

dormitory room. It was assumed that an individual is present at the start of the leak and remains in the 

room until the charge is completely released. A vertical concentration gradient is not assumed since HFC32 is highly volatile and will likely disperse fairly evenly and immediately upon release. Table 3 details 

the assumptions used in the models throughout this risk screen (i.e., in Sections 7, 8, and 9).

Table 3. End-Use Scenario Model Assumptions

Parameter Assumption

Room Type Small Dormitory Room

Size (m3) 41 (1,450 ft3)

Ventilation Rate (air changes per hour) 0.25a

Refrigeration Unit PTAC

Charge Sizes (g) 8,500b; 7,960; 1,460

Length of Release (minutes) 1

Vertical Concentration Gradient No

a Background Document (EPA 1994))

b Maximum charge size for PTAC unit (Daikin 2013)

6. POTENTIAL HEALTH EFFECTS

To assess potential health risks from exposure to the proposed substitute in room AC systems, EPA 

identified the relevant toxicity threshold values for comparison to modeled exposure concentrations for 

different scenarios. To protect consumers from the potential dangers of a catastrophic leak from a PTAC 

or other residential and light commercial air-conditioning and heat pump systems, ASHRAE Standard 34 

determined refrigerant concentration limits (RCLs) to reduce the risks of acute toxicity, asphyxiation, and 

flammability hazards in occupied spaces(ASHRAE 2010b). ASHRAE Standard 15 requires that “the 

concentration of refrigerant in an enclosed space following a complete discharge of a high-probability 

system shall not exceed the RCL” to ensure that there is not a significant risk of toxicity, asphyxiation, 

and flammability (ASHRAE 2010a). The RCL for HFC-32 was referenced throughout this risk screen as 

an additional, conservative limit to ensure flammability, asphyxiation, and end-use exposure risks do not 

occur. Table 4 lists the relevant toxicity limits and RCLs of HFC-32 and its impurities, and is followed by 

 

6 The average U.S. private office size, is 47 m3

(1660 ft3), assuming a 2.7m (9 ft) ceiling, and the minimum air change rate for 

office space used by GreenGuard Standards, based on ASHRAE 62.1 is 0.72 air changes per hour (ACH) (BOMA Experience 

Exchange Report 1999, GreenGuard Environmental Institute 2009, ASHRAE 2010c).
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Table 5, which provides an explanation of each toxicity limit. EPA’s approach for identifying or 

developing these values is discussed in Chapter 3 of the Background Document. 

Table 4. Exposure Limits of HFC-32 and Potential Impurities

Chemical

Long-term 

Workplace 

Exposure

(ppm, 8-hr TWA)

Short-term 

Workplace 

Exposure

(ppm, 15-min TWA)

Cardiotoxic 

NOAEL

(ppm, 5-min TWA)

Refrigerant 

Concentration 

Limit (RCL) 

(ppm)

Proposed Substitute

HFC-32 1,000a 3,000b 350,000a 36,000

Potential Impurities

a HFC-32 SNAP Submission (Daikin 2011)

b STEL was estimated as three times the PEL; this method of estimating a short-term exposure limit is commonly done by ACGIH.

Table 3. Explanation of Exposure Limit-Related Terminologya

Organization Definition

OSHA Occupational Safety and Health Administration

NIOSH National Institute for Occupational Safety and Health

ACGIH American Conference of Governmental Industrial Hygienists

Exposure Limit Definition Explanation

Short-Term Exposure

RCL Refrigerant Concentration Limit The RCL for a refrigerant is intended to reduce the risks of acute 

toxicity, asphyxiation, and flammability hazards in normally 

occupied, enclosed spaces. The RCL for each refrigerant is the 

lowest of the Acute-Toxicity Exposure Limit (ATEL), Oxygen 

Deprivation Limit (ODL), and Flammable Concentration Limit (FCL). 

Determination assumes full vaporization with no removal by 

ventilation, dissolution, reaction, or decomposition and complete 

mixing of refrigerant in the space to which it is released.

STEL Short-Term Exposure Limit A 15-minute TWA exposure that should not be exceeded at any 

time during a workday, even if the 8-hour TWA is within the TLV–

TWA, set by ACGIH. 

NOAELb No Observed Adverse Effect Level The highest exposure level at which there are no biologically 

significant increases in the frequency or severity of adverse effect 

between the exposed population and its appropriate control; some 

effects may be produced at this level, but they are not considered 

adverse or precursors of adverse effects.

Long-Term Exposure

PEL Permissible Exposure Limit This is an 8-hour time-weighted average exposure limit set by 

OSHA. 

TLV-TWA Threshold Limit Value –TimeWeighted AverageThe TWA concentration for a conventional 8-hour workday and a 

40-hour workweek, to which it is believed that nearly all workers 

may be repeatedly exposed, day after day, for a working lifetime 

without adverse effect according to ACGIH. 

a All information in this table taken from EPA (1994) except where otherwise noted.

b EPA (2014)

According to the MSDS, exposure to HFC-32 may be hazardous if inhalation, skin contact, eye contact, 

or ingestion of HFC-32 occurs. The most likely pathway of exposure is through inhalation. When present 

in concentrations large enough to significantly lower oxygen concentrations below 19.5 percent by 
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volume, HFC-32 can cause symptoms of asphyxiation, such as headaches, ringing in ears, dizziness, 

drowsiness, nausea, vomiting, depression of all senses, and unconsciousness. Under some circumstances 

of over-exposure (i.e., oxygen levels fall below 6 percent by volume), death may occur. HFC-32 can also

cause cardiac arrhythmia if inhaled in sufficiently great quantities. If HFC-32 is inhaled, person(s) should 

be immediately removed and exposed to fresh air. Exposures of HFC-32 to the skin may cause frostbite. 

In the case of dermal exposure, the MSDS for HFC-32 recommends that person(s) immediately wash the 

affected area with soap and water and remove all contaminated clothing. Exposures of HFC-32 to the 

eyes could cause eye irritation. In case of ocular exposure, the MSDS for HFC-32 recommends that 

person(s) immediately flush the eyes, including under the eyelids, with copious amounts of water for 15 

minutes. If HFC-32 is ingested, person(s) should consult a doctor. EPA’s review of the human health 

impacts of this proposed substitute is contained in the public docket for this decision. These risks and 

procedures after exposure are similar for other common refrigerants.

The potential health effects of HFC-32 can be minimized by following the exposure guidelines and 

ventilation and PPE recommendations outlined in the MSDS for HFC-32 and this risk screen.

7. FLAMMABILITY ASSESSMENT

ASHRAE Standard 34 has classified HFC-32 as a Class A2L refrigerant (ASHRAE 2010b), because it 

has low toxicity, low flammability, and a low burning velocity (approximately 6.7 cm/s) (Takizawa et al. 

2005). The proposed substitute is flammable when its concentration in air is in the range of 13.8 percent

and 29.9 percent by volume (138,000 ppm to 299,000 ppm). In the presence of an ignition source (e.g., 

static electricity, a spark resulting from a switch malfunction, or a cigarette), an explosion or a fire could 

occur when the concentration of HFC-32 exceeds its lower flammability limit (LFL) of 138,000 ppmv, 

posing a significant safety concern for workers and consumers. The remainder of this section assesses 

flammability risks and summarizes the recommended measures to ensure safe handling and use of the 

refrigerant during manufacture, servicing, and end-use.

7.1 Flammability Risks at Manufacture

HFC-32 PTACs are currently manufactured by the submitter outside of the United States; the 

manufacturer currently has no plans to manufacture these systems in the United States. If the manufacture 

of these HFC-32 systems occurs in the United States, the submitter indicates that release of or exposure to 

HFC-32 is possible at the charge and inspection steps on the PTAC production line at the manufacturing 

site (Daikin 2013). It is therefore important that all relevant standards be followed during the manufacture 

of PTACs, specifically UL 484. Engineering controls should include normal and local ventilation (e.g., 

chemical hoods) for standard manufacturing procedures so workers can avoid physical contact with the 

refrigerant and to limit emissions. In general, use of appropriate PPE consistent with OSHA guidelines is 

recommended, such as splash goggles, mechanically-resistance gloves when handling cylinders, 

chemically-resistant gloves when handling the gas mixture (e.g., butyl rubber, chlorinated polyethylene, 

or neoprene), and protective clothing. 

All HFC-32 storage and transport equipment should be installed with safety devices that minimize the 

likelihood of catastrophic releases. It is expected that refrigerants be properly stored and caution used 

within manufacturing facilities to minimize explosion risk and that workers adhere to the requirements set 

by OSHA under 29 CFR 1910. OSHA requirements include proper ventilation and storage practices 

within manufacturing facilities to prevent fire and explosion. Good manufacturing practices should be 

adhered to during the manufacture of equipment containing HFC-32.

6.2 Flammability Risk at Servicing and End-Use

The risk of flammability during servicing and end-use for the reasonable worst-case scenario (see Section 

5) was investigated for HFC-32. Both servicing and end-use of HFC-32 PTACs are expected to take place 
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in the same location (i.e., the place of installation and use). In order to determine the potential 

flammability risks during servicing or end-use in case of a catastrophic release of refrigerant, modeled 

concentrations of HFC-32 immediately following the release of refrigerant were compared to the LFL for 

HFC-32. As demonstrated in Error! Reference source not found. 6, the maximum instantaneous 

concentration of HFC-32 in the room under Reasonable Worst Case Scenario 1 is 95,800 ppm, which is

approximately 69 percent of the LFL (138,000 ppm). Although Reasonable Worst Case Scenario 1 (i.e., 

an 8,500-gram PTAC in a small dormitory) does not present a significant flammability concern, according 

to both UL 484 and ASHRAE Standard 34, a PTAC unit containing a charge size of 8,500 grams of HFC32 is not intended for installation in a room with a volume as small as that modeled in the Reasonable 

Worst Case scenario (i.e., 41 m

3

). The other charge sizes analyzed (i.e., 7,960 and 1,460 grams) also did 

not present a significant flammability concern. The results of the flammability assessment are presented 

in Table 6. 

Table 6. Flammability Assessmenta

Scenario Room Type/Appliance 

Type

Charge 

Size (g)

Effective 

Room Size 

(m3)

Maximum 

Instantaneous 

Concentration

(ppm) b

Reasonable Worst-Case 1 Dormitory Room/PTAC 8,500 41 (1,450 ft3

) 95,800

Reasonable Worst-Case 2 Dormitory Room/Room AC 7,960 41 (1,450 ft3

) 89,700

Reasonable Worst-Case 3 Dormitory Room/PTAC 1,460 41 (1,450 ft3

) 16,500

Threshold Analysis 1: Charge Size Dormitory Room/PTAC 12,200 41 (1,450 ft3

) 138,000

Threshold Analysis 2: Room Size Dormitory Room/PTAC 8,500 28 (1,000 ft3

) 138,000

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.

b Lower Flammability Limit of HFC-32 is equal to 138,000 ppm.

For flammability to be of concern in a 41 m3(1,450 ft3) room (i.e., when the maximum instantaneous 

concentration in the room equals the LFL for HFC-32), the charge size of the HFC-32 AC unit would 

have to be at least 12,200 grams (see Threshold Analysis 1 in Table 6), which is 50 percent larger than the 

maximum size intended for HFC-32 room AC units for any room size, and significantly larger than the 

maximum charge sizes for a PTAC and for any room AC proposed by EPA for a 41 m3room (i.e., 1,460

grams and 5,350 grams, respectively). For flammability to be of concern with an 8,500-gram HFC-32 

PTAC unit, the volume of the dormitory room would have to be decreased to at least 28 m

3

(see 

Threshold Analysis 2 in Table 6).

According to the results of this flammability analysis, the risk of fire is minimal if an HFC-32 room AC 

unit is installed in a room with volumes in accordance with standards and regulations. As dormitory 

rooms can be of smaller sizes than those modeled in this assessment7and because persons or furniture in 

the room may reduce the effective volume of the space, room AC systems containing HFC-32 should not 

be connected to rooms with an effective volume less than required to maintain maximum concentrations 

below the LFL, as described below. According to UL 484, the maximum recommended charge size for a 

HFC-32 PTAC installed in a room with a floor area of 17 m2, which corresponds to the volume of the 

enclosed dormitory room volume used in the worst-case scenario (i.e., 41 m3or 1,450 ft3),8is 

approximately 1,400 g. According to ASHRAE Standard 34, the RCL for HFC-32 (36,000 ppm or 77 g 

HFC-32/m3), which is a more conservative exposure limit than the LFL of HFC-32 (138,000 ppm), 

should not be exceeded in any room that is connected to an HFC-32 room AC system (e.g., through a vent 

or a wall-unit). End-users, therefore, should ensure to install PTAC units or other room AC systems with 

 

7

International Residential Code requires a minimum of 70 ft2for a habitable room, or 14 m3(490 ft3) (ICC IRC 2012).

8 The room sizes provided by UL 484 are based on a floor-mounted PTAC unit height of 0.6 m from the floor.
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an appropriate cooling capacity and charge size for the intended cooled space (i.e., avoid installing large 

AC units to cool small spaces) that is consistent with manufacturer recommendations and the guidelines 

of relevant safety standards (e.g., ASHRAE 15 and 34 and UL 484). The submitter intends to also

manufacture PTAC units with typical charge sizes ranging between 0.5 kg and 1.05 kg, which are more 

suitable for smaller spaces.

Leak prevention, detection, or mitigation devices should be installed and proper ventilation should be 

present to further protect against the risk of fire or explosion in small spaces cooled by HFC-32 AC 

systems. In addition, it is important that only properly trained and EPA Section 608-certified refrigerant 

technicians handle HFC-32. Proper ventilation should be maintained at all times during the manufacture, 

use and servicing of equipment containing HFC-32. During servicing operations, technicians should 

ensure that proper ventilation is in place through the use of fans (or other mechanical ventilation devices) 

and portable refrigerant detectors should be used to alert technicians to the presence of leaked refrigerant 

in the area.

8. ASPHYXIATION ASSESSMENT

The risk of asphyxiation for the reasonable worst-case scenario (see Section 5) was investigated for HFC32. In this section, risk of asphyxiation, considered to be when there is less than 12 percent oxygen

present in a space,

9

is assessed in three ways: 1) modeling the oxygen concentration under the charge size 

and room size specified in the worst-case scenario, 2) performing a threshold analysis of minimum charge 

size needed to cause an asphyxiation risk in the room size specified in the worst-case scenario, and 3) 

performing a threshold analysis of the maximum room size needed to cause a asphyxiation risk with the 

charge size specified in the worst-case scenario. This analysis does not consider other ventilation 

conditions that are likely to occur that would reduce the exposure levels, such as open doors or windows, 

fans operating, conditioned airflow (either heated or cooled), or even seepage between the door and door 

frame. If the proposed substitute passes the screening analysis with these restrictive assumptions in place,

it can be reasonably assumed that no risks of asphyxiation will be present under real-world conditions.

The model assumed that nitrogen and oxygen retain the same relative volumes in the rooms with the 

balance composed entirely of HFC-32 and that the pressure of the room does not increase significantly 

with the addition of the refrigerant. Further, the model assumes no stratification of refrigerant. The 

results of the asphyxiation assessment are summarized in Table 7 below.

Table 7. Asphyxiation Assessmenta

Scenario Room Type/Appliance 

Type

Effective Room 

Size (m3)

Charge Size

(g)

Percent Oxygen 

Concentration in 

Roomb

Reasonable Worst-Case 1 Dormitory Room/ PTAC 41 (1450 ft3

) 8,500 19

Reasonable Worst-Case 2 Dormitory Room/ PTAC 41 (1450 ft3

) 7,960 19

Reasonable Worst-Case 3 Dormitory Room/ PTAC 41 (1450 ft3

) 1,460 20

Threshold Analysis 1: Charge Size Dormitory Room/ PTAC 41 (1450 ft3

) 37,300 12

Threshold Analysis 2: Room Size Dormitory Room/ PTAC 9.3 (328 ft3

) 8,500 12

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.

b The typical concentration of oxygen in air is considered to be 21 percent (Mackenzie & Mackenzie 1995)

Under the reasonable, worst-case scenarios (see Reasonable Worst-Case 1-3 in Table 7), an asphyxiation 

risk will not occur, as the oxygen concentration in the room is between 19 and 20 percent for all charge 

sizes, well above the 12 percent level of concern. For asphyxiation to be a concern in a 41 m3(1,450 ft3) 

room, the charge size of the HFC-32 AC unit would have to be increased to at least 37,300 grams (see 

 

9 Twelve percent oxygen in air is the NOAEL for hypoxia (ICF 1997). 
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Threshold Analysis 1 in Table 7), which is more than 4 times the largest size proposed by EPA for HFC32 room AC units (i.e., 7,960 grams). For asphyxiation to be of concern with an 8,500-g HFC-32 PTAC 

unit, the volume of the dormitory room would have to be decreased to 9.4 m

3

(332 ft3), with an 

approximate floor area of 2.0 m x 2.0 m (6.5 ft x 6.5 ft), which is significantly smaller than the reasonable 

worst-case dormitory room size (41 m3[1,450 ft3]). In addition, the threshold room volume at which 

asphyxiation could occur during a catastrophic leak (9.3 m

3

[328 ft3]) is smaller than the minimum 

dormitory room volume typically found in the U.S.

10

To further protect against an asphyxiation risk, end-users should ensure PTAC units and other room AC 

systems are installed with an appropriate cooling capacity for the intended cooled space to be consistent 

with manufacturer recommendations, EPA regulations, and the guidelines of relevant safety standards 

(e.g., ASHRAE 15 and 34 and UL 484). Minimum room sizes according to the RCL stated in ASHRAE 

34 and UL 484 can be found in Section 6. Leak prevention, detection, or mitigation devices should be 

installed and the ventilation requirements outlined in the MSDS for HFC-32 should be closely followed. 

If these guidelines are followed, a catastrophic leak of HFC-32 is not anticipated to result in a significant 

asphyxiation risk. 

9. END-USE EXPOSURE ASSESSMENT

This section presents estimates of potential consumer exposure to HFC-32 in PTACs and other room AC 

systems. An exposure analysis was performed to examine potential catastrophic release of the proposed 

substitute in a dormitory room under the reasonable worst-case scenario outlined in Section 5. 

For the scenario, 15- and 30-minute time-weighted average (TWA) exposures for the proposed substitute 

were calculated using the box model described in the Background Document, which was adapted to 

estimate concentrations on a minute-by-minute basis. These exposures were then compared to the 

standard toxicity limit presented in Table 8 to assess the risk to consumers. However, the TWA values 

are fairly conservative as the analysis does not consider opened windows, fans operating, conditioned 

airflow (either heated or cooled) and other variables that would reduce the levels to which individuals 

would be exposed. The results of the assessment, which show the end-use exposure levels under the 

reasonable worst-case scenario in Section 5, are presented in Table 8. 

Table 8. End-Use Exposure Assessmenta

Room Type/Appliance

Type

HFC-32 Charge 

Size (g)

Modeled 15-minute 

TWA Exposure (ppm)

Modeled 30-minute TWA

Exposure (ppm)

Cardiotoxic NOAEL, 

5-minute TWA (ppm)b

Dorm Room/PTAC 8,500 95,000 92,100 350,000

Dorm Room/Room AC 7,960 89,000 86,000 350,000

Dorm Room/PTAC 1,460 16,300 15,800 350,000

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.

b See Table 4 for more information

The effect of a one-time exposure to a consumer can be accurately evaluated by comparing the exposure 

concentration to the cardiotoxic NOAEL (350,000 ppm), a conservative upper limit for short-term 

consumer exposure. In the case of infrequent consumer exposure (e.g., from an accidental release), a 

one-time acute concentration is better represented by the cardiotoxic NOAEL than by an occupational 

exposure limit, which is more appropriate during scenarios in which workers are exposed to the chemical 

in question on a daily basis. The modeled 15-minute and 30-minute TWA exposures for consumers are 

well below the cardiotoxic NOAEL for HFC-32 for all charge sizes. 

 

10 The 2012 International Residential Code requires bedrooms to have a minimum volume of 13.9 m3

(490 ft3) (ICC 2012). 
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Further, the model used to calculate the exposure concentrations presented in Table 8- relies upon several 

conservative assumptions. In an actual catastrophic release, only a portion of the refrigerant charge may 

be released, and the ventilation rates and mixing ratios may be much higher than those assumed for this 

analysis. Moreover, in the event that a highly unusual catastrophic release does occur, the refrigerant may 

instead leak from the outdoor air conditioning/heat pump unit, potentially causing environmental effects 

(see Section 11), but eliminating the risk to consumers.

Given that the risk screen process models a highly catastrophic release of the proposed substitute and the 

calculated 15-minute and 30-minute TWAs of the refrigerant are well below the cardiotoxic NOAEL, the 

consumer is not likely to be harmed from any accidental releases from equipment containing HFC-32. 

Smaller accidental releases of the proposed substitute therefore do not pose a significant risk to 

consumers. To prevent exposure during larger releases, EPA recommends that the charge size for HFC-32 

PTACs and room ACs does not exceed the the RCL given in ASHRAE 34 (77 g/m3or 0.005 lb/ft3) and

proposes to require compliance with UL 484. End-users should only install properly-sized PTAC units 

based on the size of the room intended to be cooled and ensure that recommended charge size limitations 

from the manufacturer or relevant safety standards are not exceeded. In addition, proper ventilation 

should be used in accordance with the MSDS for HFC-32. When these conditions are met, accidental 

catastrophic releases of the proposed substitute would not pose a significant risk to consumers.

10. OCCUPATIONAL EXPOSURE ASSESSMENT

This section assesses potential exposures to workers during manufacture, installation, servicing, and 

disposal of HFC-32 in PTAC and other room AC systems. To ensure that use of the proposed substitute in 

PTAC units does not pose an unacceptable risk to workers during servicing and disposal, occupational 

exposure modeling was performed using a box-model approach. For a detailed description of the 

methodology used for this screening assessment, the reader is referred to the occupational exposure and 

hazard analysis described in Chapter 5 of the Background Document. 

Estimates of refrigerant release per event for various release scenarios and data on number of events in 

2014 were obtained from the Vintaging Model.11 To determine the estimated level of occupational 

exposure for a constituent in proposed substitute blend, the total anticipated release rate of the refrigerant 

is multiplied by the weight percent composition of each compound and impurity. For the PTAC unit enduse, 2 percent of the equipment charge was conservatively assumed to be released during manufacture 

and servicing and 40 percent of the equipment charge was conservatively assumed to be released during 

disposal.12 The release rate per event was multiplied by the number of events estimated to occur over a 

workday. For PTAC unit servicing, it was conservatively assumed that eight events of servicing a unit 

occur in an 8-hour work day. For disposal, it was conservatively assumed that 10 units are disposed 

during an 8-hour work day. The modeled exposure concentrations were compared to short-term 

occupational exposure limits at installation and servicing and long-term exposure limits at disposal. 

 

11 ICF International maintains the Vintaging Model for EPA in order to simulate the aggregate impacts of the ODS phase-out on 

the use and emissions of various fluorocarbons and their substitutes over a period of several years across 60 different end-uses. 

The model tracks the use and emissions of various compounds for the annual vintages of new equipment that enter service in 

each end-use. The vintage of each type of equipment determines such factors as leak rate, charge size, number of units in 

operation, and the initial ODS substance that the equipment contained. The service leak rate and disposal release rate assumptions 

are consistent with the PTAC/PTHP end-use in Vintaging Model version VM IO file_v4.4_3.23.14. 

12 During disposal it is assumed that 100 percent of the refrigerant charge remains in the unit.
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10.1 Occupational Exposure during Manufacture

HFC-32 is currently manufactured by the submitter in Japan, and the manufacturer currently has no plans 

to manufacture the proposed substitute in the United States. Other companies however manufacture HFC32 in the U.S. Where manufacture occurs in the United States, the proposed substitute’s MSDS should be 

referenced and proper engineering controls and PPE used. HFC-32 is not expected to pose a risk to 

workers during manufacture when the engineering controls and PPE recommendations and referenced in 

the MSDS for HFC-32 are followed. Engineering controls should include normal and local ventilation 

(e.g., chemical hoods) for standard manufacturing procedures so workers can avoid physical contact with 

the refrigerant and to achieve emission control. In general, use of PPE consistent with OSHA guidelines

is recommended, such as respiratory protection (including a self-contained breathing apparatus [SCBA] in 

case of insufficient ventilation), tightly sealed goggles, and protective gloves (Daikin 2011). 

As indicated by the submitter, charging of the AC units typically will occur at the manufacturing site. 

When this occurs, the submitter has indicated that charging equipment is designed to minimize potential 

emissions and that maintenance manuals describe procedures to reduce leakage and prior safety training is 

required for all personnel who would be charging units. Because of established equipment design and 

installation practices, exposures to HFC-32 will be unlikely. Thus, EPA does not believe that

manufacturing, including charging, of AC units with HFC-32 presents a concern to workers.

In addition, as for other halogenated refrigerants, there is a risk of generation of toxic degradation 

products if HFC-32 is exposed to high temperatures or fire. Containers should be stored in cool, dry 

conditions (maximum storage temperature should be 40C) in well-sealed receptacles and should not be 

allowed to contact open flames, glowing metal surfaces, or electrical heating elements. EPA believes that 

when proper handling and disposal guidelines are followed in accordance with both good industrial 

hygiene and manufacturing practices and the MSDS for HFC-32, there is no significant risk to workers 

during the manufacture of HFC-32 and AC units pre-charged with it.

10.2 Occupational Exposure at Installation and Servicing

Installation and servicing activities for PTACs and other room AC systems using HFC-32 are not 

expected to result in significant worker exposure when certified technicians follow the procedures 

outlined in the HFC-32 MSDS and maintenance manual, undergo proper training, and wear appropriate 

PPE (e.g., gloves and safety glasses). Nevertheless, the potential occupational exposure during servicing 

was analyzed. The possibility of a release during installation was also considered. The maximum 30-

minute time-weighted average (TWA) exposure for HFC-32 was estimated for servicing PTAC and room 

AC units charged with the charge sizes listed in Table 3. As summarized in Table 9, occupational 

exposure to HFC-32 is anticipated to be significantly below the short-term exposure limits (STEL) for a 2

percent release of refrigerant during servicing for all three charge sizes. In addition, because the proper 

controls and PPE described in the MSDS for HFC-32 are used and good manufacturing practices and 

adequate ventilation are established during any use, handling, or storage of HFC-32 indoors, worker 

exposure during installation and servicing is not likely. Systems should be installed to ensure leak-free 

conditions, for instance by following procedures of ASHRAE Standard 147 including conducting leak 

checks once a system is installed (ASHRAE 2013). In addition, during servicing events, prior to adding 

refrigerant, all pipes should be inspected for leakages, and repairs should be performed only after all 

refrigerant has been recovered from the system. By adhering to the safety guidelines mentioned above, 

and in Section 5, worker exposure to HFC-32 during installation and servicing is not a concern.
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Table 9. Occupational Risk Assessment at Installation or Servicinga

HFC-32 Charge 

Size (g)

15-minute TWA 

Occupational Exposure 

(ppm)

30-minute TWA 

Occupational Exposure 

(ppm)

15-min Short 

Term Exposure 

Limits (ppm) b

8,500 220 170 3,000

7,960 200 150 3,000

1,460 37 28 3,000

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.

b STEL was estimated as three times the PEL; this method of estimating a short-term exposure limit is commonly done by ACGIH.

10.3 Occupational Exposure during Disposal

According to the submitter, HFC-32 is intended to be recovered and recycled, pending the development 

of recovery technology, at disposal of the PTAC unit. The submitter anticipates that disposal procedures 

for HFC-32 refrigerant will follow the same procedures as for other refrigerants, such as R-410A, and be 

supplemented with additional technician training related to handling A2L refrigerants. According to the 

MSDS for HFC-32, technicians should dispose of HFC-32 via incineration. 

Table 10 displays the maximum estimated 8-hour TWA occupational exposure level of HFC-32 during 

disposal. Based on the assumptions described in the beginning of Section 9, the modeling indicates that 8-

hour worker exposure concentrations for HFC-32 assuming 40 percent release at disposal could exceed 

the long-term exposure limit (i.e., 1,000 ppm) during disposal of HFC-32 for PTACs and room ACs with 

charge sizes of 8,500 and 7,960 grams, respectively. However, these exposures were derived using 

conservative assumptions (e.g., no ventilation or use of PPE assumed), and represent a worst-case 

scenario with a low probability of occurrence. These types of systems are typically disposed of by trained 

personnel using proper industrial hygiene techniques.

Table 10. Occupational Risk Assessment at Disposala

HFC-32 Charge Size (g) 8-hour TWA Occupational 

Exposure (ppm)

8-hour Long Term Exposure 

Limits (ppm)

8,500 2,700 1,000

7,960 2,500 1,000

1,460 470 1,000

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.

Because anticipated occupational exposures could potentially exceed the exposure limits for larger HFC32 units (i.e. 8,500 and 7,960 gram units) during disposal, the recommendations for proper engineering 

controls and PPE in the MSDS for HFC-32 should be followed. Adequate ventilation should always be 

established during any use, handling, or storage of HFC-32. Engineering controls should include vapor-in 

air detection systems and local exhaust ventilation during use of HFC-32 to prevent dispersion throughout 

the work place. In general, use of PPE is recommended, such as splash goggles, mechanically-resistance 

gloves when handling cylinders and chemically-resistant gloves when handling the gas mixture (e.g., 

butyl rubber, chlorinated polyethylene, or neoprene). EPA believes that if proper handling and disposal 

guidelines are followed in accordance with good industrial hygiene and manufacturing practices and the 

MSDS for HFC-32, there is no significant risk to workers during the manufacturing, installation, 

servicing, and disposal of HFC-32 in PTACs or room AC units.
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11. GENERAL POPULATION EXPOSURE ASSESSMENT

HFC-32 is not expected to cause a concern for human health in the general population when used as a 

refrigerant in room AC systems. At room temperature, HFC-32 is a gas and, therefore, releases to ground 

or surface water are not anticipated. Should air releases during manufacturing operations, including filling

of AC units, occur, engineering controls could be used (e.g., carbon absorption units or scrubbers) to 

collect HFC-32 and prevent the release of HFC-32 to the atmosphere. EPA believes that by using proper 

engineering controls and by following disposal and containment recommendations outlined in the 

proposed substitute’s MSDS, exposure to HFC-32 is not expected to pose a toxicity threat to the general 

population.
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12. REFERENCES

ASHRAE. 2013. ASHRAE Standard 147-2013. Reducing the Release of Halogenated Refrigerants from 

Refrigeration and Air-Conditioning Equipment and Systems. American Society of Heating, Refrigerating 

and Air-Conditioning Engineers, Inc.

ASHRAE 2010a. ASHRAE Standard 15-2010. Safety Standard for Refrigeration Systems. American 

Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 

ASHRAE 2010b. ASHRAE Standard 34-2010 and addenda. Designation and Safety Classification of 

Refrigerants. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE 2010c. ASHRAE Standard 62.1-2010. Ventilation for Acceptable Indoor Air Quality.

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Daikin SNAP Submission. 2011. “Significant New Alternatives Policy Program Submission to the United 

States Environmental Protection Agency,” June 2011.

Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. 

Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland. 2007. Changes in 

Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science 

Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel 

on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and 

H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

ICC. 2012. International residential code for one- and two-family dwellings. International Code Council. 

Available at: http://publicecodes.cyberregs.com/icod/irc/2012/index.htm?bu2=undefined. 

ICF. 1997. Physiological Effects of Alternative Fire Protection Agents - Hypoxic Atmospheres 

Conference. Stephanie Skaggs prepared the proceedings of the conference held May 22, 1997 in New 

London, CT.

Mackenzie, F.T. and J.A. Mackenzie. 1995. Our changing planet. Prentice-Hall.

Takizawa, Kenji, Akifumi Takahashi, Kazuaki Tokuhashi, Shigeo Kondo, and Akira Sekiya, 2005. 

Burning velocity measurement of fluorinated compounds by the spherical-vessel method. National 

Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1, Higashi, Tsukuba, 

Ibaraki 305-8565, Japan. http://dx.doi.org/10.1016/j.combustflame.2005.01.009 

UL 484. 2012. Underwriters Laboratories. UL 484 Standard for Safety: Room Air Conditioners. Eighth

Edition, revised August 3, 2012.

U.S. EPA. 1994. "SNAP Technical Background Document: Risk Screen on the Use of Substitutes for 

Class I Ozone-depleting Substances: Refrigeration and Air Conditioning." Stratospheric Protection 

Division. March, 1994.

U.S. EPA. 2014. Risk Assessment Glossary. Available online at: 

http://www.epa.gov/risk_assessment/glossary.htm.

WMO (World Meteorological Organization), 2011. Scientific Assessment of Ozone Depletion: 2010, 

Global Ozone Research and Monitoring Project—Report No. 52, 516 pp., Geneva, Switzerland, 2011.