June 6, 2014 -- Final

1

Significant New Alternatives Policy Program

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for CFC-12 and R-502 in Household Refrigerators and 

Freezers

Substitute: Propane (R-290)

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 250: 

Household Refrigerators and Freezers.

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 decade, 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 propane as a substitute for CFC-12 and R-502 in the refrigeration and airconditioning end use, specifically household refrigerators and freezers included under Underwriters 

Laboratory (UL) 250: Household Refrigerators and Freezers. The proposed substitute, propane, may 

contain minute quantities of impurities. Table 1 details the composition of the proposed substitute, 

including the maximum estimated concentrations of impurities which may be present in the proposed 

substitute.

Table 1. Composition of the Proposed Substitute

Component Chemical Formula CAS Number Concentration

(Weight Percent)

Proposed Substitute

Propane C3H8 74-98-6 99.5%

Potential Impurities (maximum concentration)

Isobutane C4H10 75-28-5 0.14%

Propylene C3H6 115-07-1 0.031%
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Section 2 of this risk screen summarizes the results of the risk screen for the proposed substitute. 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 Exposure Assessment

 Section 12: References

2. SUMMARY OF RESULTS

Propane is recommended for SNAP approval for household refrigerators and freezers that comply with 

Underwriters Laboratory (UL) Standard 250: Household Refrigerators and Freezers. EPA's risk screen 

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

use of CFC-12, HCFC-22 and R-502 as it is less harmful to the ozone layer, has lower climate impact, 

and a shorter atmospheric lifetime. No significant asphyxiation risks to consumers or toxicity risks to 

workers, consumers, or the general population are expected. Propane is subject to volatile organic 

compound (VOC) regulations under the CAA (40 CFR 51.100(s)). Based on analysis of potential impacts 

of hydrocarbon refrigerant emissions on ground-level ozone concentrations, VOC emissions from the use 

of propane in household refrigerators and freezers are not anticipated to contribute significantly to ground 

level ozone concentrations in the United States. It is expected that procedures identified in the MSDS for 

propane and good manufacturing practices will be adhered to. Additionally, it is expected 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 & Health Administration (OSHA) guidelines will be 

used during manufacture, installation, servicing, and disposal of household refrigerators and freezers

using propane. Because units are to be installed in locations with adequate space and/or ventilation in 

accordance with the equipment maintenance manual for propane, as discussed in greater detail in Section 

9, significant toxicity or flammability risks to consumers are also unlikely. Additional safeguards,

including specified refrigerant concentration limits (RCL) for propane, are also provided by adherence to 

industry standards, including American Society of Heating, Refrigerating and Air-Conditioning Engineers 

(ASHRAE) Standards 15,134,2and 62,3and Underwriters Laboratory (UL) Standard 250: Household 

Refrigerators and Freezers4.

3. ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to atmospheric integrity posed by the use of 

propane in household refrigerators and freezers. The ozone-depleting potential (ODP), global warming 

 

1

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

prescribes safety requirements.

2 Designation and Safety Classification of Refrigerants ASHRAE Standard 34 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.

3 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.

4 UL 250 Standard for Safety: Household Refrigerators and Freezers establishes safety requirements for self-contained household 

refrigerators and freezers designed to be installed and used in residential occupancies.
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potential (GWP), and atmospheric lifetime (ALT) of the proposed substitute are presented in Table 2.

The proposed substitute is substantially less harmful to the ozone layer, has lower climate impact, and has 

a shorter atmospheric lifetime than those of CFC-12 and R-502. In addition propane also has a lower 

climate impact and a shorter atmospheric lifetime than those predicted for other substitutes examined in 

the Background Document, as well as a commonly utilized substitute, HFC-134a. Thus, EPA believes 

that use of propane would result in substantially less harm to the ozone layer than the continued use of 

ODS and commonly used ODS substitutes. 

Table 2. Atmospheric Impacts of Propane Compared to CFC-12, R-502 and HFC-134a

Refrigerant Ozone Depleting Potential 

(ODP)

Global Warming Potential - 

100 year (GWP)a

Atmospheric Lifetime 

years (ALT)

Propane 0

a 3.3 0.03a

CFC-12 1

c 10,900 100a

R-502d 0.31c 4,650 NAe

HFC-134a 0

a 1,430 14a

NA = Not Available

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

b

IPCC/TEAP (2005). 

c ODP for R-502 was calculated using constituent ODPs from WMO 2010 Scientific Assessment Report (2011).

d R-502 is a blend consisting of HCFC-22 (49%) and CFC-115 (51%)

e Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HCFC-22 is 12 years and 

the ALT for CFC-115 is 1,700 years (IPCC 4th Assessment Report [Forster et al. 2007]).

4. VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT

Propane is regulated as a VOC under CAA regulations (40 CFR 51.100 [s]). Through regulations and 

standard industry practices, VOC emissions should be controlled. A separate analysis was prepared by 

EPA (2014) to evaluate the potential impact of the use of hydrocarbon refrigerants on ground level ozone 

concentrations in the United States. The analysis estimated refrigerant emissions from refrigeration and 

air conditioning equipment, which were assumed to contain propylene, isobutane, and/or propane 5under 

different scenarios. Under the most conservative scenario it was assumed that propylene was used in all 

refrigeration and air conditioning equipment. In the most realistic scenario, all three hydrocarbons were 

assumed to be used in certain types of refrigeration and air conditioning equipment, depending on the 

proposed use of each alternative under submissions received by the SNAP Program at the time of the 

analysis. End-uses in the evaluation included a number of types of smaller, self-contained refrigeration 

and room air-conditioning units for which SNAP hydrocarbon applications have been received and/or UL 

Standards covering flammable refrigerants exist. The hydrocarbon emissions from these scenarios were

estimated based on U.S. EPA’s Vintaging Model, and their potential contributions to ozone 

concentrations were assessed using U.S. EPA’s Community Multiscale Air Quality (CMAQ) model. 

CMAQ modeling was performed for April through the end of September, as these months presented the 

largest releases of hydrocarbon refrigerant as well as weather conditions favorable for ozone 

formation. The ozone concentrations were estimated for the Atlanta, Houston and Los Angeles regions, 

due to their distinctive geographic setting and chronic high levels of ground level ozone, and then scaled 

for national emission estimates. The results of the CMAQ modeling indicated that under the most realistic 

scenario, hydrocarbon refrigerants could potentially increase the maximum 8-hour average ground level 

ozone by no more than 0.15 ppb in Los Angeles, the city with the greatest ozone problem. This is roughly

0.2 percent of the current National Ambient Air Quality Standard (NAAQS) for ozone of 75 ppb. In the 

 

5 EPA uses the maximum incremental reactivity (MIR) of ethane (0.28 g-O3

/g-substance) as the threshold for determining 

whether a compound has negligible reactivity. Propylene (MIR = 11.57), isobutane (MIR = 1.34), and propane (MIR 0.56) are all

considered to be reactive compounds and are therefore subject to VOC regulations.
June 6, 2014 -- Final

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most conservative case which assumed that the most reactive hydrocarbon, propylene, was used in all 

refrigeration and air conditioning equipment, there could be an incremental maximum increase of the 8-

hour average as high as 6.61 ppb ozone, or an increase of up to 9 percent of the NAAQS. However, this 

upper bound level of increase is not likely, as most ozone nonattainment areas are not VOC-limited (i.e., 

the formation of ozone in these areas are not by limited by VOC emissions, but by other compounds such 

as nitrogen oxides [NOx]). In addition, the analysis assumed no use of VOC-exempt refrigerants which 

may be used in the refrigeration and air conditioning end-uses. Based on the results of this analysis, VOC 

emissions from the use of propane in vending machines are not anticipated to contribute significantly to 

ground level ozone concentrations in the United States.

5. DISCUSSION OF END-USE SCENARIOS MODELED

Propane is proposed for use in household refrigerators and freezers. A charge size was not available for 

propane in the household refrigeration end-use. Therefore, this analysis assumes that refrigeration units 

will conform to the standard UL 250 Supplement SA. Per this standard, 50 grams is the maximum 

amount of refrigerant that may leak for refrigerants with flammability limits and a heat of combustion that 

is >19,000 kJ/kg, which is the case for propane.

To represent a reasonable worst-case scenario, it was assumed that a catastrophic leak of refrigerant 

occurs while the refrigerator or freezer unit is located in a household kitchen. Because household 

refrigerators and freezers can be installed in locations with varying room volumes, the analysis in this risk 

screen conservatively assumes that the refrigeration unit is located in a kitchen with a volume of 18m3. 

This modeling scenario is also intended to be consistent with EPA’s proposed use condition for 

hydrocarbon refrigerants that limits the refrigerant charge size of any refrigerator, freezer, or combination 

refrigerator and freezers to 57 grams,6assuming that roughly 12 percent of the refrigerant charge is 

retained in the compressor oil and 88 percent of the charge leaks. 

Under the worst-case scenario, the full charge of the unit is assumed to be emitted over the course of one 

minute into a kitchen with a ventilation rate of 0.25 ACH. It is further assumed that an individual is 

present at the start of the leak and remains in the room with the door closed until the charge is completely 

released. A vertical concentration gradient is also assumed since propane is denser than air (specific 

gravity of propane relative to air is 1.52 [air = 1]) and will settle in higher concentrations closer to the 

ground. In order to simulate the vertical concentration gradient, it is assumed that 95 percent of the leaked 

refrigerant mixes evenly into the lower 0.4 meters of the room and the rest of the refrigerant mixes evenly 

in the remaining volume (Kataoka 2000). Modeling of the lower 0.4 meters of the room is consistent with 

the possibility that in a bedroom scenario individuals may be lying close to the floor. 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 Household Kitchen

Size (m3) 18a(640 ft3)

Ventilation Rate (air changes per hour) 0.25a

Refrigeration Unit Household Refrigerator or Freezer

Charge Size (g) 50b

Duration of Release (minutes) 1

Vertical Concentration Gradient Yes

 a Background Document (EPA 1994)

 

b Maximum charge size for a household refrigerator or freezer under UL 250.

 

6 EPA 40 CFR Part 82 Proposed Rulemaking EPA-HQ-OAR-2009-0286; FRL-9147-9. Available at: 

http://www.gpo.gov/fdsys/pkg/FR-2010-05-10/html/2010-10959.htm 
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6. POTENTIAL HEALTH EFFECTS

To assess potential health risks from exposure to the proposed substitute in household refrigeration units, 

EPA identified the relevant toxicity threshold values for comparison with modeled exposure 

concentrations for different scenarios. To protect consumers from the potential dangers of a catastrophic 

leak from the refrigeration unit, 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 implements the aforementioned standard, requiring that “the 

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

system shall not exceed the RCL” (ASHRAE 2010a). As such, this risk screen references the RCL in 

addition to the lower flammability limit, hypoxia NOAEL, and exposure limits as an additional, 

conservative limit to ensure that significant flammability, asphyxiation, and end-use exposure risks, 

respectively, do not occur.

For the occupational exposure analysis, potential risks from chronic and acute worker exposure were 

evaluated by comparing exposure concentrations with available occupational exposure limits. Potential

risks of chronic worker exposure were evaluated using workplace guidance levels (WGL). Risks from 

potential short-term consumer exposures were evaluated by comparing exposure concentrations with 

emergency guidance levels. In the absence of an established short-term exposure limit (STEL), acute 

exposure guideline (AEGL), or emergency response planning guideline (ERPG), potential short-term, 

end-use exposures were compared with an excursion limit, which was calculated according to the 

methodology described in ACGIH (2004).7 Table 4 lists the relevant toxicity limits and RCLs of propane

and its impurities and is followed by 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. 

 

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It should be noted that this risk screen evaluates both short-term occupational and end-use (i.e., non-occupational) exposure to 

propylene by comparison to the excursion limit, which is typically used to evaluate short-term occupational exposure. EPA 

believes that, in the absence of an AEGL, STEL, or ERPG, the excursion limit provides a reasonable proxy. Notably, the ACGIH 

methodology (i.e., using three times the TLV-TWA) has also been used by DOE (2008) to develop a temporary emergency 

exposure limit for propylene (2,500 mg/m

3

or 1,500 ppm 15-min TWA), which applies to the general population. 
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Table 4. Toxicity Levels of Propane

Component WGL (Long-term Exposure)

ppm

EGL (Short-term Exposure)

ppm

Refrigerant Concentration 

Limit (RCL) ppm

Propane 1,000a

(OSHA PEL)

10,000c,d(10 min AEGL-1)

6,900d(30 min AEGL-1) 5,300g

Potential Impurities 

Isobutane 1,000b (ACGIH TLV ) 6,900e 4,000g

Propylene 500b(ACGIH TLV) 1,500f

(30 min ACGIH 

Excursion Limit) 1,000g

a OSHA PEL available at: http://www.cdc.gov/Niosh/npg/npgd0524.html

b ACGIH TLV for aliphatic hydrocarbon gases: alkane (C1 - C4) is 1,000 ppm TWA (ACGIH 2012)

c An IDLH of 2,100 ppm has been established for propane. However, NIOSH (1996) states that "[b]ased on acute inhalation toxicity data in humans 

(ACGIH 1991; Braker 1980), a value much greater than 10,000 ppm would have been appropriate. However, the revised IDLH for propane is 2,100 

ppm based strictly on safety considerations (i.e., being 10% of the lower explosive limit of 2.1%)." Therefore, as this IDLH value is based on 

flammability concerns and not toxicity concerns, it is not used in the evaluation of toxicity risks in this risk screen.

d AEGL-1 available at: http://www.epa.gov/opptintr/aegl/pubs/results96.htm

e Because n-butane and isobutane have the same molecular formula, EGL for isobutane is conservatively assumed to be that for n-Butane. 

However, OSHA (2004) notes the following regarding isobutane: “OSHA does not have a PEL for isobutane, which is affirmed as "generally 

recognized as safe" as a direct human food ingredient (21 CFR 184.1165). No toxic effects reported below 18,000 ppm.”

f Calculated as three times the TLV-TWA. (ACGIH 2004)

g ASHRAE (2010b)

Table 5. 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

AIHA American Industrial Hygiene Association

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. 

AEGLb,c

Acute Exposure Guideline 

Level 1

AEGL-1 is the airborne concentration of a substance above which it is 

predicted that the general population, including susceptible individuals, 

could experience notable discomfort, irritation, or certain asymptomatic 

nonsensory effects. However, the effects are not disabling and are 

transient and reversible upon cessation of exposure.

Acute Exposure Guideline 

Level 2

AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a 

substance above which it is predicted that the general population, 

including susceptible individuals, could experience irreversible or other 

serious, long-lasting adverse health effects or an impaired ability to 

escape.

Acute Exposure Guideline 

Level 3

AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a 

substance above which it is predicted that the general population, 

including susceptible individuals, could experience life-threatening health 

effects or death.
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ERPG

Emergency Response 

Planning Guideline 1 

The maximum airborne concentration below which it is believed that 

nearly all individuals could be exposed for up to 1 hour without 

experiencing other than mild transient health effects or perceiving a 

clearly defined, objectionable odor according to AIHA. 

Emergency Response 

Planning Guideline 2 

The maximum airborne concentration below which it is believed that 

nearly all individuals could be exposed for up to 1 hour without 

experiencing or developing irreversible or other serious health effects or 

symptoms which could impair an individual's ability to take protective 

action according to AIHA.

Emergency Response 

Planning Guideline 3 

The maximum airborne concentration below which it is believed nearly 

all individuals could be exposed for up to 1 hour without experiencing or 

developing life-threatening health effects according to AIHA.

Excursion Limit d Excursion Limit Because methane (and other short-chain alkane gases through butane) 

does not have a TLV-short-term exposure limit, an excursion limit may 

be applied. Excursions in worker exposure levels may exceed 3 times 

the TLV-TWA for no more than a total of 30 minutes during a workday, 

and under no circumstances should they exceed 5 times the TLV-TWA, 

provided that the TLV-TWA is not exceeded according to ACGIH. 

IDLH Immediately Dangerous to 

Life and Health

If exposed to this concentration, room occupants are expected to be able 

to escape the room within 30 minutes without experiencing escapeimpairing or irreversible health effects.

TEELe

Temporary Emergency 

Exposure Limit 1

TEEL-1 is the maximum concentration in air below which it is believed 

nearly all individuals could be exposed without experiencing other than 

mild transient adverse health effects or perceiving a clearly defined, 

objectionable odor. 

Temporary Emergency 

Exposure Limit 2

TEEL-2 is the maximum concentration in air below which it is believed 

nearly all individuals could be exposed without experiencing or 

developing irreversible or other serious health effects or symptoms that 

could impair their abilities to take protective action.

Temporary Emergency 

Exposure Limit 3

TEEL-3 is the maximum concentration in air below which it is believed 

nearly all individuals could be exposed without experiencing or 

developing life-threatening health 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 (2012)

c Applicable to emergency exposure periods ranging from 10 minutes to 8 hours.

d ACGIH (2004)

e Chemical exposure guidelines to use for emergency planning if no AEGL or ERPG is available. TEELs are developed based on concentration 

limits or toxicology parameters (DOE 2008).
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According to the MSDS, exposure to propane may be hazardous if inhalation, skin contact, or eye contact 

with propane occurs. The most likely pathway of exposure is through inhalation. At concentrations high 

enough to significantly lower oxygen concentrations below 19.5 percent by volume, propane can cause 

symptoms of asphyxiation such as headaches, ringing in the ears, dizziness, drowsiness, nausea, vomiting, 

depression of all senses, and unconsciousness. Exposure when propane causes oxygen levels to fall below 

6 percent by volume may cause death. In addition, at high concentrations, propane can act as a narcotic 

and cause central nervous system depression, including dizziness, drowsiness, and headaches. 

If propane is inhaled, person(s) should be immediately removed and exposed to fresh air. In accordance 

with the MSDS, EPA further recommends that if breathing is difficult person(s) be given oxygen, 

provided a qualified operator is present, and medical attention be sought. Rescuers should not attempt to 

assist victims of exposure to propane without adequate PPE. At a minimum, a self-contained breathing 

apparatus (SCBA) should be worn. Exposures of propane to the skin may cause frostbite. In the case of 

dermal exposure, the MSDS for propane recommends that person(s) immediately wash the affected area 

with water and remove all contaminated clothing; if frostbite occurs, bathe (do not rub) the affected area 

with lukewarm, not hot, water. If water is not available, cover the affected area with a clean, soft cloth. 

Alternatively, if the fingers or hands are frostbitten, warm the affected area by placing it in the armpit.

Gently exercise the affected part while being warmed, and seek medical attention immediately. Exposures 

of propane to the eyes could cause eye irritation. In case of ocular exposure, the MSDS for propane

recommends that person(s) immediately flush the eyes, including under the eyelids, with copious amounts 

of water for 15 minutes. 

EPA’s review of the human health impacts of this proposed substitute is contained in the public docket 

for this decision. The potential health effects of propane can be minimized by following the exposure 

guidelines and ventilation and PPE recommendations outlined in the MSDS for propane and in this risk 

screen.

7. FLAMMABILITY ASSESSMENT

ASHRAE Standard 34 classifies propane as a Class A3 refrigerant. Propane is flammable when its 

concentration in air is in the range of 2.1 percent to 9.5 percent by volume (21,000 ppm to 95,000 ppm). 

In the presence of an ignition source (e.g., static electricity, a spark resulting from a closing door, or a 

cigarette), an explosion or a fire could occur if the concentration of propane were to exceed the lower 

flammability limit (LFL) of 21,000 ppm. The remainder of this section addresses 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

Release of or exposure to propane may be possible at the charging and sealing steps on the production 

line at the manufacturing site. It is therefore important that all relevant standards be followed during the 

manufacture of refrigeration units, specifically UL 250. If the manufacture of household refrigerator and 

freezer units charged with propane occurs in the United States, EPA recommends that 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-resistant gloves when handling cylinders, chemically-resistant gloves (e.g., butyl rubber, 

chlorinated polyethylene, or neoprene) when handling the gas mixture, and protective clothing.

All propane storage and transport equipment should be installed with safety devices that minimize the 

likelihood of catastrophic releases. For example, NFPA 58 Liquefied Petroleum Gas Code (NFPA 2007) 

for liquefied propane requires the use of overfill protection devices (OPD) on cylinders to minimize the 

likelihood of leaks. The NPFA 58 Code also contains propane storage and transportation 
June 6, 2014 -- Final

9

requirements/guidelines. 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 propane, e.g., using proper ventilation. 

7.2 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 propane. Both servicing and end-use of propane household refrigeration units are 

expected to take place in the same space (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 propane immediately following the release of refrigerant were compared with 

the LFL for propane. As demonstrated in Error! Reference source not found., the maximum 

instantaneous concentration in the lower 0.4 meters of the room at a charge size of 50 grams would be 

approximately 8,717 ppm. The maximum instantaneous concentration in the upper portion in the room is 

much lower, as only 5 percent of the leaked refrigerant is present in this area, which has greater volume 

than the lower 0.4 meters. The results of the flammability assessment are presented in Error! 

Reference source not found.. 

Table 6. Flammability Assessmenta

Scenario Charge Size (g) Effective Room 

Size (m3)

Maximum 

Instantaneous 

Concentration

(ppm) b,c

Reasonable Worst-Case 1 50 18 (640 ft3

) 8,717

Threshold Analysis 1: Charge Size 310 18 (640 ft3

) 21,000

Threshold Analysis 2: Room Size 50 3 (110 ft3

) 21,000

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 propane is 21,000 ppm.

c Values provided in this column refer to the concentration in the lower 0.4 meters of the room, which presents the most conservative risk 

as 95 percent of the leaked refrigerant is present in this space. 

For the flammability threshold analysis shown in Table 6, the conditions at which a flammability concern 

would exist (i.e., when the maximum instantaneous concentration in the lower 0.4 meters of the room 

equals the LFL for propane) were determined. Within the reasonable worst-case room size of 18 m

3

(640

ft3), the charge size of the propane refrigeration unit would have to be at least 310 grams for a 

flammability concern to exist, as shown in Threshold Analysis 1. This is more than the charge size of 57 

grams which EPA’s proposed use condition requires as a limit for propane in any refrigerator, freezer, or 

combination refrigerator and freezer. Using a 50-gram refrigeration unit, as shown under Threshold 

Analysis 2, the volume of the room would have to be 3 m

3

(110 ft3) or smaller for a flammability risk to 

occur.

According to the results of this flammability analysis, the risk of fire is minimal if a household 

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

kitchens can be smaller than those modeled in this assessment and because persons or furniture in the 

room may reduce the effective volume of the space, refrigeration units containing propane should not be

installed in enclosed areas with effective volumes less than indicated by UL 250 unless additional steps 

are taken to protect against a flammability risk (e.g., higher ventilation rates). According to ASHRAE 

Standard 34, the RCL for propane (9.5 g/m3of propane or 5,300 ppm by volume) should not be exceeded 
June 6, 2014 -- Final

10

in any room that contains a propane refrigeration unit. Although the RCL for propane is less conservative

than the anticipated release amount of propane under the modeled worst-case scenario (i.e., 50 grams in a 

18 m

3

space, or 2.8 g/m3), the RCL is calculated assuming that refrigerant is evenly mixed in the space, 

whereas this analysis assumes a vertical concentration gradient occurs due to the higher density of 

propane than that of air (propane = 1.52, air = 1). End-users, therefore, should ensure that propane

refrigeration units are installed in locations with areas that are consistent with manufacturer 

recommendations and the guidelines of relevant safety standards (e.g., ASHRAE 15 and 34 and UL 250).

EPA recommends that warning labels are present on the equipment indicating that flammable refrigerants 

are inside the unit as well as notifying the user to read the equipment use instructions that provide safety 

guidelines for handling propane. These guidelines should be followed to mitigate flammability risk. The 

installation of leak prevention devices would further protect against the very limited risk of explosion.

During servicing operations, EPA recommends that the ventilation requirements outlined in the MSDS 

for propane are followed through the use of fans or other mechanical ventilation devices and that portable 

refrigerant detectors are used to alert technicians to the presence of flammable gases in order to mitigate 

the risk of fire or explosion during catastrophic leak. It is also important that only properly trained and 

certified technicians handle propane. As a further precaution, certification requirements and training 

programs for technicians that handle propane should be developed using these guidelines. 

8. ASPHYXIATION ASSESSMENT

The risk of asphyxiation for the reasonable worst-case scenario (see Section 5) was investigated for 

propane. In this section, risk of asphyxiation 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 3) performing a threshold analysis of the maximum room size needed to cause 

an asphyxiation risk with the charge size specified in the worst-case scenario. This analysis does not 

consider conditions that are likely to occur that would increase the oxygen levels to which individuals 

would be exposed, such as open doors or windows, fans operating, conditioned airflow (either heated or 

cooled), or even openings at the bottom of doors that allow air to flow in and out. As specified in Section 

5, this analysis assumes a vertical concentration gradient. 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 results of the asphyxiation assessment are 

summarized in Table 7 below. 

Table 7. Asphyxiation Assessmenta

Scenario Charge Size (g) Effective Room Size 

(m3)

Percent Oxygen 

Concentration in the 

Lower 0.4 Metersb

Reasonable Worst-Case 1 50 18 (640 ft3

) 21

Threshold Analysis 1: Charge Size 3,250 18 (640 ft3

) 12

Threshold Analysis 2: Room Size 50 0.28 (9.8ft3

) 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)

In order for a risk of asphyxiation to occur, the normal concentration of oxygen in air (21 percent) must 

be reduced to 12 percent.8 Based on the worst-case scenario modeling assumptions, propane in household 

refrigeration units does not present a significant risk of asphyxiation. The concentration of propane in the 

air following the release of the 50-gram charge size does not exceed 0.11 percent, which has an 

 

8 Twelve percent oxygen in air is the NOAEL for hypoxia (ICF 1997). 
June 6, 2014 -- Final

11

insignificant impact on the concentration of oxygen in air. This modeling does not take into account any 

ventilation which is likely to occur, such as conditioned airflow, open doors, or even openings at the 

bottom of doors that allow air to flow in and out, as mentioned above; therefore, the actual asphyxiation 

risk to person(s) is likely to be even smaller than modeled. 

For the asphyxiation threshold analyses shown in Table 7, the conditions at which an asphyxiation 

concern would exist were determined. Within the reasonable worst-case room size of 18 m3(640 ft3), as 

shown under Threshold Analysis 1, the charge size of the propane refrigerator or freezer unit would have 

to be at least 19,500 grams for asphyxiation to be a concern, which is more than 340 times the charge size 

anticipated in EPA’s proposed use condition for hydrocarbon refrigerants in any refrigerator, freezer, or 

combination refrigerator and freezers. In Threshold Analysis 2, the volume of the room would have to be 

0.05 m

3 (1.8 ft3

) or smaller for asphyxiation to be of concern.

To further protect against an asphyxiation risk, end-users should ensure household refrigerators or 

freezers with propane are installed in rooms with areas consistent with manufacturer recommendations 

and the guidelines of relevant safety standards (e.g., ASHRAE 15 and 34 and UL 250). Minimum room 

sizes according to the RCL stated in ASHRAE 34 can be found in Section 7.2. Leak prevention, 

detection, and/or mitigation devices should be installed and the ventilation requirements outlined in the 

MSDS for propane should be closely followed. If these guidelines are followed, a catastrophic leak of 

propane is not anticipated to result in a significant asphyxiation risk. 

9. END-USE EXPOSURE ASSESSMENT

This section presents estimates of potential end-use exposures to propane and each of its impurities in 

household refrigerators and freezers. An exposure analysis was performed to examine potential 

catastrophic release of the proposed substitute in a kitchen under the reasonable worst-case scenario 

outlined in Section 5. 

For the end-use exposure assessment scenario, 30-minute TWA exposures for the proposed substitute and 

its impurities 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 

with the standard toxicity limits presented in Table 4 to assess the risk to end-users. 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. Modeling was performed for propane and each of its impurity constituents; 

however, only the results for propane are presented in Table 8. As propane is approximately 99.5 percent 

pure, it presents the greatest risk of exceeding the STEL and thus the most conservative assessment. 

Table 8. End-Use Exposure Assessmenta

Scenario Charge Size (g) Effective Room 

Size (m3)

30-minute TWA 

End-Use Exposure 

(ppm)b,c

Reasonable Worst-Case 1 50 18 (640 ft3) 3,300

Threshold Analysis 1: Charge Size 104 18 (640 ft3) 6,859

Threshold Analysis 2: Room Size 50 8.7 (310 ft3) 6,822

Bold font indicates modeling results.

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

b 30-min AEGL-1 STEL for propane is 6,900 ppm; See Table 4 for more information.

c Values provided in this column refer to the concentration in the lower 0.4 meters of the room, which presents the most conservative 

risk as 95 percent of the leaked refrigerant in present in this space. 

In the reasonable worst-case scenario, the catastrophic release of propane from household refrigerators 

and freezers with a charge size of 50 grams was modeled. The modeling results indicate the maximum 
June 6, 2014 -- Final

12

anticipated end-use exposure does not exceed 48 percent of the 30-min AEGL-1 for propane. To mitigate 

risk during end-use, EPA recommends that for a minimum room volume of 18 m3, the charge size does 

not exceed 104 grams, and that for a charge size of 50 grams, the household refrigerator or freezer not be 

installed in a room of volume less than 8.7 m3 (310 ft3). Because the modeling was done using a 

conservative scenario, personnel exposure to the proposed substitute at end-use is not considered a 

significant threat. To minimize the risk of exposure, EPA recommends that the charge size for a 

household refrigeration unit does not exceed the RCL (9.5 g/m3) and proposes to require compliance with 

UL 250 in any space containing a household refrigeration unit, unless proper leak protection devises are 

in place in order to prevent exposures of propane beyond the recommended limits. Proper leak protection 

devices and engineering control requirements and adherence to the MSDS will further ensure that 

exposure limits are maintained below those described in Table 8. 

10. OCCUPATIONAL EXPOSURE ASSESSMENT

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

disposal of propane in household refrigerators and freezers. To ensure that use of the proposed substitute 

in household refrigeration 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 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 were 

obtained from input parameters to the Vintaging Model.9 To determine the estimated level of 

occupational exposure for a household refrigerator charged with propane, it was conservatively assumed 

that 1 percent of the equipment charge would be released per manufacturing event, 0.4 percent during 

servicing, and 3 percent during disposal.10 Additionally, EPA is proposing to allow intentional venting or 

release of propane as a refrigerant during installation, servicing, maintenance and disposal from 

household refrigeration equipment. If venting does occur, it should be done in a well-ventilated area (i.e. 

outdoors). Therefore, scenarios in which 100 percent of the equipment charge is released during servicing 

and disposal were also considered. The release rate per event was multiplied by the number of events 

estimated to occur over a workday. For household refrigeration unit servicing, it was conservatively 

assumed that eight events of servicing a unit by one servicing technician occur in an 8-hour work day. For 

disposal, it was conservatively assumed that 10 units are disposed of in one facility during an 8-hour work 

day. The modeled exposure concentrations were compared with short-term occupational exposure limits 

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

10.1 Occupational Exposure during Manufacture

Propane is produced around the world, including in the United States, and is used for a wide variety of 

refrigerant and non-refrigerant uses. Potential points of release relevant to this analysis are during the 

charging of propane into the refrigeration system within the refrigerator or freezer (prior to being 

hermetically sealed) or through punctures (after sealing) during the subsequent manufacturing, finishing, 

assembling, packaging or handling processes. Releases prior to sealing or leaks in the hermetic system 

could release up to 50 grams of propane into the indoor air. The maximum 8-hour time-weighted average 

 

9

ICF International maintains the Vintaging Model for EPA in order to simulate the aggregate impacts of the ODS phaseout on 

the use and emissions of various ODS and their substitutes over a period of several years across more than 40 different 

applications. 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 household refrigerators and freezer end-use in Vintaging Model version VM IO 

file_v4.4_11.6.12. 

10 At the point of the unit’s disposal, it is assumed that 100 percent of the original refrigerant charge remains.
June 6, 2014 -- Final

13

(TWA) exposures for propane and the trace impurities were estimated for a manufacturing scenario and 

compared with their respective short-term exposure limits (see Table 8). For manufacturing of household 

refrigeration units, it was assumed that the release per event was 1 percent of the unit’s charge. 

Table 8. Occupational Risk Assessment at Manufacturea

Component 8-hour TWA Occupational 

Exposure (ppm)

Long Term (8-Hour) Exposure 

Limits (ppm)

Propane 273 1,000b

Potential Impurities 

Isobutane 0.29 1,000c

Propylene 0.09 500c

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

b OSHA PEL

c ACGIH TLV 

 

The modeling results indicate that the maximum anticipated occupational exposure concentrations for 

propane and its impurities during manufacture are significantly lower than the short-term exposure limits 

for household refrigerators or freezers with a 50-gram charge size. EPA believes that when proper 

handling and storage guidelines are followed in accordance with both good industrial hygiene and 

manufacturing practices and the MSDS for propane significant exposures to propane during manufacture 

will be unlikely. Thus, EPA does not believe that manufacturing, including charging, of household 

refrigeration units with propane presents a significant concern to workers.

10.2 Occupational Exposure at Installation and Servicing 

The potential occupational exposure during installation and servicing for propane household refrigeration 

units was analyzed. The maximum 30-minute time-weighted average (TWA) exposure for propane and its 

potential impurities were estimated for servicing household refrigeration units charged with 50 grams of 

refrigerant. As summarized in Table 9, occupational exposure to propane is anticipated to be significantly 

below the STEL for propane and its impurities with a 50-gram charge size for both 0.5 percent release 

and 100 percent release of refrigerant during servicing. Therefore, worker exposure to propane during 

installation and servicing is not a significant concern. Technicians should follow the procedures outlined 

in the MSDS and maintenance manual, undergo proper training, and wear appropriate PPE (e.g., gloves 

and safety glasses). Adequate ventilation should always be present during any use, handling, or storage of 

propane. Systems should be installed by following procedures of ASHRAE Standard 14 including 

conducting leak checks once a system is installed (ASHRAE 2002). In addition, prior to adding 

refrigerant during servicing events, 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 6, worker exposure to propane during installation and 

maintenance is unlikely.
June 6, 2014 -- Final

14

Table 9. Occupational Risk Assessment at Servicinga

Component

30-minute TWA Occupational Exposure 

(ppm)

Charge size: 50 grams

30-min Short Term 

Exposure Limits (ppm)

0.4% Release 100% Release

Propane 0.40 100 6,900b

Potential Impurities

Isobutane 4 x 10-4 0.11 6,900c

Propylene 2 x 10-4 0.03 1,500d

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

b AEGL-1

c AEGL-1; See Table 4 for more information

d ACGIH (2004)

10.3 Occupational Exposure at Disposal

Disposal of propane household refrigeration units is expected to occur at disposal facilities with limited 

duration of exposure to the refrigerant. Potential exposures to the refrigerant during recovery and disposal 

are expected to occur during activities related to draining the refrigerant from the refrigeration units into 

cylinders (e.g., connecting of pipes). Such activities and related exposure is anticipated to occur within 

15-30 minutes (per event/day).

Based on the assumptions described in the beginning of Section 10, the modeling indicates that 8-hour 

worker exposure concentrations for propane and its impurities during the 3 percent release and 100

percent release scenarios will not exceed the long-term exposure limits of any of the individual 

components during disposal of propane for household refrigeration units with a charge size of 50 grams. 

Table 10 displays the maximum estimated 8-hour TWA occupational exposure levels of the proposed 

substitute and its impurities during disposal. Because modeled exposure levels in both scenarios are 

significantly lower than the exposure guidelines for propane and its impurities, occupational exposure to 

the proposed substitute during disposal is not considered a toxicity threat. Further, estimated 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

Component

8-Hour TWA Occupational Exposure (ppm)

Charge size: 50 grams

8-Hour Long Term 

Exposure Limits 

(ppm)

3% Release 100% Release

Propane 5.28 175 1,000b

Potential Impurities

Isobutane 0.01 0.19 1,000c

Propylene 0.002 0.06 500b

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

 b OSHA PEL

 c ACGIH TLV

 

Although anticipated occupational exposures are well below the exposure limits for propane and each of 

its impurities in both disposal release scenarios, the recommendations for proper engineering controls and 

PPE in the MSDS for propane should be followed. Adequate ventilation should always be established 

during any use, handling, or storage of propane. Engineering controls should include vapor-in-air 

detection systems and local exhaust ventilation during use of propane to prevent dispersion throughout 
June 6, 2014 -- Final

15

the workplace. In addition, an eye wash and safety shower should be near the manufacturing facility and 

locations where propane is stored and ready for use. In general, use of PPE is recommended, such as 

splash goggles, mechanically-resistant 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 propane, there is no significant risk to workers during the 

manufacturing, installation, servicing, and disposal of propane in household refrigeration units.

11. GENERAL POPULATION EXPOSURE ASSESSMENT

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

refrigerant in household refrigeration units. At room temperature, propane is a gas and, therefore, releases 

to ground or surface water are not anticipated, as propane is anticipated to dissipate into the atmosphere 

upon release to outside air because natural ventilation rates would be higher and there is no enclosed 

space to keep propane concentrated. Should air releases during manufacturing operations occur, including 

filling of refrigeration units, engineering controls should be used (e.g., carbon absorption units or 

scrubbers) to collect propane and prevent the release of propane 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 propane is not expected to pose a significant toxicity risk

to the general population.
June 6, 2014 -- Final

16

12. REFERENCES

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