June 4, 2014 -- Final

1

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: 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 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 report 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 HCFC-22 in the residential and light commercial 

air conditioning (AC) and heat pump end-use, specifically in window AC units. Table 1 details the 

composition of the proposed substitute, including the maximum estimated concentrations of impurities,

which may be present in the proposed substitute, as provided by the submitter (allowable impurity levels 

per 40 CFR Part 82 or under AHRI Standard 700 may be different).

Table 1. Composition of Propane

Component Chemical Formula CAS Number Concentration

(Weight Percent)

Proposed Substitute

Propane C3H8 74-98-6 98.9%

Potential Impurities (maximum concentration)

Isobutane C4H10 75-28-5 0.4%

n-Butane C4H10 106-97-8 0.4%

Ethane C6H14 74-84-0 0.2%

Propene C3H6 115-07-1 0.1%
June 4, 2014 -- Final

2

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

1Error! Reference source not found.. 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 Scenario 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 residential and light commercial room AC units that 

comply with Underwriters Laboratory (UL) Standard 484: Room Air Conditioners, specifically window 

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

portable AC units. 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 as it is less harmful to the ozone layer, has lower 

climate impact, and a shorter atmospheric lifetime. 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 window AC units are not anticipated to contribute significantly to ground level ozone 

concentrations in the United States. No significant asphyxiation risks to consumers or toxicity risks to 

workers, consumers, or the general population are expected. It is expected that procedures identified in 

the material data safety sheet (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 window AC 

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

for the unit’s charge size in accordance with EPA recommendations and the equipment maintenance 

manual for propane window AC units, as discussed in greater detail in Section 9, significant toxicity or 

flammability risk to consumers is 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 15,1

34,2and 62,3and Underwriters Laboratory (UL) Standard 484.

4

 

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 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.

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 484 Standard for Safety: Room Air Conditioners establishes safety requirements for room air conditioners that are designed 

to provide delivery of conditioned air to an enclosed space, room, or zone. 
June 4, 2014 -- Final

3

3. ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to the atmosphere posed by the use of propane

in window AC units. The ozone depletion potential (ODP), global warming 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 a

shorter atmospheric lifetime compared to HCFC-22. 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, R-410A. Thus, EPA believes that use of propane

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 HCFC-22 and R-410A.

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

Refrigerant Ozone Depleting Potential 

(ODP)

Global Warming Potential –

100 year (GWP)

a

Atmospheric Lifetime in 

Years (ALT)

Propane 0

a 3.3 0.03b

HCFC-22 0.05b 1,810 12a

R-410Ac 0

a 2,088 NAd

NA = Not Available

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

b WMO 2010 Scientific Assessment Report (2011)

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

d 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]).

4. VOLATILE ORGANIC COMPOUND 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 lesson more than 0.15 ppb in Los Angeles, the city with the greatest ozone problem. This is 

 

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 4, 2014 -- Final

4

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

In the 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 window AC units are not anticipated to contribute significantly to 

ground-level ozone concentrations in the United States.

5. DISCUSSION OF END-USE SCENARIOS MODELED

Propane has been proposed for use in residential and light commercial room AC units. The remainder of 

this risk screen assesses the risk of window AC units. To represent a reasonable worst-case scenario, it 

was assumed that the full charge of the window AC unit is emitted over the course of one minute into a 

bedroom, where it is located. Because window AC units can be installed in a wide range of locations with 

varying room volumes, the analysis in this risk screen conservatively assumes that the window air 

conditioner is located in a bedroom with a volume of 41 m

3

(1,450 ft3). Under EPA’s proposed charge 

size limits which correspond to those found in UL 484, the maximum refrigerant charge allowed for 

propane window AC units installed in a room of 41m3is 180 grams. 6 However, the submission states that 

propane window AC units will have a typical charge size of 300 grams. Furthermore, UL Standard 484 

indicates that the maximum charge size of a window AC unit containing a flammable refrigerant is 1,000 

grams. Therefore, this risk screen evaluates the risks associated with all three charge sizes.

This risk screen evaluates a bedroom with air exchange rates of 0.11 ACH and 0.67 ACH. The EPA 

Exposure Factors Handbook (1997) states that the typical residential air exchange rate is 0.45 ACH, 

which factors in tests from homes that are greater than 45 years old as well as those that are less than 10 

years old. However, older homes (i.e., built before 1994) are more likely to use window AC units than 

newer homes. Based on data of AC use in U.S. homes by year of construction, 27 percent of homes using 

AC equipment use window AC units, while the remaining use central air conditioning equipment (EIA 

2013). On average, 38 percent of homes built before 1990 use window AC units in comparison to the 

average of 9 percent of homes built after 1990. Air exchange rates are expected to be greater in older 

homes that are typically built with loose construction practices (e.g., no or inadequate effort to seal 

structural panels, corners, cracks, joints, and penetrations; window and door assemblies are not rated). 

Additionally, if a home uses window AC units, EPA does not expect that there is any significant 

mechanical ventilation present in the home.

During the cooling season (May to September), air changes per hour in spaces with a floor area of 900 

square feet or less are reported to be between 0.11 ACH for tight construction and 0.67 ACH for loose 

construction (ACCA 2006). Therefore, this risk screen models both air exchange rates, 0.11 ACH and 

0.67 ACH, in order to account for installation of units in homes with different construction practices, for 

all three charge sizes (180 grams, 300 grams, and 1,000 grams).

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. UL 484 assumes that window AC units and their 

compressors are installed at a height 1 meter above the ground. Based on this location and because 

propane is denser than air (specific gravity of propane relative to air is 1.52 [air = 1]), this risk screen

assumes that a vertical concentration gradient of propane will occur. In order to simulate the vertical

concentration gradient, it is assumed that 95 percent of the leaked refrigerant mixes evenly into the lower 

 

6Under EPA’s proposed limits, for a conservative room of 41m3

, the appropriate cooling capacity would be approximately 6,500 

BTU/hr, corresponding to an associated charge size limit of 180 grams.
June 4, 2014 -- Final

5

1 meter of the room, and the rest of the refrigerant mixes evenly in the remaining volume (Kataoka 2000). 

Modeling of the lower 1 meter of the room is also consistent with the possibility that, in a bedroom 

scenario, individuals may be lying close to the floor. Table 3 details the end-use modeling assumptions 

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

Table 3. End-Use Scenario Model Assumptions

Parameter Assumptions

Room Type Bedroom

Size (m3) 41a(1,450 ft3)

Ventilation Rate (air changes per hour) 0.11b; 0.67c

Refrigeration Unit Window AC

Charge Size (g) 180d; 300e; 1,000f

Length of Release (minutes) 1

Vertical Concentration Gradient Yes

a Background Document (EPA 1994)

b Tight construction home (ACCA 2006)

c Loose construction home (ACCA 2006)

dMaximum charge size for a window AC under EPA’s proposed use conditions., based on a room size of 41 m3

.

e Typical charge size (CHEAA 2011).

fMaximum charge size for a window AC unit under UL 484.

6. POTENTIAL HEALTH EFFECTS

To assess potential health risks from exposure to the proposed substitute in window AC units, 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 the 

refrigeration unit, ASHRAE Standard 34 determined refrigerant concentration limits (RCLs) which are 

intended to reduce the risks of acute toxicity, asphyxiation, and flammability hazards in normally 

occupied, enclosed spaces during refrigerant use (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” to ensure that 

there is not a significant risk of toxicity, asphyxiation, and flammability (ASHRAE 2010a). As such, this 

risk screen references the RCL in addition to the lower flammability limit, hypoxia No Observed Adverse 

Effect Level (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 to 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 to 

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

acute exposure guidelines levels (AEGLs), or an emergency response planning guideline (ERPG), 

potential short-term, end-use exposures were compared to 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. 

 

7

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

ethane and propene by comparison to the excursion limit, which is typically used to evaluate short-term occupational exposure. 

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

Notably, the ACGIH methodology (i.e., a calculation of three times the TLV-TWA) has also been used by DOE (2008) to 

develop temporary emergency exposure limits (TEEL) for ethane (3,500 mg/m

3

or 2,900 ppm 15-min TWA) and propene (2,500 

mg/m3 or 1,500 ppm 15-min TWA), which apply to the general population. 
June 4, 2014 -- Final

6

Table 4. Exposure Limits of Propane and Potential Impurities

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) 5,300i

Potential Impurities

n-Butane 1,000b (ACGIH TLV) 6,900e (30 min AEGL-1) 4,000i

Isobutane 1,000b (ACGIH TLV) 6,900f 4,000i

Ethane 1,000b (ACGIH TLV) 3,000g

(30 min ACGIH Excursion Limit)

2,900h(15-min TEEL-1) 7,000i

Propene 500b(ACGIH TLV) 1,500g(30 min ACGIH Excursion Limit) 1,000i

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 AEGL-1 available at: http://www.epa.gov/oppt/aegl/pubs/rest102.htm

f 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.”

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

h DOE (2008)

i 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 
June 4, 2014 -- Final

7

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 lifethreatening health effects or death.

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 

escape-impairing 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)
June 4, 2014 -- Final

8

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).

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. Propane can cause 

symptoms of asphyxiation when present in concentrations high enough to significantly lower oxygen 

concentrations below 19.5 percent by volume, such as headaches, ringing in ears, dizziness, drowsiness, 

nausea, vomiting, depression of all senses, and also unconsciousness. Under some circumstances of overexposure (i.e., oxygen levels fall below 6 percent by volume), death may occur. 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 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 and 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 switch malfunction, 

or a lit cigarette), an explosion or a fire could occur if the concentration of propane exceeds the lower 

flammability limit (LFL) of 21,000 ppm. As such, propane may pose a significant safety concern for 

workers and consumers if it is not handled carefully. 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

Propane window AC units are currently manufactured by the submitter in China; the manufacturer 

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

propane systems occurs in the United States, the submitter indicates that release of or exposure to propane

is possible at the charge and sealing steps on the window AC unit production line at the manufacturing 

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

manufacture of window AC units, such as 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 
June 4, 2014 -- Final

9

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

chlorinated polyethylene, or neoprene), 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 2014) 

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 

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. 

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 window AC units are expected to 

take place 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 propane immediately following the release of refrigerant were compared to the LFL for 

propane. As demonstrated in Table 6, the maximum instantaneous concentration in the lower 1 meter of 

the room at a charge size of 180 grams would be approximately 5,400 ppm, approximately 8,980 ppm for 

a 300-gram charge size, and approximately 29,930 ppm for a 1,000-gram charge size. The 180-gram 

charge size proposed by EPA (Reasonable Worst-Case 1) and the 300-gram charge size indicated by the 

submitter (Reasonable Worst-Case 2) do not present a significant flammability concern. In contrast, the 

scenario using a 1,000-gram charge size (Reasonable Worst-Case 3) both exceed the proposed substitute’s 

LFL of 21,000 ppm. However, according to UL 484, a window unit with a charge size of 1,000 grams is 

not intended for installation in a room with a volume as small as that modeled in the worst-case scenario 

(41 m

3

). The maximum instantaneous concentration in the upper portion in the room for all modeled 

charge sizes is much lower, as only 5 percent of the leaked refrigerant is present in this area, and this area

has greater volume than the lower 1 meter of the room. EPA is also proposing to limit charge sizes that an 

equipment manufacturer may use for a given cooling capacity. The appropriate cooling capacity for a 

room of 41 m3 would be approximately 6,500 BTU/hr, with an associated charge limit of 180 grams

under EPA’s proposed use conditions. The results of the flammability assessment are presented in Table 

6.

Table 6. Flammability Assessmenta

Scenario Charge Size (g) Effective Room Size 

(m3)

Maximum 

Instantaneous 

Concentration

(ppm) b,c

Reasonable Worst-Case 1 180 41 (1,450 ft3

) 5,400

Reasonable Worst-Case 2 300 41 (1,450 ft3

) 8,980

Reasonable Worst-Case 3 1,000 41 (1,450 ft3

) 29,930

Threshold Analysis 1: Charge Size 700 41 (1,450 ft3

)

21,000

Threshold Analysis 2a: Room Size 180 11 (345 ft3

)

Threshold Analysis 2b: Room Size 300 18 (575 ft3

)

Threshold Analysis 2c: Room Size 1,000 58 (1,920 ft3

)

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 equal to 21,000 ppm.
June 4, 2014 -- Final

10

c Values provided in this column refers to the concentration in the lower 1 meter 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 analyses shown in Table 6, the conditions at which a flammability concern 

would exist (i.e., when the maximum instantaneous concentration in the lower stratum of the bedroom 

equals the LFL for propane) were determined. Within the reasonable worst-case room size of 41 m

3

(1,450 ft3), as shown under Threshold Analysis 1, the charge size of the propane window AC unit would 

have to be at least 700 grams for a flammability concern to exist, which is greater than EPA’s 

recommended charge size (i.e., 180 grams) and the largest charge size intended by the submitter (i.e., 300 

grams). For window AC units with a charge size of 180 grams (see Threshold Analysis 2a in Table 6) the 

volume of the bedroom would have to be 11 m

3

(345 ft3) or smaller for a flammability risk to occur.

Using a 300-gram window AC unit, as shown under Threshold Analysis 2b, the volume of the room 

would have to be 18 m

3

(575 ft3) or smaller for a flammability risk to occur. Using a 1,000-gram propane

window AC unit, as shown under Threshold Analysis 2c, the volume of the bedroom would have to be 58

m

3

(1,920 ft3) or less for a flammability risk to occur.

According to the results of this flammability analysis, the risk of fire is minimal if a window AC unit is 

installed in a room with volumes in accordance with standards and regulations. As bedrooms can be of 

smaller sizes than those modeled in this assessment8and because persons or furniture in the room may 

reduce the effective volume of the space, window AC units containing propane should not be installed in 

enclosed areas with effective volumes less than indicated by UL 484 or the Room Air-Conditioners with 

Flammable Refrigerants Installation and Service Manual provided by the submitter, unless additional 

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

484,

9 window AC units with charge sizes of 300 grams and 1,000 grams should not be installed in a room 

less than 120 m

3

(4,300 ft3) and 1,360 m

3

(48,100 ft3), respectively. According to ASHRAE Standard 34, 

the RCL for propane (9.5 g/m3of propane or 5,300 ppm by volume) should not be exceeded in any room 

that contains a propane window AC unit. Although the RCL for propane is less conservative than the

anticipated release amount of propane under the modeled worst-case scenarios (i.e., 180 grams in a 41m3

space, or 4.4 g/m3and 300 grams in a 41 m3space, or 7.3 g/m3), the RCL is calculated assuming that 

refrigerant is evenly mixed in the space, whereas this analysis assumes a vertical concentration gradient

due to the higher density of propane to air (propane = 1.52, air = 1). End-users, therefore, should ensure 

that propane window AC units are installed with an appropriate cooling capacity for the intended cooled 

space (i.e., avoid installing large window 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 additionally indicates 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 which provide safety guidelines for handling propane. Therefore, these guidelines should be 

acknowledged and followed to mitigate flammability risk. The installation of leak prevention devices 

would further protect against the very limited risk of explosion.

In the U.S., window AC units are typically replaced rather than serviced. However, should servicing of 

window AC units with propane occur, EPA recommends that the ventilation requirements outlined in the 

MSDS for propane be followed through the use of fans (or other mechanical ventilation devices) and 

portable refrigerant detectors be 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

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

9 The room sizes provided by UL 484 are based on a mounted window AC unit height of 1.0 m from the floor.
June 4, 2014 -- Final

11

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 and 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 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 Lower 1 

Meterb

Reasonable Worst-Case 1 180 41 (1,450 ft3

) 21

Reasonable Worst-Case 2 300 41 (1,450 ft3

) 21

Reasonable Worst-Case 3 1,000 41 (1,450 ft3

) 21

Threshold Analysis 1: Charge Size 18,520 41 (1,450 ft3

) 12

Threshold Analysis 2a: Room Size 180 0.40 (14.1 ft3

) 12

Threshold Analysis 2b: Room Size 300 0.66 (23.5 ft3

) 12

Threshold Analysis 2c: Room Size 1,000 2.21 (78.2 ft3

) 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.10 Based on the worst-case scenario modeling assumptions, propane in window 

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

lower 1 meter of the room following the release of the maximum charge size of 1,000 grams does not 

exceed 2.3 percent, which has an insignificant impact on the normal concentration of oxygen in air. 

Because 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, the actual asphyxiation risk to personnel 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 41m3(1,450ft3), as 

shown under Threshold Analysis 1, the charge size of the propane window AC unit would have to be at 

least 18,520 grams for asphyxiation to be a concern, which is more than 18 times the largest charge size

allowed by UL 484 (i.e., 1,000 grams). Using a 180-gram window AC unit, as shown under Threshold 

Analysis 2a, the volume of the room would have to be 0.40 m

3 (14.1 ft3

) or smaller for asphyxiation to be 

of concern. Using a 300-gram window AC unit, as shown under Threshold Analysis 2b, the volume of the 

room would have to be 0.66 m

3 (23.5 ft3

) or smaller for asphyxiation to be of concern. Using a 1,000-

gram window AC unit, as shown under Threshold Analysis 2c, the volume of the room would have to be 

2.21 m

3 (78.2 ft3

) or smaller for asphyxiation to be of concern. All of the room sizes modeled in the latter 

 

10 Twelve percent oxygen in air is the NOAEL for hypoxia (ICF 1997). 
June 4, 2014 -- Final

12

three scenarios are significantly smaller than the reasonable worst-case bedroom size (41 m

3

[1,450 ft3])

and the minimum bedroom volume typically found in the U.S.11

To further protect against an asphyxiation risk, end-users should ensure window AC units are installed 

with an appropriate cooling capacity for the intended cooled space to be consistent with manufacturer 

recommendations and the guidelines of relevant safety standards (e.g., ASHRAE 15 and 34 and UL 484). 

Additionally, adherence to ASHRAE 34, which provides more conservative concentration limits, will 

ensure that asphyxiation is not a significant risk. Minimum room sizes according to the RCL stated in 

ASHRAE 34 and UL 484 can be found in Section 7. Leak prevention, detection, 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 consumer exposures to propane and each of its impurities in 

window AC units. An exposure analysis was performed to examine potential catastrophic release of the 

proposed substitute in a bedroom under the reasonable worst-case scenarios outlined in Section 5 with 

charge sizes of 180 grams, 300 grams and 1,000 grams.

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

each of its impurity constituents 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 limits presented in Table 4 to assess the risk to end-users. 

The results of the assessment provide both fairly conservative and more realistic TWA values, as the 

analyses using both a 0.11 ACH and a 0.67 ACH ventilation rate do 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 all of its impurity 

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

98.9 percent pure, it presents the greatest risk of exceeding the STEL and thus the most conservative 

assessment. 

 

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

(490 ft3) (ICC IRC 2012). 
June 4, 2014 -- Final

13

Table 8. End-Use Exposure Assessmenta

Scenario Charge Size 

(g)

Effective Room 

Size (m3)

Air Exchange Rate 

(ACH)

30-minute TWA 

End-Use Exposure 

(ppm)b,c

Reasonable Worst-Case 1a 180

41 (1,450 ft3)

0.11 5,247

Reasonable Worst-Case 1b 0.67 4,602

Reasonable Worst-Case 2a 300 0.11 8,745

Reasonable Worst-Case 2b 0.67 7,670

Reasonable Worst-Case 3a 1,000 0.11 29,151

Reasonable Worst-Case 3b 0.67 25,566

Threshold Analysis 1a: Charge Size 237 41 (1,450 ft3

)

0.11

6,900

Threshold Analysis 1b: Charge Size 270 0.67

Threshold Analysis 2a: Room Size 180 31 (1,020 ft3) 0.11

Threshold Analysis 2b: Room Size 27 (890 ft3) 0.67

Threshold Analysis 3a: Room Size 300 52 (1,710 ft3) 0.11

Threshold Analysis 3b: Room Size 46 (1,510 ft3) 0.67

Threshold Analysis 4a: Room Size 1,000 173 (5,680 ft3) 0.11

Threshold Analysis 4b: Room Size 152 (5,000 ft3) 0.67

Threshold Analysis 5a: Air Exchange Rate 180

41 (1,450 ft3)

0

Threshold Analysis 5b: Air Exchange Rate 300 1.1

Threshold Analysis 5c: Air Exchange Rate 1,000 8.6

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 1 meter 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, catastrophic releases of window AC units with charge sizes of 180 

grams, 300 grams, and 1,000 grams were modeled with two different air exchange rates, 0.11 ACH and 

0.67 ACH. In Reasonable Worst-Case Scenarios 2a, 2b, 3a, and 3b, the 30-minute AEGL-1 for propane of 

6,900 ppm is likely to be exceeded (see Table 8). The 30-min TWA exposures in Reasonable Worst-Case 

Scenarios 3a and 3b, which model a 1,000-gram charge size and ventilation rates of 0.11 ACH and 0.67 

ACH respectively, exceed the AEGL-2 (17,000 ppm), but not the AEGL-3 (33,000 ppm) for propane. 

A threshold analysis was performed to determine the charge size, room volume, and ventilation rates 

where window AC units containing propane could be installed to avoid the short-term exposure limit for 

propane. Based on this end-use exposure threshold analysis, shown in Table 8, the maximum charge size 

that should be installed in a room of 41 m

3

(1,450 ft3) volume with 0.11 ACH is 237 grams and 270 grams 

with 0.67 ACH. Additionally, the threshold analysis indicates that window AC units with charge sizes of

180 grams, 300 grams and 1,000 grams should not be installed in rooms smaller than 31 m

3

(1,020 ft3), 52

m

3

(1,710 ft3), and 173 m

3

(5,680 ft3), respectively, assuming an air ventilation rate of 0.11 ACH. As 

shown in Table 8, these recommended minimum room sizes are smaller if the air ventilation rate is 

increased to 0.67 ACH. 

Because window AC units with charge sizes of 300 grams and 1,000 grams were modeled in a room size 

that is much smaller than the size recommended by UL 484 in the reasonable worst-case scenarios, it is 

not unexpected that the calculated 30-minute TWA exposures for these scenarios exceed the AEGL-1 for

propane. These potential exceedances emphasize the importance associated with proper equipment 

installation (i.e., matching charge size with room dimensions). To prevent exposure and potential serious 

side effects during larger releases, EPA recommends that the charge size for a propane window AC unit

does not exceed the RCL (9.5 g/m3) and proposes to require compliance with UL 484 in any space 

containing a window AC unit, unless proper leak protection devises are in place in order to prevent 
June 4, 2014 -- Final

14

exposures of propane beyond the recommended limits. Smaller accidental releases of the proposed 

substitute, however, do not pose a significant risk to end-users.

Thus, risk of excessive exposure is minimal if a window AC unit is installed in a room with volumes in 

accordance with standards and regulations and/or in enclosed areas with volumes larger than those 

determined in the threshold analyses. Furthermore, proper ventilation should be used in accordance with 

the MSDS for propane. When these conditions and the proposed use conditions of the rule are met, 

accidental catastrophic releases of the proposed substitute would not pose a significant risk to end-users.

10. OCCUPATIONAL EXPOSURE ASSESSMENT

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

disposal of propane in window AC units. To ensure that use of the proposed substitute in window AC 

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 in 

2010 were obtained from the Vintaging Model.12 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 window AC unit 

end-use, 0.4 percent of the equipment charge was conservatively assumed to be released during 

manufacture and servicing and 50 percent of the equipment charge was conservatively assumed to be 

released during disposal.

13 Additionally, EPA is proposing to allow intentional venting or release of 

propane as a refrigerant during installation, servicing, maintenance and disposal from window AC units. 

If venting does occur, it should be done in a well-ventilated area (e.g., outdoors). Therefore, scenarios in 

which 100 percent of the equipment charge was 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 window AC 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. 

10.1 Occupational Exposure during Manufacture

Propane window AC units are currently manufactured by the submitter in China, and the manufacturer 

currently has no plans to manufacture these systems in the United States. As indicated by the submitter, 

release of or exposure to propane is possible at the charge and sealing steps on the window AC unit 

production line. If the manufacture of these propane systems occurs in the United States, the proposed 

substitute’s MSDS should be referenced and proper engineering controls and PPE should be used. 

Propane is not expected to pose a risk to workers during manufacture when the engineering controls and 

PPE recommendations and referenced in the MSDS for propane 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 limit emissions. The manufacturing

 

12 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 ODS 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 window AC end-use in Vintaging Model version VM IO file_v4.4_11.6.12. 

13 During disposal it is assumed that 100 percent of the refrigerant charge remains in the unit. 
June 4, 2014 -- Final

15

equipment is designed to minimize potential emissions while engineering controls at the manufacturing 

facility include warning alarms for propane leakage and ventilation systems. Maintenance manuals 

describe procedures to reduce leakage and prior safety training is required for all personnel who work on 

the production line. In general, use of appropriate 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), and protective clothing.

Because of established equipment design and manufacture practices, exposures to propane will be 

unlikely. Thus, EPA does not believe that manufacturing of AC units with propane under these workplace 

conditions presents a concern to workers.

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 propane, 

there is no significant risk to workers during the manufacture of propane window AC units.

10.2 Occupational Exposure at Installation and Servicing 

Window AC units are expected to be serviced rarely, since this type of equipment is hermetically sealed 

and in the U.S. is often replaced rather than serviced if the charge leaks. Nevertheless, the potential 

occupational exposure for those situations where servicing takes place were analyzed. The possibility of a 

release during installation was also considered. The maximum 30-minute time-weighted average (TWA) 

exposure for propane and its potential impurities were estimated for servicing window AC units charged 

with 180 grams, 300 grams and 1,000 grams of refrigerant. As summarized in Table 9, occupational 

exposure to propane is anticipated to be significantly below the short-term exposure limits (STEL) with a 

180-gram, 300-gram or 1,000-gram charge size for both 0.4 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 established during any use, handling, or storage of propane. 

Systems should be installed 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 6, worker exposure to propane during installation and maintenance is unlikely.

Table 9. Occupational Risk Assessment at Servicinga

Component

30-minute TWA 

Occupational 

Exposure (ppm)

Charge size: 180 

grams

30-minute TWA 

Occupational 

Exposure (ppm)

Charge size: 300 

grams

30-minute TWA 

Occupational Exposure 

(ppm)

Charge size: 1,000 

grams

30-min Short Term 

Exposure Limits 

(ppm)

0.4% 

Release

100% 

Release

0.4% 

Release

100% 

Release

0.4% 

Release

100% 

Release

Propane 1.42 356 2.37 593 7.90 1,980 6,900b

Potential Impurities

Isobutane 0.004 1.1 0.007 1.8 0.024 6.1 6,900b

n-Butane 0.004 1.1 0.007 1.8 0.024 6.1 6,900b

Ethane 0.004 1.1 0.007 1.8 0.023 5.9 3,000c

Propene 0.002 0.4 0.003 0.6 0.008 2.1 1,500c

 a

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

b AEGL-1; See Table 4 for more information

c ACGIH (2004)
June 4, 2014 -- Final

16

10.3 Occupational Exposure at Disposal

Disposal of propane window AC 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).

Table 10 displays the maximum estimated 8-hour TWA occupational exposure levels of propane and its 

impurities during disposal. 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 

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

components during disposal of propane for window AC units with a charge size of 180 grams or 300

grams. Under the 100 percent disposal release scenario for the 300-gram unit and the 50 percent and 100

percent release scenarios for the 1,000-gram unit, the modeling indicates that occupational exposure could 

exceed the 8-hour long term exposure limits for propane. However, the occupational exposure to the 

proposed substitute during disposal does not represent a true occupational health hazard because the 

estimated exposure concentrations for all scenarios do not exceed the 8-hr AEGL-1 for propane, which is 

5,500 ppm. Furthermore, these exposures were derived using conservative assumptions (e.g., no 

ventilation or use of PPE assumed), and represent a reasonable 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: 180 grams

8-Hour TWA Occupational 

Exposure (ppm)

Charge size: 300 grams

8-Hour TWA Occupational 

Exposure (ppm)

Charge size: 1,000 grams

8-Hour Long 

Term Exposure 

Limits (ppm) 50% 

Release

100%

Release

50% 

Release

100% 

Release

50% 

Release

100% 

Release

Propane 315 629 524 1,050 1,748 3,500 1,000b

Potential Impurities

Isobutane 0.97 1.93 1.61 3.22 5.36 10.7 1,000c

n-Butane 0.97 1.93 1.61 3.22 5.36 10.7 1,000c

Ethane 0.93 1.87 1.56 3.11 5.19 10.3 1,000c

Propene 0.33 0.67 0.56 1.11 1.85 3.7 500c

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

b OSHA PEL 

 c ACGIH TLV

Because anticipated occupational exposures are above the exposure limits for propane for the 100 percent

disposal release scenario for 300g and 1000 g charge sizes, 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, storage, or disposal of propane. Engineering controls should include 

vapor-in air detection systems and local exhaust ventilation during use and disposal of propane to prevent 

dispersion throughout the work place. 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-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 propane, there is no 
June 4, 2014 -- Final

17

significant risk to workers during the manufacturing, installation, servicing, and disposal of propane in 

window AC units.

11. GENERAL POPULATION EXPOSURE ASSESSMENT

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

manufactured for use and used as a refrigerant in window AC 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 (i.e., 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 window AC 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 4, 2014 -- Final

18

12. REFERENCES

Air Conditioning Contractors of America (ACCA). 2006. Manual J Residential Load Calculation Eighth 

Edition.

ACGIH. 2004. The Documentation of the Threshold Limit Values and Biological Exposure Indices. 

American Conference of Governmental Industrial Hygienists. Available online at: www.acgih.org. 

ACGIH. 2012. Guide to Occupational Exposure Values. American Conference of Governmental 

Industrial Hygienists.

ANSI/ASHRAE. 2010a. Standard 15: Safety Standard for Refrigeration Systems. American Society of 

Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ANSI/ASHRAE. 2010b. Standard 34: Designation and Safety Classification of Refrigerants. American 

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

ANSI/ASHRAE. 2013a. Standard 62: Ventilation for Acceptable Indoor Air Quality. American Society 

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

ANSI/ASHRAE. 2013b. Standard 147: Reducing the Release of Halogenated Refrigerants from 

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

and Air-Conditioning Engineers, Inc.

Braker W, Mossman AL. 1980. Matheson gas data book. 6th ed. Secaucus, NJ: Matheson Gas Products, 

pp. 615623.

Centers for Disease Control and Prevention (CDC). 2010. NIOSH Pocket Guide to Chemical Hazards. 

Available online at: http://www.cdc.gov/niosh/npg/default.html

China Household Electrical Appliance Association (CHEAA). 2011. Propane for Use in Residential and 

Light Commercial Air Conditioning and Heat Pumps. Significant New Alternatives Policy Program 

Submission to the U.S. Environmental Protection Agency. September 2011. 

China Household Electrical Appliance Association (CHEAA). 2013. Incompleteness Letter for Propane

in Residential and Light Commercial Air Conditioning and Heat Pumps SNAP Submission. October 

2013.

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 IRC. 2012. International Residential Code. International Code Consortium. 

ICF International. 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.
June 4, 2014 -- Final

19

IPCC/TEAP. 2005. Bert Metz, Lambert Kuijpers, Susan Solomon, Stephen O. Andersen, Ogunlade 

Davidson, José Pons, David de Jager, Tahl Kestin, Martin Manning, and Leo Meyer (Eds). Safeguarding 

the Ozone Layer and the Global Climate System. Intergovernmental Panel on climate Change 

Technology and Economic Assessment Panel. Cambridge University Press, UK. pp 478.

Kataoka, O., M. Yoshizawa, & T. Hirakawa 2000. “Allowable Charge Limit of Flammable Refrigerants 

and Ventilation Requirements.” Daikin Industries. International Refrigeration and Air Conditioning 

Conference. Paper 506. Available online at: http://docs.lib.purdue.edu/iracc/506.

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

NFPA. 2014. NFPA Liquified Petroleum Gas Code. 2014 Edition.

OSHA. 2004. “Safety and Health Topics: Isobutane.” February 2004. Available online at: 

<http://www.osha.gov/dts/chemicalsampling/data/CH_247840.html>.

UL. 2007. UL 484: Standard for Room Air Conditioners. Underwriters Laboratory.

U.S. Department of Energy (DOE). 2008. DOE Handbook – Temporary Emergency Exposure Limits For 

Chemicals: Methods And Practice. Available online at: http://orise.orau.gov/emi/scapa/files/doe-hdbk1046-2008_ac.pdf.

U.S. Energy Information Administration (EIA). 2013. 2009 Residential Energy Consumption Survey. 

Table HC7.3 Air Conditioning in U.S. Homes, by Year of Construction, 2009. Available online at: 

http://www.eia.gov/consumption/residential/data/2009/#undefined.

U.S. EPA. 1994. Significant New Alternatives Policy 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. 1997. Exposure Factors Handbook. National Center for Environmental Assessment, Office of 

Research and Development. Available online at: http://www.epa.gov/ncea/pdfs/efh/front.pdf.

U.S. EPA. 2012. Acute Exposure Guidelines (AEGLs) Definitions. Available online at: 

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

U.S. EPA. 2014. Draft Assessment of the Potential Impact of Hydrocarbon Refrigerants on Ground Level 

Ozone Concentrations. Prepared for the U.S. EPA Stratospheric Protection Division by ICF International. 

February 24, 2014.

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

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