November 17, 2011

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Significant New Alternatives Policy Program

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for CFC-12, HCFC-22, and R-502 in Retail Food 

Refrigeration

Substitute: Propane

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, runs 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 largely 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 ODS-using 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) by adding to the 

list of potential substitutes for specific end-uses of CFC-12, HCFC-22 and R-502 in this sector. The 

proposed end-use application considered in this analysis is retail food refrigeration, specifically ice cream 

cabinets. The specific proposed CFC-12, HCFC-22 and R-502 substitute examined in this report is 

propane (R-290). The substitute would only be used in new equipment, not in retrofitted equipment. 

The Background Document examines the potential risks associated with use of substitutes in retail food 

refrigeration, and includes a detailed discussion of the methodologies used to conduct this risk screen. 

Occupational exposure modeling was performed to ensure that use of the proposed substitute in the 

application listed above did not pose unacceptable risk to workers during equipment manufacture. 

Modeling was performed at the end-use to ensure that potential catastrophic releases of the substitute did 

not pose unacceptable risk to store employees and customers in locations where the ice cream cabinets are 

in use. Lastly, general population exposure modeling was performed to ensure that the proposed 

substitute would not pose an unacceptable risk to the population at large. 

The proposed substitute, propane, may contain minute quantities of impurities. Table 1 details the 

composition of the proposed substitute, including the maximum estimated concentration of impurities that

may be present.
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Table 1. Composition of the Proposed Substitute

Component Concentration 

Substitute Percent by Weight

Propane 99.5%

Potential Impurities Maximum Concentration (ppm v/v)

Ethane 1700

Propylene 300

n-Butane 1000

Sulfur 1

Water 12

Section 2 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: Discussion of End-Use Scenarios Modeled

 Section 5: Flammability Assessment

 Section 6: Asphyxiation Assessment

 Section 7: Toxicity Assessment

 Section 8: Volatile Organic Compound Assessment 

 Section 9: References

2. SUMMARY OF RESULTS

Propane is recommended for SNAP approval for retail ice cream cabinets. 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. No significant toxicity risks to workers, consumers, or the general 

population are expected according to occupational and end-use exposure modeling. 

Flammability models indicate that risks of explosions are not a concern for store employees or customers. 

To further protect against the limited risk of explosion, it is recommended that the cabinets not be used in 

small, poorly ventilated spaces (see Section 4). Caution must be used in manufacturing facilities and by 

refrigeration technicians to minimize explosion risk while in the presence of large quantities of the 

substitute. This includes installation of proper safety equipment during manufacturing, transportation, 

and storage and providing proper training and certification to technicians. EPA recommends that 

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standards 151, 

342and 623be followed.

 

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.
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3. ATMOSPHERIC ASSESSMENT

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

propane in the retail food refrigeration sector. The ozone depletion potential (ODP), global warming 

potential (GWP), and atmospheric lifetime (ALT) of the proposed substitute are presented in Table 2.

The environmental impacts resulting from use of propane are generally in the range of those predicted for 

other substitutes examined in the Background Document. The substitute is substantially less harmful to 

the ozone layer, has less climate impact, and a shorter atmospheric lifetime when compared to CFC-12, 

HCFC-22 and R-502.

Table 2. Atmospheric Impacts of Propane Compared to CFC-12, HCFC-22 and R-502

Refrigerant ODP GWP ALT

Propane 0

a 3.3a 0.041b

CFC-12 1

c 10,900a 100a

HCFC-22 0.055c 1,810a 12a

R-502 d 0.33c 4650 NA

NA = Not Available

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

b IPCC/TEAP (2005). Atmospheric lifetime not provided in SNAP submission.

cMontreal Protocol and available at: http://www.epa.gov/ozone/ods.html.

d R-502 is a blend consisting of CFC-115 (51%) and HCFC-22 (49%). The ODP and GWP presented for this blend were calculated using 

values from http://www.epa.gov/ozone/ods.html (Montreal Protocol) and IPCC 4th Assessment Report (Forster et al. 2007), respectively. 

Alternatively, WMO (2006) has estimated the ODP for CFC-115 to be 0.44 based on recent atmospheric modeling (rather than 0.6, as 

previously agreed by the Parties to the Montreal Protocol). Using the more current estimate of ODP would bring the overall ODP for R-502 to 

0.24.

4. DISCUSSION OF END-USE SCENARIOS MODELED

The proposed use of this substitute is in ice cream cabinets which could reasonably be expected to be 

located either in the main area of a store, or in a storage room. Because a storage room could be much 

smaller than the main area of a store, a reasonable worst-case scenario analysis was performed to model 

catastrophic release of the refrigerant in a storage room. 

For the analysis, a storage room with a floor area of 14 m2and a height of 3 meters was assumed.4 This is 

equivalent to a room volume of 42 m3. In the analysis, the full charge5of the unit is assumed to be 

emitted over the course of one minute and the model conservatively assumes 2.5 air exchanges occur per 

hour. Horizontal stratification is also assumed since propane is denser than air and will settle in higher 

concentrations closer to the ground. In order to simulate the horizontal concentration gradient that will 

occur because of the weight differential between the refrigerant and air, it is assumed that 95 percent of 

the leaked refrigerant mixes evenly into the bottom 0.4 meter of the room, and the rest of the refrigerant 

mixes evenly in the remaining volume (Kataoka 1999). Table 3 details the assumptions used in the 

models.

 

4

This room was considered a ‘high risk room’ due to its small size and poor ventilation. (Ben and Jerry’s/Unilever 

2008)

5 All models in this risk screen conservatively assume that all retail ice cream cabinets are charged with 150g of 

propane. The submitter notes that the cabinets will have a charge size of about 90g, but that the maximum charge 

size will be 150g (Ben and Jerry’s/Unilever 2008). To ensure all models address a reasonable “worst-case” 

scenario, the maximum charge size was chosen for use in the models.
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Table 3. Worst-Case Scenario Model Assumptions

Parameter Scenario 1

Refrigeration Unit Ice Cream Cabinet

Room Storage Room

Charge size (g) 150

% of charge emitted 100

Length of release (minutes) 1

Room size (volume - m3) 42

Room ventilation (air 

exchanges per hour) 2.5

Horizontal stratification Yes

5. FLAMMABILITY ASSESSMENT

Propane is flammable when its concentration in air is in the range of 2.1%-9.5% by volume (this is equal 

to 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 when the concentration of 

propane is within these flammability limits. The remainder of this section addresses the potential for 

flammability risks at the end-use, and during manufacture and servicing and provides a discussion of 

measures to be taken to ensure safe use.

Under the assumptions outlined under the catastrophic release scenario (see Section 4)6, the maximum 

instantaneous concentration of propane in the lower stratum of the room would be approximately 66

percent of its lower flammability limit (LFL), as shown in Table 4. The maximum instantaneous 

concentration is even lower in the upper stratum of the room, as only five percent of the leaked refrigerant 

is present in this stratum, and this stratum has a greater volume than the lower stratum. 

Table 4. Flammability Assessment

Room Type/

Appliance Type

Reasonable Worst-Case Scenario Flammability Threshold Scenario

Room Size (m3)

Maximum 

Instantaneous 

Concentration

(ppm) a,b

Room Size Causing 

Flammability Risk

(m3)

Maximum 

Instantaneous 

Concentration

(ppm) a,b

Storage Room/

Ice Cream Cabinet 42 (1,483 ft3

) 13,780 28.5 (1,006.5 ft3) 20,308

a Lower Flammability Limit of propane is equal to 21,000 ppm

b Values provided in these columns refer to the concentration in the lower stratum of the room. 

For flammability to be of concern under the conservative (protective) assumptions described above, the 

volume of the storage room would have to be 28.5 m3 (1,006.5 ft3) (See Table 4); assuming a square 

room with a ceiling height of 3 m (9.8 ft), the storage room floor area would be less than 3.1 x 3.1 m 

(10.1 x 10.1 ft) . Although these dimensions equate to a very small space, since storage rooms can be of

varying size and because boxes and other equipment in the room may reduce the effective volume of the 

room, it is recommended that propane cabinets not be installed in small, poorly ventilated spaces, to avoid 

the risk of fire and explosion. However, for average-sized rooms the risk of explosion is minimal. 

Creating a hole in the bottom of storage room doors (to act as a vent and increase air circulation) and 

installing leak prevention devices will further protect against the limited risk of explosion. For example, 

in commercial refrigeration end-uses, refrigerant leak prevention systems can be used to capture leaked 

 

6 The submitter notes that “catastrophic leaks during operation have not been recorded.” (Ben and Jerry’s/Unilever 

2008)
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refrigerant in a receiving tank during over pressure events, rather than venting the refrigerant to the 

atmosphere (McKeown 1993). 

Catastrophic releases of large quantities of refrigerant during servicing and manufacturing, especially in 

areas where large amounts of refrigerant are stored, could cause an explosion. For this reason, it is 

important that only properly trained and certified refrigerant technicians handle propane. The submitter 

has provided information regarding their training program for service technicians. The program includes 

detailed information covering important topics such as potential ignition sources, proper tools to use with 

flammable refrigerants, safe workplace behavior and service procedures. At the end of the training, 

technicians must pass a multiple choice assessment (Ben and Jerry’s/Unilever 2008). All technicians who 

will be servicing cabinets using propane should receive this training and be required to pass the 

assessment. As a further precaution, 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 2008) requires the use of overfill protection devices (OPD) on cylinders to 

minimize the likelihood of leaks. The NPFA 58 Code also contains storage and transportation 

requirements/guidelines. Similar equipment safety and procedural requirements should be implemented

for this substitute. 

It is important that the strictest standards be followed during the manufacture of these ice cream cabinets. 

It is recommended 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. Proper ventilation should be maintained at all times during the manufacture of 

equipment containing propane through adherence to good manufacturing practices. If refrigerant levels in 

the air surrounding the equipment rise above one-fourth of the lower flammability limit7, the space should 

be evacuated and re-entry should only occur after the space has been properly ventilated. Ventilation is 

also of the utmost importance to mitigate the risk of fire or explosion when servicing equipment using 

propane. During servicing operations, technicians should ensure that proper ventilation is in place 

through the use of fans (or other mechanical ventilation devices) and portable refrigerant detectors should 

be used to alert technicians to the presence of flammable gases in the area. 

6. ASPHYXIATION ASSESSMENT

The risk of asphyxiation for a reasonable “worst-case” scenario was investigated for propane. This 

analysis considers the modeling assumptions outlined in Section 4. This analysis does not consider 

additional ventilation conditions (such as open doors or windows, fans operating, conditioned airflow, or 

seepage between the door and door frame) that are likely to occur and would further reduce the exposure 

concentration of propane. 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 5 below. The maximum charge of 

propane necessary to reduce the oxygen levels to 12 percent in air8in a storage room of volume 42 m3

(1,483 ft3) was calculated, assuming horizontal stratification of the refrigerant and the air. Horizontal 

stratification is assumed since propane is denser than air and will settle in higher concentrations closer to 

the ground. Assuming that nitrogen and oxygen retain the same relative volumes in the rooms with the 

balance composed entirely of propane, and that the pressure of the room does not increase significantly 

 

7 OSHA regulation 29 CFR 1910.110 considers ventilation adequate “when the concentration of the gas in a gas-air 

mixture does not exceed 25 percent of the lower flammable limit.”

8 Twelve percent oxygen in air is the NOAEL for hypoxia (ICF 1997). 
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with the addition of the refrigerant, a charge of approximately 904 g would be necessary to reach 12

percent oxygen in the lower stratum. This amount represents more than six times the maximum intended 

charge size, 150 g, of a single propane ice cream cabinet. Charge requirements to reach the same effect in 

the upper stratum would be even higher because of the stratum’s larger volume. 

Table 5. Asphyxiation Assessment

Room Type/

Appliance Type

Reasonable Worst-Case Scenario Asphyxiation Threshold Scenario

Room Size (m3)

Charge Causing 

Impairment (g)a

Room Size Causing 

Impairment(m3)

Assumed Leak Size (g)a

Storage Room/ 

Ice Cream Cabinet 42 (1,483 ft3

) 904 6.96 (245.8 ft3) 150

a Values provided in these columns refer to the charge required to cause impairment in the lower stratum of the room. In this scenario, 100% 

of the charge leaks. Charge requirements to reach the same effect in the upper strata would be even higher because of the stratum’s larger 

volume. 

For asphyxiation to be of concern with the proposed charge size under the conservative (protective) 

assumptions described above, the volume of the storage room would have to be approximately 6.96 m

3

(245.8 ft3), which is significantly smaller than the 42 m3sized room assumed in the worst case scenario 

(see Section 4). Further, as the “threshold” room sizes for asphyxiation risks are smaller than those for 

flammability risks, flammability risks would be realized before asphyxiation risks. Therefore, EPA does 

not believe that the use of propane in this end-use poses a significant risk of asphyxiation or impaired 

coordination to room occupants under the proposed end-use.

Based on the results discussed above, EPA does not believe that the use of propane in this end-use poses a 

significant risk of asphyxiation or impaired coordination to store employees or customers. 

7. TOXICITY ASSESSMENT

Section 7 summarizes the results of the toxicity assessment for propane in the retail refrigeration sector. 

This section is organized as follows: 

 Section 7.1: Toxicity Reference Values

 Section 7.2: Occupational Exposure

 Section 7.3: End-Use Exposure

 Section 7.4: General Population Exposure

7.1 TOXICITY REFERENCE VALUES

To assess potential health risks from exposure to this substitute in the retail food refrigeration sector, EPA 

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

different scenarios. For the occupational exposure analysis, potential risks from chronic and acute worker 

exposure were evaluated by comparing exposure concentrations to available occupational exposure limits. 

Occupational exposure limits are typically established for either an eight-hour or ten-hour time period for 

long-term exposure, such as the Workplace Guidance Levels (WGLs), or for a 10 to 30-minute period for 

short-term exposure, such as the Emergency Guidance Levels (EGLs), as shown in Table 6. Because they 

are designed to assess risks from acute exposure, emergency guidance levels are used to assess risks from 

short-term consumer exposures. Reference concentrations (RfCs) are used to assess risks to the general 

population from exposure to ambient air releases and to assess potential risks associated with chronic 

consumer exposures. Table 6 lists the relevant toxicity limits. Table 7 provides definitions for acronyms 

used in Table 6. EPA’s approach for identifying or developing these values is discussed in Chapter 3 of 

the Background Document. 
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Table 6. Toxicity Levels of Propane and Potential Impurities

Long-term Exposure

ppm

Short-term Exposure

ppm

Reference Concentration 

(RfC) mg/m3

Substitute

Propane 1000a(OSHA PEL/NIOSH REL) 10,000b,c

(10 minute AEGL-1) 0.9d

6,900 b (30 minute AEGL-1)

Potential Impurities

Ethane NAe NAe NA

Propylene NAf NAf NA

n-Butane 800g(NIOSH REL) NA 0.95d

Sulfur NA NA NA

NA = Not Available

a http://www.cdc.gov/Niosh/npg/npgd0524.html

b http://www.epa.gov/oppt/aegl/pubs/results96.htm

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.

dSNAP Refrigerant Background Document (EPA 1994).

e Ethane is a "simple asphyxiant." http://www.osha.gov/dts/chemicalsampling/data/CH_238900.html

f Propylene is a "simple asphyxiant." http://www.osha.gov/dts/chemicalsampling/data/CH_264442.html

g http://www.cdc.gov/niosh/npg/npgd0068.html

Table 7. Explanation of Toxicity-Related Acronymsa

Organization Definition

OSHA Occupational Safety and Health Administration

NIOSH National Institute for Occupational Safety and Health

Exposure 

Limit Definition Explanation

AEGL-1 Acute Exposure Guideline Level 1

The AEGL-1 “is the airborne concentration, expressed as parts per 

million or milligrams per cubic meter (ppm or mg/m3) 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.” “Airborne concentrations below the AEGL-1 represent 

exposure levels that can produce mild and progressively increasing but 

transient and nondisabling odor, taste, and sensory irritation or certain 

asymptomatic, nonsensory effects.”b

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.

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

REL Recommended Exposure Limit This is a 10-hour time-weighted average exposure limit set by NIOSH.

RfC Reference Concentration A concentration “designed to protect the general population against 

adverse systemic (i.e., noncancer) effects.”

aAll information in this table taken from EPA (1994).

b http://www.epa.gov/oppt/aegl/pubs/define.htm
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7.2 OCCUPATIONAL EXPOSURE 

Occupational exposure modeling was performed for the proposed substitute to ensure that use of the 

substitute does not pose an unacceptable risk to workers. The methodology used for this screening 

assessment is based on the one used in the occupational exposure and hazard analysis described in 

Chapter 5 of the Background Document. A box-model approach was used to evaluate potential worker 

exposure to alternative refrigerants. This approach has been widely used for many years to estimate 

probable exposures of workers to hazardous airborne materials, and has been described in detail by the 

National Institute for Occupational Safety and Health (NIOSH). This model takes into consideration the 

duration and magnitude of the resulting exposure which is influenced by 1) duration and intensity of the 

release, 2) rate at which contaminated air is diluted with uncontaminated air, 3) proximity of the worker 

to the source of the release, and 4) the length of time the worker remains in the affected space. 

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

obtained from the Vintaging Model.9 The release per event was conservatively assumed to be 1 percent 

of the equipment charge during manufacturing and 3 percent of the equipment charge during disposal.10

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

equipment manufacturing, the number of events per workday was assumed to equal the number of units 

containing the substitute produced per plant per year divided by 365 workdays per year. For the purposes 

of this model, it is assumed that propane will have a market penetration rate of 23%

11 and that one

production facility will be in operation. These assumptions provided by the submitter result in

approximately 274 events/manufacturing facility/workday. For disposal, it was conservatively assumed 

that 1 unit is disposed during an 8-hour work day nationwide. 

The maximum time weighted average (TWA) exposure was estimated for each exposure scenario, and 

this value compared to the Workplace Guidance Levels (WGLs) for propane and the potential impurities 

in the substitute. The modeling results indicate that the short-term (15-minute and 30-minute) and longterm (8-hour) worker exposure concentrations are, at a maximum, about 50 percent of the WGLs. Table 8 

displays the maximum estimated 15-minute TWA occupational exposure levels of propane and the 

potential impurities in the substitute. The maximum estimated 15-minute TWA occupational exposure 

levels are the most conservative of the modeled results and indicate the highest predicted exposure 

concentrations of the short-term (15-minute and 30-minute) and long-term (8-hour) exposure scenarios. 

Even the maximum estimated short-term occupational levels for propane and the potential impurities are 

significantly lower than their 8-hour or 10-hour long-term WGLs. Therefore, occupational exposure to the 

substitute is not considered a toxicity threat.

 

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 fluorocarbons 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. 

10 During disposal it is assumed that only 90 percent of the refrigerant charge remains in the unit. 

11 This number conservatively assumes that all Unilever cabinets in North America (a figure provided in the SNAP 

Submission) are in the US and that all will be replaced with propane cabinets by 2010. This number of cabinets was 

divided by the number of predicted new small retail refrigeration units produced in 2010, from the Vintaging Model.
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Table 8. Occupational Risk Assessment

Maximum 15-minute TWA 

Occupational Exposure Levels 

(ppm)

Workplace 

Guidance Levels 

(ppm) a

Workplace Guidance Levels

Time Period

Substitute

Propane 502 1000 10-hour TWAb

Potential Impurities

Ethane 0.9 NA NA

Propylene 0.2 NA NA

n-Butane 0.5 800 10-hour TWA

Sulfur 5.4 x 10-4 NA NA

NA = Not Available

a See Table 5 for more information.

b The WGL for Propane is set as a 1000 ppm 8-hr TWA by OSHA and a 10-hr TWA by NIOSH. 

7.3 END-USE EXPOSURE

This section presents estimates of potential store employee and customer exposures to propane in ice 

cream cabinets. An exposure analysis was performed to examine potential catastrophic release of the 

substitute in a small storage room (as in Sections 5 and 6) under a reasonable “worst-case” scenario. The 

analysis was undertaken to determine the 15- and 30-minute TWA exposures for the substitute, which 

were then compared to the standard toxicity limits presented in Table 6 to assess the risk to consumers. 

However, the TWA values are fairly conservative as the analysis does not consider opened windows, fans 

operating, conditioned airflow (either heated or cooled) and other variables that would reduce the levels to 

which individuals would be exposed.

The model involves a refrigerant leak from an ice cream cabinet into an enclosed storage room of volume 

42 m3(1,483 ft3) (see Section 4). The model assumes that the individual is present at the start of the leak 

and the individual remains in the room while the refrigerant is released. It is also assumed that horizontal 

stratification causes most of the refrigerant to settle in higher concentrations closer to the ground. In 

order to simulate the horizontal concentration gradient that will occur because of the weight differential 

between the refrigerant and air, it is assumed that 95 percent of the leaked refrigerant mixes evenly into 

the bottom 0.4 meter of the room, and the rest of the refrigerant mixes evenly in the remaining volume 

(Kataoka 1999). Exposure concentrations were calculated using the box model described in the 

Background Document, which was adapted to estimate concentrations on a minute-by-minute basis. In 

the analysis, the full charge of the unit is assumed to be emitted over the course of one minute and the

model conservatively assumes 2.5 air exchanges occur per hour. 

The highest expected levels of exposure at the end-use based on this analysis occur in the lower stratum 

of the room. The results of the assessment are presented in Table 9.
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Table 9. End-Use Exposure Assessment

15-minute TWA 

Exposure (ppm)

30-minute TWA 

Exposure (ppm)

Substitute

Propane 10,414 7,963

Potential Impurities

Ethane 19 15

Propylene 3.4 2.6

n-Butane 11 8.6

Sulfur 0.01 0.009

TWA = Time Weighted Average

The 15-minute TWA Exposure for propane estimated for this risk screen is 10,414 ppm, which exceeds 

the AEGL-1 value by 414 ppm. Although the calculated end-use exposure is marginally greater than the 

recommended exposure limit, toxicity is not a concern for multiple reasons. First, the AEGL-1 exposure 

limit marks the concentration 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.”

12 Specifically, if the 15-minute TWA were to reach or exceed the AEGL-1, certain 

irritation or notable discomfort would be experienced, but symptoms would be alleviated upon leaving the 

affected area and no permanent damage would be sustained. Second, due to the conservative assumptions 

used in the models, it is unlikely that this worst-case scenario would occur. The two main assumptions 

used in the End-Use Exposure Assessment (see Section 4) included room size and ventilation rate. In 

Section 4, the most conservative, yet reasonable, values were chosen for each category. Adjusting either 

of these assumptions to a value that is slightly less conservative removes the modeled toxicity threat for

propane exposure. 

In particular, the modeling used in the risk screen assumes a leak occurs in the storage room of a 

convenience store with an area of 14 m2(volume of 42 m3). This area is considerably smaller than the 

total area of a typical convenience store, which have sales areas of 100-300 m2(Armines 2008). If the 

minimum storage room area is increased to 15 m2(volume of 45 m3), the exposure becomes 9,719 ppm. 

The exposure model also conservatively assumed a ventilation rate of 2.5 ACH. 

The average ventilation rate for a typical convenience store in the U.S. is 1.9 ACH.

13 Although this rate is 

lower than the assumed rate for a storage room within a convenience store, the use of exhaust fans and 

door ventilators in the storage rooms of convenience stores significantly increases the air exchange rate. 

In addition, Occupational Safety & Health Administration (OSHA) requires that any storage room 

containing flammable material must have a ventilation system “designed to provide for a complete change 

of air within the room at least six times per hour.” 14 Though this storage room will only contain a small 

amount of propane, higher ventilation rates would further protect against flammability and toxicity 

concerns. If ventilation was increased in the storage room to 4.5 ACH, the 15-min TWA would be 8,458 

ppm. 

Further, as described above, the box-model approach used in this modeling assumes that 95% of the 

refrigerant leaks evenly into the bottom 0.4 meter of the room, while the remaining 5% of refrigerant 

mixes evenly in the top breathing zone portion of the room. Once the refrigerant disperses throughout the 

 

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

13 A sample of 70 small commercial buildings were tested in Florida for ventilation rate under normal building 

operation and uncontrolled air flow. http://www.fsec.ucf.edu/en/publications/html/FSEC-CR-1672-97/

14 http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9752&p_table=STANDARDS
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entire room, exposure will be minimized. Because the ACH and room volume assumptions used in the 

models are both very conservative, it is unlikely that these conditions would simultaneously exist and 

therefore the risk of exceeding the toxicity threshold is extremely small. It is strongly recommended, 

however, that steps to protect against toxicity threat in the space should be taken, as detailed in Section 5, 

such as ensuring there is adequate ventilation in rooms containing propane ice cream freezers. 

Finally, exposure to the minute quantities of the impurities in the formulation (see Table 9) is also not 

expected to pose a toxicity threat, given the low toxicity of these substances. Should catastrophic release 

from a cabinet located in the main area of a store occur, exposure levels are not expected to pose a 

toxicity threat as the room volumes in the store would be larger than those used in this model.

15

 Thus, 

exposure concentrations would be even lower in the main area of the store.

7.4 GENERAL POPULATION EXPOSURE

In the Background Document , the RfC value for propane is 0.9 mg/m3. This value was compared to 

estimated factory releases and on-site releases, resulting in a ratio of exposure concentration to RfC that 

varies between 1.9 x 10-4to 3.5 x 10-1, depending on the type of release scenario.16 Ratios of exposure 

concentration to RfC for the proposed substitute’s impurities (for which RfCs are available) were even 

lower. Since the exposure concentrations for the substances are lower than the RfC values, the proposed 

substitute is not expected to pose a toxicity threat to the general population.

8. VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT

Propane has not been exempted as a VOC under the CAA (40 CFR 51.000). VOC emissions from the 

production of retail ice cream cabinets using propane as a refrigerant are controlled through standard 

industry practices, and as such, emissions from the manufacture of units are likely to be minimal. For 

units in operation for retail applications, using leak estimates from the Vintaging Model, the annual 

release rate (including operating, servicing, and disposal leak rates) was calculated to be approximately 

10% of the refrigerant charge size.

17 Assuming this release rate, two assessments were performed to 

compare the annual VOC emissions from the use of propane in self-contained reach-in freezers to other 

anthropogenic sources of VOC emissions. 18 The first assessment approximates the annual VOC 

emissions that would be emitted from the use of propane in all Unilever/Ben and Jerry’s U.S. retail ice 

cream cabinets.19 The second assessment approximates the annual VOC emissions if all reach-in freezers 

in the U.S. were charged with propane.

 

15An Armines (2008) study presents data from site visits to California convenience stores, “minimarkets” and 

supermarkets during which the minimum store area encountered was 100 m2. Assuming a 3 m ceiling height (as in 

the scenarios used in this risk screen), this is equal to a volume of 300 m

3

, or more than seven times the volume of 

the store room used in this analysis.

16 Release scenarios include factory and on-site releases, with and without recycling of the refrigerant.

17 The average annual leak rate (6%), annual service rate (2%) and EOL disposal rate (35%) for small retail 

refrigeration equipment was approximated using data from the Vintaging Model (v4.4_3.23.11). Using an average 

lifetime of 20 years for small retail refrigeration equipment, a total annual release rate of 10% was determined. 

18This scenario conservatively assumes that there is immediate market saturation in 2010, and does not consider 

commercialization and initial market uptake delays.

19 The number of cabinets is calculated based on the conservative assumption that all Unilever/Ben and Jerry’s 

cabinets in North America (a figure provided in the SNAP Submission) are located within the U.S.
November 17, 2011

12

Table 10. VOC Annual Emissions Analysis

Set of Sources Assessed Annual Propane VOC Emissions Compared to VOC 

Emissions from All Anthropogenic Sourcesa(%)

All Unilever/Ben and Jerry’s U.S. Propane 

Retail Ice Cream Cabinets 7.5x10-7%

All U.S. Self-contained Reach-in Freezersb 1.3x10-4%

a Based on 2010 projections calculated using 2008 EPA annual VOC emissions data (EPA 2009) and ICF assumptions.

b Calculations based on 2011 Buildings Energy Data Book (DOE 2011), Energy Savings Potential and R&D Opportunities for 

Commercial Refrigeration (DOE 2009), and ICF assumptions.

As illustrated in Table 10, emissions from the use of propane under both scenarios are minimal compared 

to other sources of VOC emissions. Assuming all Unilever/Ben and Jerry’s ice cream cabinets in the U.S. 

were charged with propane, the resulting VOC emissions in one year would be equal to approximately

8.5x10-2percent of the VOC emissions caused by the generation of electricity used to power small retail 

food refrigeration equipment,

20 1.2x10-3

percent of all the VOC emissions caused by the generation of 

electricity for all refrigeration and air conditioning applications,

21 or 7.5x10-7

percent of all annual 

anthropogenic VOC emissions in the U.S. 

Moreover, if all reach-in freezers in the U.S. were charged with propane (the second, more conservative 

scenario), the resulting VOC emissions would be equal to approximately 1.3x10-4percent of all annual 

anthropogenic VOC emissions in the U.S. Because these emissions of propane are several orders of 

magnitude lower than the VOC emissions generated by other anthropogenic emissions, and the VOC 

emissions from all Unilever/Ben and Jerry’s ice cream cabinets is only a small fraction of VOC emissions 

from the use of electricity in the retail refrigeration sector, the environmental impacts of the incremental 

VOC emissions from propane releases for small refrigeration cabinets are not considered a threat to local 

air quality.

 

20 This figure includes commercial reach-in cabinets that are upright, self-contained refrigerated cases with solid or 

glass doors whose purpose is to hold frozen and/or refrigerated food products. These cases are commonly used in 

commercial and institutional food-service establishments. The cases are self-contained such that the entire 

refrigeration system is built into the reach-in unit and heat is rejected to the surrounding interior air.

21 Calculations based on ICF assumptions and 2010 Electricity Projections (U.S. EIA 2011). 
November 17, 2011

13

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