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Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for CFC-12 and HCFC-22 in 

Household Refrigerators and Freezers

Substitute: R-441A

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 and HCFC-22 in this sector. The proposed 

end-use application considered in this analysis is new replacements for household refrigerators and 

household freezers. The specific proposed CFC-12 and HCFC-22 substitute blend examined in this risk 

screen is R-441A (originally submitted as HCR-188C1). Table 1 presents the composition of the 

substitute.

Table 1. Composition of R-441A.

Component Concentration

(Weight Percent)

Propane 55%

n-Butane 36%

Isobutane 6%

Ethane 3%

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

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 blend in the 

applications listed above did not pose unacceptable risk to workers. End-use exposure modeling was 

performed to examine potential catastrophic releases for each of the chemical constituents of the proposed 

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

would not pose an unacceptable risk to the population at large. 
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Section 2 summarizes the results of the risk screen for the proposed substitute blend listed in Table 1. 

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 4: Flammability Assessment

 Section 5: Asphyxiation Assessment

 Section 6: Toxicity Assessment

 Section 7: Volatile Organic Compound Assessment 

 Section 8: References

2. SUMMARY OF RESULTS

R-441A is recommended for SNAP approval for household refrigerators and household freezers. EPA's 

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

continued use of CFC-12 and HCFC-22. No significant toxicity risks to workers, consumers, or the 

general population are expected according to occupational and consumer exposure modeling. 

Flammability models indicate that risks of explosion are not a concern for consumers, provided the 

refrigerator or freezer is not 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, 342, and 623be followed.

3. ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to atmospheric integrity posed by the use of R441A in the residential refrigeration sector. The ODP, GWP, and atmospheric lifetime (ALT) of the 

proposed substitute are presented in Table 2.

The environmental impacts resulting from use of R-441A 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 

and HCFC-22.

 

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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Table 2. Atmospheric Impacts of R-441A Components Compared to CFC-12 and HCFC-22.

Refrigerant Ozone Depleting Potential 

(ODP)

Global Warming Potential -

AR4a(GWP)

Atmospheric Lifetime 

(ALT)

Propane 0 3.3a 0.041b

n-Butane 0 4.0a 0.018b

Isobutane 0 NA 0.019b

Ethane 0 5.5a 0.21b

CFC-12 1

c 10,900a 100a

HCFC-22 0.055 c 1,810a 12a

NA – Not available in IPCC 4th Assessment Report.

a

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

b

IPCC/TEAP (2005).

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

4. DISCUSSION OF END-USE SCENARIOS MODELED

The proposed end-use for this substitute is household food refrigeration. The specific application 

includes household refrigerators and freezers. The submission states that the household refrigerators and 

freezers with this substitute will have a charge size of 40 grams.

For the analysis, a kitchen with an area of 7.5 m

2

and a height of 2.4 meters was assumed (EPA, 1994). 

This is equivalent to a volume of 18 m

3

.

4

 In the analysis, the full charge of the unit as specified in the 

submission is assumed to be emitted over the course of one minute and the model conservatively assumes

2.5 air changes occur per hour. Horizontal stratification is also assumed since R-441A 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 throughout the risk screen for modeling at the end-use (i.e., in Sections 5, 6, and 7.3).

Table 3. Worst-Case Scenario Model Assumptions for Submission

Parameter Assumption

Refrigeration Unit Household Refrigerator

Room Household Kitchen

Charge size (g) 40

Length of release (minutes) 1

Room size (volume - m3) 18

Room ventilation (air changes 

per hour) 2.5

Horizontal stratificationc Yes

5. FLAMMABILITY ASSESSMENT

R-441A is flammable when its concentration in air is in the range of 1.68%-11.7% by volume (16,800 

ppm to 117,000 ppm). Due to its flammable nature, R-441A could pose a significant safety concern for 

workers and consumers if it is not handled carefully. In the presence of an ignition source (e.g., static 

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

when the concentration of R-441A exceeds its lower flammability limit (LFL) of 16,800 ppm. Therefore, 

it is important to ensure that the levels of R-441A do not exceed 16,800 ppm. In production facilities or 

 

4

The range of potential flow rates for a home is believed to be 2.5 to 4.5 air changes per hour (ach) (Sheldon 1989). The lowest 

and thus most conservative, possible rate – 2.5 air changes per hour – was used in the models.
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other facilities where large quantities of the refrigerant will be stored, proper safety precautions should be 

in place to minimize the risk of explosion. Household refrigerators and freezers installed with R-441A

should be clearly labeled as containing a flammable refrigerant charge and designed to prevent 

catastrophic leaks. Furthermore, only refrigerant technicians certified to work with flammable 

refrigerants should handle these units during manufacturing, installation, servicing, transportation and 

disposal. 

Under the Reasonable Worst-Case Release Scenario, (see Table 4) the maximum instantaneous 

concentration of R-441A in the lower stratum of the kitchen would be approximately 6,236 ppm,5 which 

is 37 percent of the substitute’s LFL. This value was calculated using the assumed average room size (18 

m

3

[635 ft3]) and other assumptions outlined in Section 4. The maximum instantaneous concentration is 

even less 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 presents the full results of 

the analysis.

Table 4. Flammability Assessment.

Room Type/Appliance 

Type

Reasonable Worst-Case Release Scenario Flammability Threshold Scenario

Room Size (m3)

Maximum 

Instantaneous 

Concentration (ppm) a,b

Room Size (m3)

Maximum 

Instantaneous 

Concentration (ppm) a,b

Kitchen/Refrigerator 18 (635 ft3) 6,236c 7.5 (265 ft3) 15,827

a Lower Flammability Limit of R-441A is equal to 16,800 ppm

b

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

For the Flammability Threshold Scenario, the room size at which a flammability concern would exist 

(i.e., when the maximum instantaneous concentration in the lower stratum of the kitchen equals the LFL 

for R-441A) was determined. This calculation was also repeated for this document assuming that the 

maximum instantaneous concentration in the kitchen reaches 16.800 ppm--the LFL for R-441A—rather 

than using the maximum instantaneous concentration of 15,827 ppm from the November 6, 2009 risk 

screen (EPA-HQ-OAR-2009-0286-0020). For flammability to be of concern under the conservative 

(protective) assumptions described in Section 4, the volume of the kitchen would have to be 6.7 m

3 (235 

ft3) (see Table 4). Assuming a square room with a ceiling height of 2.4 m (8.0 ft), this equates to a 1.67 x 

1.67 m (5.5 x 5.5 ft) kitchen. Although very limited data are available regarding the distribution of 

kitchen volumes in the United States, an analysis by Murray (1997) which aggregated data from over 60 

different projects reported the minimum kitchen volume encountered as 31 m3.

6

Further, only one percent 

of houses sampled had a kitchen smaller than 53 m3. 

To avoid the risk of fire and explosion, it is recommended that the refrigerators not be installed in small, 

poorly ventilated spaces such as very small ‘galley’ kitchens or storage closets (especially as other 

equipment or appliances in the space would reduce the effective volume of the room). However, based 

on the available data regarding kitchen volumes, it is not likely that a kitchen would exist which would be 

small enough for flammability to be a concern, even under a reasonable worst-case scenario. For full-

 

5 This value decreased from 6,628 ppm at the proposal stage (EPA-HQ-OAR-2009-0286-0020) due to a 

recalculation based on the composition for R-441A on a weight percent basis instead of the molar percent basis used 

at the proposal stage.

6 Murray (1997) uses data from the Brookhaven National Laboratory PFT database. Data regarding kitchen volumes 

were only available for the Los Angeles area and the kitchen volumes are for a “kitchen zone” which may include 

associated areas, such as utility rooms, dining rooms, living rooms, and family room. The inclusion of these other 

spaces in the “kitchen zone” volume is realistic, as the presence of adjoining rooms would increase the volume into 

which the refrigerant could leak.
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sized kitchens, the risk of explosion is minimal. The installation of leak prevention devices would further 

protect against the very limited risk of explosion.

To mitigate the risks of flammability at the end-use, it is recommended that R-441A refrigerators' and 

freezers’ charge sizes are determined according to the UL 250 Supplement SA standard. Per the UL 

standard, the maximum permissible leak for refrigerants with limits of flammability and heat of 

combustion greater than 19,000 kJ/kg (such as the components of R-441A) is 50 g. Additional charge is 

not prohibited, however, if the amount of refrigerant leaked during testing does not exceed 50 grams. 

This is also consistent with EPA’s proposed use condition for hydrocarbon refrigerants that limits the 

refrigerant charge size of any refrigerator, freezer, or combination refrigerator and freezers to 577grams, 

assuming that roughly 12% of the refrigerant charge is retained in the compressor oil and 88% of the 

charge leaks. By ensuring R-441A refrigerators and freezers conform to the aforementioned standard, 

flammability risks associated with the use of R-441A in these appliances should be mitigated.

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 R-441A. The submitter 

has provided safety guidelines for handling R-441A, which should be followed. As a further precaution, 

certification requirements and training programs for technicians that handle R-441A should be developed

using these guidelines. In addition, R-441A storage and transport equipment should be installed with 

safety devices that minimize the likelihood of catastrophic releases. For example, NFPA 58 Liquefied 

Petroleum Gas Code (NFPA, 2007) for liquefied propane requires the use of overfill protection devices 

(OPD) on cylinders to minimize the likelihood of leaks. The NPFA 58 Code also contains propane 

storage and transportation requirements/guidelines. Similar equipment safety and procedural 

requirements should be developed for R-441A and other flammable refrigerants. 

It is important that the strictest standards be followed during manufacturing. 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 R-441A through adherence to good manufacturing practices. If refrigerant levels in the air 

surrounding the equipment rise above one-fourth of the lower flammability limit,8or oxygen levels in the 

room fall below 19.5% as noted in the material safety data sheet provided by the submitter, 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 R-441A. 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 “worst-case” scenario was investigated for R-441A. This analysis does not 

consider conditions that are likely to occur that would reduce the 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. If the 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.

 

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

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

8 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.”
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The results of the asphyxiation assessment are summarized in Table 5 below. The maximum charge of R441A necessary to reduce the oxygen levels to 12 percent in air,9

in a kitchen of volume 18 m3(635 ft3)

(see Section 4), was calculated, assuming horizontal stratification of the refrigerant and the air. Assuming 

that nitrogen and oxygen retain the same relative volumes in the rooms with the balance composed 

entirely of R-441A, and that the pressure of the room does not increase significantly with the addition of 

the refrigerant, a charge of approximately 535 g would be necessary to reach 12 percent oxygen in the 

lower stratum. This amount represents more than twelve times the intended charge of approximately 40 g 

for a single R-441A refrigerator or freezer. Charge requirements to reach the same effect in the upper 

stratum 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 assumptions described above, the volume of the 

kitchen would have to be about 1.3 m3(46 ft3) (see Table 5). Assuming a square room with a ceiling 

height of 2.4 m (8.0 ft), this equates to a 0.8 x 0.8 m (2.6 x 2.6 ft) kitchen. 

Table 5. Asphyxiation Assessment.

Room Type/Appliance 

Type

Appliance 

Charge (g)

Reasonable Worst-Case Scenario Asphyxiation Threshold Scenario

Room Size (m3) Charge Causing 

Impairment (g)a

Room Size (m3) Charge Causing 

Impairment (g)a

Kitchen/Refrigerator 40 18 (635 ft3) 535 1.3 (46 ft3) 40

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

larger volume.

It is recommended that R-441A refrigerators not be installed in small, poorly ventilated spaces, such as 

very small ‘galley’ kitchens, to avoid the risk of asphyxiation. However, based on the available data 

regarding kitchen volumes (see Section 4), it is not likely that a kitchen would exist which would be small 

enough for asphyxiation to be a concern, even under a reasonable worst-case scenario. 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 R-441A

in this end-use poses a significant risk of asphyxiation or impaired coordination to consumers. 

7. TOXICITY ASSESSMENT

Section 7 summarizes the results of the toxicity assessment for R-441A in the household 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 residential 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 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 for each of the 

 

9 Twelve percent oxygen in air is the No Observed Adverse Effect Level (NOAEL) for hypoxia (ICF 1997). 
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components of R-441A. 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 of the acronyms used in Table 6. EPA’s approach for identifying or 

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

Table 6. Toxicity Levels of R-441A Components.

R-441A

Component 

WGL (Long-term Exposure)

ppm

EGL (Short-term Exposure)

Ppm

Reference Concentration (RfC)

mg/m3

Propane 1,000a 

(OSHA PEL/NIOSH REL) 10,000 ppme,f (10 min AEGL-1)

6,900 ppmf(30 min AEGL-1)

0.9 mg/m3 i

n-Butane 800b (NIOSH REL) 6,900 ppmg(30 min AEGL-1) 0.95 mg/m3 i

Isobutane 800c (NIOSH REL) 18,000 h(NOAEL) 0.95 mg/m3 i

Ethane 1,000d (ACGIH TLV) NA NA

NA = Not Available

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

b NIOSH REL available at: http://www.cdc.gov/NIOSH/NPG/npgd0068.html

c NIOSH REL available at: http://www.cdc.gov/Niosh/npg/npgd0350.html

d ACGIH TLV available at: http://www.cdc.gov/niosh/ipcsneng/neng0266.html.

e 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.

f AEGL-1 available at: http://www.epa.gov/opptintr/aegl/pubs/tsd96.pdf

g AEGL-1 available at: http://www.epa.gov/opptintr/aegl/pubs/tsd102.pdf

h 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.”

i SNAP Refrigerant Background Document, 1994.
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Table 7. Explanation of Toxicity-Related Acronymsa

Organization Definition

ACGIH American Conference of Governmental Industrial Hygienists

OSHA Occupational Safety and Health Administration

NIOSH National Institute for Occupational Safety and Health

Exposure Limit Definition Explanation

AEGL-1 Acute Exposure Guideline Level The AEGL-1 “is the airborne 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” (EPA 2008a).

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.

NOAEL No Observed Adverse Effect Limit “The highest exposure level at which there are no biologically 

significant increases in the frequency or severity of adverse effect 

between the exposed population and its appropriate control; some 

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

adverse or precursors of adverse effects.”b

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.”

TLV Threshold Limit Value An 8-hour time-weighted average health-based concentration set by 

ACGIH. Exposure at or below this concentration is believed to “not 

create an unreasonable risk of disease or injury.” d

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

b From http://www.epa.gov/riskassessment/glossary.htm#n

c http://www.cdc.gov/niosh/npg/pgintrod.html#exposure

d http://www.acgih.org/TLV/

7.2 OCCUPATIONAL EXPOSURE 

Occupational exposure modeling was performed for the components of the proposed blend to ensure that 

use of the blend 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. To evaluate potential worker exposure to alternative 

refrigerants, a box-model approach was used. This model 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. 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 in 

2007 were obtained from the Vintaging Model.10 To determine the estimated level of occupational 

 

10 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 
***** November 17, 2011 *****

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exposure for a constituent in a blend, the total release rate of the refrigerant is multiplied by the weight 

percent composition of each compound in the blend. For all end-uses 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.11 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 240 workdays per year.12 For the purposes of this model, it is assumed that R-441A will have 

a market penetration rate of 3.3% and that 12 production facilities will be in operation. These 

assumptions result in approximately 106 events/manufacturing facility/day. This is an extremely 

conservative estimate, considering less than 100 pounds of R-441A is intended to be produced annually, 

for a maximum of 1145 units produced annually or at the most five events/manufacturing facility/day.13 

For disposal, it was conservatively assumed that 100 units are disposed during an 8-hour work day. 

The maximum time weighted average (TWA) exposure was estimated for each occupational exposure 

scenario, and these values compared to the Workplace Guidance Levels (WGLs) for each constituent of 

the blend. The modeling results indicate that both the short-term (15-minute and 30-minute) and longterm (8-hour) worker exposure concentrations at no point exceed 2 percent of the WGLs. Table 8

displays the maximum estimated 15-minute TWA occupational exposure levels of the R-441A

constituents. 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 the components of R-441A are significantly lower than their

8-hour long-term or 10-hour long term WGLs. Therefore occupational exposure to the substitute is not 

considered a toxicity threat. 

Table 8. Occupational Risk Assessment

R-441A Component Maximum 15-minute TWA 

Occupational Exposure 

Levels (ppm)

Workplace Guidance 

Levels (ppm)a

Workplace Guidance 

Levels Time Period

Propane 15.64 1,000 10-hr TWAb

n-Butane 5.93 800 10-hr TWA

Ethane 1.91 1,000 8-hr TWA

Isobutane 0.99 800 10-hr TWA

a See Table 6 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 consumer exposures to R-441A in home refrigeration

appliances. A consumer exposure analysis was performed to examine potential catastrophic releases for 

each of the chemical constituents of R-441A. Estimates for acute/short-term consumer exposures 

resulting from catastrophic leakage of refrigerant from residential refrigerators were examined. The 

analysis was undertaken to determine the 15- and 30-minute TWA for each component of R-441A, which 

was 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 

 

in operation, and the initial ODS substance that the equipment contained. 

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

12 Assuming 240 workdays/year = 52 weeks/year x 5 workdays/week – 10 holidays/year.- 10 vacation days

13 HCR-188C SNAP application states that less than 100 pounds of HCR-188C is intended to be produced annually. It was 

assumed the same quantity would be produced of R-441A. If all of the units produced are refrigerators of charge 39.6 g a

maximum of 1145 units will be produced annually leading to five events/manufacturing facility/day (assuming only one 

production plant is in operation and that there are 240 workdays per year).
***** November 17, 2011 *****

10

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

which individuals would be exposed.

The scenario modeled (see Section 4) involves a refrigerant leak from a refrigerator into an enclosed 

kitchen of volume 18 m3(635 ft3). It is assumed 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 R-441A to settle in higher concentrations closer to the ground. 

Considering the horizontal stratification is important because children, a particularly vulnerable segment 

of the population, breathe air that is 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 for the 

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

adapted to estimate concentrations on a minute-by-minute basis. It was assumed that 100 percent of the 

unit’s charge would be released during a time span of 1 minute, at which time the concentration of R441A will peak, and then steadily decline onwards. Refrigerant concentrations were modeled under two 

air change scenarios believed to represent the range of potential flow rates for a home, assuming flow 

rates of 2.5 and 4.5 air changes per hour (ACH) (Sheldon 1989). 

The highest concentrations of R-441A occur in the lower stratum of the room and when assuming 2.5 

ACH. The highest expected levels of consumer exposure based on this analysis are presented in Table 9

below. Even under the conservative assumptions used in the consumer exposure modeling, the estimated 

15-minute consumer exposure level of propane is 47% of the chemical’s 30-minute AEGL-1 and the 15-

minute consumer exposure level of n-butane is approximately 18% of the chemical’s 30-minute AEGL-1. 

Further, exposure levels of R-441A are 1 percent of its NOAEL and while short-term toxicity limits are 

not available for ethane, its 15-minute consumer exposure level is approximately 39% of the 8-hour TWA 

long-term occupational exposure limit. Therefore, consumer exposure to R-441A should not pose a 

toxicity threat.

Table 9. End-Use Exposure Assessment

R-441A

Component

15-minute TWA 

Consumer Exposure 

(ppm)

30-minute TWA 

Consumer Exposure 

(ppm)

Short-term Exposure 

Limits (ppm)

Propane 3,225 2,492 6,900a

n-Butane 1,223 945 6,900a

Isobutane 204 158 18,000b

Ethane 394 305 NA

a 30-minute AEGL-1; see Table 6 for more information.

b NOAEL; see Table 6 for more information.

TWA = Time Weighted Average

NA = Not available

7.4 GENERAL POPULATION EXPOSURE

In the SNAP Background document for refrigerants, the RfC values for propane, n-butane, and isobutane 

are 0.9 mg/m3, 0.95 mg/m3and 0.95 mg/m3, respectively. These three compounds make up 95 percent of 

the R-441A blend (w/w). We assumed a conservative RfC of 0.9 mg/m3for the whole blend, and 

compared this RfC to estimated factory releases and on-site releases. This gives a ratio of exposure 

concentration to RfC that varies between 1.3 x 10-5to 1.8 x 10-1, depending on the type of release 

scenario. Since the exposure concentrations for these components are lower than the RfC values, R-441A

is not expected to pose a toxicity threat to the general population.
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8. VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT

Most of the components of R-441A, except ethane, have not been exempt as a VOC under the CAA (40 

CFR 51.100(s)). VOC emissions from the production of refrigerators and freezers using R-441A as a 

refrigerant are controlled through standard industry practices, and as such, emissions from manufacture of 

units are likely to be minimal. For units in operation for consumer applications, using leak estimates from 

the Vintaging Model, the annual release rate (including operating, servicing, and disposal leak rates) for 

household refrigerators was calculated to be approximately 4% of refrigerant charge size, annually.14

Assuming this release rate, two assessments were performed to compare the annual VOC emissions from 

use of R-441A in household refrigerators to other anthropogenic sources of VOC emissions. The first 

assessment approximates the annual VOC emissions that would be emitted from R-441A refrigerators 

produced in one year, assuming the submitter’s current production plans. The second analysis 

approximates the annual VOC emissions if all refrigerators in U.S. households were charged with R441A.

15

Table 10. VOC Annual Emissions Analysis

Set of Sources Assessed Annual

VOC Emissions (MT)

Annual R-441A VOC Emissions 

Compared to VOC Emissions from All 

Anthropogenic Sourcesa(%)

R-441A Refrigerators Produced in 

One Yearb

0.002 MT 1.6x10-8%

All U.S. Household Refrigeratorsc 446 MT 3.4x10-3%

a Calculations based on 2008 EPA annual VOC emissions data (EPA 2009b).

b Current production of R-441A based on R-441 SNAP submission (A.S. Trust & Holdings, Inc. 2009). 

c Calculations based on A.S. Trust & Holdings SNAP Submission and 2010 Residential Equipment Stock Projections (A.S. Trust & Holdings, 

Inc. 2009 and U.S. EIA 2011).

As illustrated in Table 10, the VOC emissions from the use of R-441A under both scenarios are minimal 

compared to other sources of VOC emissions. Assuming the submitter’s current production plans, the 

resulting VOC emissions from R-441A refrigerators manufactured in one year would be equal to 

approximately 1.4x10-4percent of the VOC emissions caused by the generation of electricity used to 

power household refrigerators and freezers,16 2.5x10-5percent of all the VOC emissions caused by the 

generation of electricity for all refrigeration and air conditioning applications, or 1.6x10-8percent of all 

annual anthropogenic VOC emissions in the U.S. 

Moreover, if all the refrigerators in U.S. households were charged with R-441A (the second, more 

conservative, scenario), the resulting VOC emissions would be equal to approximately 3.4x10-3percent of 

all annual anthropogenic VOC emissions in the U.S. Because these emissions of R-441A are several 

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

VOC emissions from the anticipated production of refrigerators by the submitter is only a small fraction 

of VOC emissions from the use of electricity to power household refrigerators and freezers, the 

environmental impacts of these VOCs are not considered a threat.

 

14 The average annual leak rate (0.2%), annual service rate (0.7%) and EOL disposal rate (50%) for household refrigerators and 

freezers was approximated using data from the Vintaging Model (v4.4_3.23.11). Using an average lifetime of 14 years for 

household refrigerators and freezers, a total annual release rate of 4% was determined. 

15This scenario, conservatively assumes that there is immediate market saturation in 2010, and does not consider 

commercialization and initial market uptake delays.

16 Calculations based on ICF assumptions and 2010 Electricity Projections (U.S. EIA 2011).
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12

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