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Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes in Household Refrigerators and Freezers 

and Water Coolers

Substitute: R-450A

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

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

1. INTRODUCTION

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

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

the Clean Air Act Amendments of 1990 (CAAA). The U.S. Environmental Protection Agency (EPA), as 

authorized by Section 612 of the CAAA, administers the Significant New Alternatives Policy (SNAP) 

Program, which identifies acceptable and unacceptable substitutes for ODS in specific end-uses based on 

assessment of their health and environmental impacts. 

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

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

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

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

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

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

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

evaluates the potential use of R-450A as a substitute in the household refrigerator and freezer end-use and 

the drinking water cooler end-use. Table 1 presents the composition of the proposed substitute.

Table 1. Composition of R-450A and Potential Impurities

Constituent Chemical Formula CAS Number Concentration

(Weight Percent)a

1,1,1,2-Tetrafluoroethane (HFC-134a) CF3CH2F 811-97-2 42%

trans-1,3,3,3,-Tetrafluoro-1-propene 

(HFO-1234ze(E)) CHFCHCF3 29118-24-9 58%

Potential Impurities
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Constituent Chemical Formula CAS Number Concentration

(Weight Percent)a
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Constituent Chemical Formula CAS Number Concentration

(Weight Percent)a

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: 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

R-450A is recommended for SNAP approval for use in household refrigerators and freezers and water 

coolers. 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, R-502, and HCFC-22, as well as other commonly used 

refrigerants, as it is less harmful to the ozone layer, has lower climate impact, and a shorter atmospheric 

lifetime. Neither of the components of R-450A are subject to volatile organic compound (VOC) 

regulations under the CAA (40 CFR 51.100(s)), so environmental impact from the release of these 

substances is not a concern. It is expected that manufacturers and technicians will adhere to the material 

safety data sheet (MSDS) for R-450A and good manufacturing practices. 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 and Health Administration (OSHA) guidelines will be 

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

and water coolers using R-450A. Because household refrigerators and freezers and water coolers are to be 

installed in locations with adequate space and/or ventilation in accordance with EPA recommendations and 

the equipment maintenance manuals for R-450A in each end-use, significant asphyxiation or toxicity risk 

to consumers is also unlikely. In addition, because R-450A is considered to be nonflammable, the 

proposed substitute is not expected to present a flammability concern. Additional safeguards, including 
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specified refrigerant concentration limits (RCL) of R-450A components, are also provided by adherence to 

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

(ASHRAE) Standards 15,1 34,2and 623.

3. ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to atmospheric integrity posed by the use of R450A in household refrigerators and freezers and water coolers. 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 when compared to ODS refrigerants currently in these end-uses such as CFC12, R-502, and HCFC-22. In addition, R-450A also has lower climate impact and a shorter atmospheric 

lifetime than those predicted for other substitutes examined in the Background Document as well as 

commonly utilized refrigerant HFC-134a. Thus, EPA believes that the use of R-450A would result in 

substantially less harm to the climate and ozone layer than the continued use of ODS and other commonly 

used refrigerants.

Table 2. Atmospheric Impacts of R-450A Components Compared to Other Refrigerants for 

Household Refrigerator and Freezer and Water Cooler

Refrigerant Ozone Depleting Potential

(ODP)

a

Global Warming Potential

(GWP)

b

Atmospheric Lifetime in 

Years (ALT)

b

R-450A 0 601 NAc

Individual Components

HFC-134a 0 1,430 14

HFO-1234ze(E) 0 1

d 16.4 daysd

CFC-12 0.82 10,900 100

R-502e 0.2 4,650 NAf

HCFC-22 0.13 1,810 12a

HFC-134a 0 1,430 14

a WMO 2010 Scientific Assessment Report (2011)

b

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

c Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-134a is 14 years and 

the ALT for HFO-1234ze(E) is 10 days (IPCC 4th Assessment Report [Forster et al. 2007], Hodnebrog, O. et al. [2013]).

d Hodnebrog, O. et al. (2013)

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

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

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

4. VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS

HFC-134a and HFO-1234ze(E) are both exempt from the definition of volatile organic compound (VOC) 

under CAA regulations (40 CFR 51.100(s)). Therefore, environmental impacts from the release of HFC134a and HFO-1234ze(E) as VOCs are not a concern. 

 

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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5. DISCUSSION OF END-USE SCENARIOS MODELED

The submission states that both R-450A household refrigerators and freezers and water coolers will have a 

typical charge size of 200 grams and a maximum charge size of 1,000 grams. Household refrigerators and 

freezers and water coolers can be installed in a wide range of locations with varying room volumes (e.g., 

residential homes, commercial office buildings). To represent a reasonable worst-case scenario for the 

household refrigerators and freezers end-use and water coolers end-use, it is assumed that a catastrophic 

leak of refrigerant occurs while a household refrigerator is installed at the end-use (i.e., a small kitchen) for 

both the typical and maximum charge size provided by the submitter. The analysis in this risk screen 

conservatively assumes that the household refrigerator is located in a small residential kitchen with an 

effective volume of 18 m3(640 ft3) (i.e., excluding the space filled by cabinets, other kitchen equipment, 

etc.) and a height of 2.4 meters.

Under the reasonable worst-case scenario, the full charge of the unit is assumed to be emitted into the 

kitchen with 2.3 air changes per hour (ACH) over the course of two time durations: 1) one minute, which

represents a catastrophic release of refrigerant due to a puncture or other major damage to the refrigeration 

system, and 2) fifteen minutes, which represents the accidental release of refrigerant due to a noncatastrophic leak in the system (e.g., valve failure, pinhole leaks). The one-minute time duration is most 

appropriate for flammable refrigerants and presents a less relevant scenario for R-450A, which is 

nonflammable. Therefore, while we evaluate both of these scenarios in this risk screen for consistency 

purposes, the scenario which analyzes a release of refrigerant over a 15-minute time duration more 

accurately represents a reasonable worst-case scenario for R-450A in household refrigerators and freezers 

and water coolers. A vertical concentration gradient is also assumed since R-450A is denser than air (i.e., 

the specific gravities of both HFC-134a and HFO-1234ze(E) are greater than 1) and will settle in higher 

concentrations closer to the ground. In order to simulate the vertical concentration gradient of refrigerant 

following release, it is assumed that 95 percent of the leaked refrigerant mixes evenly into the bottom 0.4 

meter (1.3 feet) of the room, and the rest of the refrigerant mixes evenly in the remaining volume (Kataoka 

2000). Additionally, because the average breathing zone is above 0.4 meters and mixing is likely to occur 

upon release of R-450A from the unit because the system pressure is higher than the surrounding 

atmospheric pressure, the absence of the vertical concentration gradient was also evaluated in the end-use 

exposure assessment (Section 9). Table 3 details the end-use modeling assumptions used throughout the 

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

Table 3. End-Use Scenario Model Assumptions

Parameter Assumption

Room Type Household Kitchen

Size (m3) 18a(640 ft3)

Ventilation Rate (air changes per hour) 2.3a

Refrigeration Unit Household Refrigerator

Charge Size (g) 200b; 1,000c

Duration of Release (minutes) 1

d

; 15e

Vertical Concentration Gradient Yes; No

 a Background Document (EPA 1994)

 

b Typical charge size for household refrigerators and freezers and water coolers (Honeywell 2014b)

c Maximum charge size for household refrigerators and freezers and water coolers(Honeywell 2014b)

d Represents catastrophic release due to puncture and/or destruction of system

e Represents non-catastrophic release due to leak in the system (e.g., valve failure, pinhole leak)

EPA recognizes that household refrigerators and freezers and water coolers may be placed in a variety of 

locations with different room sizes and ventilation rates. When units are installed in smaller, enclosed 

spaces, there is a higher risk for asphyxiation or exposure concerns. To address this variability in room 

volumes and charge sizes for installed household refrigerators and freezers and water coolers, this risk 

screen incorporates threshold analyses in addition to the worst-case scenario modeling. The threshold 
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analyses are performed in order to determine the room size and charge size requirements that ensure that 

the use of R-450A in these end-uses does not present risk to end-users or servicing technicians.

6. POTENTIAL HEALTH EFFECTS

To assess potential health risks from exposure to the proposed substitute in household refrigerators and 

freezers and water coolers, EPA identified the relevant toxicity threshold values for comparison to 

modeled exposure concentrations for different scenarios. In March 2014, R-450A was submitted to 

ASHRAE’s Standing Standard Project Committee (SSPC) for inclusion in ASHRAE Standard 34 under

safety group A1 with an RCL of 72,000 ppm. ASHRAE 34 RCLs are intended to reduce the risks of acute 

toxicity, asphyxiation, and flammability hazards in normally occupied, enclosed spaces during refrigerant 

use and protect end-users from the potential dangers of a catastrophic leak from refrigeration unit 

(ASHRAE 2010b). ASHRAE Standard 15 implements the aforementioned standard, requiring that “the 

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

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

RCL for R-450A 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 (WGLs). Risks from potential 

short-term consumer exposures were evaluated by comparing exposure concentrations to emergency 

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

guideline level (AEGL), or emergency response planning guideline (ERPG) for R-450A, potential shortterm, end-use exposures were evaluated on a component basis (i.e., HFC-134a and HFO-1234ze(E)).

Table 4 lists the relevant toxicity limits for R-450A and its components 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. 

Table 4. Exposure Limits of R-450A Components

R-450A 

Component

WGL

(Long-term Exposure)

ppm

EGL 

(Short-term Exposure)

ppm

Refrigerant Concentration 

Limit (RCL)

ppm

R-450A 880 (8-hour AEL) 2,640 (15-min STEL)

a 72,000

Individual Components

HFC-134a 1,000 (8-hour WEEL)

b

8,000 (10-min AEGL-1)

8,000 (30-min AEGL-1) 50,000

HFO-1234ze(E) 800 (8-hour WEEL)

b 2,400 (15-min STEL)c NAd

NA = Not available

a Neither ACGIH nor AIHA recommend ceiling or short term exposure limits for the blend R-450A. A STEL for R-450A of 2,640 ppm was 

developed by EPA based on the 880 ppm AEL value. The STEL was estimated as three to five times the AEL, which is an established method of 

estimating a short-term exposure limit by ACGIH. [STEL] = [AEL] x 3 = 880 ppm x 3 ≈ 2,640 ppm

b Honeywell (2014a)

c Neither ACGIH nor AIHA recommend ceiling or short term exposure limits for HFO-1234ze(E). A STEL for HFO-1234ze(E) of 2,400 ppm was 

developed by EPA based on the 800 ppm WEEL value. The STEL was estimated as three to five times the AEL, which is an established method 

of estimating a short-term exposure limit by ACGIH. [STEL] = [AEL] x 3 = 800 ppm x 3 ≈ 2,400 ppm

d Although an RCL has not been proposed for HFO-1234ze(E), the recommended ATEL for HFO-1234ze(E) is 59,000 ppm (Honeywell 2014a).
Final -- October 10, 2014

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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

OARS Occupational Alliance for Risk Science

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.

ATEL Acute Toxicity Exposure Limit The ATEL is the refrigerant concentration limit intended to reduce the 

risks of acute toxicity hazards in normally occupied, enclosed spaces 

according to ASHRAE Standard 34. The ATEL includes consideration of 

mortality, cardiac sensitization, anesthetic or central nervous system 

effects and other escape impairing effects and permanent injury. The 

ATEL is similar to the Immediately Dangerous to Life or Health (IDLH)

concentrations set by NIOSH.

STEL Short-Term Exposure Limit A 15-minute time-weighted average (TWA) exposure that should not be 

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

TWA, set by ACGIH. 

AEGLb,c

Acute Exposure Guideline 

Level 1

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

predicted that the general population, including susceptible individuals, 

could experience notable discomfort, irritation, or certain asymptomatic 

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

transient and reversible upon cessation of exposure.

Acute Exposure Guideline 

Level 2

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

substance above which it is predicted that the general population, 

including susceptible individuals, could experience irreversible or other 

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

escape.

Acute Exposure Guideline 

Level 3

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

substance above which it is predicted that the general population, 

including susceptible individuals, could experience life-threatening health 

effects or death.

Long-Term Exposure

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

AEL Acceptable Exposure Limit The maximum 8-hour time weighted average (TWA) at which a worker 

can be exposed regularly without adverse effects.

WEEL Workplace Environmental 

Exposure Level

Developed by OARS for to protect healthy workers against acute and 

chronic health effects, this limit is based on repeated daily exposures 

over a working lifetime and averaged over an 8-hour workday. 

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.
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According to the MSDS, exposure to R-450A may be hazardous if inhalation, skin contact, or eye contact 

with R-450A occurs. The most likely pathway of exposure is through inhalation. R-450A 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. 

If R-450A 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 or irregular, person(s) be given 

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

attempt to retrieve victims of exposure to R-450A without adequate PPE. At a minimum, a self-contained 

breathing apparatus (SCBA) should be worn. Exposures of R-450A to the skin may cause frostbite. In the 

case of dermal exposure, the MSDS for R-450A recommends that person(s) immediately wash the affected 

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

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

seek medical attention immediately. Exposures of R-450A to the eyes could cause eye irritation. In case of 

ocular exposure, the MSDS for R-450A 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 R-450A can be minimized by following the exposure 

guidelines and ventilation and PPE recommendations outlined in the MSDS for R-450A and this risk 

screen.

7. FLAMMABILITY ASSESSMENT

R-450A has been submitted to the ASHRAE SSPC 34 committee for classification as an A1 refrigerant, 

and is considered to be nonflammable (Honeywell 2014a). Based on this classification, manufacture, 

servicing, and use of R-450A is not expected to present a flammability risk in household refrigerators and 

freezers and water coolers.

8. ASPHYXIATION ASSESSMENT

The risk of asphyxiation for the reasonable worst-case scenario was investigated for R-450A. In this 

section, risk of asphyxiation is assessed in three ways: 1) modeling the oxygen concentration under the 

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

minimum charge size needed to cause an asphyxiation risk in the room size specified in the worst-case 

scenario 3) performing a threshold analysis of the maximum room size needed to cause an asphyxiation 

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

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, the 

reasonable worst-case scenario 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 6 below.
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Table 6. Asphyxiation Assessmenta,b

Scenario Charge Size (g) Effective Room Size (m3)

Percent Oxygen 

Concentration in 

Lower 0.4 Meters

Reasonable Worst-Case 1 200 18 (640 ft3) 21%

Reasonable Worst-Case 2 1,000 18 (640 ft3) 19%

Threshold Analysis 1: Charge Size 5,640 18 (640 ft3) 12%

Threshold Analysis 2a: Room Size 200 0.64 (22.5 ft3) 12%

Threshold Analysis 2b: Room Size 1,000 3.19 (113 ft3) 12%

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios in which the charge and room sizes evaluated in this risk screen are acceptable according to the 

threshold analysis or the scenarios with acceptable oxygen concentrations, 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.4 Based on the reasonable worst-case scenario modeling, a release of R-450A from

household refrigerators has an insignificant impact on the concentration of oxygen in the air and therefore 

does not present a significant risk of asphyxiation. This modeling does not take into account any 

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

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

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

For the asphyxiation threshold analyses shown in Table 6, the conditions at which an asphyxiation concern 

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

under Threshold Analysis 1, the charge size of the R-450A refrigerator would have to be at least 5,640

grams for asphyxiation to be a concern, which is approximately 5 times the maximum charge size 

anticipated by the submitter. In Threshold Analyses 2a and 2b, the volume of the room would have to be 

.64m3 (22.5 ft

3

) and 3.19m3 (113 ft3) or smaller for asphyxiation to be of concern for units with 200-gram 

and 1,000-gram charge sizes, respectively.

Based on the worst-case modeling results and threshold analysis, EPA does not believe that the use of R450A in household refrigerators and freezers or water coolers poses a significant risk of asphyxiation or 

impaired coordination to end-users or servicing technicians, provided systems are installed in appropriate 

spaces according to guidelines from the manufacturer and the MSDS for R-450A.

9. END-USE EXPOSURE ASSESSMENT

This section presents estimates of potential end-user exposures to R-450A and each of its chemical 

constituents in the event of a catastrophic release from the proposed substitute’s use in household 

refrigerators and freezers and water coolers. An end-use exposure analysis was performed to examine 

potential catastrophic releases of R-450A under the reasonable worst-case scenario outlined in Section 5.

For the end-use exposure assessment scenario, 15-minute TWA exposures for the proposed substitute were 

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

concentrations on a minute-by-minute basis. Estimates for acute/short-term end-use exposures resulting 

from catastrophic leakage of refrigerant from household refrigerators were examined. The analysis was 

undertaken to determine the 15-minute exposures of R-450A, which were then compared to the standard 

toxicity limits presented in Table 4 to assess the risk to end-users. Because HFO-1234ze(E) is present in 

larger concentrations and because it has a lower exposure limit than HFC-134a, Table 7 displays only 

HFO-1234ze(E), the component with greater potential concerns. The estimated TWA values are fairly 

 

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

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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.

Table 7. End-Use Exposure Assessment for HFO-1234ze(E) Componenta

Scenario Charge 

Size (g)

Room Size 

(m3)

Vertical 

Concentration 

Gradient

Duration 

of Release 

(min)

15-min TWA EndUse Exposure 

(ppm)b

Reasonable Worst-Case Scenario 1a

200 18 (640 ft3)

Yes 1 5,970

Reasonable Worst-Case Scenario 1b No 1 994

Reasonable Worst-Case Scenario 1c Yes 15 3,470

Reasonable Worst-Case Scenario 2a

1,000 18 (640 ft3)

Yes 1 29,800

Reasonable Worst-Case Scenario 2b No 1 4,970

Reasonable Worst-Case Scenario 2c Yes 15 17,400

Threshold Analysis 1: Charge Size 80.5 18 (640 ft3)

Threshold Analysis 2a: Room Size 200 44.7 (1,470 ft Yes 1 2,400 3)

Threshold Analysis 2b: Room Size 1,000 224 (7,340 ft3)

Bold font indicates modeling results.

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

b 15-min STEL for HFO-1234ze(E) is 2,400 ppm and ATEL for HFO-1234ze(E) is 59,000 ppm; see Table 4 for more information.

Under the reasonable worst-case scenarios described in Section 5 for household refrigerators, catastrophic 

releases of the typical and maximum charge sizes of R-450A (i.e., 200 grams and 1,000 grams, 

respectively) were modeled. The modeling scenarios evaluate the presence and absence of a vertical 

concentration gradient as well as two refrigerant release time durations (i.e., 1 minute and 15 minutes). The 

anticipated 15-minute TWA exposures of the HFO-1234ze(E) component of R-450A do exceed its STEL

(i.e., 2,400 ppm) for all scenarios except Reasonable Worst-Case Scenario 1b, which does not assume the 

presence of a vertical concentration gradient. Although most of the exposure estimates for the reasonable 

worst-case scenarios exceed the STEL (i.e., 2,400 ppm) (see Table 7), the STEL is a conservativelyderived exposure limit that is intended to protect against risk with a wide safety margin for even the most 

sensitive of populations. All of these exposure estimates are significantly lower than the acute toxicity 

exposure limit (ATEL) of 59,000 ppm for HFO-1234ze(E), which is a refrigerant concentration limit 

intended to reduce the risks of acute toxicity hazards in normally occupied, enclosed spaces according to 

ASHRAE Standard 34. Furthermore, the estimated exposures for R-450A in each of these scenarios are 

also significantly lower than the RCL for R-450A (i.e., 72,000 ppm). 

In addition, these exposure estimates were derived using fairly conservative assumptions (e.g., minimum 

room volume, low ventilation rate) that do not necessarily reflect the actual room attributes where R-450A 

household refrigerators and freezers and water coolers will be installed. Specifically, Reasonable WorstCase Scenarios 1a through 1c model a 200-gram refrigerator, which represents an average refrigerator size

(i.e., 20 – 25 ft3capacity), in a fairly small kitchen size that would likely contain a smaller refrigerator 

(e.g., 10 ft3 capacity). In addition, a 1,000-gram refrigerator represents a high-end, commercial-sized

refrigerator, that is generally installed in large homes (i.e., greater than 5,000 ft2 or 465 m2) and are 

therefore unlikely to be installed in a kitchen with an effective volume of 18 m3(640 ft3). Furthermore, 

kitchen spaces are often connected to other rooms through open pathways without doors (e.g., an eat-in 

space or a dining area in an open floor plan home), which would increase the effective volume of the space 

into which a refrigerant would be released, thereby reducing the likelihood that end-users would be

exposed to modeled concentrations. 

Finally, these exposures represent concentrations of leaked refrigerant in the bottom 0.4 meter (1.3 feet) of 

the room, accounting for 95 percent of the refrigerant charge in this lower portion of the room. The 

probability that an individual would be present in this lower portion (e.g., prone or supine on the floor or 

crawling infant) in the event of the catastrophic release of refrigerant is low.
Final -- October 10, 2014

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To further analyze potential risks of exposure during end-use, threshold analyses were conducted to 

determine the room size and charge size requirements that ensure that the use of R-450A in these end-uses

does not present risk to end-users or servicing technicians. Based on these results, EPA recommends that 

for a minimum room volume of 18 m3, the charge size does not exceed 80.5 grams (see Threshold 

Analysis 1in Table 7), and that for charge sizes of 200 grams and 1,000 grams, the refrigeration unit not be 

installed in a room of effective volume less than 44.7 m3 (1,470 ft3) and 224 (7,340 ft3), respectively (see 

Threshold Analyses 2a and 2b in Table 7).

To prevent exposure and potential serious side effects during larger releases, EPA recommends that the 

proposed RCL for R-450A (i.e., 72,000 ppm or 320 g/m3) is not exceeded in any location where an R450A system is installed, unless proper leak protection devices are in place in order to prevent exposures 

of R-450A beyond the recommended limits. Proper leak protection devices, engineering control 

requirements, and adherence to the MSDS will further ensure that exposure limits are maintained below 

those described in Table 7. 

10. OCCUPATIONAL EXPOSURE ASSESSMENT

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

disposal of R-450A household refrigerators and freezers and water coolers. To ensure that use of the 

proposed substitute in household refrigeration units does not pose an unacceptable risk to workers during 

servicing and disposal, occupational exposure modeling was performed using a box-model approach. For 

a detailed description of the methodology used for this screening assessment, the reader is referred to the 

occupational exposure and hazard analysis described in Chapter 5 of the Background Document.

Estimates of refrigerant release per event for various release scenarios were obtained from the Vintaging 

Model.5 To determine the estimated level of occupational exposure for a constituent in a blend, the total 

anticipated release rate of the refrigerant is multiplied by the weight percent composition of each 

compound in the blend; however, only the exposure concentrations for the HFO-1234ze(E) component are 

shown. For the household refrigerator and freezer and water coolers end-uses, the release per event was 

conservatively assumed to be 0.4 percent of the equipment charge during charging and servicing and 63

percent of the equipment charge during disposal.

6 The release rate per event was multiplied by the number 

of events estimated to occur over a workday. For equipment charging and servicing, the number of events 

per workday was conservatively assumed that eight events of servicing a unit by one servicing technician 

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

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.

 

5

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

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

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

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

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

with the household refrigerators and freezer end-use in Vintaging Model version VM IO file_v4.4_7.29.14. 

6 CARB (2013) estimates an end-of-life loss rate of 63% for domestic refrigerated appliances. A proposed update to EPA’s 

Vintaging Model recommends an end-of-life loss rate of 63% based on this estimate and other assumptions found in recent 

literature. 
Final -- October 10, 2014

12

10.1 Occupational Exposure at Manufacture

HFC-134a is obtained by the submitter from other manufacturers and HFO-1234ze(E) is manufactured by 

the submitter in the United States. During manufacture of the components and blending of R-450A, the 

MSDS for both HFC-134a and HFO-1234ze(E) should be referenced and proper engineering controls and 

PPE used. 

R-450A and its components are not expected to pose a risk to workers during manufacture or blending 

when the engineering controls and PPE recommendations referenced in the MSDS for HFC-134a, HFO1234ze(E), and R-450A are followed. Release points/exposure in chemical manufacturing would typically 

be where temporary lines are connected or disconnected (i.e., filling of portable cylinders and portable 

bulk containers). Refrigerant quality control testing may result in release of de minimus quantities of 

refrigerant, which would typically be to exhaust ducts or fume hoods. Engineering controls should include 

normal and local ventilation (e.g., chemical hoods) and vapor-in-air detection systems for standard 

manufacturing procedures so workers can avoid physical contact with the refrigerant and to achieve 

emission control. In general, use of PPE consistent with OSHA guidelines is recommended, such as 

respiratory protection (including a self-contained breathing apparatus [SCBA] in case of insufficient 

ventilation), tightly sealed goggles, and protective gloves (OSHA 1994).

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

such as hydrogen fluoride and hydrogen chloride if HFC-134a or HFO-1234ze(E) are exposed to high 

temperatures or fire. Other reaction products such as carbon dioxide might also be present. 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 R-450A and its components, 

there is no significant risk to workers during the manufacture of R-450A.

10.2 Occupational Exposure at Charging and Servicing

As indicated by the submitter, household refrigerators and freezers and water coolers would typically be 

charged by the Original Equipment Manufacturer (OEM). During OEM system manufacture (i.e., charging 

at OEM location), points of release for charging and servicing these leak-tight systems would be from 

connection/disconnection of temporary lines for charging and recovery equipment.

During servicing, used refrigerant from R-450A household refrigerators and freezers and water coolers is 

pumped into a canister, where it is stored until it is recycled (i.e., filtered and reused). During the transfer

to the initial canister, incidental refrigerant releases may occur during connection and disconnection of the 

recharging hose fittings (Honeywell 2014a). Isolation and evacuation of lines or equipment prior to 

servicing or repair and the use of compatible seals, gaskets, O-rings, thread sealants, and minimization of 

threaded joints all contribute to limiting releases. The submitter indicated that servicing equipment is 

operated only by trained technicians. Room ventilation, leak monitors, and alarms also minimize exposure. 

Installation and servicing activities for household refrigerators and freezers and water coolers are not 

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

in the R-450A MSDS and maintenance manual, undergo proper training, and wear appropriate PPE (e.g., 

gloves and safety glasses). Nevertheless, the potential occupational exposure during servicing was 

analyzed. The maximum 15-minute time weighted average (TWA) exposures for each R-450A constituent 

were estimated and compared to their respective short-term exposure limits (see Table 8). The modeling 

results indicate that the maximum anticipated occupational exposure concentrations at no point exceed the 

short-term exposure limit for either component.
Final -- October 10, 2014

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Table 8. Occupational Risk Assessment at Servicinga

Component 15-minute TWA Occupational Exposure (ppm) Short Term Exposure 

Charge Size: 200 grams Charge Size: 1,000 grams Limits (ppm)

HFC-134a 0.38 1.9 8,000b

HFO-1234ze(E) 0.47 2.4 2,400c

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios that are deemed to be acceptable given various modeling assumption options.

b 10-minute and 30-minute AEGL-1; see Table 4 for more information.

c EPA-derived 15-minute STEL; see Table 4 for more information.

The estimated exposures were derived using conservative assumptions, and represent a worst-case scenario 

with a low probability of occurrence. These types of systems are typically serviced by trained personnel 

using proper industrial hygiene techniques and using proper engineering controls (e.g., local ventilation, 

refrigerant detectors, and alarm systems). Thus, EPA does not believe that installation or servicing of

household refrigerators and freezers and water coolers containing R-450A presents a significant concern to 

workers.

10.3 Occupational Exposure at Disposal

Disposal of R-450A household refrigerators and freezers and water coolers is expected to occur with 

limited frequency (up to approximately ten disposal events per day) at disposal facilities and with limited 

duration of exposure to the installed 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 9 displays the maximum estimated 8-hour TWA occupational 

exposure levels for each component of R-450A during disposal. Because modeled exposure levels for both 

the typical and maximum charge sizes are significantly lower than the 8-hour exposure limits for each 

component, occupational exposure to the proposed substitute during disposal is not considered a toxicity

risk. Further, estimated exposures were derived using conservative assumptions (e.g., no ventilation or use 

of PPE assumed) and represent a worst-case scenario with a low probability of occurrence. These types of 

systems are typically disposed of by trained personnel using proper industrial hygiene techniques.

Table 9. Occupational Risk Assessment at Disposala

Component 8-hour TWA Occupational Exposure (ppm) 8-Hour Long Term Exposure 

Charge Size: 200 grams Charge Size: 1,000 grams Limits (ppm)

HFC-134a 80.7 403 1,000b

HFO-1234ze(E) 99.7 499 800b

Bold font indicates modeling results.

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

b 8-hour WEEL

Although anticipated occupational exposures are well below the exposure limits for both R-450A 

components for both typical and maximum charge sizes, the recommendations for proper engineering 

controls and PPE in the MSDS for R-450A should be followed. Adequate ventilation should always be 

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

air detection systems and local exhaust ventilation during use of R-450A to prevent dispersion throughout 

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

locations where R-450A 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 R-450A, there is no significant risk to workers during the 

manufacturing, installation, servicing, and disposal of R-450A in household refrigerators and freezers and 

water coolers.
Final -- October 10, 2014

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11. GENERAL POPULATION EXPOSURE ASSESSMENT

R-450A is not expected to cause a significant risk to human health in the general population when

manufactured for use and used as a refrigerant in household refrigerators and freezers and water coolers. 

The proposed substitute will be manufactured in a closed process and is proposed for use in closed 

systems; thus, significant releases are not anticipated. At room temperature, R-450A is a gas and, 

therefore, releases to ground or surface water are not anticipated, as R-450A 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 maintain a high concentration of R-450A). Should air releases during 

manufacturing operations occur, engineering controls should be used (e.g., carbon absorption scrubbers) to 

collect R-450A and prevent the release of R-450A 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 R-450A is not expected to pose a significant toxicity risk to the 

general population.
Final -- October 10, 2014

15

12. REFERENCES

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.

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.

Hodnebrog, Ø., Etminan, M., Fuglestvedt, J. S., Marston, G., Myhre, G., Nielsen, C. J., Shine, K. P., 

Wallington, T. J. 2013. Global Warming Potentials and Radiative Efficiencies of Halocarbons and 

Related Compounds: A Comprehensive Review, Reviews of Geophysics, 51, 300-378, 

doi:10.1002/rog.20013.

Honeywell, Inc. 2014a. Solstice® N-13 (R-450A) in Household Refrigerators and Freezers and Water 

Coolers. Significant New Alternatives Policy Program Submission to the United States Environmental

Protection Agency. May 2014.

Honeywell, Inc. 2014b. Response to Incompleteness Letter for Solstice® N-13 (R-450A) Significant New 

Alternatives Policy Program Submission to the United States Environmental Protection Agency. August 

11, 2014.

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

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

London, CT.

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.

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

http://www.epa.gov/oppt/aegl/pubs/define.htm.
Final -- October 10, 2014

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

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