March 29, 2016 – Final 

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Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector 

Risk Screen on Substitutes in Very Low Temperature Refrigeration 

Substitutes: Ethane (R-170) and Propane (R-290) 

This risk screen is restricted to very low temperature (VLT) refrigeration applications covered 

under UL 471: Commercial Refrigerators and Freezers. 

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

and, therefore, may be disclosed to the public. Brackets [ ] represent redacted CBI content. 

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 ethane (R-170) and propane (R-290) as substitutes in very low temperature 

(VLT) refrigeration, specifically in VLT freezers. VLT refrigeration systems require maintaining 

temperatures at approximately -86°C (-176°F) or lower. This type of equipment requires extremely reliable 

refrigeration cycles to maintain low temperatures and must meet stringent technical standards that do not 

typically apply to refrigeration systems (EPA 2013). Table 1 presents the composition of the proposed 

substitute. 

Table 1. Composition of Ethane and Propane 

Constituent Chemical Formula CAS Number Concentration

(Weight Percent)a

Ethane (R-170) C2H6; CH3CH3 74-84-0 >99% 

Propane (R-290) C3H8 74-98-6 >99.7% 

a

 Negligible amounts of impurities may be present.

Section 2 of this report summarizes the results of the risk screen for the proposed substitute. The remainder 

of the risk screen is organized into the following sections: 
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• Section 3: Atmospheric Assessment 

• Section 4: Volatile Organic Compound Assessment 

• Section 5: Discussion of End-Use Scenarios Modeled 

• Section 6: Potential Health Effects 

• Section 7: Flammability Assessment 

• Section 8: Asphyxiation Assessment 

• Section 9: End-Use Exposure Assessment 

• Section 10: Occupational Exposure Assessment 

• Section 11: General Population Exposure Assessment 

• Section 12: References

2. SUMMARY OF RESULTS 

Ethane and propane are recommended for SNAP approval for use in VLT freezers, included under 

Underwriters Laboratory (UL) Standard 471: Commercial Refrigerators and Freezers. Ethane is currently 

SNAP-approved as a refrigerant in VLT freezers.1 This risk screen evaluates the use of ethane and propane 

in a two-stage cascade refrigeration system and also recommends propane as an acceptable refrigerant for 

use in VLT freezers, whether using a single refrigeration cycle or in a two-stage system. EPA’s risk screen 

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

use of ODS other commonly used refrigerants as they are less harmful to the ozone layer, have lower 

climate impact, and shorter atmospheric lifetimes. No significant asphyxiation risks to personnel or toxicity 

risks to workers, personnel, or the general population are expected. Ethane’s contribution to volatile organic 

compound (VOC) emissions is not significant, as ethane is exempt under CAA regulations (40 CFR 

51.100(s)). Although propane is regulated as a VOC, VOCs from the use of propane are not anticipated to 

result in greater impacts on local air quality in the United States than other available options based on 

analysis of potential propane emissions. 

It is expected that procedures in the safety data sheets (SDS) for ethane and propane and good 

manufacturing practices will be adhered to. Additionally, it is expected that the appropriate safety and 

personal protective equipment (PPE) (e.g. protective gloves, tightly sealed goggles, protective work 

clothing, and suitable respiratory protection in case of leakage or insufficient ventilation) consistent with 

Occupational Safety and Health Administration (OSHA) guidelines will be used during manufacture, 

installation and servicing, and disposal of VLT freezers using ethane and propane. Because units are to be 

installed in locations with adequate space or ventilation in accordance with the VLT freezer manual for 

ethane and propane, as discussed in greater detail in Section 9, significant toxicity or flammability risk to 

workers is also unlikely. 

Additional safeguards, including the refrigerant concentration limits (RCL) for ethane and propane, are 

provided in industry standards such as American Society of Heating, Refrigerating and Air-Conditioning

Engineers (ASHRAE) Standards 15,2

 34,3 and 624 and Underwriters Laboratory (UL) Standard 471.5 The 

RCL for a refrigerant is intended to reduce the risks of acute toxicity, asphyxiation, and flammability 

 

1

 Ethane was listed as acceptable for use, subject to use conditions, in very low temperature refrigeration equipment on April 10, 

2015 (80 FR 19454). 

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

prescribes safety requirements. 

3 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. 

4 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. 

5 UL 471 Standard for Commercial Refrigerators and Freezers establishes safety requirements for the construction, electrical 

system, electrical components, refrigeration system, and performance of commercial refrigerators and freezers. 
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hazards in normally occupied, enclosed spaces. This and other exposure terminology are defined in Section 

6.

3. ATMOSPHERIC ASSESSMENT 

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

and propane in VLT freezers. The ozone depletion potential (ODP), global warming potential (GWP), and 

atmospheric lifetime (ALT) of the proposed substitutes are presented in Table 2. The proposed substitutes 

are substantially less harmful to the ozone layer, have a lower climate impact, and shorter atmospheric 

lifetimes when compared to refrigerants currently used in these end-uses, such as CFC-12, CFC-13, R13B1, and R-503. In addition, ethane and propane have lower climate impacts and shorter atmospheric 

lifetimes than other utilized VLT refrigerant substitutes, such as R-508B and HFC-23. 

Table 2. Atmospheric Impacts of Ethane and Propane Compared to Other VLT Refrigerants 

Refrigerant Ozone Depleting Potential 

(ODP)a 

Global Warming Potential

(GWP)b 

Atmospheric Lifetime in 

Years (ALT)b 

Ethane 0 6

c 0.17d 

Propane 0

b 3 0.03a

R-13B1 (Halon 1301) 15.9 7,140 65

CFC-12 0.82 10,900 100

CFC-13 1 14,400 640

R-503 0.599 14,560 NAe

R-508B 0 13,396 NAf 

HFC-23 0 14,800 270

a

 World Meteorological Organization (WMO) 2010 Scientific Assessment Report (2011) 

b

 Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (Forster et al. 2007), unless otherwise noted. 

c

 Global Cooling Inc. (2012) 

d

 Gonzalez et al. (2011) 

e

 R-503 is a blend consisting of CFC-13 (60%) and HFC-23 (40%). The ALT for CFC-13 is 640 years and the ALT for HFC-23 is 270 years. 

f

 R-508B is a blend consisting of HFC-23 (46%) and perfluoroethane (PFC-116) (54%). The ALT for HFC-23 is 222 years and the ALT for PFC116 is 10,000 years. 

4. VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS 

Ethane is exempt from the definition of VOC under CAA regulations (40 CFR 51.100(s)). Therefore, 

environmental impacts from the release of ethane as a VOC are not a significant concern. 

Propane is regulated as a VOC under CAA regulations (40 CFR 51.100 [s]). Emissions of propane should 

be controlled according to CAA and other regulations by adhering to standard industry practices. 

EPA prepared a separate analysis in 20146

 and a follow-on analysis in 20167 to evaluate the potential 

impact of the use of hydrocarbon refrigerants on ground-level ozone concentrations in the United States. 

These analyses estimated refrigerant emissions from refrigeration and air conditioning equipment, which 

were assumed to contain propylene, isobutane, and/or propane8 under different scenarios and compared 

their resulting relative increases in ozone concentrations against the National Ambient Air Quality Standard 

(NAAQS) for ozone of 70 ppb.9

 Under the most conservative scenario it was assumed that propylene was 

used in all refrigeration and air conditioning equipment. In more realistic scenarios, all three hydrocarbons 

(and/or blends thereof) were assumed to be used in certain types of refrigeration and air conditioning

 

6 Assessment of the Potential Impact of Hydrocarbon Refrigerants on Ground Level Ozone Concentrations (February 2014) [EPAHQ-OAR-2013-0748-0003] 

7 Follow-on Assessment of the Potential Impact of Hydrocarbon Refrigerants on Ground Level Ozone Concentrations (March 2016)

8 EPA uses the maximum incremental reactivity (MIR) of ethane (0.28 g-O3/g-substance) as the threshold for determining whether a 

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

to be reactive compounds and are therefore subject to VOC regulations.

9 On October 1, 2015, EPA strengthened the NAAQS for ground-level ozone to 70 ppb from 75 ppb, based on scientific evidence 

about ozone’s effects on public health and welfare (EPA 2015).
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equipment, depending on the proposed use of each alternative under submissions received by the SNAP 

program at the time of the analysis. 

End-uses in the evaluation included a number of types of smaller, self-contained refrigeration and room airconditioning units for which SNAP hydrocarbon applications have been received and/or UL Standards 

covering flammable refrigerants exist.10 The hydrocarbon emissions from these scenarios were estimated 

based on EPA’s Vintaging Model, and their potential contributions to ozone concentrations were assessed 

using EPA’s Community Multiscale Air Quality (CMAQ) model.11 

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

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

ozone concentrations were estimated for the Atlanta, Houston, and Los Angeles regions, due to their 

distinctive geographic setting and chronic high levels of ground-level ozone, and then scaled for national 

emission estimates. 

The results of the CMAQ modeling indicated that under the most conservative case which assumed that the 

most reactive hydrocarbon, propylene, was used in all refrigeration and air conditioning equipment, there 

could be an incremental maximum increase of the 8-hour average as high as 7.8 ppb ozone in 2040.By 

comparison, the most realistic scenario, in which a mixture of hydrocarbon refrigerants are used, refrigerant 

emissions could potentially increase the maximum 8-hour average ground-level ozone by no more than 2.5

ppb in 2040 in Los Angeles, the city with the greatest ozone problem. 

This upper bound level of increase for the realistic scenario is not likely, as most ozone nonattainment areas 

are not VOC-limited (i.e., the formation of ozone in these areas is not limited by VOC emissions, but by 

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

refrigerants which will also likely be used in refrigeration and air conditioning end-uses along with 

hydrocarbon refrigerants. Based on the results of this analysis, VOC emissions from the use of propane in 

VLT refrigeration are not anticipated to contribute significantly to ground level ozone concentrations in the 

United States. 

5. DISCUSSION OF END-USE SCENARIOS MODELED 

Ethane has already been SNAP-approved for use in VLT freezers. Based on the application provided by the 

submitter, this risk screen evaluates the use of both ethane and propane in a two-stage cascade VLT 

refrigeration system. This risk screen also covers the use of propane in VLT using a single refrigeration 

cycle. 

[ ]

The submission states that the VLT freezers will typically contain 98 grams of ethane and 120 grams of

propane (Eppendorf 2015), with a maximum charge size of 150 grams per refrigerant loop according to UL

Standard 471. Both the typical (i.e., 98 grams and 120 grams) and maximum (i.e., 150 grams) charge sizes 

are modeled in this risk screen. 

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

while the VLT freezer is installed at the end-use. VLT freezers are typically used in bio-repositories, 

pharmaceutical production facilities, and university laboratories. In these locations, the freezers are 

typically clustered side by side, spaced 25.4 centimeters (10 inches) apart and in laboratory rooms with 3.0-

meter (10-foot) ceilings (Carnegie Mellon University 2007). A typical laboratory module has a minimum 

width of approximately 10 feet, but will vary in length based on the number of modules configured in a

 

10 VLT refrigeration was not included as an end-use in the CMAQ modeling assessment. Because the incremental changes in 

ground-level ozone were insignificant between all modeled refrigeration and air-conditioning equipment, use in VLT refrigeration 

is not expected to significantly affect the estimated impact on ground-level ozone concentration. 

11 VM version VM_IO file_v4.4_10.13.14 and CMAQ model version 5.0.2 were used in this analysis.
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row, typically ranging up to an ideal length of approximately 33 feet long (National Institutes of Health 

2008). Therefore, the analysis in this risk screen conservatively assumes that the VLT freezer is installed in 

one laboratory module that is approximately 3.0 meters (10 feet) wide, 3.0 meters (10 feet) long, and 3.0 

meters (10 feet) high, which corresponds to an effective volume of 28 m3 (1,000 ft3), with an effective floor 

area of 9.3 m2 (100 ft2) (i.e., excluding the space filled by the freezers and other items in the laboratory). 

Under the reasonable worst-case scenario, the full charge of both refrigerant loops in the unit are assumed 

to be emitted over the course of one minute into the laboratory with 4 air changes per hour (ACH) (E.O. 

Lawrence Berkeley National Laboratory 2013). It is not likely that the two refrigerants would mix in the air 

during release, because the refrigerants have different densities relative to air. Ethane has approximately the 

same density as air (specific gravity of ethane relative to air is 1.05 [air = 1]), and, therefore, when the full 

charge is released, the proposed substitute is expected to disperse evenly and immediately throughout the 

room. Propane is denser than air (specific gravity of propane relative to air is 1.52 [air = 1]), so it will settle 

in higher concentrations closer to the ground. Therefore, a vertical concentration gradient is assumed in the 

worst-case scenarios for propane. It was assumed that an individual is present at the start of the leak and 

remains in the room until the charge is completely released. Table 3. End-Use Scenario Model 

AssumptionsTable 3 details the assumptions in the models throughout this risk screen (i.e., in Sections 7, 8, 

9, and 10). 

Table 3. End-Use Scenario Model Assumptions 

Parameter Assumption

Refrigeration Unit VLT Freezer

Room Laboratory Module 

Charge Sizes (g) Ethane: 98a and 150b

Propane: 120a and 150b

Length of Release (minutes) 1

Effective Room Size (volume - m3) 28 (1,000 ft3)

Room Ventilation (ACH) 4

c 

Vertical Concentration Gradient Yesd

a

 Eppendorf (2015) 

b

 UL 471 

c E.O. Lawrence Berkeley National Laboratory (2013) 

d

 Propane only. 

EPA recognizes that VLT freezers may be placed in a variety of room types with different sizes and 

ventilation rates. In addition, more than one VLT freezer may be installed in the same space, as the units are 

fairly small with a typical volume of 1.71 m3 (60 ft3) and dimensions of 1.0 m x 0.87 m x 2.0 m (3.3 ft x 2.9 

ft x 6.6 ft), which is similar in capacity to a household refrigerator (Eppendorf 2016). When units are 

installed in smaller, enclosed spaces, there is a higher risk for flammability, asphyxiation, or toxicity 

concerns. To address these concerns, this risk screen incorporates threshold analyses in addition to the 

reasonable worst-case scenario modeling. The results from the threshold analyses are used to establish

guidelines for choosing an effective room size and charge size such that use of ethane and propane in VLT 

freezers does not present risk to end-users or servicing technicians. 

6. POTENTIAL HEALTH EFFECTS 

To assess potential health risks from exposure to the proposed substitutes in VLT freezers, EPA identified 

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

scenarios. To protect consumers from the potential dangers of a catastrophic refrigerant leak from a VLT 

freezer, ASHRAE Standard 34 determined RCLs to reduce the risks of acute toxicity, asphyxiation, and 

flammability hazards in occupied spaces (ASHRAE 2010b). ASHRAE Standard 15 implements the 

aforementioned standard, requiring that “the concentration of refrigerant in an enclosed space following a 

complete discharge of a high-probability system shall not exceed the RCL” (ASHRAE 2010a). As such, this 
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risk screen references the RCL in addition to the lower flammability limit, hypoxia No Observed Adverse 

Effect Level (NOAEL), and exposure limits, as an additional, conservative limit to ensure that significant 

flammability, asphyxiation, and end-use exposure risks, respectively, do not occur. 

For the occupational exposure analysis, potential risks from chronic worker exposure to ethane and propane 

concentrations were evaluated by comparison to the workplace guidance level (WGL). In the absence of an 

established short-term exposure level (STEL), acute exposure guideline level (AEGL), or an emergency 

response planning guideline (ERPG), potential short-term, end-use exposures to ethane was compared to its 

excursion limit.12 Table 4 lists the relevant toxicity limits for ethane and propane, followed by Table 5 

which describes each of these exposure limits in more detail. EPA’s approach for identifying or developing 

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

Table 4. Exposure Limits of Ethane and Propane 

Alternative 

Workplace Guidance Limit 

(Long-term Exposure) 

ppm 

Excursion Limit 

(Short-term Exposure) 

ppm 

Refrigerant 

Concentration 

Limit (RCL) ppma

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

 (30-min ACGIH Excursion Limit) 

2,900d

 (15-min TEEL-1) 7,000 

Propane 1,000e (OSHA PEL/NIOSH REL) 10,000f,g (10-min AEGL-1) 

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

An explanation of each exposure limit and exposure-limit related terminology is described in Table 5. 

a ASHRAE (2010b)

b

 ACGIH (2012) 

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

d DOE (2008) 

e

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

f 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. 

g

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

Table 5. Explanation of Exposure Limit-Related Terminologya 

Organization Definition

OSHA Occupational Safety and Health Administration

NIOSH National Institute for Occupational Safety and Health

ACGIH American Conference of Governmental Industrial Hygienists

AIHA American Industrial Hygiene Association

Exposure Limit Definition Explanation

Short-Term Exposure

STEL Short-Term Exposure Limit A 15-minute TWA exposure that should not be exceeded at any 

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

TWA, set by ACGIH. 

AEGLb,c 

Acute Exposure Guideline Level 1 AEGL-1 is the airborne concentration (expressed as 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 

 

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

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

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

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

emergency exposure limit for ethane (3,500 mg/m3 or 2,900 ppm 15-min TWA), which applies to the general population. 
March 29, 2016 – Final 

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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 lifethreatening health effects or death. 

ERPG

Emergency Response Planning 

Guideline 1 

The maximum airborne concentration below which it is believed 

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

experiencing other than mild transient health effects or perceiving a 

clearly defined, objectionable odor according to AIHA. 

Emergency Response Planning 

Guideline 2 

The maximum airborne concentration below which it is believed 

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

experiencing or developing irreversible or other serious health 

effects or symptoms which could impair an individual's ability to 

take protective action according to AIHA. 

Emergency Response Planning 

Guideline 3 

The maximum airborne concentration below which it is believed 

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

experiencing or developing life-threatening health effects according 

to AIHA. 

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

butane) does not have a TLV-short-term exposure limit, an 

excursion limit may be applied. Excursions in worker exposure 

levels may exceed 3 times the TLV-TWA for no more than a total of 

30 minutes during a workday, and under no circumstances should 

they exceed 5 times the TLV-TWA, provided that the TLV-TWA is 

not exceeded according to ACGIH. 

IDLH Immediately Dangerous to Life and 

Health 

If exposed to this concentration, room occupants are expected to 

be able to escape the room within 30 minutes without experiencing 

escape-impairing or irreversible health effects. 

TEELe 

Temporary Emergency Exposure 

Limit 1 

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

believed nearly all individuals could be exposed without 

experiencing other than mild transient adverse health effects or 

perceiving a clearly defined, objectionable odor. 

Temporary Emergency Exposure 

Limit 2 

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

believed nearly all individuals could be exposed without 

experiencing or developing irreversible or other serious health 

effects or symptoms that could impair their abilities to take 

protective action. 

Temporary Emergency Exposure 

Limit 3 

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

believed nearly all individuals could be exposed without 

experiencing or developing life-threatening health effects. 

RCL Refrigerant Concentration Limit The RCL for a refrigerant is intended to reduce the risks of acute 

toxicity, asphyxiation, and flammability hazards in normally 
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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. 

Long-Term Exposure

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

OSHA. 

TLV-TWA Threshold Limit Value –TimeWeighted Average The TWA concentration for a conventional 8-hour workday and a 

40-hour workweek, to which it is believed that nearly all workers 

may be repeatedly exposed, day after day, for a working lifetime 

without adverse effect according to ACGIH. 

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

b EPA (2012) 

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

d

 ACGIH (2004) 

e

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

or toxicology parameters (DOE 2008). 

According to the respective SDS for ethane and propane, exposure to ethane or propane may be hazardous

if inhalation, skin contact, or eye contact with the proposed substitutes occurs. The most likely pathway of 

exposure is through inhalation. Ethane and propane can cause symptoms of asphyxiation when present in 

concentrations high enough to significantly lower oxygen concentrations below 19.5 percent by volume, 

such as headaches, ringing in ears, dizziness, drowsiness, nausea, vomiting, depression of all senses, and 

also unconsciousness. Under some circumstances of over-exposure (i.e., oxygen levels fall below 6 percent 

by volume), death may occur. 

If ethane or propane is inhaled, person(s) should be immediately removed from the contaminated space and 

exposed to fresh air. In accordance with the SDS, EPA further recommends that if breathing is difficult or 

irregular, person(s) should be given oxygen, provided a qualified operator is present, and medical attention 

be sought. Exposures of ethane or propane to the skin may cause frostbite. In the case of dermal exposure, 

the SDS for ethane and propane 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 ethane or propane to the eyes could cause eye irritation. In case of 

ocular exposure, the SDS for ethane and propane recommends that person(s) immediately flush the eyes, 

including under the eyelids, with copious amounts of water for 15 minutes. 

EPA’s review of the human health impacts of the proposed substitutes is contained in the public docket for 

this decision. The potential health effects of ethane and propane can be minimized by following the 

exposure guidelines and ventilation and PPE recommendations outlined in the SDS for ethane and propane

and this risk screen. 

7. FLAMMABILITY ASSESSMENT 

ASHRAE Standard 34 classifies ethane and propane as Class A3 refrigerants. Ethane is flammable when its 

concentration in the air is in the range of between 3.0 percent and 12.5 percent by volume (30,000 ppm to 

125,000 ppm) and propane is flammable when its concentration in air is in the range of 2.1 percent to 9.5 

percent by volume (21,000 ppm to 95,000 ppm). In the presence of an ignition source (e.g., static 

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

when the concentration of ethane or propane exceeds their respective lower flammability limits (LFL) of 

30,000 ppm or 21,000 ppm, posing a significant safety concern for workers and personnel if they are not 
March 29, 2016 – Final 

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handled carefully. Only refrigerant technicians certified to work with flammable refrigerants should handle 

VLT units containing ethane and propane during manufacturing, installation, servicing, and disposal. The 

remainder of this section assesses the flammability risks and summarizes the recommended measures to 

ensure safe handling and use of the refrigerant during servicing, disposal, and end-use. 

7.1 Flammability Risk during Manufacture 

In production facilities or other facilities where large quantities of the refrigerant will be stored, proper 

safety precautions should be in place to minimize the risk of explosion. As indicated by the submitter, the 

proposed substitute is purchased by a third-party supplier and not manufactured on site. However, 

Eppendorf manufactures the very low temperature freezers and, during the final stage of freezer 

manufacture, the two refrigerant stages are filled with the proposed substitutes. [ ] Any release of refrigerant 

is expected to take place during this filling activity which is assumed to occur in a factory area with proper 

ventilation rates. 

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

minimize the likelihood of catastrophic releases. VLT freezers installed with ethane and propane should be 

clearly labeled as containing a flammable refrigerant. EPA believes that because relevant safety standards, 

the SDS for ethane and propane, and OSHA requirements under 29 CFR 1910 (e.g., proper ventilation and 

storage practices within manufacturing facilities to prevent fire and explosion) are followed by workers, 

flammability during manufacture is not a concern. 

7.2 Flammability Risk during Servicing and End-Use 

The risk of flammability during servicing and end-use for the reasonable worst-case scenario (see Section 5) 

was investigated for ethane and propane. Both servicing and end-use of VLT freezers charged with ethane 

and propane are expected to take place in the same location. During servicing, the proposed substitute is 

expected to be recovered using recovery equipment designed specifically for flammable hydrocarbon 

refrigerants (i.e., equipped with flammable gas leak detectors and monitors and without potential sources of 

ignition) with sufficient onboard storage capacity and suitable for the refrigerant in terms of the pressure 

rating and compatibility of valve seals (GIZ 2010).

The submitter indicates that the substitutes will be recovered using approved recovery equipment and the 

amount released during recovery operation will be a fraction of a gram (Eppendorf 2015). In order to 

determine the potential flammability risks during servicing or end-use in case of a catastrophic release of 

refrigerant in the laboratory module, concentrations of ethane and propane immediately following a 

complete release of both refrigerants, were compared to the lower flammability limit (LFL) for ethane 

(30,000 ppm) and propane (21,000 ppm). Table 6 presents the results of the analysis. 

Table 6. Flammability Assessmenta

Scenario Substitute Charge 

Size (g) 

Effective Room 

Size (m3) 

Maximum Instantaneous 

Concentration 

 (ppm)b,c 

Reasonable Worst-Case 1 Ethane 98 28 (1,000 ft3) 2,800 

Propane* 120 17,800 

Reasonable Worst-Case 2 Ethane 150 28 (1,000 ft3) 4,280 

Propane* 150 22,200 

Threshold Analysis 1: Charge Size 

Ethane 142 

 28 (1,000 ft3) 

4,040 

Propane* 142 21,000 

Threshold Analysis 2a: Room Size Ethane* 98 24 (840 ft3) 3,300 

Propane* 120 21,000 

Threshold Analysis 2b: Room Size Ethane 150 30 (1,050 ft3) 4,040 

Propane* 150 21,000 
March 29, 2016 – Final 

10 

Bold font indicates modeling results. 

*Vertical concentration gradient is assumed. 

a

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

b

 Lower Flammability Limits for ethane and propane are equal to 30,000 ppm and 21,000 ppm, respectively. 

c Values provided in these columns refer to the concentration in entire room because a vertical concentration gradient is not assumed. In this 

scenario, 100% of the charge size leaks. The air flow rate is 4 ACH. 

d

 Because ethane and propane have different LFLs, the threshold analyses were based on the propane concentration reaching the LFL (i.e., 

21,000 ppm). 

As demonstrated in Table 6, the maximum instantaneous concentrations of ethane and propane in the entire 

room at the typical charge sizes (i.e., 98 grams of ethane and 120 grams of propane) would be 

approximately 2,800 ppm and 17,800 ppm, respectively. At the maximum charge size (i.e., 150 grams of 

each refrigerant), the maximum instantaneous concentrations of ethane and propane in the room would be

approximately 4,280 ppm and 22,200 ppm, respectively (Reasonable Worst-Case Scenario 2). Under 

Reasonable Worst-Case Scenario 2, the maximum instantaneous concentration of ethane is significantly 

below the LFL for ethane, while the modeled concentration for propane is slightly greater (approximately 6 

percent) than the LFL for propane. However, the estimated exposures were derived using conservative 

assumptions, and represent a worst-case scenario with a low probability of occurrence, as the analysis

assumes the minimum required laboratory ventilation rate and does not consider opened windows, fans 

operating, or other variables that would reduce the concentration levels in the air. Therefore, under the 

reasonable worst-case scenarios, ethane and propane are not expected to present a significant risk of 

flammability. Given these results, it is not expected that propane used in a single refrigeration loop in this 

end-use will present a significant risk of flammability. 

EPA also performed threshold analyses to determine the minimum room size in which a VLT freezer 

should be installed for flammability to not be of concern. Because ethane and propane have different LFLs, 

the threshold analyses were based on the propane concentration reaching the LFL (i.e., 21,000 ppm), which 

is the more conservative value. 

• The results of Threshold Analysis 1 indicate that for flammability to be of concern within an 

effective room size of 28 m3

, the total charge size should be at least 284 grams (or 142 grams per 

refrigerant circuit). 

• As shown in Threshold Analyses 2a and 2b, an individual VLT freezer with typical charge sizes (98 

grams of ethane and 120 grams of propane) and maximum charge sizes (150 grams of both ethane 

and propane) should not be placed in a room smaller than 24 m3 (840 ft3) or 30 m3 (1,050 ft3), 

respectively. 

Although the results of Threshold Analysis 1 equate to individual circuit charge sizes less than the 

maximum allowable charge size and the results of Threshold Analysis 2b equates to a room size larger than 

that in the reasonable worst-case scenario, the results were derived using conservative assumptions as

mentioned above. Furthermore, it is extremely unlikely that the entire charge of both refrigerant circuits 

would accidentally and simultaneously release into the space. [ ] 

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

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

guidelines for handling propane. Therefore, these guidelines should be acknowledged and followed to 

mitigate flammability risk. The installation of leak prevention devices would further protect against the very 

limited risk of explosion. 

EPA also recognizes that multiple VLT freezers may be used in one room as the submitter states that 

anywhere from one to two units to hundreds of VLT freezers are likely to be installed side-by-side in 

laboratories and other proposed end-use locations. However, a scenario in which more than one unit leaks 

simultaneously is extremely unlikely and therefore does not pose any additional flammability risk. 

ASHRAE Standard 34 also more conservatively recommends that the RCLs for ethane (8.7 g/m3

 or 7,000 

ppm by volume) and propane (9.5 g/m3 or 5,300 ppm by volume) should not be exceeded. Thus, EPA 
March 29, 2016 – Final 

11 

believes that when VLT freezer units are installed in spaces that are consistent with manufacturer 

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

risk is not a significant concern. End-users, however, should still ensure that there is adequate space (i.e., 

the effective volume of the room should be larger than 24 m3 or 30 m3), depending on the charge size of the 

VLT freezer (see Table 6) and ventilation in any room where the VLT freezers are installed to mitigate the 

risk of fire or explosion resulting from a catastrophic leak during end-use or servicing activities. 

Catastrophic releases of large quantities of refrigerant, especially in areas where refrigerant is stored, could 

lead to an explosion in the presence of an ignition source. For this reason, it is important that only properly 

trained and certified technicians handle ethane and propane. As a further precaution, certification 

requirements and training programs for technicians that handle ethane and propane should be developed 

using these guidelines. 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. In addition, VLT freezers 

installed with ethane and propane should be clearly labeled as containing flammable refrigerants. Because 

relevant safety standards and the SDS for ethane and propane are followed by service technicians and 

because these refrigeration units will be installed in areas with adequate space and ventilation, EPA believes 

that flammability during servicing and end-use is not expected to be of concern. 

8. ASPHYXIATION ASSESSMENT 

The risk of asphyxiation for the reasonable worst-case scenarios described in Section 5 were investigated 

for ethane and propane. In this section, risk of asphyxiation is assessed in three ways: 

1) modeling the oxygen concentration under the charge size and room size specified in the worstcase scenario, 

2) performing a threshold analysis of minimum charge size at which an asphyxiation risk could 

occur in the room size specified in the worst-case scenario (i.e., charge sizes greater than this are 

expected to cause an asphyxiation risk), and 

3) performing a threshold analysis of the maximum room size at which an asphyxiation risk could 

occur with the charge size specified in the worst-case scenario (i.e., room sizes smaller than this are 

expected to cause an asphyxiation risk). 

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 7 below. 

Table 7. Asphyxiation Assessmenta

Scenario Substitute Charge Size 

(g) 

Effective Room 

Size (m3) 

Percent Oxygen 

Concentration in 

Roomb

Reasonable Worst-Case Ethane 98 28 (1,000 ft3) 20 Propane 120 

Reasonable Worst-Case Ethane 150 28 (1,000 ft3) 20 Propane 150 

Threshold Analysis 1: Charge Size Ethane 1,100 28 (1,000 ft3) 12 Propane 1,940 
March 29, 2016 – Final 

12 

Threshold Analysis 2a: Room Size 

Ethane 98 

0.34 (12 ft3) 12 

Propane 120 

Threshold Analysis 2b: Room Size Ethane 150 0.48 (17 ft3) 12 

Propane 150 

 Bold font indicates modeling results. 

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

 b The typical concentration of oxygen in air is considered to be 21 percent (Mackenzie & Mackenzie 1995). 

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

reduced to 12 percent.13 Based on the worst-case scenario modeling assumptions, ethane and propane in a 

VLT freezer have an insignificant impact on the concentration of oxygen in the air and therefore do not 

present a significant risk of asphyxiation. Given these results, it is expected that propane used in a single 

refrigeration loop in this end-use will also present an insignificant 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 personnel is likely to be even smaller than modeled. 

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

would exist were determined. 

• As shown under Threshold Analysis 1, the charge sizes of ethane and propane in a VLT freezer in a 

28 m3 room would have to be at least 1,100 grams and 1,940 grams, respectively, for asphyxiation 

to be a concern, which is more than seven times greater than the maximum charge size proposed by 

UL (i.e., 150 grams). 

• Using the typical charge sizes of 98 grams and 120 grams for ethane and propane, respectively, as 

shown under Threshold Analysis 2a, the volume of the room would have to be approximately 0.34 

m3 (12 ft3), or approximately 80 times smaller than the modeled laboratory volume for asphyxiation 

to be of concern. 

• Using the charge size of 150 grams for both ethane and propane, as shown under Threshold 

Analysis 2b, the volume of the room would have to be approximately 0.48 m3 (17 ft3), or 

approximately 58 times smaller than the modeled laboratory volume for asphyxiation to be of 

concern. 

The space where a VLT freezer containing ethane and propane is installed must allow for adequate room for 

end-users to access the machine. To further prevent risk of asphyxiation, end-users should ensure that there 

is adequate space accounting for other appliances, furniture, or storage (i.e., the effective volume of the 

room should be larger than 0.35 m3 or 0.48 m3, depending on the charge size of the refrigeration unit [see 

Table 7]) and ventilation (in accordance with the SDS for ethane and propane) in any room where the VLT 

freezers are installed. Additionally, adherence to ASHRAE 34, which provides more conservative 

concentration limits, will ensure that asphyxiation is not a risk. Minimum room sizes according to the RCL 

stated in ASHRAE 34 can be found in Section 6. Because VLT freezers are unlikely to be installed in 

spaces where full release of ethane and propane would displace enough oxygen to cause asphyxiation, EPA 

does not believe that the use of ethane and propane in VLT freezers with either the typical or maximum

charge sizes poses a significant risk of asphyxiation or impaired coordination to laboratory personnel. 

9. END-USE EXPOSURE ASSESSMENT 

This section presents estimates of potential personnel exposures to ethane and propane during use of VLT 

freezers. Personnel exposure analysis was performed to determine acute/short-term laboratory personnel

exposures resulting from potential catastrophic leakage of refrigerant from VLT freezers. The analysis was 

undertaken to determine the 30-minute TWAs for ethane and propane, which were compared to the 30-min 

 

13 Twelve percent oxygen in air is the No Observed Adverse Effect Level (NOAEL) for hypoxia (ICF 1997).
March 29, 2016 – Final 

13 

Excursion Limit for ethane and STEL for propane. The results of the end-use exposure assessment are 

presented in Table 8 to assess the risk to personnel. The estimated exposures were derived using 

conservative assumptions, and represent a worst-case scenario with a low probability of occurrence, as the 

analysis assumes the minimum required laboratory ventilation rate and does not consider opened windows, 

fans operating, or other variables that would reduce the levels to which individuals would be exposed. 

Table 8. End-Use Exposure Assessmenta

Scenario Substitute Charge 

Size (g) 

Effective Room 

Size (m3) 

30-min TWA End-Use 

Exposure (ppm)b,c 

Reasonable Worst-Case 1 Ethane 98 28 (1,000 ft3) 1,570 

Propane* 120 2,560 

Reasonable Worst-Case 2 Ethane 150 28 (1,000 ft3) 2,400 

Propane* 150 3,200 

Threshold Analysis 1: Charge Size Ethane 187 28 (1,000 ft3) 3,000 

Propane* 187 4,000 

Threshold Analysis 2a: Room Size 

Ethane 98 

10 (360 ft3) 

4,200 

Propane* 120 6,900 

Threshold Analysis 2b: Room Size Ethane 150 22 (790 ft3) 3,000 

Propane* 150 4,000 

*Vertical concentration gradient is assumed. 

Bold font indicates modeling results.

a

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

b See Table 4 for more information. 

c

 The limiting factor in each threshold analysis scenario was assumed to be the most conservative component (e.g., greatest charge size in 

Threshold Analysis 2a and lowest exposure limit in Threshold Analysis 2b). 

Under the reasonable worst-case scenario described in Section 5, catastrophic releases of ethane and 

propane from a VLT freezer with typical charge sizes (98 grams of ethane and 120 grams of propane) and

maximum charge sizes (150 grams of both ethane and propane) were modeled. The modeling indicates that 

the maximum anticipated personnel exposure concentration at the maximum charge sizes for ethane and 

propane are 2,400 ppm and 3,200 ppm, respectively, which are below the 30-min Excursion Limit of 3,000

ppm for ethane and the STEL of 6,900 ppm for propane. The maximum anticipated personnel exposure 

concentration at the typical charge sizes (98 grams of ethane and 120 grams of propane) are also well below 

the 30-minute Excursion Limit and STEL for ethane and propane, respectively (see Table 8). Given these

results, it is expected that propane used in a single refrigeration loop in this end-use will also not present a 

significant personnel exposure risk at end-use. 

A threshold analysis was performed to determine the charge size and room volume where VLT freezers 

containing ethane and propane could be installed to avoid the short-term exposure limit for each refrigerant. 

Based on Threshold Analysis 1 shown in Table 8 and assuming the limiting factor is the lower exposure 

limit of ethane, the maximum charge size that should be installed in a room of 28 m3 (1,000 ft3) volume is 

374 grams (i.e., 187 grams per refrigerant circuit). Additionally, an individual VLT freezer with typical 

charge sizes (98 grams of ethane and 120 grams of propane) and maximum charge sizes (150 grams of both

ethane and propane) should not be placed in a room smaller than 10 m3 (360 ft3) or 22 m3 (790 ft3), 

respectively. Because the modeling was done using a conservative laboratory module size, personnel 

exposure to the proposed substitute at end-use is not considered a significant risk. To mitigate risk during 

end-use, EPA recommends that for a minimum room volume of 28 m3, the charge size not exceed 285 

grams for either ethane or propane refrigerant circuit, and for a maximum charge size of 150 grams each, 

the VLT freezer not be installed in a room of volume less than 15 m3 (520 ft3). 

To minimize the risk of exposure, EPA recommends that refrigeration units be installed in rooms with 
March 29, 2016 – Final 

14 

adequate space and/or the ventilation and engineering control (e.g., local ventilation such as a fan or vents 

on doors to adjoining rooms) outlined in the SDS for ethane and propane. To prevent exposure and potential 

serious side effects during larger releases, EPA recommends that the charge size for an ethane and propane 

VLT freezer does not exceed the RCL for either refrigerant (7,000 ppm for ethane and 5,300 for propane) 

and proposes to require compliance with UL 471. Proper leak protection devices and engineering control

requirements and adherence to the SDS will further ensure that exposure limits are maintained below those 

described in Table 8. 

10. OCCUPATIONAL EXPOSURE ASSESSMENT 

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

disposal of propane and ethane. As indicated by the submitter and discussed in Section 5.1, the proposed 

substitute is purchased and not manufactured on site. The charging of ethane and propane VLT freezer units 

occurs at the final stage of freezer manufacture. To ensure that use of the proposed substitutes in VLT 

freezers does not pose an unacceptable risk to workers during servicing and disposal, occupational exposure 

modeling was performed using a box-model approach. For a detailed description of the methodology used 

for this screening assessment, the reader is referred the occupational exposure and hazard analysis described 

in Chapter 5 of the Background Document. The modeled exposure concentrations were compared to shortterm occupational exposure limits at servicing and long-term exposure limits at disposal. The sections

below describe the occupational exposure assessments conducted for the manufacture, servicing, and 

disposal of ethane and propane VLT freezers. 

10.1 Occupational Exposure during Manufacture 

As indicated by the submitter, the proposed substitute is purchased by a third-party supplier and not 

manufactured on site. Ethane and propane are produced around the world, including in the United States, 

and are used in a wide variety of refrigerant and non-refrigerant uses. During manufacture of ethane and 

propane, the SDS should be referenced and proper engineering controls and PPE used. Ethane and propane

are not expected to pose a risk to workers during manufacture when the engineering controls and PPE 

recommendations referenced in the SDS for ethane and propane are followed. Engineering controls should

include high local ventilation (e.g., chemical hoods) for standard manufacturing procedures so workers can 

avoid physical contact with the refrigerant and to achieve emission control. 

Occupational exposure to ethane and propane may occur during VLT freezer manufacturing. During 

manufacture, points of refrigerant release would be from connection/disconnection of temporary lines for 

charging and recovery equipment. However, charging is controlled and occurs in the manufacturing facility 

equipped with automatic ventilation, refrigerant detectors, and alarm systems. Furthermore, only trained 

technicians will be handling the hydrocarbon refrigerants and specialized charging equipment. [ ] The 

submitter estimates the magnitude of release to be limited to less than one gram of refrigerant per 

refrigeration circuit (Eppendorf 2015).

EPA believes that when proper handling and disposal guidelines are followed in accordance with both good 

industrial hygiene and manufacturing practices and the SDS for ethane and propane, there is no significant 

risk to workers during the manufacture of ethane and propane. 

10.2 Occupational Exposure during Servicing 

During servicing, ethane and propane refrigerants from the VLT freezer are removed using recovery 

equipment designed for hydrocarbon refrigerants and pumped into a canister, where they are stored until 

repairs are made before the system is refilled. 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. Room ventilation, leak monitors, and alarms also 

minimize exposure. 
March 29, 2016 – Final 

15 

Servicing activities for VLT freezers are not expected to result in significant worker exposure when 

certified technicians follow the procedures outlined in the ethane and propane SDS and maintenance 

manual, undergo proper training, and wear appropriate PPE (e.g., gloves, safety glasses). Nevertheless, the 

potential occupational exposure during servicing was analyzed. The release rate per servicing event was 

multiplied by the number of events estimated to occur over a workday. For the VLT freezer end-use, the

release per event was conservatively assumed to be 0.25 percent of the equipment charge during servicing. 

It was conservatively assumed that eight events of servicing a unit by one servicing technician occur in an 

8-hour work day. 

The maximum 30-minute TWA exposures for ethane and propane were estimated and compared to their 

respective STELs (see Table 9). The modeling results indicate that the maximum anticipated occupational 

exposure concentrations at no point exceed the STEL for ethane or propane. 

Table 9. Occupational Risk Assessment during Servicinga 

Component 30-minute TWA Occupational Exposure (ppm) Short Term Exposure 

Charge Size: Typical Charge Size: Maximum Limits (ppm) 

Ethane 0.67 1.0 3,000b

Propane 0.56 0.70 6,900c

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

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

c 30-minute AEGL-1; see Table 4 for more information 

The modeling results indicate that the maximum anticipated occupational exposure concentrations are very 

low with the typical charge sizes (98 grams of ethane and 120 grams of propane) and maximum charge 

sizes (150 grams of both ethane and propane). Occupational exposure concentrations during servicing from 

the use of propane in a single refrigeration loop are expected to be even lower. Further, the estimated 

exposures were derived using conservative assumptions, and represent a worst-case scenario with a low 

probability of occurrence. 

To further mitigate potential exposures 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. If a 

technician is servicing a bank of VLT freezer units charged with ethane and propane and venting occurs

frequently, EPA recommends the use of this safety equipment to prevent the concentration of ethane in the 

room from exceeding its RCL. 

10.3 Occupational Exposure during Disposal 

According to the submitter, at disposal of the VLT freezer, the proposed substitutes will be recovered using 

approved recovery equipment into a cylinder, labeled accordingly, and returned to a disposal location where 

the refrigerants can be recycled or combusted (Eppendorf 2015). Disposal of VLT freezers is expected to 

occur with limited frequency at disposal facilities and with limited duration of exposure to the refrigerant 

charge. Typically, potential exposures to the refrigerants during recovery and disposal are expected to occur 

during activities related to decommissioning refrigeration systems (e.g., attaching of hoses associated with 

draining or otherwise discharging of refrigerant from the refrigeration units into cylinders) and would be 

similar to those during servicing, because similar refrigerant charging and/or recovery equipment would be 

used (see Section 10.2 and Table 9 for information and modeling results related to exposure during 

servicing activities). 

For disposal, it was conservatively assumed that 10 units are disposed of during an 8-hour work day; 

however, it was assumed that of the 10 units, only the last unit per workday would experience a catastrophic 

release of refrigerant (i.e., 100 percent of the equipment charge). The remaining 9 units were assumed to 

release an incidental amount of refrigerant (i.e., 1 percent per unit) from the connecting and disconnecting 
March 29, 2016 – Final 

16 

of lines, as it is likely that if a worker was exposed to the entire charge of a system during disposal 

activities, they would immediately stop working, clear the area until all refrigerant has been removed from 

the space (e.g., through ventilation), and adhere to the exposure procedures recommended in the SDS for 

the proposed substitutes (see Section 10.3). 

Table 10 displays the maximum estimated 8-hour TWA occupational exposure levels for ethane and 

propane during disposal. Because modeled exposure levels for both the typical charge sizes (98 grams of 

ethane and 120 grams of propane) and maximum charge sizes (150 grams of both ethane and propane) are 

significantly lower than the 8-hour exposure limits for ethane and propane, occupational exposure to the 

proposed substitute during disposal is not considered a toxicity risk. Occupational exposure concentrations 

during disposal from the use of propane in a single refrigeration loop are expected to be even lower. 

Further, estimated exposures were derived using conservative assumptions (e.g., no ventilation) 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 while wearing PPE. 

Furthermore, it is highly unlikely that a facility would be decommissioning 10 VLT freezers containing

ethane and propane consecutively, considering the specialized nature of this equipment. A more realistic 

scenario might consider the disposal of one ethane and propane VLT freezer among the disposal of several 

domestic refrigerators and freezers containing other refrigerants. Nonetheless, the estimated exposures for 

the worst-case scenario are not considered to be significant. 

Table 10. Occupational Risk Assessment during Disposala 

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

Charge Size: Typical Charge Size: Maximum Exposure Limits (ppm) 

Ethane 55 85 1,000b

Propane 46 58 1,000c

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 ACGIH (2012) 

c

 OSHA PEL and NIOSH REL 

Although anticipated occupational exposures are well below the exposure limits for ethane and propane, the 

recommendations for proper engineering controls and PPE in the SDS for ethane and propane should be 

followed. Adequate ventilation should always be established during any use, handling, or storage of ethane 

and propane. Engineering controls should include vapor-in air detection systems and local exhaust 

ventilation during use of ethane and propane to prevent dispersion of the proposed substitute throughout the 

work place. EPA believes that if proper handling and disposal guidelines are followed in accordance with 

good industrial hygiene and manufacturing practices and the SDS for ethane and propane, there is no 

significant risk to workers during the disposal of ethane and propane in VLT freezers. 

11. GENERAL POPULATION EXPOSURE 

This section presents an assessment of potential risks to the general population posed by the use of ethane 

and propane in VLT freezers. The general population is defined in this risk screen as non-personnel who are 

subject to exposure of the proposed substitute near industrial facilities, including manufacturing or 

equipment production factories, equipment operating sites (for on-site installation or disposal activities 

only), or recycling centers, rather than consumers at end-use. 

General population exposures to ambient air, surface water and solid waste to releases of ethane and 

propane are not expected when manufactured for use and used as a refrigerant in VLT freezers. The 

proposed substitutes are proposed for use in separate refrigerant circuits that are hermetically sealed. Thus, 

significant releases are not anticipated. At room temperature, ethane and propane are gases and, therefore, 

releases to ground or surface water are not anticipated, as ethane and propane are anticipated to dissipate 

into the atmosphere upon release to outside air (i.e., because natural ventilation rates would be higher and 

there is no enclosed space to keep ethane or propane concentrated). Should air releases during 
March 29, 2016 – Final 

17 

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

collect ethane and propane and prevent any releases to the atmosphere. EPA believes that by using proper 

engineering controls and by following disposal and containment recommendations outlined in the proposed 

substitute’s SDS, exposure to ethane and propane is not expected to pose a significant toxicity risk to the 

general population. 
March 29, 2016 – Final 

18 

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ANSI/ASHRAE. 2013a. Standard 15: Safety Standard for Refrigeration Systems. American Society of 

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GIZ. 2010. Guidelines for the safe use of hydrocarbon refrigerants: A handbook for engineers, technicians, 

trainers and policy-makers – For a climate friendly cooling. Available at: 

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Gonzalez, G. Abad, N. D. C. Allen, P. F. Bernath, C. D. Boone, S. D. McLeod, G. L. Manney, G. C. Toon,

C. Carouge, Y. Wang, S. Wu, M. P. Barkley, P. I. Palmer, Y. Xiao, and T. M. Fu. 2011. Ethane, ethyne and 

carbon monoxide concentrations in the upper troposphere and lower stratosphere from ACE and GEOSChem: a comparison study. Atmos. Chem. Phys. 11, 9927-9941. Available at: http://www.atmos-chemphys.net/11/9927/2011/acp-11-9927-2011.pdf. 

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. 

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March 29, 2016 – Final 

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