March 28, 2016 – Final 

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Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector 

Risk Screen on Substitutes in Chillers and Cold Storage Warehouses 

Substitute: Propylene (R-1270) 

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-uses and applications within all of the major 

ODS-using sectors including: refrigeration and air conditioning; solvent cleaning; foam blowing; aerosols; 

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

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

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

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

evaluates the potential use of propylene (R-1270) as a substitute in the chillers and cold storage warehouse 

end-uses. Table 1 presents the composition of the proposed substitute. 

Table 1. Composition of Propylene and Potential Impurities 

Constituent Chemical Formula CAS Number Concentration

(Weight Percent) 

Propylene (R-1270) C3H6 115-07-1 >99.5 

Potential Impurities 

Hexane C6H14 110-54-3 <0.005 

Water H2O 7732-18-5 <0.0025 

Butadiene C4H6 106-99-0 <0.0005 

Sulfur S 7704-34-9 <0.0002 

Benzene C6H6 71-43-2 <0.0001 

Residue NA NA <0.005 

Acid NA NA <0.000002 

Othera NA NA <0.5 

NA - Not available 

a The composition of “Other” impurities was not specified by the submitter. 

 
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Section 2 summarizes the results of the risk screen for the proposed substitute 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: Potential Health Effects 

• Section 6: Flammability Assessment 

• Section 7: Occupational Exposure Assessment 

• Section 8: General Population Exposure Assessment 

• Section 9: References 

2. SUMMARY OF RESULTS 

Propylene is not recommended for SNAP approval as a refrigerant in chillers or cold storage warehouses

due to its potential impacts on local air quality relative to available substitutes in these end-uses. 

Propylene is regulated as a volatile organic compound (VOC) under CAA regulations (40 CFR 51.100(s)). 

Based on analysis of potential impacts of hydrocarbon refrigerant emissions on ground-level ozone 

concentrations, VOCs from the use of propylene are anticipated to result in greater impacts on local air 

quality in the United States than other available options. 

According to the results of the assessments in this risk screen, significant flammability and toxicity risks 

are likely for chillers and cold storage systems (see Sections 6 and 7 of this document). Exposure during 

end-use is captured in the occupational exposure assessment (see Section 7 of this document), as consumer 

use of chillers and cold storage equipment is not anticipated. In addition, potential health risks from 

exposure to the proposed substitute is considered to be a larger concern for workers, due to the large

spaces in which chillers and cold storage equipment are installed and serviced. Therefore, an asphyxiation 

assessment was not conducted. 

3. ATMOSPHERIC ASSESSMENT 

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

propylene in chillers and cold storage warehouses. 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 ALT when compared to refrigerants such as CFC-12, HCFC-22, and R-502. In addition, propylene 

also has lower climate impact and a shorter ALT than those predicted for other substitutes examined in the 

Background Document as well as commonly utilized refrigerants HFC-134a, R-407C, and R-404A. 
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Table 2. Atmospheric Impacts of Propylene Compared to Other Refrigerants Used in Chillers and 

Cold Storage Warehouses 

Refrigerant Ozone Depleting Potential

(ODP)a

Global Warming Potential

 (GWP)b

Atmospheric Lifetime in 

Years (ALT)b 

Propylene 0 1.8 0.35 daysa

CFC-12 0.82 10,900 100

R-502c 0.2 4,650 NAd

HCFC-22 0.13 1,810 12

HFC-134a 0 1,430 14

R-407Ce 0 1,774 NAf

R-404Ag 0 3,922 NAh

NA - Not applicable 

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

b Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (Forster et al. 2007) 

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

d

 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]).

e

 R-407C is a blend consisting of HFC-32 (29%), HFC-125 (25%) and HFC-134a (52%).

f

 Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-32 is 4.9 years, the ALT 

for HFC-125 is 29 years, and the ALT for HFC-134a is 14 years (IPCC 4th Assessment Report [Forster et al. 2007]). 

g

 R-404A is a blend consisting of HFC-143a (52%), HFC-125 (44%) and HFC-134a (4%). 

h

 Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-143a is 52 years, the 

ALT for HFC-125 is 29 years, and the ALT for HFC-134a is 14 years (IPCC 4th Assessment Report [Forster et al. 2007]). 

4. VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS 

Propylene is regulated as a VOC under CAA regulations (40 CFR 51.100 [s]). Emissions of propylene 

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

EPA prepared a separate analysis in 20141

 and a follow-on analysis in 20162 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 propane under different scenarios. 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.3 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 analysis considers the propensity of organic compounds to form ozone according to their maximum 

incremental reactivity (MIR). The MIR scale assesses a compound’s contributions to the photochemical 

ozone formation in urban plumes and is reflective of its use in North America, where ground-level ozone 

formation is considered an urban issue. Table 3 lists the MIR for several compounds, including the 

hydrocarbons examined in this analysis. 

 

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

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

2016)

3 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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Table 3. Propensity of Refrigerants to Form Tropospheric Ozone

Compound North America MIR Scale 

(g-O3/g-substance) 

HCFC-22 <0.1 

HFC-134a <0.1 

Propylene 11.57 

Ethanea 0.28 

Isobutane 1.34 

Propane 0.56 

Source: IPCC (2005) 

a EPA uses the reactivity of ethane as the threshold for determining whether a compound has negligible 

reactivity. Compounds that are less reactive than, or equally reactive to, ethane under certain assumed 

conditions may be deemed negligibly reactive and therefore suitable for exemption from the definition of a 

VOC (EPA 2012a). 

As demonstrated in Table 3, propylene’s MIR is more than 20 times greater than the MIR for propane, and 

approximately 9 times greater than the MIR for isobutane. Therefore, propylene is significantly more 

likely to form tropospheric ozone than other refrigerants examined in this analysis. 

These analyses estimated hydrocarbon refrigerant emissions in 2030 (EPA 2014) and 2040 (EPA 2016) 

from different scenarios and compared their resulting relative increases in ozone concentrations against the 

National Ambient Air Quality Standard (NAAQS) for ozone of 70 ppb.4 All three regions examined in 

these analyses (i.e., Los Angeles, Atlanta and Houston) are forecast to be in attainment of the 2015 8-hr 70 

ppb ozone standard by 2040. 

Isobutane, a less reactive hydrocarbon than propylene, was modeled in all refrigeration and air 

conditioning equipment. The results of this scenario indicate there could be an incremental increase up to 

0.72 ppb in 2030. In the alternative case, which assumed that the most reactive hydrocarbon, propylene, 

was used in all refrigeration and air conditioning equipment, there could be an incremental maximum 

increase of the 8-hour average as high as 6.6 ppb ozone in 2030 (EPA 2014) or 7.8 ppb ozone in 2040. 

Although potential impacts from isobutane were only modeled in 2030, the relative impact of isobutane in 

2040 is still anticipated to be significantly less than that of propylene, because isobutane is significantly 

less reactive. 

EPA performed an additional analysis to determine refrigerant emissions resulting from the use of 

propylene in a limited number of refrigeration and air conditioning end-uses including chillers, cold 

storage warehouses, and certain residential and light commercial air conditioning applications and their 

potential contributions to tropospheric ozone generation. Emissions from these select end-uses were 

estimated to result in an incremental maximum increase of the 8-hour average of up to 4.5 ppb in 2040. In 

addition, EPA examined a more realistic scenario in which refrigerant emissions from propylene and R443A, a hydrocarbon refrigerant blend containing approximately 55 percent propylene, were modeled in 

cold storage warehouses, residential and light commercial air conditioning, and large commercial air 

conditioning applications including chillers, as well as refrigerant emissions from R-441A and propane in 

room air conditioners. Refrigerant emissions from this scenario resulted in an incremental maximum 

increase of the 8-hour average of 2.6 ppb in 2040. The increase in ozone is estimated to be about 95 

percent associated with the use of propylene as a refrigerant, including its use as a component of R-443A, 

and 4 percent from propane, including its use as a component of R-443A and R-441A, under this scenario.

The results of the CMAQ modeling are summarized in Table 4. 

 

4 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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Table 4. Estimated Maximum Increase in the Daily 8-hour Ground-Level Ozone in 2040 from 

Hydrocarbon Refrigerant Emissions

Equipment Refrigerant 

8-hr Ozone 

Maximum Change 

(ppb) 

All refrigeration and air conditioning 

equipment 

Propylene 7.8 

Isobutane 0.72a

Chillers, cold storage warehouses, and 

certain residential and light commercial air 

conditioning applications 

Propylene 4.5 

Propane, Propylene, R-441A, 

R-443A 2.6b

a The 8-hr maximum increase in ground-level ozone is observed in 2030 for the isobutane scenario. 

b 95 percent of the change in ozone is associated with the use of propylene as a refrigerant and as a 

component of R-443A, and 4 percent from propane as a refrigerant and as a component of R-441A and R443A, under this scenario. 

Although most ozone nonattainment areas are not VOC-limited (i.e., the formation of ozone in these areas 

is not by limited by VOC emissions, but by other compounds such as nitrogen oxides [NOx]), allowing the 

use of propylene in chillers and cold storage facilities could introduce VOC loading that would place a 

further burden on reaching attainment and extend the timeline for compliance for some areas. 

Furthermore, substitutes such as ammonia, R-450A, and R-513A are approved in these end-uses and 

contain only compounds exempt from the definition of VOC. Because propylene is highly reactive, VOC 

emissions from the use of propylene in chillers and cold storage warehouses are anticipated to contribute to 

ground-level ozone concentrations in the United States significantly more than less reactive hydrocarbons 

and other available options for these end-uses. Therefore, propylene is not recommended for SNAP 

approval as a refrigerant in chillers or cold storage warehouses. 

5. POTENTIAL HEALTH EFFECTS 

To assess potential health risks from exposure to the proposed substitute in chillers and cold storage

warehouses, EPA identified the relevant toxicity threshold values for comparison to modeled exposure 

concentrations for different scenarios. According to American Society of Heating, Refrigerating, and AirConditioning Engineers (ASHRAE) Standard 34, propylene is listed under safety group A3 with a 

refrigerant concentration limit (RCL) of 1,000 ppm (ASHRAE 2013b). 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 a 

refrigeration unit (ASHRAE 2013b). 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 2013a). As such, this risk screen references

the RCL for propylene in addition to the lower flammability limit (LFL), hypoxia no observed adverse 

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

flammability, asphyxiation, and occupational 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 with available occupational exposure limits. Potential 

risks of chronic worker exposure were evaluated using workplace guidance levels (WGL). Risks from 

potential short-term consumer exposures were evaluated by comparing exposure concentrations with 

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

exposure guideline (AEGL), or emergency response planning guideline (ERPG), potential short-term, 

occupational exposures were compared with an excursion limit, which was calculated according to the 
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methodology described by the American Conference of Governmental Industrial Hygienists (ACGIH) 

(2004).5 Table 5 lists the relevant toxicity limits of propylene and its potential impurities and is followed 

by Table 6, 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 5. Exposure Limits of Propylene 

Component 

 WGL 

(Long-term Exposure) 

ppm 

EGL 

(Short-term Exposure) 

ppm 

IDLH 

(Short-term Exposure) 

ppm 

Refrigerant

Concentration 

Limit (RCL) 

ppm 

Propylene 500 (ACGIH-TLV) 1,500 (30-min ACGIH 

Excursion Limit)a

NA 1,000b

Potential Impurities 

Hexane 50 (ACGIH-TLV)c 150 (15-min STEL)c 1,100c,d NA 

Butadiene 1 (OSHA-PEL)e 5 (15-min STEL)e 2,000e,f NA

Benzene 1 (OSHA-PEL)g 5 (15-min STEL)g 500g,h NA 

An explanation of each exposure limit and exposure-limit related terminology is described in Table 6. 

a Calculated as three times the threshold limit value-time-weighted average (TLV-TWA) (ACGIH 2004). 

b ASHRAE (2013b) 

c The ACGIH-TLV, STEL, and IDLH for hexane are available at: https://www.osha.gov/dts/chemicalsampling/data/CH_245400.html. 

d Although an RCL is not available for hexane, the Immediately Dangerous to Life or Health (IDLH) concentration of 1,100 ppm is most 

similar to the Acute-Toxicity Exposure Limit (ATEL), which is an RCL intended to reduce the risks of acute toxicity hazards in normally 

occupied, enclosed spaces. 

e The permissible exposure limit (PEL), STEL, and IDLH for butadiene are available at: 

https://www.osha.gov/dts/chemicalsampling/data/CH_222100.html. 

f

 Although an RCL is not available for butadiene, the IDLH concentration of 2,000 ppm is most similar to the ATEL, which is an RCL 

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

g The PEL, STEL, and IDLH for benzene are available at: https://www.osha.gov/dts/chemicalsampling/data/CH_220100.html. 

h Although an RCL is not available for benzene, the IDLH concentration of 500 ppm is most similar to the ATEL, which is an RCL intended 

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

Table 6. 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

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 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. 

 

5

 It should be noted that this risk screen evaluates short-term occupational exposure to propylene by comparison to the excursion 

limit, which is typically used to evaluate short-term occupational exposure. EPA believes that, in the absence of an AEGL, STEL, 

or ERPG, the excursion limit provides a reasonable proxy. Notably, the ACGIH methodology (i.e., using three times the TLVTWA) has also been used by the Department of Energy (DOE) (2008) to develop a temporary emergency exposure limit for 

propylene (2,500 mg/m3

 or 1,500 ppm 15-min TWA), which applies to the general population. 
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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 IDLH concentrations set by NIOSH. 

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

workday, even if the 8-hour TWA is within the TLV–TWA, set by ACGIH. 

ACGIH 

Excursion 

Limitsb

Short-Term Exposure Limit Because methane and other short-chain alkane gases through butane 

do not have a TLV-STEL, 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 or Health 

If exposed to this concentration, room occupants are expected to be able 

to escape the room within 30 minutes without experiencing escapeimpairing or irreversible health effects. 

Long-Term Exposure

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

AEL Acceptable Exposure Limit The maximum 8-hour 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 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 ACGIH (2004) 

According to the safety data sheet (SDS), exposure to propylene may be hazardous if inhalation, skin 

contact, or eye contact with the proposed substitute occurs. The most likely pathway of exposure is 

through inhalation. Propylene 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 propylene 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 propylene to the skin may cause frostbite. In the case of dermal exposure, the SDS 

for propylene 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 propylene to the eyes could cause eye irritation. In case of ocular exposure, the 

SDS for propylene 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 propylene can be minimized by following the exposure 
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guidelines and ventilation and personal protective equipment (PPE) recommendations outlined in the SDS

for propylene and this risk screen.

6. FLAMMABILITY ASSESSMENT 

ASHRAE Standard 34 classifies propylene as an A3 refrigerant. Propylene is flammable when its 

concentration in air is in the range of 2.0 percent to 11.1 percent by volume (20,000 ppm to 111,000 ppm). 

In the presence of an ignition source (e.g., static electricity or a cigarette), an explosion or a fire could 

occur if the concentration of propylene were to exceed the LFL of 20,000 ppm. The remainder of this 

section addresses flammability risks and summarizes the recommended measures to ensure safe handling 

and use of the refrigerant during manufacture and servicing. 

6.1 Flammability Risk at Equipment Manufacture 

The submitter intends to manufacture packaged propylene chillers and cold storage units that are factorybuilt and installed on-site. Thus, release of or exposure to propylene may be possible at the charging and 

sealing steps at the manufacturing site. It is therefore important that all relevant standards be followed 

during the manufacture of propylene refrigeration units. EPA recommends that engineering controls 

should include normal and local ventilation (e.g., chemical hoods) for standard manufacturing procedures 

so workers can avoid physical contact with the refrigerant and to limit emissions. In general, use of 

appropriate PPE consistent with the Occupational Safety and Hazard Administration’s (OSHA’s) 

guidelines is recommended, such as splash goggles, mechanically-resistant gloves when handling 

cylinders, chemically-resistant gloves (e.g., butyl rubber, chlorinated polyethylene, or neoprene) when 

handling the gas mixture, and protective clothing. 

All propylene storage and transport equipment should be installed with safety devices that minimize the 

likelihood of catastrophic releases. For example, the National Fire Protection Association (NFPA) 58 

Liquefied Petroleum Gas Code (NFPA 2007) for liquefied propylene requires the use of overfill protection 

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

propylene storage and transportation requirements/guidelines. It is expected that refrigerants be properly 

stored and caution used within manufacturing facilities to minimize explosion risk and that workers adhere 

to the requirements set by OSHA under 29 CFR 1910. OSHA requirements include proper ventilation and 

storage practices within manufacturing facilities to prevent fire and explosion. Good manufacturing 

practices should be adhered to during the manufacture of equipment containing propylene, e.g., using 

proper ventilation. 

6.2 Flammability Risk at Servicing 

The risk of flammability during servicing was investigated for propylene. To represent the reasonable 

worst-case scenario for the proposed and typical charge sizes for positive displacement chillers and cold 

storage units (i.e., 12, 315 kg respectively) and the typical charge size for centrifugal chillers (i.e., 930 

kg),6 it is assumed that a catastrophic leak of refrigerant occurs while the unit is serviced at end-use (i.e., 

rooftop of a commercial building). The average refrigerant concentration in the closest proximity to the 

emission source following a catastrophic release was modeled using the box-model approach, which is 

described in Chapter 5 of the Background Document. This approach has been widely used for many years 

to estimate probable exposures of workers to hazardous airborne materials, and has been described in 

 

6 EPA’s Vintaging Model (VM_IO file_v4.4_10.13.14) models three types of positive displacement chillers: screw, scroll, and 

reciprocating, with average charge sizes of 300 kilograms, 240 kilograms, and 315 kilograms, respectively, and centrifugal chillers 

with charge sizes ranging from 700 kilograms to approximately 930 kilograms. This risk screen models the largest of the typical 

charge sizes for each chiller type (i.e., 315 kilograms for reciprocating chillers and 930 kilograms for centrifugal chillers). 
March 28, 2016 – Final 

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

consideration the duration and magnitude of the resulting exposure which is influenced by the following: 

1) Duration and intensity of the release, 

2) Rate at which contaminated air is diluted with uncontaminated air, 

3) Proximity of the worker to the source of the release, and 

4) Length of time the worker remains in the affected space. 

In order to determine the potential flammability risks during servicing in case of a catastrophic release of 

refrigerant, modeled concentrations of propylene immediately following the release of refrigerant were

compared with the LFL for propylene (20,000 ppm). The results of the flammability assessment are 

presented in Table 7. 

Table 7. Flammability Assessmenta

Scenario Equipment Charge 

Size (kg) 

Maximum 

Instantaneous 

Concentration (ppm)b

Reasonable Worst-Case Scenario 1 Proposed Chillers and Cold Storage 12 8,200 

Reasonable Worst-Case Scenario 2 Positive Displacement Chillers 315 215,300

Reasonable Worst-Case Scenario 3 Centrifugal Chillers 930 635,600

Threshold Analysis 1 All Chillers and Cold Storage 29 20,000

Bold font indicates modeling results. 

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

b

 LFL of propylene is 20,000 ppm. 

As demonstrated in Table 7, the maximum instantaneous concentration does not exceed the LFL for 

propylene units with a 12-kilogram charge size, as proposed by the submitter. However, the maximum 

instantaneous concentration exceeds the LFL for propylene under Reasonable Worst-Case Scenarios 2 and 

3 for the typical charge sizes of a positive displacement chiller (i.e., 315 kilograms) and a centrifugal 

chiller (i.e., 930 kilograms). The threshold condition at which a flammability concern would exist (i.e., 

when the maximum instantaneous concentration following a complete release equals the LFL for 

propylene) was also determined. As shown under Threshold Analysis 1, a flammability concern could 

occur if the charge size of a propylene chiller or cold storage unit is 29 grams or more, which is 

approximately 2.5 times greater than the charge size proposed by the submitter and approximately 11 times 

smaller than the typical charge size for positive displacement chillers. Furthermore, positive displacement 

and centrifugal chillers can have a wide variety of charge sizes, including as large as 10,000 kilograms. 

The catastrophic release of such a large system would present an extremely significant flammability risk, 

resulting in exposures of approximately 300 times the LFL for propylene (i.e., 6,830,000 ppm). 

For the proposed packaged positive displacement chillers and cold storage systems, the submitter indicates 

the units are equipped with an additional safety package that contains a hydrocarbon gas sensor, an 

evacuation fan, and explosion panels. If the sensor detects hydrocarbons at a concentration of 5 percent of 

the LFL (i.e., 1,000 ppm), the compressor and pump operation will shut down and the condenser fans will 

operate at full speed. In the case of an explosion, the explosion panels are designed to lift and guide the 

substitute upwards towards the condenser fans which then completely ventilate the unit until it is manually 

turned off (Frigadon AB 2015a). 

According to the submitter, warning labels are present on the equipment indicating that flammable 

refrigerants are in use and that the user should read the equipment use instructions that provide safety 

guidelines for handling propylene in order to mitigate flammability risk. The submitter also indicates leak 
March 28, 2016 – Final 

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prevention devices would be installed to further protect against the risk of explosion, and that only 

properly trained and certified technicians are expected to handle propylene (Frigadon AB 2015b). 

7. OCCUPATIONAL EXPOSURE ASSESSMENT 

To ensure that use of the proposed substitute in chillers and cold storage warehouses does not pose an

unacceptable toxicity risk to workers during charging, servicing, and disposal, occupational exposure 

modeling during charging at manufacture was performed for the proposed substitute. The methodology 

used for this screening assessment is described in Chapter 5 of the Background Document and Section 6.

Although modeling is only performed for the system’s initial charging, it is assumed that exposure during 

servicing and disposal would not exceed exposure during charging because similar refrigerant charging 

and/or recovery equipment would be used. Furthermore, because it is likely that less refrigerant remains in 

the unit at disposal, it is assumed that charging of packaged chillers and cold storage equipment would 

require transfer of a greater amount of refrigerant, and result in greater worker exposure. Thus, 

occupational exposure was conservatively modeled based on charging. 

The modeled scenario assumes a charge size for chillers and cold storage equipment of 12 kilograms, as

indicated by the submitter, along with more typical charge sizes of 315 kilograms for positive 

displacement chillers and 930 kilograms for centrifugal chillers. Because these systems can have a variety 

of charge sizes, including up to 10,000 kilograms, this maximum charge size was also modeled. Charging

of chillers and cold storage equipment is expected to occur with limited frequency (up to approximately 

one event per day) and with limited duration of exposure to the refrigerant charge. Release points during 

charging would be connection/disconnection of temporary lines from charging equipment. 

The release per event was assumed to be 0.2 percent and 1 percent of the equipment charge for chillers and 

cold storage equipment, respectively.7,8 The release per event was multiplied by the estimated number of 

units charged over a workday. The maximum 30-minute TWA exposures for propylene was estimated for 

the charging scenario and compared to the short-term exposure limit for propylene (see Table 8). 

Table 8. Occupational Risk Assessment at Charging for Propylenea 

Equipment Charge Size 

(kg) 

30-minute TWA Occupational 

Exposure (ppm) 

30-min Short Term 

Exposure Limit 

(ppm)b

0.2% Release 1% Release

Proposed Chillers and Cold Storage 12 3 12

1,500 Positive Displacement Chillers 315 65 330

Centrifugal Chillers 930 190 960

All Chillers and Cold Storage 10,000 2,070 10,370

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

 EPA-derived STEL (see Table 5) 

Based on the assumptions described above, the modeling indicates that short-term (15-minute) worker 

exposure concentrations are not likely to exceed the STEL (1,500 ppm) for propylene in the proposed and 

typical charge sizes for chillers and cold storage equipment. However, worker exposure concentrations are 

 

7

 IPCC (2006) estimates that first-fill losses during installation of chillers can range from 0.2% to 1%; DECC (2011) estimates 

first-fill losses for chillers is approximately 0.5%; however, industry representatives indicate that the first-fill leak rate for chillers 

is lower than 0.5% (McQuay 2011). A proposed update to EPA’s Vintaging Model recommends a first-fill emissions rate of 0.2% 

from chillers manufactured after 1990.

8 IPCC (2006) estimates that first-fill losses during installation of cold storage warehouse systems can range from 0.5% to 3%; 

DECC (2011) estimates that first-fill losses for cold storage units is approximately 1%; and, SKM Enviros (2011) suggests that 

this loss rate should be less than 4%. A proposed update to EPA’s Vintaging Model recommends a first-fill emissions rate of 1% 

from cold storage units manufactured after 1990. 
March 28, 2016 – Final 

11 

likely to significantly exceed the STEL for propylene in larger chillers and cold storage units with a

10,000-kilogram charge size. Although these types of systems are typically charged, maintained, and 

disposed by trained and EPA Section 608-certified refrigerant technicians using proper industrial hygiene 

techniques, propylene is still likely to present a toxicity risk during charging, servicing, and disposal when 

used in large chiller and cold storage systems. 

8. GENERAL POPULATION EXPOSURE ASSESSMENT 

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

propylene in chillers and cold storage warehouses. 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. 

Propylene 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 chillers and cold storage warehouses. 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, propylene is a gas; therefore, releases to 

ground or surface water are not anticipated, as propylene 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 propylene). Should air releases during manufacturing operations 

occur, engineering controls should be used (e.g., carbon absorption scrubbers) to collect propylene and 

prevent the release of the chemical 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 and this risk screen, exposure to propylene is not expected to pose a significant toxicity risk to the 

general population.
March 28, 2016 – Final 

12 

9. REFERENCES 

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Industrial Hygienists. 

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

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

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ANSI/ASHRAE. 2013b. Standard 34: Designation and Safety Classification of Refrigerants. 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. 

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Frigadon AB. 2015a. Propylene for use in Chillers. Significant New Alternatives Policy Program. 

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

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March 28, 2016 – Final 

13 

U.S. EPA. 2016. Follow-on Assessment of the Potential Impact of Hydrocarbon Refrigerants on GroundLevel Ozone Concentrations. Prepared for the U.S. EPA Stratospheric Protection Division by ICF 

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