May 30, 2014 -- Final

1

Significant New Alternatives Policy Program 

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for CFC-12, HCFC-22 and R-502 in Vending Machines

Substitute: Isobutane (R-600a)

This risk screen is restricted to vending machines meeting the requirements of UL 541: 

Refrigerated Vending Machines.

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

and, therefore, may be disclosed to the public.

1. INTRODUCTION

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

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

Protocol and the Clean Air Act Amendments of 1990 (CAAA). The U.S. Environmental Protection 

Agency (EPA), as authorized by Section 612 of the CAAA, administers the Significant New Alternatives 

Policy (SNAP) Program, which identifies acceptable and unacceptable substitutes for ODS in specific 

end-uses based on assessment of their health and environmental impacts. 

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

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

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

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

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

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

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

evaluates the potential use of isobutane as a substitute for CFC-12, HCFC-22, and R-502 in the vending 

machine end-use. The proposed substitute, isobutane, may contain minute quantities of impurities. Table 

1 presents the composition of the proposed substitute assuming high-purity refrigerant-grade isobutane is 

used.

Table 1. Composition of Isobutane

Component Chemical Formula CAS Number Concentration

(Weight Percent)a

Isobutane C4H10 75-28-5 >99%

a Negligible amounts of impurities may be present (i.e., unsaturated hydrocarbons, sulfur, moisture, etc.).

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: Discussion of End-Use Scenario Modeled

 Section 6: Potential Health Effects

 Section 7: Flammability Assessment

 Section 8: Asphyxiation Assessment

 Section 9: End-Use Exposure Assessment 
May 30, 2014 -- Final

2

 Section 10: Occupational Exposure Assessment

 Section 11: General Population Exposure Assessment

 Section 12: References

2. SUMMARY OF RESULTS

Isobutane is recommended for SNAP approval for vending machines that comply with Underwriters 

Laboratory (UL) Standard 541: Refrigerated Vending Machines. EPA's risk screen indicates that the use 

of the proposed substitute will be less harmful to the atmosphere than the continued use of CFC-12, 

HCFC-22, and R-502 as it is less harmful to the ozone layer, has lower climate impact, and a shorter 

atmospheric lifetime. Isobutane is subject to volatile organic compound (VOC) regulations under the 

CAA (40 CFR 51.100(s)). Based on analysis of potential impacts of hydrocarbon refrigerant emissions on 

ground-level ozone concentrations, VOC emissions from the use of isobutane in vending machines are 

not anticipated to contribute significantly to ground level ozone concentrations in the United States. It is 

expected that procedures in the material data safety sheet (MSDS) for isobutane 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 vending machines using isobutane. Because vending machines are to be 

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

and the equipment maintenance manual for isobutane, as discussed in greater detail in Section 9, 

significant toxicity or flammability risk to consumers is also unlikely. Additional safeguards, including 

specified refrigerant concentration limits (RCL) for isobutane, are also provided by adherence to industry 

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

(ASHRAE) Standards 15,

1

34,

2

and 623and Underwriters Laboratory (UL) Standard 541, Supplement 

SA.4

3. ATMOSPHERIC ASSESSMENT

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

isobutane in vending machines. The ozone depletion potential (ODP), global warming potential (GWP), 

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

The proposed substitute is substantially less harmful to the ozone layer, has lower climate impact, and a 

shorter atmospheric lifetime when compared to CFC-12, HCFC-22, and R-502. In addition, isobutane

also has lower climate impact and a shorter atmospheric lifetime than those predicted for other substitutes 

examined in the Background Document, as well as commonly utilized substitutes R-404A and HFC-134a.

Thus, EPA believes that the use of isobutane would result in substantially less harm to the climate and 

ozone layer than the continued use of ODS and commonly used ODS substitutes.

 

1

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

prescribes safety requirements.

2 Designation and Safety Classification of Refrigerants ASHRAE Standard 34 is establishes a uniform system for assigning 

reference numbers, safety classifications, and refrigerant concentration limits to refrigerants. Safety classifications based on 

toxicity and flammability data are included.

3 Ventilation for Acceptable Indoor Air Quality ASHRAE Standard 62 establishes minimum ventilation rates and other measures 

intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects.

4 UL 541: Refrigerated Vending Machines Supplement SA: Requirements for Refrigerated Venders Employing a Flammable 

Refrigerant in the Refrigerating System
May 30, 2014 -- Final

3

Table 2. Atmospheric Impacts of Isobutane Compared to Other Vending Machine Refrigerants

Refrigerant ODPa GWPb ALT (Years)

Isobutane 0 ~4 0.016b

CFC-12 0.82 10,900 100b

R-502c 0.2 4,650 NAd

HCFC-22 0.05 1,810 12b

R-404Ae 0 3,922 NAf

HFC-134a 0 1,430 14b

NA= Not Available.

aWMO 2010 Scientific Assessment Report (2011).

b

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

f 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.

4. VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS

Isobutane is regulated as a VOC under the CAA (40 CFR 51.100 [s]). Through regulations and standard 

industry practices, VOC emissions should be controlled. A separate analysis was prepared by EPA ( 

2014) to evaluate the potential impact of the use of hydrocarbon refrigerants on ground level ozone 

concentrations in the United States. The analysis estimated refrigerant emissions from refrigeration and 

air conditioning equipment which were assumed to contain propylene, isobutane, and/or propane 4under 

different scenarios. Under the most conservative scenario it was assumed that propylene was used in all 

refrigeration and air conditioning equipment. In the most realistic scenario, all three hydrocarbons were 

assumed to be used in certain types of refrigeration and air conditioning 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 air-conditioning units, for which SNAP hydrocarbon applications have been received and/or UL 

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

estimated based on U.S. EPA’s Vintaging Model, and their potential contributions to ozone 

concentrations were assessed using U.S. EPA’s Community Multiscale Air Quality (CMAQ) model. 

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 realistic 

scenario, hydrocarbon refrigerants could potentially increase the maximum 8-hour average ground level 

ozone by no more than 0.15 ppb in Los Angeles, the city with the greatest ozone problem. This is roughly

0.2 percent of the current National Ambient Air Quality Standard (NAAQS) for ozone of 75 ppb. In 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 6.61 ppb ozone, or an increase of up to 9 percent of the NAAQS. However, this 

upper bound level of increase is not likely, as most ozone nonattainment areas are not VOC-limited (i.e., 

the formation of ozone in these areas are not by 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 

may be used in the refrigeration and air conditioning end-uses. Based on the results of this analysis, VOC 

 

4 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.
May 30, 2014 -- Final

4

emissions from the use of isobutane in vending machines are not anticipated to contribute significantly to 

ground level ozone concentrations in the United States.

5. DISCUSSION OF END-USE SCENARIO MODELED

Isobutane has been proposed for the vending machine refrigeration end-use. EPA expects that isobutane

vending machines will have a charge size of less than 150 grams. This is consistent with UL Standard 

541: Refrigerated Vending Machines, which states that vending machines containing flammable 

refrigerants may have a charge size of up to 150 grams of A3 refrigerant. 

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

while the vending machine is installed at the end-use. Because vending machines can be installed in a 

wide range of locations with varying room volumes, the analysis in this risk screen conservatively 

assumes that the vending machine contains the maximum charge size indicated by UL 541 (150 grams), 

and is located in the minimum room size, an enclosed alcove of a commercial building that can be 

isolated by a door. The alcove is assumed to have an effective floor area of 6.15 m2(i.e., excluding the 

space filled by the vending machine, furniture, boxes, etc.) and a height of 2.4 meters), equivalent to a 

volume of 15 m3(530 ft3). Under the worst-case scenario, the full charge of the unit is assumed to be 

emitted over the course of one minute, into the enclosed alcove with 0.5 air changes per hour (ACH). A 

vertical concentration gradient is also assumed since isobutane is denser than air (specific gravity of 

isobutane relative to air is 2 [air = 1]) and will settle in higher concentrations closer to the ground. In 

order to simulate the vertical concentration gradient, it is assumed that 95 percent of the leaked refrigerant 

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

remaining volume (Kataoka 2000).

To represent a more typical scenario, this risk screen also evaluates potential risk associated with less 

conservative conditions. Based on ICF expert opinion, the enclosed alcove is assumed to have an 

effective floor area of 10m2(108 ft2) with a height of 2.7 m (9 ft), equivalent to a volume of 27.5 m3(972 

ft3), with an air exchange rate of 1.5 ACH (EPA 1997). Additionally, because the typical breathing zone 

is above 0.4 meters (1.3 feet) and mixing is likely to occur upon release of isobutane from the unit 

because the system pressure is higher than the surrounding atmospheric pressure, a vertical concentration 

gradient is not assumed. Table 3 details the end-use modeling assumptions used throughout the risk 

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

Table 3. End-Use Scenario Model Assumptions

Parameter Assumption

Reasonable Worst-Case Scenario Typical Scenario

Room Type Enclosed Alcove Enclosed Alcove

Effective Size (m3)

a 15 (530 ft3

) 27.5 (972 ft3)

Ventilation Rate (air changes per hour) 0.5 1.5

Refrigeration Unit Vending Machine Vending Machine

Charge Size (g) 150 150

Length of Release (minutes) 1 1

Vertical Concentration Gradient Yes No

a The volume of the room minus the volume occupied by the vending machine or other large pieces of equipment or furniture present. 

EPA recognizes that while the majority of vending machines may be placed outdoors or in other wellventilated areas, which would largely minimize the risks of exposure, there may a few instances in which 

the consumer chooses to place multiple vending machines in an enclosed space (thus further limiting the 

effective volume of the space) or chooses to place a single vending machine unit in a very small enclosed 

space (with the size of the vending machine being the limiting factor). A typical beverage vending

machine measures 72 in x 39 in x 33 in, which is equal to 53.6 ft3or 1.5 m3(Vending Solutions 2009). To 
May 30, 2014 -- Final

5

address these concerns, this risk screen incorporates threshold analyses in addition to the worst-case and 

more typical case scenario modeling. The results from the threshold analyses are used to establish 

guidelines for choosing an effective room size, charge size, and ventilation rate such that use of isobutane

in vending machines does not present risk to consumers or servicing technicians. 

6. POTENTIAL HEALTH EFFECTS

To assess potential health risks from exposure to the proposed substitute in vending machines, 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 leak from the 

refrigeration unit, ASHRAE Standard 34 determined refrigerant concentration limits (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 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 and acute worker exposure were 

evaluated by comparing exposure concentrations to available occupational exposure limits. Potential risks 

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

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

guidance levels (EGL). Table 4 lists the relevant toxicity limits and RCLs of isobutane, and is followed 

by Table 5, which provides an explanation of each toxicity limit. EPA’s approach for identifying or 

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

Table 4. Exposure Limits of Isobutane

Component

8-hr WGL (Long-term 

Exposure)

ppm

EGL (Short-term Exposure)

ppm

Refrigerant Concentration 

Limit (RCL)

ppm

Isobutane 1,000a (ACGIH TLV) 6,900b(30-min) 4,000c

a ACGIH TLV for aliphatic hydrocarbon gases: alkane (C1 - C4) is 1,000 ppm TWA (ACGIH 2012)

b Because n-Butane and isobutane have the same molecular formula, EGL for isobutane is conservatively assumed to be that for n-Butane

(i.e., 30-min AEGL-1 of 6,900 ppm). However, OSHA (2004) notes the following regarding isobutane: “OSHA does not have a PEL for 

isobutane, which is affirmed as "generally recognized as safe" as a direct human food ingredient (21 CFR 184.1165). No toxic effects reported 

below 18,000 ppm.”

c ASHRAE (2010b)

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

Exposure Limit Definition Explanation

Short-Term Exposure

RCL Refrigerant Concentration 

Limit

The RCL for a refrigerant is intended to reduce the risks of acute toxicity, 

asphyxiation, and flammability hazards in normally occupied, enclosed 

spaces. The RCL for each refrigerant is the lowest of the Acute-Toxicity 

Exposure Limit (ATEL), Oxygen Deprivation Limit (ODL), and Flammable 

Concentration Limit (FCL). Determination assumes full vaporization with 

no removal by ventilation, dissolution, reaction, or decomposition and 
May 30, 2014 -- Final

6

complete mixing of refrigerant in the space to which it is released.

STEL Short-Term Exposure Limit A 15-minute time-weighted average (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 of a substance above which it is 

predicted that the general population, including susceptible individuals, 

could experience notable discomfort, irritation, or certain asymptomatic 

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

transient and reversible upon cessation of exposure.

Acute Exposure Guideline 

Level 2

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

substance above which it is predicted that the general population, 

including susceptible individuals, could experience irreversible or other 

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

escape.

Acute Exposure Guideline 

Level 3

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

substance above which it is predicted that the general population, 

including susceptible individuals, could experience life-threatening health 

effects or death.

Long-Term Exposure

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

TLV-TWA Threshold Limit Value –TimeWeighted AverageThe TWA concentration for a conventional 8-hour workday and a 40-

hour workweek, to which it is believed that nearly all workers may be 

repeatedly exposed, day after day, for a working lifetime without adverse 

effect according to ACGIH. 

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

b EPA (2012)

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

According to the MSDS, exposure to isobutane may be irritating if inhalation, skin contact, or eye contact 

with isobutane occurs. The most likely pathway of exposure is through inhalation. Isobutane can cause 

symptoms of asphyxiation when present in concentrations high enough to significantly lower oxygen 

concentrations below 19.5 percent by volume, such as headaches, ringing in ears, dizziness, drowsiness, 

nausea, vomiting, depression of all senses, and also unconsciousness. Under some circumstances of overexposure (i.e., oxygen levels fall below 6 percent by volume), death may occur.

If isobutane is inhaled, person(s) should be immediately removed and exposed to fresh air. In accordance 

with the MSDS, EPA further recommends that if breathing is difficult, person(s) be given oxygen, 

provided a qualified operator is present, and medical attention be sought. Isobutane is not irritating to 

skin, but rapid evaporation of isobutane on the skin may cause frostbite. In the case of dermal exposure, 

the MSDS for isobutane recommends that person(s) immediately wash the affected area with water; if 

frostbite occurs, bathe (not rub) the affected area with lukewarm, not hot, water and consult a doctor. If 

water is not available, cover the affected area with a clean, soft cloth. Alternatively, if the fingers or hands 

are frostbitten, warm the affected area by placing it in the armpit; gently exercise the affected part while 

being warmed, and seek medical attention immediately. Isobutane exposure to the eye can cause 

irritation. In case of ocular exposure, the MSDS for isobutane recommends that person(s) immediately 

flush the eyes, including under the eyelids, with copious amounts of water for several 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 isobutane can be minimized by following the exposure 

guidelines and ventilation and PPE recommendations outlined in the MSDS for isobutane and this risk 

screen.
May 30, 2014 -- Final

7

7. FLAMMABILITY ASSESSMENT

ASHRAE Standard 34 classifies isobutane as a Class A3 refrigerant. Isobutane is flammable when its 

concentration in air is in the range of 1.8 percent and 8.5 percent by volume (18,000 ppm to 85,000 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 isobutane exceeds its lower 

flammability limit (LFL) of 18,000 ppm, posing a significant safety concern for workers and consumers if 

it is not handled carefully. The remainder of this section assesses flammability risks and summarizes the 

recommended measures to ensure safe handling and use of the refrigerant during manufacture, servicing, 

and end-use. 

7.1 Flammability Risks at Manufacture

EPA expects manufacturing to occur in a closed system and that all units are completely sealed before 

delivery and installation. If the vending machines are not charged and sealed in a closed system, EPA 

expects personnel to wear proper PPE (see Section 2) to protect themselves from releases or exposure to 

isobutane. In addition, manufacturing facilities are anticipated to maintain proper ventilation at all times 

during the manufacture of equipment containing isobutane and adhere to good manufacturing practices.

As a result, releases of isobutane during these manufacturing and installation operations in the presence of 

an ignition source are not anticipated. 

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

likelihood of catastrophic releases. For example, NFPA 58 Liquefied Petroleum Gas Code (NFPA 2014) 

for liquefied propane requires the use of overfill protection devices (OPD) on cylinders to minimize the 

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

requirements/guidelines. Similar equipment safety and procedural requirements should be developed for 

isobutane and other flammable refrigerants. EPA believes that because relevant safety standards, the 

MSDS for isobutane, 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 at Servicing and End-Use

The risk of flammability during servicing and end-use for the reasonable worst-case scenario and typical 

scenario (see Section 5) was investigated for propane. Both servicing and end-use of isobutane vending 

machines are expected to take place in the same room. In order to determine the potential flammability 

risks during servicing or end-use in case of a catastrophic release of refrigerant in an enclosed alcove (see 

Section 5), concentrations of isobutane immediately following a complete release of refrigerant, either 

accidental or deliberate (e.g., through vandalism or theft), were compared to the LFL for isobutane. The 

reasonable worst-case scenario assumes an effective room size of 15 m

3

and air exchange rate of 0.5 

ACH. In this scenario, the modeling results reflect the maximum concentration in the lower 0.4 meters of 

the room, as the upper portion of the room presents a much lower risk, with only 5 percent of the leaked 

refrigerant is present in this area, which also has a greater volume than the lower 0.4 meters of the room.

In the typical scenario, an effective room size of 27.5 m

3

is assumed while the modeling results reflect the 

maximum concentration in the entire room, as a vertical concentration gradient is not assumed. Table 6 

presents the results of the analysis. 
May 30, 2014 -- Final

8

Table 6. Flammability Assessmenta

Scenario Charge Size

(g)

Effective Room 

Size (m3)

Vertical 

Concentration 

Gradient Height 

(m)

Maximum 

Instantaneous 

Concentration

(ppm) b,c

Reasonable Worst-Case 150 15 (530 ft3

) 0.4 23,500

Typical 150 27.5 (972 ft3

) None 2,140

Threshold Analysis 1a: Charge Size 115 15 (530 ft3

) 0.4

18,000

Threshold Analysis 1b: Charge Size 1,260 27.5 (972 ft3) None

Threshold Analysis 2a: Room Size 150 19.6 (644 ft3

) 0.4

Threshold Analysis 2b: Room Size 150 3.3 (107 ft3

) None

Bold font indicates modeling results.

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

b Lower Flammability Limit of isobutane is equal to 18,000 ppm.

c Values provided in these columns refer to the concentration in the lower 0.4 meters of the room, which presents the most conservative risk as 

95 percent of the leaked refrigerant in present in this space.

In the reasonable worst-case scenario, at a charge size of 150 grams, the maximum instantaneous 

concentration of isobutane in the lower 0.4 meters of the room would be approximately 23,500 ppm, 

which is 130 percent of the LFL for isobutane (see Table 6). In the typical scenario, the maximum 

instantaneous concentration of isobutane in the entire room would be approximately 2,140 ppm, which is 

12 percent of the LFL for isobutane. However, the accidental release of all refrigerant into the enclosed 

alcove is highly unlikely. This is because the refrigerant system is located in a protected compartment on 

the back side of the vending machine and accidents resulting in a puncture to the compressor, whether 

through attempted theft of the vending machine contents or vandalism, would be unlikely. In the case of 

accidental release, however, isobutane is likely to be dispersed into the air evenly and almost 

instantaneously upon release; the vending machine compressor is pressurized, which will cause isobutane

to be released into the room (assumed to be at atmospheric pressure of approximately 14.7 psi) under 

pressure, resulting in the refrigerant’s quick and turbulent release, and subsequent mixing into the air. 

However, it is also unlikely that 100 percent of the refrigerant charge will be released from the system 

because as the refrigerant leaks, the system pressure will decrease and eventually equilibrate with 

atmospheric pressure, leaving a small amount of refrigerant in the system. To completely remove the 

entire refrigerant charge from the system, a vacuum pump must be used.

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

could cause an explosion. For the flammability threshold analysis, the conditions at which a flammability 

concern would exist (i.e., when the maximum instantaneous concentration in the lower 0.4 meters of the 

enclosed alcove equals the LFL for isobutane) was determined. Under the room size, ventilation rate, and 

vertical concentration gradient assumed within the reasonable worst-case scenario, the charge size of the 

isobutane refrigeration unit would have to be at least 115 grams for a flammability concern to exist, as 

shown in Threshold Analysis 1a. Under the room size and ventilation rate assumed within the typical 

scenario, the charge size of the isobutane refrigeration unit would have to be at least 1,260 grams for a 

flammability concern to exist, as shown in Threshold Analysis 1b. Using a 150-gram refrigeration unit, as 

shown under Threshold Analysis 2a and 2b, the volume of the room would have to be smaller than 20 m

3

(710 ft3) or 3.3 (107 ft3) for a flammability risk to occur under the reasonable worst-case and typical

scenarios, respectively. EPA recommends that in addition to the RCL, these guidelines be followed to 

further minimize risk of flammability. 

According to the results of this flammability analysis, the risk of fire is minimal if a vending machine is 

installed in a room with volumes in accordance with standards and regulations. According to ASHRAE 

Standard 34, the RCL for isobutane (9.6 g/m3of isobutane or 4,000 ppm by volume) should not be 
May 30, 2014 -- Final

9

exceeded in any room that contains an isobutane vending machine. EPA recommends that in addition to 

the RCL, these guidelines be followed to further minimize risk of flammability. For this reason, it is 

important that only properly trained and certified technicians handle isobutane. As a further precaution, 

certification requirements and training programs for technicians that handle isobutane 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.

Vending machines should not be installed in small, poorly ventilated spaces such as very small enclosed

areas or storage closets (especially as other equipment or appliances in the space would reduce the 

effective volume of the room). For vending machines installed in larger areas, the risk of fire and 

explosion is minimal. Vending machines installed with isobutane should be clearly labeled as containing 

a flammable refrigerant and designed to prevent catastrophic leaks. The installation of leak prevention 

devices would further protect against the very limited risk of explosion. EPA believes that the risk of fire 

is minimal if an isobutane vending machine is installed in a room with volumes and ventilation in 

accordance with standards, MSDS, and recommendations. 

8. ASPHYXIATION ASSESSMENT

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

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

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

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

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

risk with the charge size specified in the worst-case scenario. This analysis does not consider 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, this analysis 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 Charge Size (g) Effective Room Size 

(m3)

Vertical 

Concentration 

Gradient Height 

(m)

Percent Oxygen 

Concentrationb

Reasonable Worst-Case 150 15 (530 ft3

) 0.4 21

Typical 150 27.5 (972 ft3

) None 21

Threshold Analysis 1a: Charge Size 2,550 15 (530 ft3

) 0.4 12

Threshold Analysis 1b: Charge Size 28,020 27.5 (972 ft3

) None 12

Threshold Analysis 2b: Room Size 150 0.88 (31.2 ft3

) 0.4 12

Threshold Analysis 2b: Room Size 150 0.15 (5.2 ft3

) None 12

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) in the 

lower 0.4 meters of the room must be reduced to 12 percent.5 Based on the worst-case scenario and 

typical scenario modeling assumptions, isobutane in vending machines does not present a significant risk 

of asphyxiation. The concentration of isobutane in the air following the release of the 150-gram charge 

 

5 Twelve percent oxygen in air is the No Observed Adverse Effect Level (NOAEL) for hypoxia (ICF 1997).
May 30, 2014 -- Final

10

size does not exceed 2.5 percent or 1.4 percent in the reasonable worst-case and typical scenarios, 

respectively, which has an insignificant impact on the normal concentration of oxygen in air. Because 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, 

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 in Threshold Analysis 1a and 1b, the minimum charge of 

isobutane necessary to reduce the oxygen levels to 12 percent in air in the lower 0.4 meters of a room of 

volume 15 m

3

(530 ft3) and 27.5 m3(972 ft3) was calculated to be 2,550 grams and 28,020 grams, which 

are 17 and 187 times the maximum UL 541 charge size of 150 grams. These analyses, Threshold Analysis 

1a and 1b, assumed that 1) nitrogen and oxygen retain the same relative volumes in the rooms with the 

balance composed entirely of isobutane, and 2) the pressure of the room does not increase significantly 

with the addition of the refrigerant. As shown in Threshold Analysis 2a, for asphyxiation to be of concern 

with the proposed maximum charge size of 150 grams, the effective volume of the enclosed alcove would 

have to be about 0.88 m

3

(31.2 ft3) (see Table 7), which is smaller than the size of the vending machine 

itself. As shown in Threshold Analysis 2b, for asphyxiation to be of concern with the proposed maximum 

charge size of 150 grams and assuming no vertical concentration gradient in a 27.5 m3room, the effective 

volume of the enclosed alcove would have to about 0.15 m3(5.2 ft3), which is also smaller than the size of 

the vending machine itself. Based on the worst-case modeling results and threshold analysis, EPA does 

not believe that the use of isobutane in vending machines poses a significant risk of asphyxiation or 

impaired coordination to consumers.

9. END-USE EXPOSURE ASSESSMENT

This section presents estimates of potential consumer exposures to isobutane in vending machines. An

end-use exposure analysis was performed to examine potential catastrophic releases release of the 

proposed substitute under the reasonable worst-case scenario and typical scenario outlined in Section 5. 

For the end-use exposure assessment scenario, 30-min TWA exposures for the proposed substitute were 

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

concentrations on a minute-by-minute basis. The analysis was undertaken to determine the 30-minute 

TWA exposures of isobutane, because consumers are anticipated to only spend short amounts of time in 

the presence of vending machines while purchasing and consuming products. These exposure were then 

compared to the standard toxicity limits presented in Table 4 to assess the risk to end-users. However, the 

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

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

individuals would be exposed. Modeling results are presented in Table 8.
May 30, 2014 -- Final

11

Table 8. End-Use Exposure Assessmenta

Scenario Charge 

Size (g)

Effective Room 

Size (m3)

Ventilation 

Rate (ACH)

Vertical 

Concentration 

Gradient

Height (m)

30-minute TWA 

End-Use 

Exposureb,c

(ppm)

Reasonable Worst-Case 150 15 (530 ft3) 0.5 0.4 20,900

Typical 150 27.5 (972 ft3) 1.5 None 1,520

Threshold Analysis 1: Charge Size 50 15 (530 ft3) 0.5 0.4

6,900

Threshold Analysis 1b: Charge Size 680 27.5 (972 ft3) 1.5 None

Threshold Analysis 2a: Room Size 150 45 (1,590 ft3) 0.5 0.4

Threshold Analysis 2b: Room Size 150 6.1 (199 ft3) 1.5 None

Threshold Analysis 3a: Ventilation Rate 150 15 (530 ft3) 6.6 0.4

Threshold Analysis 3b: Ventilation Rate 150 27.5 (972 ft3) 0 None

Bold font indicates modeling results.

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

b 30-min AEGL-1 STEL for propane is 6,900 ppm ;See Table 4 for more information.

c Values provided in this column refer to the concentration in the lower 0.4 meters of the room, which presents the most conservative risk as 95 

percent of the leaked refrigerant in present in this space. 

In the reasonable worst-case scenario and typical scenario described in Section 5, catastrophic releases of 

isobutane from a vending machine with a charge size of 150 grams was modeled. During the release event 

in the typical scenario, the 30-min TWA end-use exposure concentration does not exceed 22 percent of 

the EGL for isobutane of 6,900. Under the reasonable worst-case scenario, the EGL for isobutane of 

6,900 ppm is likely to be exceeded (see Table 8). However, such consumer exposure is unlikely, as the 

reasonable worst-case scenario (see Section 5) assumes that 95 percent of the refrigerant is leaked into the 

lower 0.4 meters of the room, where it is unlikely that persons would be contained. In addition, these 

modeled exposures were derived using conservative assumptions (e.g., minimum room volume, low 

ventilation rate [0.5 ACH], maximum charge size) that do not necessarily reflect the typical location for 

isobutane vending machine installations (e.g., vending machines will be installed in commercial 

buildings, which have higher ventilation rates).

Nonetheless, these potential exposures emphasize the importance associated with proper equipment 

installation (i.e. matching charge size with room dimensions). A threshold analysis was performed to 

determine the charge size, minimum room volume, and ventilation rates where vending machines 

containing isobutane could be installed to avoid the short-term exposure limit for isobutane. Under the 

reasonable worst-case scenario in Threshold Analysis 1a, the maximum charge size that should be 

installed in a room of 15 m

3

(530 ft3) volume is 50 grams. Under the typical scenario in Threshold 

Analysis 1b, the maximum charge size that should be installed in a room of 27.5 m3(972 ft3) volume is 

680 grams. If the maximum charge size of 150 grams is used in vending machines, the vending machines 

should be installed in larger spaces with higher ventilation rates (i.e., assuming the conditions in the 

reasonable worst-case scenario, vending machines should be installed in rooms that are at least 45 m

3

[1,590 ft3] at a ventilation rate of 0.5 ACH or vending machines installed in a space of 15 m

3

[530 ft3] 

must have a ventilation rate of at least 6.6 ACH [see Threshold Analysis 2a and 3a]). Assuming more 

conservative conditions in the typical scenario in Threshold Analysis 2b and 3b, vending machines should 

be installed in rooms that are at least 6.1 m3(199 ft3) at a ventilation rate of 1.5 ACH while vending 

machines installed in a large space of 27.5 m

3

(972 ft3) do not require ventilation.

Because end-use exposure is only a concern under the most conservative scenario, EPA recommends 

these minimum room and ventilation rate guidelines to ensure that if a catastrophic leak of isobutane

occurs, it is not anticipated to result in a significant risk to consumers at end-use. To prevent exposure and 

potential serious side effects during larger releases, EPA recommends that the charge size for an 

isobutane vending machine does not exceed the RCL (9.6 g/m3) and proposes to require compliance with 

UL 541 in any space containing a vending machine, unless proper leak protection devises are in place in 
May 30, 2014 -- Final

12

order to prevent exposures of isobutane beyond the recommended limits. Additionally, these room 

volume and ventilation rate requirements simultaneously ensure that there is not a significant 

flammability or asphyxiation risk, as these requirements are more restrictive than the room sizes 

recommended in the flammability and asphyxiation assessments (see Sections 7 and 8). Proper leak 

protection devices and engineering control requirements and adherence to the MSDS 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 isobutane. EPA expects that the manufacture of isobutane refrigerant (i.e., formulation 

mixing) and the charging of isobutane vending machines (i.e., receiving, blending. and filling operations) 

is expected to occur in a closed system; all units should be completely sealed before delivery and 

installation. As a result, exposure during these manufacturing and installation operations is not 

anticipated. 

To ensure that use of the proposed substitute in vending machines does not pose an unacceptable risk to 

workers during servicing and disposal, occupational exposure modeling was performed using a boxmodel 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. Estimates of refrigerant release per event for various release scenarios and data 

on number of events were obtained from the Vintaging Model.6 For the vending machine end use,7the 

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

and 35 percent of the equipment charge during disposal.8 Additionally, EPA is proposing to allow 

intentional venting or release of isobutane as a refrigerant during installation, servicing, maintenance and 

disposal from vending machines. If venting does occur, EPA recommends that it is done in a wellventilated area (e.g., outdoors). Therefore, scenarios in which 100 percent of the equipment charge was 

released during servicing and disposal were also considered. The release rate per event was multiplied by 

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

per workday was assumed to equal the maximum number of units anticipated to be serviced in one day

(eight units) divided by eight hours per workday. These assumptions result in approximately 8 events per 

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

The modeled exposure concentrations were compared to short-term occupational exposure limits at 

installation and servicing and long-term exposure limits at disposal.

10.1 Occupational Exposure at Servicing

The potential occupational exposure during servicing was analyzed. The maximum 30-minute TWA 

exposure for isobutane was estimated for the servicing exposure scenario and compared to its STEL. As 

summarized in Table 9, modeling results indicate that the maximum occupational exposure 

concentrations to isobutane at no point exceed 0.01 percent and 3.3 percent of the STEL for isobutane 

with a 150-gram charge size for both 0.25 percent release and 100 percent release of refrigerant during 

servicing, respectively. Because the exposure concentrations modeled under the conservative assumptions 

is significantly lower than the exposure limits for each constituent, occupational exposure to the proposed 

substitute during servicing is not considered a significant risk to workers. Further, the estimated 

 

6

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

the use and emissions of various ODS and their substitutes over a period of several years across 60 different end-uses. The 

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

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

and the initial ODS substance that the equipment contained. 

7

For the purposes of this assessment, vending machines were modeled as small retail food refrigeration units.

8 During disposal it is assumed that 100 percent of the refrigerant charge remains in the unit. 
May 30, 2014 -- Final

13

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

probability of occurrence. These types of systems are typically serviced by trained personnel using proper 

industrial hygiene techniques. 

Table 9. Occupational Risk Assessment at Servicinga

Component

30-minute TWA Occupational 

Exposure (ppm)

30-min Short Term 

Exposure Limits 

(ppm)

0.25% Release 100% Release

Isobutane 0.56 227 6,900b

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

b See Table 4 for more information.

10.2 Occupational Exposure at Disposal

Disposal of isobutane vending machines is expected to occur with limited frequency (up to approximately 

one disposal event per day) at disposal facilities and with limited duration of exposure to the refrigerant 

charge. Potential exposures to the refrigerant during recovery and disposal are expected to occur during 

activities related to draining the refrigerant from the vending machine into cylinders (e.g., connecting of 

pipes). Such activities and related exposure is anticipated to occur within 15-30 minutes (per event/day).

Table 10 displays the maximum estimated 8-hour TWA occupational exposure levels of isobutane during 

disposal. Based on the assumptions described in the beginning Section 10, the modeling indicates that 8-

hour worker exposure concentration for isobutane during the 35 percent and 100 percent release scenarios 

will at no point exceed 14 percent and 40 percent of the long-term exposure limit for isobutane during 

disposal of isobutane vending machines with a 150-gram charge size. Because each value is significantly 

lower than the exposure guidelines for each constituent, occupational exposure to the proposed substitute

during disposal does not represent a true occupational health hazard. Further, the estimated exposures

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

of occurrence. These types of systems are typically disposed of by trained personnel using proper 

industrial hygiene techniques.

Table 10. Occupational Risk Assessment at Disposala

Component

8-Hour TWA Occupational 

Exposure (ppm)

8-Hour Long Term 

Exposure Limits 

(ppm)

35% Release 100% Release

Isobutane 139 401 1,000b

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

options.

b ACGIH TLV

Although anticipated occupational exposures are well below the exposure limits for each of the 

components of isobutane, the recommendations for proper engineering controls and PPE (e.g., safety 

glasses and gloves) in the MSDS for isobutane should be followed. Adequate ventilation should always 

be established during any use, handling, or storage of isobutane. Engineering controls should include 

vapor-in air detection systems and local exhaust ventilation during use of isobutane to prevent dispersion 

of isobutane throughout the work place. In addition, an eye wash and safety shower should be near the 

manufacturing facility and locations where isobutane is stored and ready for use. EPA believes that if 

proper handling and disposal guidelines are followed in accordance with good industrial hygiene and 
May 30, 2014 -- Final

14

manufacturing practices and the MSDS for isobutane, there is no significant risk to workers during the 

manufacturing, installation, servicing, and disposal of isobutane in vending machines.

11. GENERAL POPULATION EXPOSURE ASSESSMENT

Isobutane is not expected to cause a concern for human health in the general population when

manufactured for use and used as a refrigerant in vending machines. The proposed substitute will be 

manufactured in a closed process and is proposed for use in closed systems, and thus, significant releases 

are not anticipated. At room temperature, isobutane is a gas and, therefore, releases to ground or surface 

water are not anticipated, as isobutane 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 keep 

isobutane concentrated). Should air releases during manufacturing operations occur, engineering controls 

should be used (e.g. carbon absorption scrubbers) to collect isobutane and prevent the release of isobutane 

to the atmosphere. EPA believes that by using proper engineering controls and by following disposal and 

containment recommendations outlined in the proposed substitute’s MSDS, exposure to isobutane is not 

expected to pose a significant toxicity risk to the general population.
May 30, 2014 -- Final

15

12. REFERENCES

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

American Conference of Governmental Industrial Hygienists. Available online at: www.acgih.org. 

ACGIH. 2012. Guide to Occupational Exposure Values. American Conference of Governmental 

Industrial Hygienists.

ANSI/ASHRAE. 2010a. Standard 15: Safety Standard for Refrigeration Systems. American Society of 

Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ANSI/ASHRAE. 2010b. Standard 34: Designation and Safety Classification of Refrigerants. American 

Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 

ANSI/ASHRAE. 2013a. Standard 62: Ventilation for Acceptable Indoor Air Quality. American Society 

of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Braker W, Mossman AL. 1980. Matheson gas data book. 6th ed. Secaucus, NJ: Matheson Gas Products, 

pp. 615623. 

Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. 

Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland. 2007. Changes in 

Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007:The Physical Science 

Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel 

on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and 

H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

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.

IPCC/TEAP. 2005. Bert Metz, Lambert Kuijpers, Susan Solomon, Stephen O. Andersen, Ogunlade 

Davidson, José Pons, David de Jager, Tahl Kestin, Martin Manning, and Leo Meyer (Eds). Safeguarding 

the Ozone Layer and the Global Climate System. Intergovernmental Panel on climate Change 

Technology and Economic Assessment Panel. Cambridge University Press, UK. pp 478.

Kataoka, O., M. Yoshizawa, & T. Hirakawa 2000. “Allowable Charge Limit of Flammable Refrigerants 

and Ventilation Requirements.” Daikin Industries. International Refrigeration and Air Conditioning 

Conference. Paper 506. Available online at: http://docs.lib.purdue.edu/iracc/506.

Mackenzie, F.T. and J.A. Mackenzie. 1995. Our changing planet. Prentice-Hall.

NFPA. 2014. NFPA Liquified Petroleum Gas Code. 2014 Edition.

NIOSH. 1996. Propane: IDLH Documentation. August 1996. Accessed 17 Feburary 2009. Available 

online at: < http://www.cdc.gov/niosh/idlh/74986.html>.

OSHA. 2004. “Safety and Health Topics: Isobutane.” February 2004. Available online at: 

http://www.osha.gov/dts/chemicalsampling/data/CH_247840.html. 

UL. 2011. UL 541: Standard for Refrigerated Vending Machines. Underwriters Laboratory.
May 30, 2014 -- Final

16

U.S. Department of Energy (DOE). 2008. DOE Handbook – Temporary Emergency Exposure Limits For 

Chemicals: Methods And Practice. Available online at: http://orise.orau.gov/emi/scapa/files/doe-hdbk1046-2008_ac.pdf.

U.S. EPA. 1994. Significant New Alternatives Policy Technical Background Document: Risk Screen on 

the Use of Substitutes for Class I Ozone-depleting Substances: Refrigeration and Air Conditioning. 

Stratospheric Protection Division. March, 1994.

U.S. EPA. 1997. Exposure Factors Handbook. National Center for Environmental Assessment, Office of 

Research and Development. Available online at: http://www.epa.gov/ncea/pdfs/efh/front.pdf.

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

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

U.S. EPA. 2014. Draft Assessment of the Potential Impact of Hydrocarbon Refrigerants on Ground Level 

Ozone Concentrations. Prepared for the U.S. EPA Stratospheric Protection Division by ICF International. 

February 24, 2014.

Vending Solutions. 2009. “Soda Machines.” Available online at: 

http://www.vendingsolutions.com/vending-machines/. 

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

Global Ozone Research and Monitoring Project—Report No. 52, 516 pp., Geneva, Switzerland, 2011.