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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: Carbon Dioxide (CO2)

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) by adding to the 

list of potential substitutes for CFC-12, HCFC-22 and R-502 in the vending machine end-use. The 

specific proposed ODS substitute examined in this risk screen is carbon dioxide (CO2, or R-744) for new 

vending machines. Table 1 presents the composition of the proposed substitute.

Table 1. Composition of CO2

Constituent Chemical 

Formula

CAS Number Concentration

(Weight Percent)a

Carbon Dioxide 

(R-744) CO2 124-38-9 ≥99.5%

Water H2O 7732-18-5 0.002%

Nitrogen N2 7727-37-9 0.0005%

Acid SO2 7446-09-5 0.00001%

aNote that less than 0.05 percent of CO2 is composed of impurities. These impurities are reasonably 

anticipated to be present when the proposed substitute is manufactured for commercial purposes; however, 

these impurities are not thought to be present in quantities sufficient to pose a risk to humans or to the 

environment.

The potential risks associated with the use of substitutes in refrigeration and air conditioning have been 

examined at length in the Background Document. The reader is referred to this reference for a detailed 

discussion of the methodologies used to conduct this risk screen. This risk screen addresses flammability

risk from use and manufacture of CO2 in vending machines. Asphyxiation modeling was performed to 

ensure that use of CO2 in vending machines does not present an unacceptable risk of asphyxiation;

occupational exposure modeling was performed to ensure that manufacture, installation, servicing, and 

disposal of the CO2 in vending machines does not pose an unacceptable risk to workers; and end-use 
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2

exposure modeling was also performed to ensure that typical use and potential catastrophic refrigerant 

releases of CO2 from vending machines does not pose an unacceptable risk to consumers. The proposed 

substitute is not anticipated to pose an unacceptable risk to the population at large. 

Section 2 summarizes the results of the risk screen for the proposed substitute blend listed in Table 1. 

The remainder of the risk screen is organized into the following sections:

 Section 3: Atmospheric Assessment

 Section 4: Discussion of End-Use Scenario Modeled

 Section 5: Flammability Assessment

 Section 6: Potential Health Effects 

 Section 7: Asphyxiation Assessment

 Section 8: End-Use Exposure Assessment 

 Section 9: Occupational Exposure Assessment

 Section 10: General Population Exposure Assessment

 Section 11: Volatile Organic Compound Assessment 

 Section 12: References

2. SUMMARY OF RESULTS

CO2 is recommended for SNAP approval for the vending machine end-use. 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. No significant asphyxiation risks to consumers or toxicity risks to 

workers, consumers, or the general population are expected. Given that the CO2 MSDS and vending 

machine installation manual will be adhered to and that the appropriate safety and personal protective 

equipment (PPE) (OSHA Category B) will be used during manufacture, installation and servicing, and 

disposal of CO2 vending machines, worker exposure to CO2 will be unlikely. Because units are to be

installed in locations with adequate space or ventilation in accordance with the vending machine 

installation manual, as discussed in greater detail in Section 9, significant risk to consumers is also 

unlikely. Additional safeguards are also provided by adherence to industry standards including American 

Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standards 15,

1

34,

2

62.1,

and 62.2,

3

and American National Standards Institute (ANSI)/Underwriters Laboratories (UL) 5414. 

3. ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to atmospheric integrity posed by the use of CO2 

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 and has lower climate impact than

CFC-12, HCFC-22 and R-502, as well as other substitutes examined in the Background Document. 

 

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 62.1 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.

Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings ASHRAE Standard 62.2 defines minimum 

requirements to provide acceptable indoor air quality in low-rise residential buildings.

4ANSI/UL 541: Refrigerated Vending Machines 
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3

Table 2. Atmospheric Impacts of CO2 Compared to Other Vending Machine Refrigerants

Refrigerant Ozone Depleting Potential 

(ODP)

Global Warming Potential

(GWP)a

Atmospheric Lifetime in 

Years (ALT)b

CO2 0 1 ~100c

CFC-12 0.82d 10,900 100 a

R-502e 0.2d 4,650 NA

HCFC-22 0.04d 1,810 12 a

R-410Ae 0 2,088 NA

R-404Af 0 3,922 NA

a

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

b NA= not available. Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. 

c CDIAC (2012)

dWMO (2010) 

e R-502 is a blend consisting of HCFC-22 (49%) and CFC-115 (51%). The ALT for HCFC-22 is 12 years and the ALT for CFC-115 is 1,700 

years.

f R-410A is a blend consisting of HFC-32 (50%) and HFC-125 (50%). The ALT for HFC-32 is 4.9 years and the ALT for HFC-125 is 29 years.

g R-404A is a blend consisting of HFC-143a (52%), HFC-125 (44%) and HFC-134a (4%). The ALT for HFC-143a is 52 years, the ALT for HFC125 is 29 years, and the ALT for HFC-134a is 14 years.

4. DISCUSSION OF END-USE SCENARIOS MODELED

Four factors are considered when deriving end-use scenarios to model potential exposures. The first is the 

refrigerant charge size – higher charge sizes would lead to higher potential exposures. The second is room 

size for units installed inside – smaller room sizes would lead to higher potential exposures. The third 

factor is ventilation – lower ventilation rates would lead to higher potential exposures. The fourth factor is 

whether the refrigerant stratifies within a space over a specified time; if stratification occurs, then during a 

leak concentrations would be higher where the refrigerant has stratified (e.g., close to the floor) and lower 

elsewhere (e.g., close to the ceiling).

For each of these factors, two situations are examined, as explained below. Of the possible 16 

combinations of these factors, two are examined in terms of asphyxiation (Section 7) and seven are 

examined for end-use exposure (Section 8).

Charge Size. The submission states that CO2 vending machines will have a typical charge size of eight 

ounces (227 grams), although the compressor manufacturer indicates a maximum charge size of 500

grams may be used. The submitter indicates, however, that while the specific compressor model allows 

for up to 500 grams, the other refrigeration components (e.g., gas-cooler, cold-end heat exchanger, 

capillary tube expansion device) of an R-744 vending machine will not require the entire 500-gram 

charge size and can be charged with a smaller amount of refrigerant. To represent various scenarios, it is 

assumed that a catastrophic leak of refrigerant occurs while the vending machine is installed at the enduse and the full charge of the unit is assumed to be emitted over the course of one minute. Because 

vending machines can be installed in a wide range of locations with varying room volumes, the analysis 

in this risk screen conservatively examines a vending machine containing either the maximum charge size 

(500 grams) or the typical charge size (227 grams). 

Room Size. Likewise, both the minimum room size indicated by the submitter (Coca-Cola 2011)—a floor 

area of 108 ft2(10.0 m

2

) and a height of 9 ft (2.7 m), equivalent to a volume of 27.5 m

3

(972 ft3)—and a 

larger, more typical room size of 63.0 m3(2,225 ft3) are considered.

Ventilation Rate. These rooms are assumed to have a conservatively low ventilation rate (1.5 air changes 

per hour) or no ventilation at all (0 air changes per hour). 

Stratification. Horizontal stratification is also examined. If stratification is assumed, since CO2 is denser 

than air (specific gravity of CO2 relative to air is 1.52 [air = 1]), it is assumed the refrigerant will settle in 

higher concentrations closer to the ground. In order to simulate the horizontal stratification, it is assumed 
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that 95 percent of the leaked refrigerant mixes evenly into the bottom 0.4 meter of the room, and the rest 

of the refrigerant mixes evenly in the remaining volume (Kataoka 1999). Table 3 details the worst-case 

scenario end-use modeling assumptions used throughout the risk screen (i.e., in Sections 7, 8, and 9).

Table 3. Worst-Case Scenario Model Assumptions for Submission

Parameter Assumption

Refrigeration Unit Vending Machine

Room Enclosed Room

Charge Size (g) 500

Length of Release (minutes) 1

Room Size (volume - m3) 27.5

Room Ventilation (air 

changes per hour) 0

Horizontal Stratification Yes

EPA recognizes that while the majority of vending machines may be placed outdoors or in other wellventilated areas, which would largely address the risk of asphyxiation and end-use exposure, there may a 

few instances in which the end user chooses to include multiple vending machines in an enclosed space or 

chooses to place a vending machine unit in a very small enclosed space (with the size of the vending 

machine being the limiting factor). To address these concerns, this risk screen incorporates threshold

analyses in addition to the scenario modeling described above, in order to determine the room size, charge 

size, and ventilation rate requirements to ensure that use of CO2 in vending machines does not present a 

significant risk to consumers. 

5. FLAMMABILITY ASSESSMENT

CO2 is classified by ASHRAE Standard 34 as an A1 refrigerant, and is considered to be nonflammable. 

Based on this classification, manufacture, servicing, and use of CO2 is not expected to present a 

flammability risk.

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. For the occupational exposure analysis, potential risks from chronic and acute worker 

exposure were evaluated by comparing exposure concentrations to available occupational exposure limits. 

Table 4 lists the relevant toxicity limits. EPA’s approach for identifying or developing these values is 

discussed in Chapter 3 of the Background Document. 

Table 4. Exposure Limits for Carbon Dioxide

Proposed 

Substitute

8-Hour TWA Longterm Exposure

Limit (ppm)

15-Minute Short-term 

Exposure Limit (ppm)

Impairment Exposure 

Level (ppm) 

CO2

5,000a

(OSHA PEL/NIOSH 

REL/ACGIH TLV)

30,000a

(NIOSH STEL-REL/

NIOSH STEL-REL/ACGIH 

STEL-TLV)

40,000a,b

(NIOSH IDLH)

aOSHA PEL, NIOSH REL and NIOSH IDLH available at: http://www.cdc.gov/Niosh/npg/npgd0103.html

b IDLH = “Immediately Dangerous to Life and Health,” an airborne concentration over 30 minutes that is “likely to cause death or 

immediate or delayed permanent adverse health effects or prevent escape from such an environment.”
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CO2 is considered to be a generally recognized as safe (GRAS) substance by the U.S. Food and Drug 

Administration (FDA). However, according to the MSDS, exposure to CO2 may be hazardous if 

inhalation, skin contact, or eye contact with the proposed substitute occurs at sufficiently high levels. CO2

is moderately irritating to the respiratory system and can cause rapid suffocation, and, like other instances 

of low oxygen volumes, can cause symptoms of asphyxiation when present in concentrations high enough 

to significantly lower oxygen concentrations below 19.5% by volume, such as headaches, ringing in ears, 

dizziness, drowsiness, nausea, vomiting, depression of all senses, and also unconsciousness. Damage may 

occur to the lungs, cardiovascular system, and central nervous system and under some circumstances of 

over-exposure (i.e., oxygen levels fall below 6% by volume), death may occur. Concentrations of CO2 of 

4% by volume (40,000 ppm) may cause headache, dizziness, increased blood pressure, or uncomfortable 

dyspnea (shortness of breath) within a few minutes. Concentrations of CO2 of 6% by volume may cause 

effects such as hearing and visual disturbances, alterations to heartbeat, headache and dyspnea in a few 

minutes, with more severe effects at higher concentrations (EPA 2000).

If excess quantities of CO2 are inhaled, person(s) should be immediately removed and exposed to fresh 

air. In accordance with the MSDS, EPA further recommends that if the person is not breathing or the 

breathing is irregular, person(s) be given oxygen or artificial respiration, provided a qualified operator is 

present. Tight clothing, including collar or belt should be loosed and medical attention should 

immediately be sought. Rescuers should not attempt to retrieve victims of exposure to CO2 without 

adequate PPE. At a minimum, a self-contained breathing apparatus (SCBA) should be worn. 

Exposures of CO2 to the skin may cause frostbite or burns. In the case of dermal exposure, the MSDS for 

CO2 recommends that person(s) immediately wash the affected area with water for at least 15 minutes 

while removing all contaminated clothing; if frostbite occurs, bathe (do not rub) the affected area with 

lukewarm, not hot, water. 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. Clothing 

and shoes should be cleaned thoroughly before reuse. Exposures of CO2 to the eyes could cause eye 

irritation. In case of ocular exposure, the MSDS for CO2 recommends that person(s) immediately flush 

the eyes, including under the eyelids, with copious amounts of water for at least 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 CO2 are unlikely to occur when following the exposure guidelines and the 

ventilation and PPE recommendations outlined in the MSDS for CO2 and this risk screen.

7. ASPHYXIATION ASSESSMENT

This section summarizes an assessment of the asphyxiation risk associated with leakage of CO2 from 

vending machines and includes a discussion on the worst-case and threshold modeling performed. Based 

on the worst-case room size and charge size provided by the submitter (see Table 3), concentrations of O2

could drop to 14,030 ppmv, leaving oxygen levels above the asphyxiation threshold of 12,000 ppmv5 O2

(ICF 1997). Therefore, use of CO2 does not present an asphyxiation risk in the event of a catastrophic 

release. 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. If the proposed substitute passes the screening analysis with these restrictive 

 

5 Twelve percent oxygen in air is the No Observed Adverse Effect Level (NOAEL) for hypoxia. 
***** Final - July 26, 2012 *****

6

assumptions in place, it can be reasonably assumed that no risks of asphyxiation will be present under 

real-world conditions.

Additionally, a threshold analysis was also performed to evaluate the minimum room size and maximum

charge size that would present an asphyxiation risk, based on other assumptions provided by the submitter

being held constant. The results of the asphyxiation assessment are summarized in Table 5 below. 

Table 5. Asphyxiation Assessment

Room Type/Appliance 

Type

Reasonable Worst-Case Scenarios Asphyxiation Threshold 

Room 

Dimensions

(m3)

Stratification 

Height Charge (g)a

Room Size 

Causing 

Impairment (m3)

Charge Causing 

Impairment (g)

Enclosed Space/Vending 

Machine

27.5 (972 ft3) 0.4 m 500 20.8 (735 ft3) 647

27.5 (972 ft3) None 500 3.0 (32.5 ft3) 4,434

Based on the worst-case scenario modeling assumptions shown in the first row of Table 5, CO2 in 

vending machines does not present a significant risk of asphyxiation. The minimum charge of CO2

necessary to reduce the oxygen levels to 12 percent in air in the lower stratum (0.4 m above the ground) 

of a room of volume 27.5 m

3

(972 ft3) was calculated to be approximately 647 g assuming that 1) nitrogen 

and oxygen retain the same relative volumes in the rooms with the balance composed entirely of CO2, and 

2) the pressure of the room does not increase significantly with the addition of the refrigerant. This 

amount represents a charge size that is nearly 30% greater than the maximum CO2 vending machine 

charge size (500 grams), and over 60% greater than the typical charge size (227 grams). Charge 

requirements to reach the same effect in the upper stratum would be even higher because of the stratum’s 

larger volume and its lower CO2 concentration compared to the lower stratum. For asphyxiation to be of 

concern with the maximum charge size (500 grams), the volume of the enclosed room would need to be 

about 20.8 m3(735 ft3) or smaller (see Table 4). Assuming a square room with a square floor and a 

ceiling height of 2.7 m (9.0 ft), this equates to a 2.8 x 2.8 m (9.1 x 9.1 ft) space. Based on a more typical 

charge size of 227 grams, the enclosed room would have to be about 8.4 m3, or a 1.9 x 1.9 m space, 

assuming a 2.7 m ceiling height. 

Because the typical breathing zone is above 0.4 meters (1.3 feet) and mixing is likely to occur upon 

release of CO2 from the unit due to the system’s high pressure, an additional, more typical scenario, was 

modeled based on no stratification occurring (as shown in the second row of Table 5). Based on the 

maximum charge size (500 grams) the volume of the enclosed room would need to be about 3.0 m

3

(32.5

ft3) or smaller for an asphyxiation risk to occur (see Table 4), which is less than one-ninth of the smallest 

room size anticipated; based on a room size of 27.5 (972 ft3), the charge size would need to be over 4,434 

grams, over eight times the maximum charge size.

Because this threshold modeling does not take into account any ventilation that is likely to occur, such as 

conditioned airflow, open doors, or openings at the bottom of doors that allow air to flow in and out, as 

mentioned above, the actual asphyxiation risk to consumers is likely to be less than modeled. Further, 

these risks would be eliminated when adhering to the installation space and ventilation guidelines detailed 

in the MSDS and vending machine installation manual. Based on this information, EPA does not believe 

that use of the use of CO2 in vending machines poses a significant risk of asphyxiation to consumers. 

8. END-USE EXPOSURE ASSESSMENT

This section presents the results of an analysis that was performed to examine the acute/short-term 

consumer exposures associated with catastrophic leakage of the CO2 refrigerant charge from a vending 

machine. The analysis was undertaken to determine the 15-minute exposure for the proposed substitute 

because consumers are anticipated to be in the proximity of a vending machine only for short periods of 
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time (i.e., during purchase and delivery of the vended item from the machine). The 15-minute exposure 

concentration for CO2 was then compared to the exposure limits presented in Table 4 and the exposure 

levels causing health effects in section 6 (Potential Health Effects) to assess the risk to consumers. 

However, the modeled exposures 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 concentrations to which individuals would be exposed.

Using the reasonable worst-case scenario described in Section 4, modeling indicated that the highest 

concentrations of CO2 occur in the lower stratum of the room. The modeled levels of consumer exposure 

based on this analysis are presented as Scenario 1 in Table 6 below. Under these worst-case assumptions, 

the estimated 15-minute level of CO2 is about two times the proposed substitute’s STEL (30,000 ppm). 

This level is sufficiently high to cause visual and hearing disturbances, headache, dyspnea and possibly

alter heartbeat. However, it is important to consider that these exposures were derived using very 

conservative assumptions (e.g., no ventilation, maximum charge size, stratification occurring). Under the 

stratification assumptions, the potentially excessive exposure would occur below the breathing zone of 

most consumers (less than 0.4 meters, or 1.3 feet, above the ground).

Table 6. CO2 End-Use Exposure Assessment

Scenario

Air 

Exchange 

Rate (ACH)

Room Size (m3)

Horizontal 

Stratification 

Assumed?

Charge 

Size (g)

15-minute 

Consumer 

Exposure (ppm)

1-Worst-Case 0 27.5 (972 ft3) Yes 500 64,500

2 0 27.5 (972 ft3) No 500 9,900

3 0 27.5 (972 ft3) Yes 227 29,300

4 1.5 27.5 (972 ft3) Yes 500 54,400

5 0 63.0 (2,225 ft3) Yes 500 28,200

6 1.5 27.5 (972 ft3) No 500 8,300

7- Typical Conservative 

Conditions 1.5 27.5 (972 ft3

) No 227 3,800

In particular, the worst-case scenario was derived using conservative assumptions that do not necessarily 

reflect the typical location for CO2vending machine installations. For example, approximately half of 

vending machines are installed outdoors (Coca-Cola 2012). Further, most locations would be anticipated 

to have some level of ventilation, either through a ventilation system, room design, open windows, or 

spaces between the door and door frame in an enclosed room. An air exchange rate of 1.5 ACH, which is 

typical in commercial buildings (Turk et al. 1987 and Bennett et al. 2012), would reduce exposure 

concentrations by more than 10,000 ppm, as shown in Scenario 4 of Table 6.

In addition, the charge size modeled was 500 grams. This maximum charge size was based on the 

refrigerant capacity of a specialty model that is not a typical or average unit; the full 500 gram charge size 

is not necessary for the standard size vending machine which has a typical charge size of 227 grams. 

Under this typical charge size and the remaining worst-case scenario assumptions (Scenario 3), exposure 

would be below the 15-minute short-term exposure limit. 

The modeled worst-case exposure concentrations also reflect the highest concentration within the room 

(i.e., within the lower level of stratification). Because CO2 has a vapor density greater than one, it is 

likely to settle in the lower portion of the room, and so the reasonable worst-case scenario (see Section 4) 

conservatively assumes that 95% of the refrigerant is leaked into the lower 0.4 meters of the room. 

However, the proposed substitute will be used in vending machines under high pressure, especially as 

compared to that of a typical vending machine. This will cause CO2 to be released into the room (assumed 

to be at atmospheric pressure of approximately 1 bar [14.5 psi]) under high pressure, likely resulting in a 
***** Final - July 26, 2012 *****

8

quick and turbulent release of the refrigerant, and subsequent mixing into the air before any stratification 

would occur. Without the conservative stratification assumption, modeled maximum exposure 

concentrations would be 9,900 ppm over 15 minutes (Scenario 2), which is well below the STEL. It

should also be noted that a lower stratum of 0.4 meters would be below the typical breathing zone of most 

consumers for most of the time. 

Considering the typical conditions in which a CO2 vending machine would be used with conservative 

assumptions on room size and air exchange rate (Scenario 7), the potential consumer exposure could 

reach up to 3,800 ppm—about one-eighth the 15-minute STEL. Because consumer exposures are only a 

concern under the most conservative scenarios, EPA recommends that if the maximum charge size (500 

grams) is to be used in vending machines, that the vending machines be installed in larger spaces and/or

spaces with higher ventilation rates and/or engineering control requirements (e.g., local ventilation such 

as a fan or vents on doors to adjoining rooms) to reduce or eliminate the likelihood that potential 

consumer exposures exceed those described in Table 4. These recommendations are expected to be met 

when the vending machine installation manuals are followed. As such, a catastrophic leak of CO2 is not 

anticipated to result in a significant risk to consumers at end-use. 

9. OCCUPATIONAL EXPOSURE ASSESSMENT

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

disposal of CO2. To ensure that use of the proposed substitute in vending machines does not pose an 

unacceptable risk to workers during manufacture, servicing, and disposal, occupational exposure 

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

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

described in Chapter 5 of the Background Document. Estimates of refrigerant release for various release 

scenarios and data on number of manufacturing and disposal events in 2010 were obtained from the 

Vintaging Model.6 For the vending machine end use,7the release was conservatively assumed to be 3 

percent of the equipment charge during disposal.8 The release rate was multiplied by the number of units 

estimated to be disposed of during a workday, which was conservatively assumed to be 10 units during an 

8-hour work day. 

9.1 Occupational Exposure at Manufacture

To evaluate the risk of occupational exposure at manufacture, EPA modeled the exposure concentrations 

according to the method described in Chapter 5 of the background document, and according to release 

data from EPA’s Vintaging Model. These modeling results indicate that the maximum occupational 

exposure at manufacture would be 471 ppm (8-hour TWA), which is significantly below the 5,000 OSHA 

limit. Further, as indicated by the submitter, occupational exposure at manufacture is anticipated to occur 

only during charging of the vending machine at an average concentration of 350-360 ppm. These 

concentrations are similar to average global atmospheric concentrations of CO2, suggesting that actual 

releases of CO2 from manufacture of the units are too small to increase the typical occupational exposure 

concentrations above the background atmospheric concentration during these activities. Because the 

modeling results indicate that maximum occupational exposure at manufacture is well below levels of 

 

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 fluorocarbons 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, because vending machines are not modeled independently in the Vintaging Model, vending 

machines were modeled as small retail food refrigeration units.

8 During disposal it is assumed that only 90 percent of the refrigerant charge remains in the unit. 
***** Final - July 26, 2012 *****

9

concern and typical exposure concentrations are expected to be minimal, EPA does not believe that CO2

presents a significant risk to workers during manufacture.

9.2 Occupational Exposure at Installation and Servicing

As indicated by the submitter, charging of the vending machine unit typically will occur at the site of enduse. When this occurs, the submitter has indicated that charging equipment is designed to minimize 

potential emissions and that installation manuals describe procedures to reduce leakage and prior safety 

training is required for all personnel that would be charging units on site. Because of established 

equipment design and installation practices, exposures to emissions will be unlikely. Thus, EPA does not 

believe that installation, including charging, of a vending machine unit presents a concern to workers.

According to the submitter, CO2 vending machines are hermetically sealed and do not require periodic 

maintenance other than routine cleaning of the gas cooler coil. Thus, exposure to CO2 is not expected to 

occur. Furthermore, for cassette-type vending machines, the entire cassette (which contains the 

refrigerant) is sealed and can be replaced without breaching the refrigerant circuit while allowing the rest 

of the vending machine to remain on location. If a failure were to occur at the site of the vending machine

installation, the unit would be returned to the manufacturer. Repairs occurring in the manufacturer’s 

facility are not expected to exceed exposure concentrations at manufacture or disposal, and thus, are not 

considered to present a significant risk to workers. 

9.3 Occupational Exposure at Disposal

According to the submitter, the proposed substitute will not be recycled or reclaimed, but occupational 

exposure may occur at disposal during dismantling of the units. Disposal of vending machines is assumed 

to occur with limited frequency (approximately 1.25 disposal events per hour) at disposal facilities, over a 

typical 8-hour work day. The operating environment at disposal facilities required for typical units 

containing ODS or HFCs (negative pressure workplace air collection and processing) is such that

significant exposure to CO2 during dismantling operations would be unlikely.

Based on the assumptions described in this section, the modeling indicates that the 8-hour TWA 

concentration for CO2 will at no point exceed 1 percent of the long-term exposure limit for CO2 during 

disposal of the proposed substitute. Table 7 displays the maximum estimated 8-hour TWA occupational 

exposure level of CO2 during disposal. Because the value is significantly lower than the exposure 

guideline, occupational exposure to the proposed substitute during disposal is considered not to be a

toxicity concern. 

Table 7. Occupational Risk Assessment at Disposal

Proposed Substitute

Maximum 8-hour TWA 

Occupational Exposure 

Level (ppm)

8-Hour TWA LongTerm Exposure Limit

(ppm)a

CO2 17.7 5,000

aSee Table 5 for more information

Further, anticipated occupational exposures to CO2 are expected to be minimal when the proper 

engineering controls and PPE in the MSDS for CO2 are used and followed; following these precautions 

will also guard against the potential hazards associated with exposure to and handling of CO2 (see Section 

6). Adequate ventilation should always be established during any use, handling, or storage of CO2. 

Engineering controls are expected to include vapor-in air detection systems and local exhaust ventilation 

during use of CO2 to prevent dispersion of CO2 throughout the work place. In addition, an eye wash and 

safety shower should be near the manufacturing facility and locations where CO2 is stored and ready for 

use. In general, use of OSHA Category B or higher PPE is recommended, such as splash goggles,

chemically-resistance gloves, and a NIOSH-approved respirator. A self-contained breathing apparatus and 

full chemical-resistant suit should be worn in case of an accidental release (Coca-Cola 2011). EPA
***** Final - July 26, 2012 *****

10

believes that because proper handling and disposal guidelines are to be followed in accordance with good 

industrial hygiene and manufacturing practices and the MSDS for CO2, there is not a significant risk to 

workers during the manufacturing, installation, servicing, and disposal of CO2.

10. GENERAL POPULATION EXPOSURE

CO2 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 vending machines. As substantial quantities of CO2 exist

in the environment, releases of the proposed substitute are not expected to make significant additional 

contributions to ambient air, solid waste, or surface water. Thus, general population exposure is not 

expected to pose a toxicity concern to the general population. Furthermore, any commercial CO2 sales 

are based on recovery and distillation from ambient air and hence, any releases of ambient air-derived 

CO2 do not constitute an additional atmospheric CO2 contribution.

11. VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS

Carbon dioxide has been exempted as a VOC under the CAA (40 CFR 51.100).
***** Final - July 26, 2012 *****

11

12. REFERENCES

Bennett, D. H., Fisk, W., Apte, M. G., Wu, X., Trout, A., Faulkner, D. and Sullivan, D. 2012. Ventilation, 

temperature, and HVAC characteristics in small and medium commercial buildings in California. 

Indoor Air. doi: 10.1111/j.1600-0668.2012.00767.x. February 18, 2012.

Coca-Cola Refreshments USA, Inc. 2011. CO2 in Vending Machines. Significant New Alternatives Policy 

Program Submission to the United States Environmental Protection Agency. December 24, 2011. 

Coca-Cola Refreshments USA, Inc. 2012. Response to Incomplete SNAP Submission for CO2 in Vending 

Machines. March 2011. 

Carbon Dioxide Information Analysis Center (CDIAC). 2012. Recent Greenhouse Gas Concentrations. 

Updated February 2012. Available online at http://cdiac.ornl.gov/pns/current_ghg.html. Accessed 

May 1, 2012. 

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.

EPA 2000. Carbon Dioxide as a Fire Suppressant: Examining the Risks. Appendix B. Available online at 

http://www.epa.gov/ozone/snap/fire/co2/co2report.html

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.

Kataoka. 1999. “Allowable Charge Limit of Flammable Refrigerants and Ventilation Requirements.” 

Draft Proposal. O. Kataoka/Daikin/Japan, June, 1999.

NOAA (National Oceanic and Atmospheric Administration). 2012. Recent Global CO2. Trends in 

Atmospheric Carbon Dioxide. January 2012. Available online at: 

http://www.esrl.noaa.gov/gmd/ccgg/trends/global.html

Turk, BH; Brown, JT; Geisling-Sobotka, K; Froehlich, DA; Grimsrun, DT; Harrison, J; Koonce, JF; Prill, 

RJ; Revzan, KL. 1987. Indoor air quality and ventilation measurements in 38 Pacific Northwest 

commercial buildings. Volume 1: measurement results and interpretation. Final report. Prepared 

for U.S. DOE. DEAC03-76SF00098.

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.