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 ODS-using sectors including: refrigeration and air conditioning, solvent cleaning, foam blowing, aerosols, fire suppression, adhesives, coatings and inks, and sterilization. The results of these risk screens are presented in a series of Background Documents that are available in EPA's docket.
The purpose of this risk screen is to supplement EPA's Background Document on the refrigeration and air conditioning sector (EPA 1994) (hereinafter referred to as the Background Document) 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%
           [a]Note 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 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, 34, 62.1, and 62.2,  and American National Standards Institute (ANSI)/Underwriters Laboratories (UL) 541. 
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. 

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
                                    ~100[c]
                                    CFC-12
                                    0.82[d]
                                    10,900
                                     100 a
                                   R-502[e]
                                    0.2[d]
                                     4,650
                                      NA
                                    HCFC-22
                                    0.04[d]
                                     1,810
                                     12 a
                                   R-410A[e]
                                       0
                                     2,088
                                      NA
                                   R-404A[f]
                                       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)
[d] WMO (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 HFC-125 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 end-use 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 ft[2] (10.0 m[2]) and a height of 9 ft (2.7 m), equivalent to a volume of 27.5 m[3] (972 ft[3]) -- and a larger, more typical room size of 63.0 m[3] (2,225 ft[3]) 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 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 - m[3])
                                     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 well-ventilated 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 Long-term Exposure Limit (ppm)
                   15-Minute Short-term Exposure Limit (ppm)
                       Impairment Exposure Level (ppm) 
                                      CO2
                                    5,000a
                        (OSHA PEL/NIOSH REL/ACGIH TLV)
                                   30,000[a]
                (NIOSH STEL-REL/ NIOSH STEL-REL/ACGIH STEL-TLV)
                                  40,000[a,b]
                                 (NIOSH IDLH)
        [a]OSHA 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."

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 ppmv 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 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 (m[3])
                             Stratification Height
                                 Charge (g)[a]
                      Room Size Causing Impairment (m[3])
                         Charge Causing Impairment (g)
                        Enclosed Space/Vending Machine
                               27.5 (972 ft[3])
                                     0.4 m
                                      500
                               20.8 (735 ft[3])
                                      647
                                       
                               27.5 (972 ft[3])
                                     None
                                      500
                               3.0 (32.5 ft[3])
                                     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 ft[3]) 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 m[3] (735 ft[3]) 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 m[3], 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 ft[3]) 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 ft[3]), 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 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 (m[3])
                      Horizontal Stratification Assumed?
                                Charge Size (g)
                       15-minute Consumer Exposure (ppm)
                                 1-Worst-Case
                                       0
                               27.5 (972 ft[3])
                                      Yes
                                      500
                                    64,500
                                       2
                                       0
                               27.5 (972 ft[3])
                                      No
                                      500
                                     9,900
                                       3
                                       0
                               27.5 (972 ft[3])
                                      Yes
                                      227
                                    29,300
                                       4
                                      1.5
                               27.5 (972 ft[3])
                                      Yes
                                      500
                                    54,400
                                       5
                                       0
                              63.0 (2,225 ft[3])
                                      Yes
                                      500
                                    28,200
                                       6
                                      1.5
                               27.5 (972 ft[3])
                                      No
                                      500
                                     8,300
                      7- Typical Conservative Conditions
                                      1.5
                               27.5 (972 ft[3])
                                      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 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.  For the vending machine end use, the release was conservatively assumed to be 3 percent of the equipment charge during disposal.  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 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 end-use. 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 Long-Term Exposure Limit (ppm)[a]
                                      CO2
                                     17.7
                                     5,000
                   [a]See 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 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).
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.
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