Final - October 10, 2014 1 

## Significant New Alternatives Policy Program

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes in Refrigerated Transport

Substitute: Carbon Dioxide (CO 2 

### or R-744)

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 th e 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 sterili zation. 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 carbon dioxide (CO 2 or R-744) in the refrigerated transport end-use, specifically marine containers, trailers, trucks, a nd direct drive applications. Table 1 presents the composition of the proposed substitute, including the estimated concentrations of impurities, which may be present in the proposed substitute.
Table 1. Composition of CO 2

Constituent Chemical Formula CAS Number Concentration (Weight Percent) a Carbon Dioxide (R-744) CO 2 124-38-9 ≥ 99.9% Potential Impurities
Water H 2 O 7732-18-5 ≤ 10 ppm

Air N/A 132259-10-0 ≤ 250 ppm Hydrocarbons N/A N/A ≤ 50 ppm High Boiling Residue N/A N/A ≤ 5 ppm

Section 2 summarizes the results of the risk screen fo r 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: Volatile Organic Compound Assessment

 Section 5: Potential Health Effects

 Section 6: Discussion of End-Use Scenarios

 Section 7: Flammability AssessmentFinal - October 10, 2014 2  Section 8: Asphyxiation Assessment

 Section 9: End-Use Exposure Assessment

 Section 10: Occupational Exposure Assessment

 Section 11: General Population Exposure Assessment

 Section 12: References



### 2. SUMMARY OF RESULTS

CO 2 is recommended for SNAP approval for the refrige rated transport end-use, specifically marine containers, trailers, trucks , and direct drive applications. EPA's ri sk screen indicates that the use of the proposed substitute will be less harmful to the atmosp here than the continued use of CFC-12, R-502, and HCFC-22, as well as other commonly used refrigerants. In addition, CO 2 contributions to volatile organic compound (VOC) emissions are not a concern as CO 2 is exempt under CAA regulations (40 CFR 51.100(s)). No significant toxicity or asphyxiation ri sks to workers, end-users, or the general population are expected. It is expected that procedures identif ied in the material data safety sheet (MSDS) for CO 2 and good manufacturing practices w ill be adhered to, and 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 in sufficient ventilation) cons istent with Occupational Safety and Health Administration (OSHA) guidelines will be used during manufacture, servicing, and disposal of refrigerated tr ansport equipment using CO 2 . In addition, it is expected that CO 2 monitors will be installed inside refrigerated tr ansport containers and container d oors will be open during end-use to prevent significant exposure to CO 2 in the case of catastrophic leakage. Because units are to be installed in locations with adequate space or ventilation (i.e., outdoors) as discussed in greater detail in Section 9, significant toxicity risk to end-users is also un likely. Additional safeguards are also provided by adherence to industry standards including Ameri can Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) Standards 15, 1 34, 2 Air Conditioning, Heating, and Refrigeration Institute (AHRI) Standards 700, 3 1110, 4 Compressed Gas Association (CGA) Standard G-6, 5 and UL Advisory on New CO 2 Systems.



### 3. ATMOSPHERIC ASSESSMENT
This section presents an assessment of the potential risk s to atmospheric integrity posed by the use of CO 2 in refrigerated transport. The oz one depletion potential (ODP), glob al warming potential (GWP), and atmospheric lifetime (ALT) of the propo sed 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 than refrigerants used in refrigerated transport, such as CFC-12, R-502, and HCFC-22. In addition, CO 2 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

1 Safety Standard for Refrigeratio n Systems ASHRAE Standard 15 establishes safegu ards for life, limb, health, and property and prescribes safety requirements.

2 Designation and Safety Classification of Refrigerants ASHRAE Standard 34 is esta blishes 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 AHRI Standard 700: Standard for Specifica tions for Refrigerants establishes purity sp ecifications, to verify composition, and to specify the associated methods of testing for acceptability of refrigerants regardless of sour ce (new, reclaimed, and/or repackaged) for use in new and existing refrigeration an d air conditioning products within the scope of AHRI.

4 AHRI Standard 1100: Performance Rating of Me chanical Transport Refriger ation Units establishes a single set of requirements for the testing and rating of cooling capacities and electric standby cooling capacities for mechanical transport refrigeration units employed forced-circulation air-coolers.

5 CGA Standard G-6: Carbon Dioxide provides information on pro duction, storage, transportation, uses and safe handling of carbon dioxide in its gaseous, liqui d and solid (dry ice) forms.Final - October 10, 2014 3 refrigerants, R-404A and HFC-134a. Furthermore, the submitter anticipates using recycled CO 2 in refrigerated transport units which is typically cap tured, recovered, and processed from industrial CO 2 emission sources (e.g., power plants); therefore, any releases of recycled CO 2 are not considered to contribute as additional atmospheric CO 2 and atmospheric impacts are considered to be neutral (Carrier 2013a).

Table 2. Atmospheric Impacts of CO 2 Compared to Other Refrigerated Transport Refrigerants

Refrigerant Ozone Depleting Potential (ODP) a Global Warming Potential (GWP) b Atmospheric Lifetime in Years (ALT)
CO 2 0 1 c 5-200 b,d CFC-12 0.82 10,900 100 b R-502 e 0.2 4,650 NA f HCFC-22 0.04 1,810 12 a R-404A g 0 3,920 NA h HFC-134a 0 1,430 14 b

a WMO 2010 Scientific Assessment Report (2011).

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

c If the substitute is obtained via recycling, the GWP is considered to be zero, as atmospheric impacts are considered to be neu tral.

d The CO 2 response function used in the IPCC 4 th Assessment Report is based on the revised version of the Bern Carbon Cycle Model using a background CO 2 concentration value of 378 ppm. The decay of a pulse of CO 2 with time t is given by

where a 0 = 0.217, a 1 = 0.259, a 2 = 0.338, a 3 = 0.186, t 1 = 172.9 years, t 2 = 18.51 years, and t 3 = 1.186 years. (Forster et al. 2007)

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

f Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HCFC-22 is 12 y ears and the ALT for CFC-115 is 1,700 years (IPCC 4 th Assessment Report [Forster et al. 2007]).

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

h Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-143a is 52 years, the ALT for HFC-125 is 29 years, and the ALT for HFC-134a is 14 years.



### 4. VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT

CO 2 is not a volatile organic compound (VOC) accordi ng to CAA regulations (40 CFR 51.100(s)) due to its negligible photochemical reactivity. Therefore, environmental impacts from the release of CO 2 as a VOC is not a concern.



### 5. POTENTIAL HEALTH EFFECTS
To assess potential health risks from exposure to the proposed substitute in refrigerated transport, EPA identified the relevant toxicity threshold values fo r comparison to modeled exposure concentrations for different scenarios. To protect end-users and work ers from the potential dangers of a catastrophic leak from the refrigeration unit, ASHRAE Standard 34 dete rmined 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 aforemen tioned standard, requiring that “the concentration of refrigerant in an enclosed space following a comple te discharge of a high-probability system shall not exceed the RCL” (ASHRAE 2010a). As such, this ri sk screen references the RCL in addition to the hypoxia No Observed Adverse Effect Level (NOAEL) a nd exposure limits, as an additional, conservative limit to ensure that significant toxicity a nd asphyxiation risks, do not occur.

For the occupational exposure analysis, potential ri sks from chronic and acute worker exposure were evaluated by comparing exposure concentrations to av ailable occupational exposure limits. Potential risks of chronic worker exposure were evaluated using wo rkplace guidance levels (WGL). Risks from potentialFinal - October 10, 2014 4 short-term end-use exposures were evaluated by comparing exposure concentrations to emergency guidance levels (EGL).

Table 3 lists the relevant toxicity limits and RCL for CO 2 , and is followed by Table 4, 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 3. Exposure Limits for Carbon Dioxide
Proposed Substitute WGL (Long-term Exposure)
ppm EGL (Short-term Exposure)
ppm Refrigerant Concentration Limit (RCL)
ppm

CO 2 5,000 a (8-hour OSHA PEL) 30,000 a (15-minute ACGIH STEL) 40,000 a (30-minute NIOSH IDLH) 40,000 b

a OSHA PEL, ACGIH TLV, and NIOSH IDLH available at: h ttp://www.cdc.gov/Niosh /npg/npgd0 103.html

b ASHRAE (2010b)

Table 4. Explanation of Exposure Limit-Related Terminology a

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 in tended 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 complete mixing of refrigerant in the space to which it is released. STEL Short-Term Exposure Limit A 15-minute TWA exposure that should not be exceeded during a workday, even if the 8-hour TWA is within the TLV–TWA, set by ACGIH. IDLH Immediately Dangerous to Life and Health If exposed to this concentration, room occupants are expected to be able to escape the room within 30 minutes without experiencing escape-impairing or irreversible health effects. Long-Term Exposure PEL Permissible Exposure Limit This is an 8-hour time-weighted average exposure limit set by OSHA.

a All information in this ta ble taken from EPA (1994) e xcept where otherwise noted.Final - October 10, 2014 5 According to the MSDS, exposure to CO 2 may be hazardous if inhalation, skin contact, or eye contact with the proposed substitute occurs at sufficiently high levels. CO 2 is moderately irritating to the respiratory system and can cause rapid suffocation and/or symptoms of asphyxiation when present in concentrations high enough to significantly lower oxygen concentrations below 19.5 percent by volume (e.g., headaches, ringing in ears, dizziness, drowsin ess, nausea, vomiting, depression of all senses, and unconsciousness). Damage may occur to the lungs, ca rdiovascular system, and central nervous system and under some circumstances of over-exposure (i.e., oxygen levels fall below 6 percent by volume), death may occur. Concentrations of CO 2 of 4 percent by volume (i.e., 40,000 ppm) may cause headache, dizziness, increased blood pressure, or uncomfortable dy spnea (shortness of breath) within a few minutes. Concentrations of CO 2 of 6 percent by volume (i.e., 60,000 ppm) may cause effects such as hearing and visual disturbances, alterations to heartbeat, head ache and dyspnea in a few minutes, with more severe effects at higher concentrations (EPA 2000).

If excess quantities of CO 2 are inhaled, person(s) should be imme diately removed and exposed to fresh air. In accordance with the MSDS, EPA further reco mmends that if breathing is difficult or irregular, person(s) be given oxygen or artificial respiration, provided a qualified operato r is present, and medical attention be sought. Rescuers should not attemp t to retrieve victims of exposure to CO 2 without adequate PPE. At a minimum, a self-contained breathing apparatus (SCBA) should be worn.

Exposures of CO 2 to the skin may cause frostbite or burns. In the case of dermal exposure, the MSDS for CO 2 recommends that person(s) immediately wash the affected area with water for at least 15 minutes while removing all contaminated clothing to avoid irri tation; 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 ar e frostbitten, warm the affected area by placing it in the armpit; gently exercise the affected part while bei ng warmed, and seek medical attention immediately. Clothing and shoes should be cleaned thoroughly before reuse. Exposures of CO 2 to the eyes could cause eye irritation. In case of ocular exposure, the MSDS for CO 2 recommends that person(s) immediately flush the eyes, including under the eyelids, with copious amounts of water for 15 minutes.

EPA’s review of the human health impacts of this proposed substitute is contained in the public docket for this decision. The potential health effects of CO 2 can be minimized by following the exposure guidelines and the ventilation and PPE recommendations outlined in the MSDS for CO 2 and this risk

screen.



### 6. DISCUSSION OF END-USE SCENARIOS

CO 2 has been proposed for use as a refrigerant in refrigerated transport units. As provided by the submitter, the maximum and typical charge sizes and typical and minimum container sizes of the refrigerated transport units proposed for use with CO 2 systems (i.e., marine containers, trailers, and trucks) are listed in Table 5.

Table 5. Typical and Maximum Charge Sizes a nd Typical and Minimum Container Sizes of CO 2 Refrigerated Transport Units Refrigerated Transport Unit Typical Charge Size (kg) Maximum Charge Size (kg) Typical Container Size (m 3 ) Minimum Container Size (m 3 )Final - October 10, 2014 6 To evaluate potential end-use exposures to CO 2 in refrigerated transport un its, this risk screen examines a scenario in which personnel are located inside th e refrigerated transport unit containing goods. A reasonable worst-case scenario for this assessment woul d consider the catastrophic leak of refrigerant occurring while the container doors are open because EPA expects the refrigerated container door to be open while personnel are present inside the container at end-use. However, the limitations of the box model used for this assessment do not allow considera tion of this scenario; calculating the concentration of CO 2 in the container as it exchanges with the warm, outside air through the open door would require more complex computational fluid dynamic modeling.

Given these limitations, the risk screen evaluates a more unlikely scenario, in which it is assumed that the full charge of the refrigerated transport unit is emitted over the course of one minute into the refrigerated container with the door closed. Although CO 2 is denser than air (specific gravity of CO 2 relative to air is 1.52 [air = 1]), a vertical concentration gradient is not assumed, because when the full charge is released, the presence of ventilation and the high pressure operati ng conditions of the refrigerant are expected to disperse the proposed substitute evenly and immediatel y throughout the refrigerated transport container. It was assumed that an individual is present at the star t of the leak and remains in the container until the charge is completely released.

Furthermore, this risk screen evaluates a refrigera ted transport unit with a ventilation rate of 25 m 3 /hr, a lower ventilation rate appropriate for less peri shable produce (perishable items require a higher ventilation rate up to 60 m 3 /hr) (Brecht et. al 2000). Hence, based on suggested ventilation rates for refrigerated transport units for vari ous types of produce, this analys is conservatively assumes a ventilation rate of 25 m 3 /hr. 6

Because refrigerated transport units can be installed in a wide range of end-uses with varying charge sizes and container sizes, the analysis in this risk screen evaluates all possible combinations provided by the submitter (i.e., the minimum and maximum charges sizes within the typical and minimum container sizes). Table 6 details the end-use modeling assumptions used in Sections 8 and 9.

Table 6. End-Use Scenario Model Assumptions
Parameter Assumptions End-Use Area Refrigerated Transport Container

Container Size (m 3 ) [ ] Charge Size (g) [ ] Ventilation Rate (m 3 /hr) 25 a Length of Release (minutes) 1 Vertical Concentration Gradient No

a Brecht et. al (2000); Hamburg Süd (2010)



### 7. FLAMMABILITY ASSESSMENT

CO 2 is classified by ASHRAE Standard 34 as an A1 refrigerant, and is consid ered to be nonflammable (ASHRAE 2010b). Based on this classification, manufacture, servicing, and use of CO 2 is not expected to present a flammability risk.



### 8. ASPHYXIATION ASSESSMENT
The risk of asphyxiation was investigated for CO 2 in refrigerated transport units. In this section, risk of asphyxiation is assessed in three ways: 1) modeling th e oxygen concentration under the charge sizes and

6 Ventilation rates range from 0 to 60 m 3 /hr depending on the type of good that is transported (Hamburg Süd 2010).Final - October 10, 2014 7 container sizes specified by the submitter for marine containers, trucks, and tr ailers, 2) performing a threshold analysis of minimum charge size needed to cause an asphyxiation risk in the container sizes specified by the submitter and 3) performing a threshol d analysis of the typical container size needed to cause an asphyxiation risk with the charge sizes spec ified by the submitter. This analysis does not consider conditions that are likely to occur that w ould increase oxygen levels to which individuals would be exposed, such as open container doors, or even ope nings at the bottom of container doors that allow air to flow in and out. This analysis does not assume a vertical concentration gradient. If the proposed substitute passes the screening analysis with these rest rictive 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 

### 7a below.

Table 7a. Asphyxiation Assessment – Worst Case Scenario a Refrigerated

Transport Container Scenario Charge Size (g) Container Size (m 3 ) Percent Oxygen Concentration b

Marine Containers Worst-Case 1a – Minimum Container Size/Typical Charge Size 20

Worst-Case 1b – Typical Container Size/Maximum Charge Size 20

Trailers Worst-Case 2a – Minimum Container Size/Typical Charge Size 20

Worst-Case 2b – Typical Container Size/Maximum Charge Size 20

Trucks Worst-Case 3a – Minimum Container Size/Typical Charge Size 17

Worst-Case 3b – Typical Container Size/Maximum Charge Size 19

Bold font indicates modeling results.

a Cells highlighted in green are the scenarios with acceptable oxygen concentrations 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 norm al concentration of oxygen in air (21 percent) must be reduced to 12 percent. 7 Based on the worst-case scenario modeling assumptions, CO 2 in refrigerated transport units does not present a significant risk of asphyxiation. The oxygen concentration inside a refrigerated container following the release of [ ] is no t anticipated to fall below 17 percent, which is well above the concentration that would cause a risk of asp hyxiation. Because this modeling does not take into account any ventilation which is likely to occur, such as open container doors or openings at the bottom of container doors that allow air to flow in and ou t, as mentioned above, the actual asphyxiation risk to personnel is likely to be even smaller than modeled.
Table 7b. Asphyxiation Assessment – Charge and Container Sizes a

Scenario Charge Size (g) Container Size (m

3 ) Percent Oxygen Concentration b

Bold font indicates modeling results.

7 Twelve percent oxygen in air is the NOAEL for hypoxia (ICF 1997).Final - October 10, 2014 8 a Cells highlighted in green are the scenarios in which the charge and container sizes evaluated in this risk screen are acceptab le according

to the threshold analysis.

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

For the asphyxiation threshold analyses shown in Ta ble b, the conditions at which an asphyxiation concern would exist were determined. Within the small est container size of [ ], as shown under Threshold Analysis 1a, the charge size of the CO 2 refrigeration unit would have to be at least [ ] for asphyxiation to be a concern, [ ]. Using the largest charge size of [ ] unit, as shown under Threshold Analysis 2b, the volume of the container would have to be [ ] or smaller for asphyxiation to be of concern, [ ].
To further protect against an asphyxiation risk, e nd-users should ensure container doors are open while personnel are inside to allow released CO 2 to diffuse into the outside air. Leak prevention, detection, or mitigation devices should be installed and the vent ilation requirements outlined in the MSDS for CO 2 should be closely followed. If these guidelin es are followed, a catastrophic leak of CO 2 is not anticipated to result in a significant asphyxiation risk.



### 9. END-USE EXPOSURE ASSESSMENT
This section presents estimates of poten tial personnel end-use exposures to CO 2 in refrigerated transport units. [ ]. Personnel exposure to the proposed substitut e at end-use (e.g., personnel located inside truck cab or refrigerated trailer) is not expected to be a significant concern because of established equipment design.
This end-use exposure assessment examines a scenar io in which personnel are located inside the refrigerated transport unit containing goods; such scenarios are expected to occur while the container doors are open. When the container door is opened, a stack effect exists from the presence of the denser, cold air coming into contact with the warm, moist air outside. This effect will cause the colder air to flow outside of the container and become replaced by th e warm, outside air through infiltration. Therefore, EPA expects that if a release of the proposed s ubstitute occurs while personnel are present inside the refrigerated transport container (e.g ., during loading and unloading of refrigerated goods), the container doors would be open, increasing the air exchange rate in side of the unit and also resulting in diffusion of any CO 2 to flow towards the outside of the container.
To simulate a worst-case scenario, the catastrophic release of the entire charge of the unit into the refrigerated container was modeled. The estimated exposures are conservative, as the analysis assumes that a catastrophic release occurs while the refrigerate d transport container doors are closed and also does not consider other variables that would reduce the le vels to which individuals would be exposed. This analysis also conservatively compares the modeled exposures to the STEL for CO 2 , which represents the maximum concentration limit at which a worker should be exposed over 15 minutes.Final - October 10, 2014 9 Table 8a. End-Use Exposure - Worst Case Scenario a,b Refrigerated

Transport Container Scenario Charge Size (g) Container Size (m

3 ) 15-minute TWA End-Use Exposure (ppm) c

Marine Containers Worst-Case 1a – Minimum Container Size/Typical Charge Size 55,900

Worst-Case 1b – Typical Container Size/Maximum Charge Size 27,700

Trailers Worst-Case 2a – Minimum Container Size/Typical Charge Size 61,300

Worst-Case 2b – Typical Container Size/Maximum Charge Size 37,600

Trucks Worst-Case 3a – Minimum Container Size/Typical Charge Size 155,800

Worst-Case 3b – Typical Container/Maximum Charge Size 75,300

a Bold font indicates modeling results.

b Cells highlighted in green are the scenarios with acceptable exposure levels, i.e., below the STEL, given various modeling assu mption options.

c 15-min STEL for CO 2 is 30,000 ppm; see Table 3 for more information. In Worst-Case Scenarios 1a and through 3b in Table 8a, the catastrophic release of CO 2 from marine containers, trailers, and trucks w ith various charge sizes was modeled. The modeling results indicate that the 15-minute STEL is likely to be exceeded for all scen arios except for marine containers in a typical container size and maximum charge size (Worst-Case Scenario 1b).
Because the worst-case scenarios prese nted in this assessment reflect an emergency situation, it is also relevant to compare potential end-use exposures to the 30-minute Immediately Dangerous to Life and Health (IDLH) value for CO 2 (i.e., 40,000 ppm), which represents th e concentration at which personnel should be able to escape the container within 30 minutes without experiencing escape-impairing or irreversible health effects. For each scenario pr esented in Table 8a, the 30-minute TWA exposure is slightly less than the corresponding 15-minute TWA. Therefore, the scenario that does not exceed the 15- minute STEL also does not exceed the IDLH (i.e., Wo rst Case Scenario 1b). Although the 15-minute STEL is projected to be exceeded for trailers with a typical container size and maximum charge size (Worst-Case Scenario 2b), the IDLH is not likely to be exceeded. The other scenarios that exceed the STEL also exceed the IDLH, (i.e., scenarios 1a, 2a, 3a and 3b. However, because the modeling was done using a conservative worst-case scenario where the refr igerated transport container door is closed, and because normally personnel would be exposed in a situ ation where the door is open with significantly higher ventilation levels, pers onnel exposure to the proposed substitute at end-use is not expected to reach the modeled concentrations shown in Table 8a. Theref ore, end-use exposure is not considered to be a significant risk.Final - October 10, 2014 10 A threshold analysis was performed to determine th e combinations of charge sizes and container sizes with a 25 m 3 /hr ventilation rate that would avoid end-use exposures above the STEL for CO 2 (i.e., 30,000 ppm). The results from the threshold analyses are used to establish guidelines for choosing an effective container size, charge size, and ventilation rate such that use of CO 2 in refrigerated transport units does not present risk to personnel at end-use. The results of the threshold analyses on charge and container sizes are presented in Table 8b.
Table 8b. End-Use Exposure Threshold Analysis – Charge and Container Sizes a,b,c

Refrigerated

Transport Container Scenario Charge Size (g) Container Size (m

3 ) 15-minuteTWA EndUse Exposure

(ppm)

a Analysis was performed using a 25 m 3 /hr ventilation rate.

b Bold font indicates modeling results.

c Cells highlighted in green are the scenarios in which the charge and container sizes evaluated in this risk screen are accepta ble according to

the threshold analysis.

As shown in Threshold Analysis 1a in Table 8b, th e maximum charge size that should be installed in a refrigerated transport container of [ ], is [ ]. Additionally, the threshold analysis indicates that refrigerated transport units with charge sizes of [ ] and [ ], the minimum and maximum charge sizes provided by the submitter, should not be installed in containers smaller than [ ] and [ ], respectively, assuming a ventilation rate of 25 m 3 /hr. As shown in Table 8b, these recommended minimum container sizes vary in direct correlation with charge size. The modeling resu lts presented in Table 8a and 8b reflect conditions that are assumed to be a worst-case scenario, as described in Section 6.
Infiltration rates through the opening of a refrigerate d truck container have been measured to be approximately 2,520 m 3 /hr, which is roughly 100 times the ventila tion rates used in the threshold analyses (Bonjour et. al 2011). As previously discussed, EPA expects the refrigerated container door to be open while personnel are present inside the container at end- use, increasing the air exchange rate inside of the unit and also encouraging any CO 2 to flow towards the outside air. Therefore, under a reasonable worstcase scenario where the refrigerated container door s are open, the exposures shown in the modeling results are unlikely.
Because refrigerated transport units using the propos ed substitute were modeled using a conservative, worst-case scenario where the refri gerated transport container door is closed, personnel exposure above the proposed substitute’s STEL of 30,000 ppm is unlikely. However, these potential exceedances emphasize the importance associated with proper equipm ent use, employment of engineering controls to limit releases and/or exposures, and the need for wo rkforce training. To prevent exposure and potential serious side effects during larger releases of the proposed substitute, EPA recommends the installation of CO 2 monitors on both ends of the refrigerated containe r, especially near the refrigeration system unit, and ensure the doors to the refrigerated container ar e open while personnel are inside. In addition, EPA recommends that warning labels are present in the refrigerated transport container indicating that CO 2 refrigerants are in use and can cause suffocation, injury, or death. An example of this warning label would read: “WARNING: Carbon dioxide gas can cause injury or death. Ventilate the area before entering. A high carbon dioxide concentration can occur in this area and can cause suffocation.” Training materials and an operations manual describing procedures for pr oper use of the equipment and safety guidelines forFinal - October 10, 2014 11 handling CO 2 , and prior safety training is required for all personnel. These procedures and guidelines should be acknowledged an d followed to mitigate exposure in case of CO 2 leakage.

[ ]

Personnel exposure to the proposed substitute at end- use (e.g., personnel located inside truck cab or refrigerated trailer) is not considered a significan t concern because of established equipment design. Proper leak protection devices, engineering control re quirements, and adherence to the MSDS will further ensure that exposure limits are maintain ed below those described in Table 3.



### 10. OCCUPATIONAL EXPOSURE ASSESSMENT
This section assesses potential exposures to workers du ring manufacture, installation, servicing, and disposal of CO 2 refrigerated transport units. To evaluate occupational exposure, EPA has assessed the risks associated with refrigerant release scenar ios which are assumed to occur accidentally.

10.1 Occupational Exposure at Manufacture
EPA expects that the charging of refrigerated tr ansport units occur in a closed system. [ ].

As indicated by the submitter, occupational exposure at manufacture is anticipated to occur only during the activities listed [ ]. Exposures were measured for a ll three activities [ ]. These concentrations are well below the exposure limits for CO 2 as listed in Table 3. Because the expected maximum occupational exposure at manufacture is well below levels of concer n and typical exposure concentrations are expected to be minimal, EPA does not believe that CO 2 presents a significant risk to workers during manufacture.

10.2 Occupational Exposure at Servicing and Disposal
[ ]. Potential exposures to CO 2 can occur during [ ].

The submitter estimated background concentrations in the air during [ ]. These concentrations are well below the exposure limits for CO 2 as listed in Table 3. [ ], occupational exposures greater than the maximum anticipated concentration is not likely (Carrier 2013a).

According to the submitter, the proposed substitute will not be recycled or reclaimed at disposal (Carrier 2013a); therefore disposal recommendations outlined in the proposed substitute’s MSDS should be followed. Occupational exposure may occur at dis posal during dismantling of the units. However, exposure during disposal is not expected to exceed concentrations anticipated during servicing [ ] and therefore occupational exposures great er than the exposure limits for CO 2 as listed in Table 3 are not likely.

Training materials and an operations manual describ ing procedures to reduce leakage during servicing and disposal and prior safety training is require d for all personnel servicing and disposing of units. Because of established equipment design and servicing and disposal practices, exposures to emissions of CO 2 will be unlikely. Thus, EPA believes that servicing a nd disposal of a refrigerated transport unit is not expected to pose a significant toxicity risk to workers.Final - October 10, 2014 12 

### 11. GENERAL POPULATION EXPOSURE

CO 2 is not expected to cause a significant concern to human health in the general population when used as a refrigerant in refrigerated transport. The proposed su bstitute is proposed for use in closed systems, and thus, significant releases are not likely. At room temperature, CO 2 is a gas, and therefore, releases to ground or surface water are not anticipated, as CO 2 is expected 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 CO 2 concentrated). Should air releases during manufacturing, servicing, or disposal operations occur, engineering controls should be used (e.g., carbon absorption scrubbers) to collect CO 2 and prevent its release into 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 CO 2 is not expected to pose a significant toxicity risk to the general population.Final - October 10, 2014 13 

### 12. REFERENCES

AHRI. 2014. Standard 700: Specifications for Refrige rants. Air Conditioning, Heating and Refrigeration Institute.

ANSI/AHRI. 2013. Standard 1110: Performance Rating of Mechanical Transport Refrigeration Units. Air Conditioning, Heating and Refrigeration Institute.

ANSI/ASHRAE. 2010a. Standard 15: Safety Standard for Refrigeration Systems. American Society of Heating, Refrigerating and Ai r-Conditioning Engineers, Inc.

ANSI/ASHRAE. 2010b. Standard 34: Designation and Sa fety Classification of Refrigerants. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Brecht, P., Hinsch, T., Kader, A., and Thompson, J. 2000. Marine container trans port of chilled perishable produce. University of California Agriculture a nd Natural Resources Publications: Oakland, CA.

Bonjour, J. Ducoulombier, M., and Sartre, V. 2011. Experi mental Investigation of the Infiltration Heat Load During the Opening of a Refrigerated Truck Body. Inte rnational Institute of Refrigeration: International Congress of Refrigeration. Available online at http://bright-blue.eu/wp-content/uploads/2012/11/artikel392_DucoulombierSartreBonjour_revised_final.pdf

.
Carbon Dioxide Information Analysis Center (C DIAC). 2012. Recent Greenhouse Gas Concentrations. Updated February 2012. Available online at http://cdiac.ornl.gov/pns/current_ghg.html . Accessed May 1, 2012.

Carrier Corporation. 2013a. CO 2 in Refrigerated Transport. Signif icant New Alternatives Policy Program Submission to the U.S. Environmental Protection Agency. July 19, 2013.

Carrier Corporation. 2013b. Response to Incompleteness Letter for CO 2 in Refrigerated Transport. November 30, 2013.

Carrier Corporation. 2014. Respon se to Incompleteness Letter for CO 2 in Refrigerated Transport. July 2, 2014.

CGA. 2009. Standard G-6: Carbon Dioxide. 7 th Edition. Compressed Gas Association.

Hamburg Süd. 2010. Reefer Guide. Available online at http://www.hamburgsud.com/group/media/sharedmedia/dokumente/brochures/Reefer_guide.pdf

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.Final - October 10, 2014 14 ICF International. 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.

U.S. EPA. 1994. Significant New Alternatives Polic y 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. 2000. Carbon Dioxide as a Fire Suppressan t: Examining the Risks. Appendix B. Available online at http://www.epa.gov/ozone /snap/fire/co2/co2report.html

WMO (World Meteorological Organization). 2011. Sc ientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project—Rep ort No. 52, 516 pp., Geneva, Switzerland, 2011.