Significant New Alternatives Policy Program 
Refrigeration and Air Conditioning Sector
Risk Screen on Substitutes for CFC-12, HCFC-22, and R-502 in Retail Food Refrigeration
                              Substitute: R-441A
This risk screen is restricted to retail food refrigeration applications covered under UL 471: Commercial Refrigerators and Freezers.
                                       
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). This risk screen evaluates the potential use of R-441A as a substitute for CFC-12, HCFC-22, and R-502 in the retail refrigeration end-use, specifically for stand-alone commercial refrigerators, freezers, and refrigerated display cases. Table 1 presents the composition of the proposed substitute. 
                        Table 1.  Composition of R-441A
                                  Constituent
                               Chemical Formula
                                  CAS Number
                                 Concentration
                              (Weight Percent)[a]
                                    Propane
                                     C3H8
                                    74-98-6
                                      55%
                                   n-Butane
                                     C4H10
                                   106-97-8
                                      36%
                                   Isobutane
                                     C4H10
                                    75-28-5
                                      6%
                                    Ethane
                                     C6H14
                                    74-84-0
                                      3%
     [a] There are no impurities of toxicological or ecological significance anticipated for this formulation. Isomers of hydrocarbons present in formulation mixture will exist, but are not considered to be an impurity, contaminant or byproduct.
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: Volatile Organic Compound Assessment 
         * Section 5: Discussion of End-Use Scenario Modeled 
         * Section 6: Potential Health Effects 
         * Section 7:  Flammability Assessment
         * Section 8: Asphyxiation Assessment 
         * Section 9: End-Use Exposure Assessment
         * Section 10: Occupational Exposure Assessment 
         * Section 11: General Population Exposure Assessment 
         * Section 12: References
2.	 SUMMARY OF RESULTS						
R-441A is recommended for SNAP approval for the retail food refrigeration end-use for stand-alone refrigeration equipment that comply with Underwriters Laboratory (UL) Standard 471: Commercial Refrigerators and Freezers.  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, R-502, and HCFC-22 as it is less harmful to the ozone layer, has lower climate impact, and a shorter atmospheric lifetime. Three of the four components of R-441A -- propane, n-butane, and isobutane -- are subject to volatile organic compound (VOC) regulations under the CAA (40 CFR 51.100(s)). Based on analysis of potential impacts of hydrocarbon refrigerant emissions on ground-level ozone concentrations, VOC emissions from the use of R-441A in retail food refrigeration end-use for stand-alone refrigeration equipment are not anticipated to contribute significantly to ground level ozone concentrations in the United States. It is expected that the material safety data sheet (MSDS) for R-441A and good manufacturing practices will be adhered to. Additionally, it is expected that the appropriate safety and personal protective equipment (PPE) (e.g., protective gloves, tightly sealed goggles, protective work clothing, and suitable respiratory protection in case of leakage or insufficient ventilation) consistent with Occupational Safety and Health Administration (OSHA) guidelines will be used during manufacture, installation and servicing, and disposal of retail food refrigeration systems using R-441A. Because retail food refrigeration systems are to be installed in locations with adequate space and/or ventilation in accordance with EPA recommendations and the equipment maintenance manual for R-441A, significant toxicity or flammability risk to consumers is also unlikely. Additional safeguards, including specified refrigerant concentration limits (RCL) of R-441A components, are also provided by adherence to industry standards including American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standards 15, 34, and 62 and Underwriters Laboratory (UL) Standard 471.[4]
3. 	ATMOSPHERIC ASSESSMENT
This section presents an assessment of the potential risks to atmospheric integrity posed by the use of R-441A in commercial refrigeration and freezers.  The ozone depletion potential (ODP), global warming potential (GWP), and atmospheric lifetime (ALT) of the proposed substitute are presented in Table 2.	
The proposed substitute is substantially less harmful to the ozone layer, has lower climate impact, and a shorter atmospheric lifetime when compared to CFC-12, R-502, and HCFC-22. In addition, R-441A also has lower climate impact and a shorter atmospheric lifetime than those predicted for other substitutes examined in the Background Document as well as commonly utilized substitutes R-410A and R-404A. Thus, EPA believes that the use of R-441A would result in substantially less harm to the climate and ozone layer than the continued use of ODS and commonly used ODS substitutes. 
Table 2.  Atmospheric Impacts of R-441A Components Compared to Other Retail Food Refrigerants
                                  Refrigerant
                           Ozone Depleting Potential
                                   (ODP)[a]
                           Global Warming Potential
                                    (GWP)[b]
                     Atmospheric Lifetime in Years (ALT) 
                                    Propane
                                       0
                                      3.3
                                    0.03[a]
                                   n-Butane
                                       0
                                      4.0
                                   0.018[c]
                                   Isobutane
                                       0
                                      ~4
                                   0.016[a]
                                    Ethane
                                       0
                                      5.5
                                   0.21[c] 
                                    CFC-12
                                     0.82
                                    10,900
                                    100[b]
                                   R-502[d]
                                      0.2
                                     4,650
                                     NA[e]
                                    HCFC-22
                                     0.13
                                     1,810
                                     12[a]
                                   HFC-134a
                                       0
                                     1,430
                                    14[b] 
                                   R-404A[f]
                                       0
                                     3,922
                                     NA[g]
[a] WMO 2010 Scientific Assessment Report (2011)
[b] IPCC 4th Assessment Report (Forster et al. 2007)
[c] IPCC/TEAP (2005) 
[d] R-502 is a blend consisting of HCFC-22 (49%) and CFC-115 (51%). 
[e] Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HCFC-22 is 12 years and the ALT for CFC-115 is 1,700 years (IPCC 4th Assessment Report [Forster et al. 2007]).
[f] R-404A is a blend consisting of HFC-143a (52%), HFC-125 (44%) and HFC-134a (4%). 
[g] Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-143a is 52 years, the ALT for HFC-125 is 29 years, and the ALT for HFC-134a is 14 years.
4.	VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS
Three of the four components of R-441A -- propane, n-butane, and isobutane  - - are regulated as VOCs under the CAA (40 CFR 51.000), and as such, emissions of R-441A should be controlled.  A separate analysis was prepared by EPA (2014) to evaluate the potential impact of the use of hydrocarbon refrigerants on ground level ozone concentrations in the United States. The analysis estimated refrigerant emissions from refrigeration and air conditioning equipment, which were assumed to contain propylene, isobutane, and/or propane  under different scenarios.  Under the most conservative scenario it was assumed that propylene was used in all refrigeration and air conditioning equipment. In the most realistic scenario, all three hydrocarbons were assumed to be used in certain types of refrigeration and air conditioning equipment, depending on the proposed use of each alternative under submissions received by the SNAP Program at the time of the analysis. End-uses included in the evaluation included self-contained refrigeration units, for which SNAP hydrocarbon applications have been received and/or UL Standards covering flammable refrigerants exist.  The hydrocarbon emissions from these scenarios were estimated based on U.S. EPA's Vintaging Model, and their potential contributions to ozone concentrations were assessed using U.S. EPA's Community Multiscale Air Quality (CMAQ) model. 
CMAQ modeling was performed for April through the end of September, as these months presented the largest releases of hydrocarbon refrigerant as well as weather conditions favorable for ozone formation. The ozone concentrations were estimated for the Atlanta, Houston and Los Angeles regions, due to their distinctive geographic setting and chronic high levels of ground level ozone, and then scaled for national emission estimates. The results of the CMAQ modeling indicated that under the most realistic scenario, hydrocarbon refrigerants could potentially increase the maximum 8-hour average ground level ozone by lesson more than 0.15 ppb in Los Angeles, the city with the greatest ozone problem. This is roughly 0.2 percent of the current National Ambient Air Quality Standard (NAAQS) for ozone of 75 ppb. In the most conservative case which assumed that the most reactive hydrocarbon, propylene, was used in all refrigeration and air conditioning equipment, there could be an incremental maximum increase of the 8-hour average as high as 6.61 ppb ozone, or an increase of up to 9 percent of the NAAQS. However, this upper bound level of increase is not likely, as most ozone nonattainment areas are not VOC-limited (i.e., the formation of ozone in these areas are not by limited by VOC emissions, but by other compounds such as nitrogen oxides [NOx]). In addition, the analysis assumed no use of VOC-exempt refrigerants which may be used in the refrigeration and air conditioning end-uses. Based on the results of this analysis, VOC emissions from the use of R-441A in self-contained retail food refrigeration equipment are not anticipated to contribute significantly to ground level ozone concentrations in the United States.
5.	DISCUSSION OF END-USE SCENARIOS MODELED
R-441A has been proposed for the retail food refrigeration end-use, specifically for stand-alone commercial refrigerators, freezers, and refrigerated display cases. The submission states that R-441A retail food refrigeration equipment will have a typical charge size of 103 grams for commercial refrigerators, 150 grams for commercial freezers, and 135 grams for refrigerated display cases; however, UL Standard 471: Commercial Refrigerators and Freezers states that commercial refrigeration equipment containing a flammable refrigerant may have a charge size up to 150 grams of A3 refrigerant. 
To represent a reasonable worst-case scenario, it is assumed that a catastrophic leak of refrigerant occurs while a commercial freezer is installed at the end-use. To account for retail food refrigeration models which could utilize the maximum amount of refrigerant allowed under UL 471, the reasonable worst-case scenario is modeled using a charge size of 150 grams. Because retail refrigeration equipment can be installed in a wide range of locations with varying room volumes, the analysis in this risk screen conservatively assumes that the commercial refrigeration unit is located in the kitchen of a small fast food restaurant with a volume of 50 m[3] that is connected to a customer area of 100 m[3] (A.S. Trust & Holdings, Inc. 2012). Under the reasonable worst-case scenario, the full charge of the unit is assumed to be emitted over the course of one minute, into the food preparation area (50 m[3]) with a conservative ventilation rate of 1.5 air changes per hour (A.S. Trust & Holdings, Inc. 2012 citing Turk, et. al. 1989). A vertical concentration gradient is also assumed since R-441A is denser than air (specific gravity of R-441A relative to air is 1.67 [air = 1]) and will settle in higher concentrations closer to the ground. In order to simulate the vertical concentration gradient, it is assumed that 95 percent of the leaked refrigerant mixes evenly into the bottom 0.4 meter of the room, and the rest of the refrigerant mixes evenly in the remaining volume (Kataoka 2000). Table 3 details the end-use modeling assumptions used throughout the risk screen (i.e., in Sections 7, 8, and 9).
                 Table 3. End-Use Scenario Model Assumptions 
Parameter
                                  Assumption
Refrigeration Unit
                              Commercial Freezer
Room
              Food Preparation Area of Small Fast Food Restaurant
Charge Size (g) 
                                      150
Length of Release (minutes)
                                       1
Room Size (volume - m[3])
                                      50
Room Ventilation (air changes per hour)
                                      1.5
Vertical Concentration Gradient
                                      Yes


To address the variability in installation locations and room volumes for retail food equipment, this risk screen incorporates threshold analyses in addition to the worst-case scenario modeling, in order to determine the room size and charge size requirements to ensure that use of R-441A in retail food refrigeration does not present risk to consumers or servicing technicians.
6.	POTENTIAL HEALTH EFFECTS
To assess potential health risks from exposure to the proposed substitute in retail food refrigeration, EPA identified the relevant toxicity threshold values for comparison to modeled exposure concentrations for different scenarios. To protect consumers from the potential dangers of a catastrophic leak from the refrigeration unit,  ASHRAE Standard 34 determined refrigerant concentration limits (RCLs) for the components of R-441A which are intended to reduce the risks of acute toxicity, asphyxiation, and flammability hazards in normally occupied, enclosed spaces during refrigerant use (ASHRAE 2010b). ASHRAE Standard 15 implements the aforementioned standard, requiring that "the concentration of refrigerant in an enclosed space following a complete discharge of a high-probability system shall not exceed the RCL" (ASHRAE 2010a). As such, this risk screen references the RCL of the R-441A components in addition to the lower flammability limit, hypoxia NOAEL, and exposure limits, as an additional, conservative limit to ensure that significant flammability, asphyxiation, and end-use exposure risks, respectively, do not occur.  

For the occupational exposure analysis, potential risks from chronic and acute worker exposure were evaluated by comparing exposure concentrations to available occupational exposure limits.  Potential risks of chronic worker exposure were evaluated using workplace guidance levels (WGL). Risks from potential short-term consumer exposures were evaluated by comparing exposure concentrations to emergency guidance levels (EGL). In the absence of an established short-term exposure limit (STEL), acute exposure guideline level (AEGL), or emergency response planning guideline (ERPG), potential short-term, end-use exposures were compared to an excursion limit, which was calculated according to the methodology described in ACGIH (2004).  Table 4 lists the relevant toxicity limits of each component of R-441A, and is followed by Table 5, which provides an explanation of each toxicity limit.  EPA's approach for identifying or developing these values is discussed in Chapter 3 of the Background Document. 
                Table 4.  Exposure Limits of R-441A Components
                               R-441A Component
                         8-hr WGL (Long-term Exposure)
                                      ppm
                           EGL (Short-term Exposure)
                                      ppm
                     Refrigerant Concentration Limit (RCL)
                                      ppm
                                    Propane
                                    1,000a
                                  (OSHA PEL)
                           10,000c,d (10 min AEGL-1)
                            6,900d (30 min AEGL-1)
                                   5,300[g]
                                   n-Butane
                             1,000[b]  (ACGIH TLV)
                           6,900[e]  (30 min AEGL-1)
                                   4,000[g]
                                   Isobutane
                             1,000[b]  (ACGIH TLV)
                                   6,900[f] 
                                   4,000[g]
                                    Ethane
                             1,000[b]  (ACGIH TLV)
                    3,000h (30 min ACGIH Excursion Limit) 
                           2,900[i] (15-min TEEL-1)
                                   7,000[g]
[a] OSHA PEL available at: http://www.cdc.gov/Niosh/npg/npgd0524.html
[b] ACGIH TLV for aliphatic hydrocarbon gases: alkane (C1 - C4) is 1,000 ppm TWA (ACGIH 2012)
[c] An IDLH of 2,100 ppm has been established for propane.  However, NIOSH (1996) states that "[b]ased on acute inhalation toxicity data in humans (ACGIH 1991; Braker 1980), a value much greater than 10,000 ppm would have been appropriate. However, the revised IDLH for propane is 2,100 ppm based strictly on safety considerations (i.e., being 10% of the lower explosive limit of 2.1%)."  Therefore, as this IDLH value is based on flammability concerns and not toxicity concerns, it is not used in the evaluation of toxicity risks in this risk screen.
[d] AEGL-1 available at: http://www.epa.gov/opptintr/aegl/pubs/tsd96.pdf
[e] AEGL-1 available at: http://www.epa.gov/opptintr/aegl/pubs/tsd102.pdf
[f] Because n-Butane and isobutane have the same molecular formula, EGL for isobutane is conservatively assumed to be that for n-Butane. However, OSHA (2004) notes the following regarding isobutane: "OSHA does not have a PEL for isobutane, which is affirmed as "generally recognized as safe" as a direct human food ingredient (21 CFR 184.1165). No toxic effects reported below 18,000 ppm."
[g] ASHRAE (2010b)
[h] Calculated as three times the TLV-TWA (ACGIH 2004).
[i] DOE (2008)
         Table 5. 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
AIHA
American Industrial Hygiene Association
Exposure Limit
Definition
Explanation
Short-Term Exposure
RCL
Refrigerant Concentration Limit
The RCL for a refrigerant is intended to reduce the risks of acute toxicity, asphyxiation, and flammability hazards in normally occupied, enclosed spaces. The RCL for each refrigerant is the lowest of the Acute-Toxicity Exposure Limit (ATEL), Oxygen Deprivation Limit (ODL), and Flammable Concentration Limit (FCL). Determination assumes full vaporization with no removal by ventilation, dissolution, reaction, or decomposition and complete mixing of refrigerant in the space to which it is released.
STEL
Short-Term Exposure Limit
A 15-minute time-weighted average (TWA) exposure that should not be exceeded at any time during a workday, even if the 8-hour TWA is within the TLV - TWA, set by ACGIH. 
AEGL[b,c]
Acute Exposure Guideline Level 1
AEGL-1 is the airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure. 

Acute Exposure Guideline Level 2
AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.

Acute Exposure Guideline Level 3
AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.
ERPG
Emergency Response Planning Guideline 1  
The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient health effects or perceiving a clearly defined, objectionable odor according to AIHA. 

Emergency Response Planning Guideline 2  
The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action according to AIHA.

Emergency Response Planning Guideline 3  
The maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects according to AIHA.
Excursion Limit [d]
Excursion Limit 
Because methane (and other short-chain alkane gases through butane) does not have a TLV-short-term exposure limit, an excursion limit may be applied. Excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the TLV-TWA, provided that the TLV-TWA is not exceeded according to ACGIH. 
IDLH
Immediately Dangerous to Life 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. 
TLV-TWA
Threshold Limit Value  - Time-Weighted Average
The TWA concentration for a conventional 8-hour workday and a 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed, day after day, for a working lifetime without adverse effect according to ACGIH. 
[a] All information in this table taken from EPA (1994) except where otherwise noted.
[b] EPA (2012)
[c] Applicable to emergency exposure periods ranging from 10 minutes to 8 hours.
[d] ACGIH (2004)

According to the MSDS, exposure to R-441A may be hazardous if inhalation, skin contact, or eye contact with R-441A occurs. The most likely pathway of exposure is through inhalation. R-441A can cause symptoms of asphyxiation when present in concentrations high enough to significantly lower oxygen concentrations below 19.5 percent by volume, such as headaches, ringing in ears, dizziness, drowsiness, nausea, vomiting, depression of all senses, and also unconsciousness. Under some circumstances of over-exposure (i.e., oxygen levels fall below 6 percent by volume), death may occur. In addition, at high concentrations, propane, a major component of the R-441A blend, can act as a narcotic and cause central nervous system depression, including dizziness, drowsiness, and headaches. 
If R-441A is inhaled, person(s) should be immediately removed and exposed to fresh air. In accordance with the MSDS, EPA further recommends that if breathing is difficult, person(s) be given oxygen, provided a qualified operator is present, and medical attention be sought.  Rescuers should not attempt to retrieve victims of exposure to R-441A without adequate PPE. At a minimum, a self-contained breathing apparatus (SCBA) should be worn. Exposures of R-441A to the skin may cause frostbite. In the case of dermal exposure, the MSDS for R-441A recommends that person(s) immediately wash the affected area with water and remove all contaminated clothing; if frostbite occurs, bathe (not rub) the affected area with lukewarm, not hot, water. If water is not available, cover the affected area with a clean, soft cloth. 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. Exposures of R-441A to the eyes could cause eye irritation. In case of ocular exposure, the MSDS for R-441A 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 R-441A can be minimized by following the exposure guidelines and ventilation and PPE recommendations outlined in the MSDS for R-441A and this risk screen.
7.	FLAMMABILITY ASSESSMENT
ASHRAE Standard 34 classifies R-441A as a Class A3 refrigerant. R-441A is flammable when its concentration in air is in the range of 2.05 percent and 9.25 percent by volume (20,500 ppm to 92,500 ppm). In the presence of an ignition source (e.g., static electricity, a spark resulting from a switch malfunction, or a cigarette), an explosion or a fire could occur if the concentration of R-441A were to exceed the lower flammability limit (LFL) of 20,500 ppm.  As such, R-441A may pose a significant safety concern for workers and consumers if it is not handled carefully.  The remainder of this section assesses flammability risks and summarizes the recommended measures to ensure safe handling and use of the refrigerant during manufacture, servicing, and end-use. 

7.1	Flammability Risks at Manufacture
As indicated by the submitter, the manufacture of R-441A refrigerant (i.e., formulation mixing) and the charging of R-441A retail food refrigeration equipment (receiving, blending. and filling operations) occurs in a closed system; all units are completely sealed before delivery and installation. As a result, releases of R-441A during these manufacturing and installation operations in the presence of an ignition source are not anticipated. 
All R-441A storage and transport equipment should be installed with safety devices that minimize the likelihood of catastrophic releases. For example, NFPA 58 Liquefied Petroleum Gas Code (NFPA 2014) for liquefied propane requires the use of overfill protection devices (OPD) on cylinders to minimize the likelihood of leaks.  The NPFA 58 Code also contains propane storage and transportation requirements/guidelines.  Similar equipment safety and procedural requirements should be developed for R-441A and other flammable refrigerants. EPA believes that because workers follow relevant safety standards in manufacturing facilities, the MSDS for isobutane, and OSHA requirements under 29 CFR 1910 (e.g., proper ventilation and storage practices within manufacturing facilities to prevent fire and explosion), flammability during manufacture is not expected to be of concern.

7.2	Flammability Risk at Servicing and End-Use
The risk of flammability during servicing and end-use for the reasonable worst-case scenario and typical scenario (see Section 5) was investigated for R-441A. Both servicing and end-use of R-441A retail food refrigeration equipment are expected to take place in the same space (i.e., the place of installation and use). In order to determine the potential flammability risks during servicing or end-use in case of a catastrophic release of refrigerant in a food preparation area (see Section 5), concentrations of R-441A immediately following the release of refrigerant were compared to the LFL for R-441A. The maximum instantaneous concentration of R-441A in the lower 0.4 meters of the room at a charge size of 150 grams would be approximately 8,490 ppm, which is 41 percent of the proposed substitute's LFL (see Table 6).  The maximum instantaneous concentration in the upper portion of the room for both modeled charge sizes is much lower, as only 5 percent of the leaked refrigerant is present in this area, which also has a greater volume than the lower 0.4 meters of the room. Table 6 presents the results of the analysis.

                     Table 6.  Flammability Assessment[a]
                                   Scenario
                                Charge Size (g)
                          Effective Room Size (m[3])
                      Maximum Instantaneous Concentration
                                 (ppm) [b][,c]
                             Reasonable Worst-Case
                                      150
                              50.0 (1,770 ft[3])
                                    8,490 
                       Threshold Analysis 1: Charge Size
                                      354
                              50.0 (1,770 ft[3])
                                    20,050
                        Threshold Analysis 2: Room Size
                                      150
                               21.2 (749 ft[3])
                                    20,050
 Bold font indicates modeling results.
  [a] Cells highlighted in green are the scenarios with exposure levels deemed acceptable given various modeling assumption options 
 [b] Lower Flammability Limit of R-441A is equal to 20,500 ppm
 [c] Values provided in these columns refer to the concentration in the lower 0.4 meters of the room

The results of the threshold analysis indicate that the charge size would have to be significantly larger, or the room size smaller, than what is assumed in the worst-case scenario (see Section 5) for a flammability risk to occur. As shown in Threshold Analysis 1, for flammability to be of concern within a room size of 50 m[3] (1,770 ft[3]) (see Table 6), the charge size released would have to be at least 354 grams. As shown in Threshold Analysis 2, for flammability to be of concern for commercial freezers with a charge size of 150 grams, the volume of the room would have to be 21.2 m3 (749 ft[3]) (see Table 6). 
It is unlikely that a store or restaurant as small as that determined in the flammability threshold analysis would exist and it is further unlikely that the entire refrigerant charge would accidentally release into the convenience store. In addition, R-441A is likely to be dispersed into the air evenly and almost instantaneously upon accidental release; the retail food refrigeration unit compressor is pressurized between 135 and 160 psi, which will cause R-441 to be released into the room (assumed to be at atmospheric pressure of approximately 14.7 psi) under high pressure, resulting in the refrigerant's quick and turbulent release, and subsequent mixing into the air (A.S. Trust & Holdings, Inc. 2011). EPA recommends that the ventilation requirements outlined in the MSDS for R-441A are followed to mitigate the risk of fire or explosion during catastrophic leak during end-use or when servicing equipment using R-441A.  In addition, EPA recommends that retail food refrigeration equipment with charge sizes of 150 grams are not installed in enclosed areas with volumes smaller than 21.2 m3 (749 ft[3]) in order to mitigate flammability risk. 
Catastrophic releases of large quantities of refrigerant, especially in areas where refrigerant is stored, could result in an explosion in the presence of an ignition source.  For this reason, it is important that only properly trained and certified technicians handle R-441A.  The submitter has provided safety guidelines for handling R-441A, which should be followed.  As a further precaution, certification requirements and training programs for technicians that handle R-441A should be developed using these guidelines.  During servicing operations, technicians should ensure that proper ventilation is in place through the use of fans (or other mechanical ventilation devices) and portable refrigerant detectors should be used to alert technicians to the presence of flammable gases in the area. Furthermore, EPA recommends that consumers should not be present during servicing activities. 
It is recommended that retail food refrigeration equipment not be installed in small, poorly ventilated spaces such as very small enclosed areas or storage closets (especially as other equipment or appliances in the space would reduce the effective volume of the room).  For retail food refrigeration equipment installed in larger areas, the risk of fire and explosion is minimal. Retail food refrigeration equipment installed with R-441A should be clearly labeled as containing a flammable refrigerant and designed to prevent catastrophic leaks.  The installation of leak prevention devices would further protect against the very limited risk of explosion. Because relevant safety standards and the MSDS for isobutane are followed by service technicians and because isobutane refrigeration units will be installed in areas with adequate space and ventilation, EPA believes that flammability during servicing and end-use is not expected to be of concern. 
8.	ASPHYXIATION ASSESSMENT	
The risk of asphyxiation for the reasonable worst-case scenario was investigated for R-441A. In this section, risk of asphyxiation is assessed in three ways: 1) modeling the oxygen concentration under the charge size and room size specified in the worst-case scenario, 2) performing a threshold analysis of minimum charge size needed to cause an asphyxiation risk in the room size specified in the worst-case scenario 3) performing a threshold analysis of the maximum room size needed to cause an asphyxiation risk with the charge size specified in the worst-case scenario.  This analysis does not consider ventilation or conditions that are likely to occur that would increase oxygen levels to which individuals would be exposed, such as open doors or windows, fans operating, conditioned airflow (either heated or cooled), or even openings at the bottom of doors that allow air to flow in and out. As specified in Section 5, the reasonable worst-case scenario assumes a vertical concentration gradient. If the proposed substitute passes the screening analysis with these restrictive assumptions in place, it can be reasonably assumed that no risks of asphyxiation will be present under real-world conditions. The results of the asphyxiation assessment are summarized in Table 7 below. 
                     Table 7.  Asphyxiation Assessment[a]
                                   Scenario
                              Charge Size (g)[a]
                          Effective Room Size (m[3])
               Percent Oxygen Concentration in Lower 0.4 Meters
                             Reasonable Worst-Case
                                      150
                              50.0  (1770  ft[3])
                                      21
                       Threshold Analysis 1: Charge Size
                                     7,242
                              50.0  (1770  ft[3])
                                      12
                        Threshold Analysis 2: Room Size
                                      150
                               1.0 (36.6 ft[3]) 
                                      12
     Bold font indicates modeling results.
       [a] Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
  [b] The typical concentration of oxygen in air is considered to be 21 percent (Mackenzie & Mackenzie 1995).
  
In order for a risk of asphyxiation to occur, the normal concentration of oxygen in air (21 percent) in the lower 0.4 meters of the room must be reduced to 12 percent. Based on the worst-case scenario modeling assumptions, R-441A in retail food refrigeration equipment does not present a significant risk of asphyxiation. As shown in Threshold Analysis 1, the minimum charge of R-441A necessary to reduce the oxygen levels to 12 percent in air in the lower 0.4 meters of a room of volume 50 m[3] (1,770 ft[3]) was calculated to be 7,242 grams assuming that 1) nitrogen and oxygen retain the same relative volumes in the rooms with the balance composed entirely of R-441A, and 2) the pressure of the room does not increase significantly with the addition of the refrigerant. This amount represents nearly 50 times the intended charge of approximately 150 grams for a single R-441A retail food refrigeration unit.  Because this threshold modeling does not take into account any ventilation which is likely to occur, such as conditioned airflow, open doors, or even openings at the bottom of doors that allow air to flow in and out, as mentioned above, the actual asphyxiation risk to consumers is likely to be smaller than modeled. 
For the Asphyxiation Threshold Scenario, the room size at which an asphyxiation concern would exist (i.e., when the oxygen concentration in the lower 0.4 meters of the room is 12 percent) was determined. For asphyxiation to be of concern with the maximum charge size of 150 grams, the volume of the food preparation area would have to be about 1.0 m[3] (36.6 ft[3]) (see Threshold Analysis 2 in Table 7).  Based on the worst-case modeling results and threshold analysis, EPA does not believe that the use of R-441A in commercial freezers poses a significant risk of asphyxiation or impaired coordination to personnel.


9.	END-USE EXPOSURE ASSESSMENT	
This section presents estimates of potential end-user exposures to R-441A and each of its chemical constituents in the event of a catastrophic release from the proposed substitute's use in retail food refrigeration. An end-use exposure analysis was performed to examine potential catastrophic releases of R-441A under the reasonable worst-case scenario outlined in Section 5.
For the end-use exposure assessment scenario, 30-min TWA exposures for the proposed substitute were calculated using the box model described in the Background Document, which was adapted to estimate concentrations on a minute-by-minute basis. Estimates for acute/short-term end-use exposures resulting from catastrophic leakage of refrigerant from commercial freezers were examined. The analysis was undertaken to determine the 30-minute exposures for each component of R-441A, which were then compared to the standard toxicity limits presented in Table 4 to assess the risk to end-users. However, the TWA values are fairly conservative as the analysis does not consider opened windows, fans operating, conditioned airflow (either heated or cooled) and other variables that would reduce the levels to which individuals would be exposed. 
                   Table 8.  End-Use Exposure Assessment[a]
                               R-441A Component
                     30-minute TWA End-Use Exposure (ppm)
                 Short-term (30-min) Exposure Limits (ppm)[b]
                                    Propane
                                     4,390
                                     6,900
                                   n-Butane
                                     2,180
                                     6,900
                                   Isobutane
                                      360
                                     6,900
                                    Ethane
                                      350
                                      NA
      [a] Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
      [b] See Table 4 for more information.

Under the reasonable worst-case scenario described in Section 5, catastrophic releases of R-441A from a commercial freezer with a charge size of 150 grams was modeled. For a charge size of 150 grams, the estimated 30-min TWA exposures of the components of R-441A do not exceed 64 percent of the respective STELs. As such, use of R-441A in commercial freezers is not anticipated to present a significant risk to end-users. Furthermore, these exposures were derived using fairly conservative assumptions (e.g., minimum room volume, low ventilation rate [1.5 ACH], maximum charge size) that do not necessarily reflect the typical location for R-441A retail food refrigeration equipment installations (e.g., retail food refrigeration equipment will be installed in large food and drink establishments and supermarkets [A.S. Trust & Holdings, Inc. 2012]). To prevent exposure and potential serious side effects during larger releases, EPA proposes that the charge size for an R-441A commercial refrigeration unit to require compliance with UL 471 in any space containing a commercial refrigeration unit, unless proper leak protection devises are in place in order to prevent exposures of isobutane beyond the recommended limits. Proper leak protection devices and engineering control requirements and adherence to the MSDS will further ensure that exposure limits are maintained below those described in Table 8.
10.	OCCUPATIONAL EXPOSURE ASSESSMENT
This section assesses potential exposures to workers during manufacture, installation, servicing, and disposal of R-441A. As indicated by the submitter, the manufacture of R-441A refrigerant (i.e., formulation mixing) and the charging of R-441A retail food refrigeration equipment (receiving, blending. and filling operations) occurs in a closed system; all units are completely sealed before delivery and installation. As a result, exposure during these manufacturing and installation operations is not anticipated. 
To ensure that use of the proposed substitute in retail food refrigeration does not pose an unacceptable risk to workers during 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 per event for various release scenarios and data on number of events in 2010 were obtained from the Vintaging Model.  To determine the estimated level of occupational exposure for a constituent in a blend, the total anticipated release rate of the refrigerant is multiplied by the weight percent composition of each compound in the blend. For the retail food refrigeration end use, the release per event was conservatively assumed to be 0.25 percent of the equipment charge during servicing and 35 percent of the equipment charge during disposal. Additionally, EPA is proposing to allow intentional venting or release of R-441A as a refrigerant during installation, servicing, maintenance and disposal from stand-alone retail food refrigeration equipment. If venting does occur, EPA recommends that it is done in a well-ventilated area (i.e. outdoors). Therefore, scenarios in which 100 percent of the equipment charge was released during servicing and disposal were also considered. The release rate per event was multiplied by the number of events estimated to occur over a workday.  For equipment servicing, the number of events per workday was assumed to equal the maximum number of units anticipated to be serviced in one day (i.e., eight units [A.S. Trust & Holdings, Inc. 2011]) divided by eight hours per workday.  These assumptions result in approximately 1 event per hour.  For disposal, it was conservatively assumed that 10 units are disposed during an 8-hour work day. The modeled exposure concentrations were compared to short-term occupational exposure limits at installation and servicing and long-term exposure limits at disposal. 

10.1	Occupational Exposure at Servicing
As indicated by the submitter, when R-441A retail food refrigeration equipment is serviced, the used refrigerant is pumped into a canister, where it is stored until it is recycled (i.e., filtered and reused) (A.S. Trust & Holdings, Inc. 2011). During the transfer to the initial canister, incidental refrigerant releases may occur during connection and disconnection of the recharging hose fittings, which should last approximately 30 seconds per unit (A.S. Trust & Holdings, Inc. 2011).  
The maximum 30-minute time weighted average (TWA) exposure for each R-441A constituent were estimated for the servicing exposure scenario and  compared to their respective short term exposure limits (see Table 9).  The modeling results indicate that the maximum anticipated occupational exposure concentrations at no point exceed 0.3 percent of the short-term exposure limits for retail food refrigeration units with a 150-gram charge size during the 0.25 percent or 100 percent release scenarios.  Because the exposure concentrations modeled under the conservative assumptions is significantly lower than the exposure limits for each constituent, occupational exposure to the proposed substitute during servicing is not considered a significant risk to workers. Further, the estimated exposures were derived using conservative assumptions, and represent a worst-case scenario with a low probability of occurrence. These types of systems are typically serviced by trained personnel using proper industrial hygiene techniques.     


            Table 9.  Occupational Risk Assessment at Servicing[a]
                               R-441A Component
                   30-minute TWA Occupational Exposure (ppm)
                    30-min Short Term Exposure Limits (ppm)
                                       
                                 0.25% Release
                                 100% Release
                                       
                                    Propane
                                     0.05
                                     19.2
                                   6,900[b]
                                   n-Butane
                                     0.02
                                      9.6
                                   6,900[b]
                                    Ethane
                                     0.004
                                      1.5
                                   3,000[c]
                                   Isobutane
                                     0.004
                                      1.6
                                   6,900[b]
[a] Cells highlighted in green are the scenarios that are deemed to be acceptable given various modeling assumption options.
 	[b] 30 min AEGL-1
 	[c] ACGIH (2004)

10.2	Occupational Exposure at Disposal
Disposal of R-441A retail food refrigeration equipment is expected to occur with limited frequency (up to approximately ten disposal events per day) at disposal facilities and with limited duration of exposure to the refrigerant charge. Potential exposures to the refrigerant during recovery and disposal are expected to occur during activities related to draining the refrigerant from the refrigeration units into cylinders (e.g., connecting of pipes). Such activities and related exposure is anticipated to occur within 15-30 minutes (per event/day).
Table 10 displays the maximum estimated 8-hour TWA occupational exposure levels of the components of R-441A during disposal. Based on the assumptions described in the beginning of Section 10, the modeling indicates that 8-hour worker exposure concentrations for each of the R-441A blend components will at no point exceed 23 percent of their respective long-term exposure limits during disposal of R-441A for retail food refrigeration units with a 150 gram charge size during the 35 percent and 100 percent release scenarios. Table 10 displays the maximum estimated 8-hour TWA occupational exposure levels of the R-441A constituents during disposal. Because each value is significantly lower than the exposure guidelines for each constituent, occupational exposure to the proposed substitute during disposal is not considered a toxicity threat.  Further, the estimated exposures were derived using conservative assumptions, and represent a worst-case scenario with a low probability of occurrence. These types of systems are typically disposed of by trained personnel using proper industrial hygiene techniques.  
            Table 10.  Occupational Risk Assessment at Disposal[a]
                               R-441A Component
                    8-Hour TWA Occupational Exposure (ppm)
                    8-Hour Long Term Exposure Limits (ppm)
                                       
                                  35% Release
                                 100% Release
                                       
                                    Propane
                                     81.7
                                     233.3
                                    1,000b
                                   n-Butane
                                     40.6
                                     115.9
                                   1,000[c]
                                    Ethane
                                      6.5
                                     18.7
                                   1,000[c]
                                   Isobutane
                                      6.8
                                     19.3
                                   1,000[c]
      	[a] Cells highlighted in green are the scenarios with exposure levels deemed to be acceptable given various modeling assumption options.
      	[b] OSHA PEL
                          [c] ACGIH TLV

Although anticipated occupational exposures are well below the exposure limits for each of the components of R-441A, the recommendations for proper engineering controls and PPE in the MSDS for R-441A should be followed. Adequate ventilation should always be established during any use, handling, or storage of R-441A. Engineering controls should include vapor-in air detection systems and local exhaust ventilation during use of R-441A to prevent dispersion throughout the work place. In addition, an eye wash and safety shower should be near the manufacturing facility and locations where R-441A is stored and ready for use. In general, use of OSHA Category B or higher PPE is recommended, such as splash goggles, mechanically-resistance gloves when handling cylinders and chemically-resistant gloves when handling the gas mixture (e.g., butyl rubber, chlorinated polyethylene, or neoprene). SCBA and fire retardant protective clothing should be worn in case of an accidental release or spill (A.S. Trust & Holdings, Inc. 2011). EPA believes that if proper handling and disposal guidelines are followed in accordance with good industrial hygiene and manufacturing practices and the MSDS for R-441A, there is no significant risk to workers during the manufacturing, installation, servicing, and disposal of R-441A in retail food refrigeration units.
11.  	GENERAL POPULATION EXPOSURE ASSESSMENT
R-441A is not expected to cause a threat to human health in the general population when manufactured for use and used as a refrigerant in retail food refrigeration. The proposed substitute will be manufactured in a closed process and is proposed for use in closed systems, and thus, significant releases are not anticipated. At room temperature, R-441A is a gas and, therefore, releases to ground or surface water are not anticipated, as R-441A is anticipated to dissipate into the atmosphere upon release to outside air (i.e., because natural ventilation rates would be higher and there is no enclosed space to keep R-441A concentrated). Should air releases during manufacturing operations occur, engineering controls should be used (e.g. carbon absorption scrubbers) to collect R-441A and prevent the release of R-441A to the atmosphere. EPA believes that by using proper engineering controls and by following disposal and containment recommendations outlined in the proposed substitute's MSDS, exposure to R-441A is not expected to pose a significant toxicity risk to the general population. 

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

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