Significant New Alternatives Policy Program 
Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for HCFC-22 in Residential and Light Commercial Air Conditioning and Heat Pumps
                              Substitute: R-441A
This risk screen is restricted to residential and light commercial window air conditioner applications and other self-contained room air conditioners meeting the requirements of UL 484: Room Air Conditioners.

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 HCFC-22 in the residential and light commercial air conditioning (AC) and heat pump end-use that meets the requirement of Underwriters Laboratory (UL) Standard 484: Room Air Conditioners, specifically in window AC units, packaged terminal AC (PTAC), packaged terminal heat pumps (PTHP), and portable AC units. Table 1 details 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 of this report summarizes the results of the risk screen for the proposed substitute blend listed in Table 1. The remainder of the report 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 residential and light commercial room AC units that comply with Underwriters Laboratory (UL) Standard 484: Room Air Conditioners, specifically window AC units, packaged terminal AC (PTAC), packaged terminal heat pumps (PTHP), and portable AC units. EPA's risk screen indicates that the use of the proposed substitute and its constituents will be less harmful to the atmosphere than the continued use of HCFC-22 as it is less harmful to the ozone layer, has lower climate impact, and a shorter atmospheric lifetime. No significant asphyxiation risks to consumers or toxicity risks to workers, consumers, or the general population are expected.  Three of the four components of R-441A 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 window air conditioners are not anticipated to contribute significantly to ground level ozone concentrations in the United States. It is expected that procedures identified in the MSDS for R-441A and good manufacturing practices will 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 insufficient ventilation) consistent with Occupational Safety & Health Administration (OSHA) guidelines will be used during manufacture, installation, servicing, and disposal of room AC systems using R-441A. Because units are to be installed in locations with adequate space or ventilation in accordance with the AC maintenance manual for R-441A window AC units, as discussed in greater detail in Section 9, significant toxicity or flammability risk to consumers is also unlikely. Additional safeguards, including specified refrigerant concentration limits (RCL) 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 Laboratories (UL) Standard 484.

3. 	ATMOSPHERIC ASSESSMENT
This section presents an assessment of the potential risks to the atmosphere posed by the use of R-441A in window AC units.  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 compared to 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 a commonly utilized substitute, R-410A.  Thus, EPA believes that 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, such as HCFC-22 and R-410A. 

Table 2.  Atmospheric Impacts of R-441A Components Compared to HCFC-22 and R-410A
                                  Refrigerant
                        Ozone Depleting Potential (ODP)
                Global Warming Potential  -  100 year (GWP)[a]
                      Atmospheric Lifetime in Years (ALT)
                                    Propane
                                       0
                                      3.3
                                    0.03[b]
                                   n-Butane
                                       0
                                      4.0
                                   0.018[c]
                                   Isobutane
                                       0
                                      ~4
                                   0.016[b]
                                    Ethane
                                       0
                                      5.5
                                   0.21[c] 
                                    HCFC-22
                                    0.13[b]
                                     1,810
                                     12[a]
                                   R-410A[d]
                                       0
                                     2,088
                                     NA[e]
NA = not applicable
a IPCC 4th Assessment Report (Forster et al. 2007)
[b] WMO (2011) 
[c] IPCC/TEAP (2005) 
[d] R-410A is a blend of 50% HFC-32 and 50% HFC-125.
[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]).
4.	VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS
Propane, isobutane and n-butane are regulated as VOCs under the CAA, while ethane is exempted (40 CFR 51.100 [s]). Through regulations and standard industry practices, VOC emissions should be controlled. A separate analysis was prepared by EPA (2014) to evaluate the potential impact of the use of hydrocarbon refrigerants on ground-level ozone concentrations in the United States. The analysis estimated refrigerant emissions from refrigeration and air conditioning equipment, which were assumed to contain propylene, isobutane, and/or propane  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 in the evaluation included residential AC units (e.g., window units, PTAC/PTHP), 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 less 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 window AC units are not anticipated to contribute significantly to ground level ozone concentrations in the United States.
5.	DISCUSSION OF END-USE SCENARIOS MODELED
R-441A is proposed for use in residential and light commercial room AC units. The remainder of this risk screen assesses the risk of window AC units. To represent a reasonable worst-case scenario, it was assumed that the full charge of the window AC unit is emitted over the course of one minute into a bedroom, where it is located. Because window AC units can be installed in a wide range of locations with varying room volumes, the analysis in this risk screen conservatively assumes that the window air conditioner is located in a bedroom with a volume of 41 m[3] (1,450 ft[3]). Under EPA's proposed charge size limits, which correspond to those found in UL 484, the maximum refrigerant charge allowed for R-441A window AC units installed in a room of 41m[3] (1,450 ft[3]) is 195 grams.  However, the submission states that R-441A window AC units will have a typical charge size of 125 grams. Furthermore, UL Standard 484 indicates that the maximum charge size of a window AC unit containing a flammable refrigerant is 1,000 grams. Therefore, this risk screen evaluates the risks associated with all three charge sizes.
This risk screen evaluates a bedroom with air exchange rates of 0.11 ACH and 0.67 ACH. The EPA Exposure Factors Handbook (1997) states that the typical residential air exchange rate is 0.45 ACH, which factors in tests from homes that are greater than 45 years old as well as those that are less than 10 years old. However, older homes (i.e., built before 1994) are more likely to use window AC units than newer homes. Based on data of AC use in U.S. homes by year of construction, 27 percent of homes using AC equipment use window AC units, while the remaining use central air conditioning equipment (EIA 2013). On average, 38 percent of homes built before 1990 use window AC units in comparison to the average of 9 percent of homes built after 1990. Air exchange rates are expected to be greater in older homes that are typically built with loose construction practices (e.g., no or inadequate effort to seal structural panels, corners, cracks, joints, and penetrations; window and door assemblies are not rated). Additionally, if a home uses window AC units, EPA does not expect that there is any significant mechanical ventilation present in the home.
During the cooling season (May to September), air changes per hour in spaces with a floor area of 900 square feet or less are reported to be between 0.11 ACH for tight construction and 0.67 ACH for loose construction (ACCA 2006). Therefore, this risk screen models both air exchange rates, 0.11 ACH and 0.67 ACH, in order to account for installation of units in homes with different construction practices, for all three charge sizes (125 grams, 195 grams, and 1,000 grams). 
It is further assumed that an individual is present at the start of the leak and remains in the room until the charge is completely released.  UL 484 assumes that window AC units and their compressors are installed at a height of 1 meter above the ground. Based on this location and because R-441A is denser than air (specific gravity of R-441A relative to air is 1.67 [air = 1]), this risk screen assumes that a vertical concentration gradient of R-441A will occur.  In order to simulate the vertical concentration gradient, it is assumed that 95 percent of the leaked refrigerant mixes evenly into the lower 1 meter of the room, and the rest of the refrigerant mixes evenly in the remaining volume (Kataoka 2000). Modeling of the lower 1 meter of the room is consistent with the possibility that, in a bedroom scenario, individuals may be lying close to the floor. Table 3 details the assumptions used in the models throughout this risk screen (i.e., in Sections 7, 8, and 9).
                  Table 3. End-Use Scenario Model Assumptions
Parameter
                                  Assumption
Room Type
                                    Bedroom
 Size (m[3])
                               41a (1,450 ft[3])
 Ventilation Rate (air changes per hour)
                               0.11[b]; 0.67[c]
Air Conditioning Unit
                                   Window AC
 Charge Size (g)
                           125[d]; 195[e]; 1,000[f]
 Length of Release (minutes)
                                       1
 Vertical Concentration Gradient
                                      Yes
        [a] Background Document (EPA 1994)
              b Tight construction home (ACCA 2006)
              [c] Loose construction home (ACCA 2006)
              d Maximum charge size for a window AC under EPA's proposed use conditions., based on a room size of 41 m[3][,] and capacity of 6500 BTU/hr.
              [e] Typical charge size (A.S. Trust & Holdings, Inc. 2012).
              f Maximum charge size for a window AC unit under UL 484.
6.	POTENTIAL HEALTH EFFECTS
To assess potential health risks from exposure to the proposed substitute in window AC units, EPA identified the relevant toxicity threshold values for comparison to modeled exposure concentrations for different scenarios for each constituent of R-441A. 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" to ensure that there is not a significant risk of toxicity, asphyxiation, and flammability (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). Potential short-term, end-use exposures are compared to an established short-term exposure limit (STEL), acute exposure guideline level (AEGL), or emergency response planning guideline (ERPG); in the absence of these limits, an excursion limit, calculated according to the methodology described in ACGIH (2004), is applied. When evaluating the toxicity of R-441A, the cumulative effects and additivity of toxicities of short-chain aliphatic hydrocarbons are not considered to be a concern. ACGIH and OSHA do not consider these cumulative risks. Furthermore, a recent study evaluated alkane gases (ethane, propane, n-butane, and isobutane) in combined repeated exposure studies with reproduction/development toxicity screening tests. No significant effects on systemic toxicity or neurotoxicity were found at concentrations from 9,000 to 16,000 ppm, and no significant effects on developmental or reproductive toxicity were found at the highest concentrations tested (McKee RH et. al. 2013). Furthermore, the components of R-441A do not share an end-point of concern.  

Table 4 lists the relevant toxicity limits of R-441A components, 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
                       30-min 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
STEL
Short-Term Exposure Limit
A 15-minute 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, set by EPA. 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, set by EPA.

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, set by EPA.
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, as indicated by NIOSH.
TEEL[e]
Temporary Emergency Exposure Limit 1
TEEL-1 is the maximum concentration in air below which it is believed nearly all individuals could be exposed without experiencing other than mild transient adverse health effects or perceiving a clearly defined, objectionable odor set by DOE. 

Temporary Emergency Exposure Limit 2
TEEL-2 is the maximum concentration in air below which it is believed nearly all individuals could be exposed without experiencing or developing irreversible or other serious health effects or symptoms that could impair their abilities to take protective action set by DOE.

Temporary Emergency Exposure Limit 3
TEEL-3 is the maximum concentration in air below which it is believed nearly all individuals could be exposed without experiencing or developing life-threatening health effects set by DOE. 
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)
[e] Chemical exposure guidelines to use for emergency planning if no AEGL or ERPG is available. TEELs are developed based on concentration limits or toxicology parameters (DOE 2008).

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 soap and 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 to 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 manufacturing, 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 window air conditioners occurs in a closed system. As a result, releases of R-441A during manufacturing 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.  
It is important that all relevant standards be followed during the manufacture of window air conditioners.  It is expected that refrigerants be properly stored and caution used within manufacturing facilities to minimize explosion risk and that workers adhere to the requirements set by OSHA under 29 CFR part 1910.  OSHA requirements include proper ventilation and storage practices within manufacturing facilities to prevent fire and explosion.  Good manufacturing practices should be adhered to during the manufacture of equipment containing R-441A.

7.2	Flammability Risk at Servicing and End-Use
The risk of flammability during servicing and end-use for the reasonable worst-case scenario (see Section 5) was investigated for R-441A. Both servicing and end-use of R-441A window AC units 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, modeled concentrations of R-441A immediately following the release of refrigerant were compared to the LFL for R-441A. As demonstrated in Table 6, the maximum instantaneous concentration in the lower 1 meter of the room at a charge size of 125 grams would be approximately 3,450ppm, approximately 5,390 ppm for a 195-gram charge size, and approximately 27,620 ppm for a 1,000-gram charge size. The 125-gram charge size indicated by the submitter (Reasonable Worst-Case 1) and the 195-gram charge size proposed by EPA (Reasonable Worst-Case 2) do not present a significant flammability concern. In contrast, the scenario using a 1,000-gram charge size (Reasonable Worst-Case 3) exceeds the proposed substitute's LFL of 20,500 ppm. However, according to UL 484, a window unit with a charge size of 1,000 grams in not intended for installation in a room with a volume as small as that modeled in the worst-case scenario (41 m[3]). The minimum room size for a  charge size of 125 grams according to UL 484 is approximately 18 m[3] (630 ft[3]), assuming a 2.4 m ceiling height, and the maximum charge size for a 41 m[3] (1,450 ft[3]) room according to UL 484 is approximately 195 grams. 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, and this area has greater volume than the lower 1 meter. EPA is also proposing to limit charge sizes that an equipment manufacturer may use for a given cooling capacity. The appropriate cooling capacity for a room of 41 m[3] would be approximately 6,500 BTU/hr, with an associated charge limit of 195 grams under EPA's proposed use conditions. The results of the flammability assessment are presented in Table 6. 










                     Table 6.  Flammability Assessment[a]
                                   Scenario
                                Charge Size (g)
                          Effective Room Size (m[3])
                      Maximum Instantaneous Concentration
                                  (ppm) b[,c]
                            Reasonable Worst-Case 1
                                      125
                               41 (1,450 ft[3])
                                    3,450 
                            Reasonable Worse-Case 2
                                      195
                               41 (1,450 ft[3])
                                     5,390
                            Reasonable Worst-Case 3
                                     1,000
                               41 (1,450 ft[3])
                                    27,620
                       Threshold Analysis 1: Charge Size
                                      742
                               41 (1,450 ft[3])
                                    20,500
                       Threshold Analysis 2a: Room Size
                                      125
                                 7 (244 ft[3])
                                       
                       Threshold Analysis 2b: Room Size
                                      195
                                11 (380 ft[3])
                                       
                       Threshold Analysis 2c: Room Size
                                     1,000
                               55 (1,950 ft[3])
                                       
  Bold font indicates modeling results.
  [a] Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
  [b] Lower Flammability Limit of R-441A is equal to 20,500 ppm.
  [c] Values provided in these columns refer to the concentration in the lower 1 meter of the room.
  
For the Flammability Threshold analysis shown in Table 6, the conditions at which a flammability concern would exist (i.e., when the maximum instantaneous concentration in the lower 1 meter of the room equals the LFL for R-441A) were determined. Within the reasonable worst-case room size of 41 m[3] (1,450 ft[3]), the charge size of the R-441A window AC would have to be at least 742 grams (see Threshold Analysis 1 in Table 6) for a flammability concern to exist, which is approximately 5.9 times larger than the largest size intended by the submitter (i.e., 125 grams) and approximately 3.8 times larger than EPA's recommended charge size (i.e., 195 grams) for R-441A window AC units. For window AC units with a charge size of 125 grams (see Threshold Analysis 2a in Table 6) the volume of the bedroom would have to be 7 m[3] (244 ft[3]) or smaller for a flammability risk to occur. For window AC units with a charge size of 195-grams (see Threshold Analysis 2b in Table 6) the volume of the room would have to be 11 m[3] (380 ft[3]) or smaller for a flammability risk to occur. Using a charge size of 1,000-grams for window AC units (see Threshold Analysis 2c in Table 6) the volume of the bedroom would have to be 55 m[3] (1,950 ft[3]) or smaller for a flammability risk to occur. 
According to the results of this flammability analysis, the risk of fire is minimal if a window AC unit is installed in a room with volumes in accordance with standards and regulations. As bedrooms can be of smaller sizes, and because persons or furniture in the room may reduce the effective volume of the space, window AC units containing R-441A should not be installed in rooms with effective volumes less than what UL 484 indicates with respect to charge size, unless additional steps are taken to protect against a flammability risk (e.g., higher ventilation rates). According to UL 484 and assuming a mounting height of 1 meter, R-441A window AC units with charge sizes of 125 grams, 195 grams, and 1,000 grams should not be installed in a room less than 17 m[3] (610 ft[3]), 41 m[3] (1,450 ft[3]) and 1,332 m3 (47,000 ft[3]) , respectively. In addition, 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.  
It is also 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, although considered rare, since this type of equipment is hermetically sealed and is often replaced rather than serviced if the charge leaks, 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.  The installation of leak prevention devices would further protect against the very limited risk of explosion. When the guidelines recommended by EPA and industry standards including UL 484 are followed, EPA does not believe that use of R-441A in window AC units presents a significant risk of flammability at servicing or end-use.
8.	ASPHYXIATION ASSESSMENT
The risk of asphyxiation for the reasonable worst-case scenario (see Section 5) 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 conditions that are likely to occur that would increase oxygen levels to which individuals would be exposed, such as open doors or windows, fans operating, conditioned airflow (either heated or cooled), or even openings at the bottom of doors that allow air to flow in and out. As specified in Section 5, this analysis assumes a vertical concentration gradient. If the proposed substitute passes the screening analysis with these restrictive assumptions in place, it can be reasonably assumed that no risks of asphyxiation will be present under real-world conditions. The results of the asphyxiation assessment are summarized in Table 7 below.
                      Table 7. Asphyxiation Assessment[a]
                                   Scenario
                              Charge Size (g)[b]
                          Effective Room Size (m[3])
                Percent Oxygen Concentration in Lower 1 Meter 
                            Reasonable Worst-Case 1
                                     125 
                               41 (1,450 ft[3])
                                      21
                            Reasonable Worst-Case 2
                                      195
                               41 (1,450 ft[3])
                                      21
                            Reasonable Worst-Case 3
                                    1,000 
                               41 (1,450 ft[3])
                                      21
                       Threshold Analysis 1: Charge Size
                                    18,520 
                               41 (1,450 ft[3])
                                      12
                       Threshold Analysis 2a: Room Size
                                      125
                               0.28 (9.8 ft[3])
                                      12
                       Threshold Analysis 2b: Room Size
                                      195
                               0.43 (15.2 ft[3])
                                      12
                       Threshold Analysis 2c: Room Size
                                     1,000
                               2.2 (78.2 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)
   applicationsne.  mmended that pens r than the room assumed in the worst case scenario (see Section 4). 
Under the reasonable, worst-case scenario (see Reasonable Worst-Case 1 and Reasonable Worst-Case 2 in Table 7), an asphyxiation risk will not occur, as the oxygen concentration in the room is 21 percent, well above the 12 percent level of concern. The concentration of R-441A in the air in the lower 1 meter of the room following the release of the maximum charge size of 1,000 grams does not exceed 2.3 percent, which has an insignificant impact on the normal concentration of oxygen in air. This modeling does not take into account any ventilation which is likely to occur, such as conditioned airflow, open doors, or even openings at the bottom of doors that allow air to flow in and out, as mentioned above, therefore, the actual asphyxiation risk to personnel is likely to be even smaller than modeled. 
For the asphyxiation threshold analyses shown in Table 7, the conditions at which an asphyxiation concern would exist were determined. Within the reasonable worst-case room size of 41 m[3] (1,450 ft[3]) (see Threshold Analysis 1 in Table 7) the charge size of the R-441A AC unit would have to be at least 18,520 grams for asphyxiation to be a concern, which is more than 18 times the largest charge size allowed for R-441A window AC units according to UL 484 (i.e., 1,000 grams). For asphyxiation to be of concern with a 125-gram R-441A window AC unit (see Threshold Analysis 2a in Table 7) the volume of the bedroom would have to be 0.28 m3 (9.8 ft[3]). Using a 195-gram window AC unit, as shown under Threshold Analysis 2b, the volume of the room would have to be 0.43 m3 (15.2 ft[3]) or smaller for asphyxiation to be of concern. Using a 1,000-gram R-441A window AC unit (see Threshold Analysis 2c in Table 7) the volume of the bedroom would have to be 2.2 m3 (78.2 ft[3]) for asphyxiation to be a concern, which is significantly smaller than the reasonable worst-case bedroom size (41 m[3] [1,450 ft[3]]). In addition, the threshold room volumes at which asphyxiation could occur during a catastrophic leak of a 125-gram, 195-gram or 1,000-gram unit are smaller than the minimum bedroom volume typically found in the U.S.  
To further protect against an asphyxiation risk, end-users should ensure window AC units are installed with an appropriate cooling capacity for the intended cooled space to be consistent with manufacturer recommendations and the guidelines of relevant safety standards (e.g., ASHRAE 15 and UL 484). Leak prevention, detection, or mitigation devices should be installed and the ventilation requirements outlined in the MSDS for R-441A should be closely followed. If these guidelines are followed, a catastrophic leak of R-441A is not anticipated to result in a significant asphyxiation risk. 
9.	END-USE EXPOSURE ASSESSMENT
This section presents estimates of potential consumer exposures to R-441A and each of its chemical constituents in window AC units. An exposure analysis was performed to examine potential catastrophic release of the proposed substitute in a bedroom under the reasonable worst-case scenario outlined in Section 5 with a charge size of 125 grams, 195 grams, and 1,000 grams. 

For the end-use exposure assessment scenario, 30-minute time-weighted average (TWA) exposures for the constituents of 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.  These exposures were then compared to the standard toxicity limit presented in Table 4 to assess the risk to end-users. The results of the assessment provide both fairly conservative and more realistic TWA values, as the analyses using both a 0.11 ACH and a 0.67 ACH ventilation rate do not consider opened windows, fans operating, conditioned airflow (either heated or cooled) and other variables that would reduce the levels to which individuals would be exposed. Modeling was performed for all constituents of R-441A, however, only the results for propane, which show the end-use exposure levels under the reasonable worst-case scenario in Section 4, are presented in Table 8. As the primary component of R-441A, propane presents the greatest risk of exceeding the STEL and thus the most conservative assessment. 

      Table 8. End-Use Exposure Assessment of R-441A Propane Component[a]
                                   Scenario
                                Charge Size (g)
                          Effective Room Size (m[3])
                            Air Exchange Rate (ACH)
                  30-minute TWA End-Use Exposure (ppm)[b, c]
                           Reasonable Worst-Case 1a 
                                      125
                               41 (1,450 ft[3])
                                       
                                     0.11
                                     2,028
                           Reasonable Worst-Case 1b
                                       
                                       
                                     0.67
                                     1,785
                           Reasonable Worst-Case 2a 
                                      195
                                       
                                     0.11
                                     3,163
                           Reasonable Worst-Case 2b
                                       
                                       
                                     0.67
                                     2,784
                           Reasonable Worst-Case 3a
                                     1,000
                                       
                                     0.11
                                    16,223
                           Reasonable Worst-Case 3b
                                       
                                       
                                     0.67
                                    14,277
                      Threshold Analysis 1a: Charge Size
                                      425
                               41 (1,450 ft[3])
                                     0.11
                                       
                                       
                                     6,900
                      Threshold Analysis 1b: Charge Size
                                      483
                                       
                                     0.67
                                       
                       Threshold Analysis 2a: Room Size
                                      125
                                12 (430 ft[3])
                                     0.11
                                       
                       Threshold Analysis 2b: Room Size
                                       
                                11 (370 ft[3])
                                     0.67
                                       
                       Threshold Analysis 3a: Room Size
                                      195
                                19 (660 ft[3])
                                     0.11
                                       
                       Threshold Analysis 3b: Room Size
                                       
                                17 (580 ft[3])
                                     0.67
                                       
                       Threshold Analysis 4a: Room Size
                                     1,000
                               96 (3,400 ft[3])
                                     0.11
                                       
                       Threshold Analysis 4b: Room Size
                                       
                               85 (3,000 ft[3])
                                     0.67
                                       
                   Threshold Analysis 5a: Air Exchange Rate
                                      125
                               41 (1,450 ft[3])
                                       0
                                       
                   Threshold Analysis 5b: Air Exchange Rate
                                      195
                                       
                                       0
                                       
                   Threshold Analysis 5c: Air Exchange Rate
                                     1,000
                                       
                                      4.4
                                       
Bold font indicates modeling results.
[a] Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options. 
[b] 30-min AEGL-1 STEL for propane is 6,900 ppm; See Table 4 for more information
[c] Values provided in this column refer to the concentration in the lower 1 meter of the room, which presents the most conservative risk as s 95 percent of the leaked refrigerant in present in this space.

In the reasonable worst-case scenario described in Section 5, catastrophic releases of R-441A from a window AC unit with charge sizes of 125 grams, 195 grams, and 1,000 grams were modeled with two different air exchange rates, 0.11 ACH and 0.67 ACH. In Reasonable Worst-Case Scenarios 3a and 3b, which model a 1,000-gram charge size and ventilation rates of 0.11 ACH and 0.67 ACH respectively, the 30-minute AEGL-1 for propane of 6,900 ppm is likely to be exceeded (see Table 8). However, the 30-min TWA exposures in Reasonable Worst-Case Scenarios 3a and 3b do not exceed the AEGL-2 (17,000 ppm) or the AEGL-3 (33,000 ppm) for propane.

A threshold analysis was performed to determine the charge size, minimum room volume, and ventilation rates where window AC units containing R-441A could be installed to avoid the STEL for each of the components of R-441A. Based on this end-use exposure threshold analysis, shown in Table 8, the maximum charge size that should be installed in a room of 41 m[3] (1,450 ft[3]) volume with 0.11 ACH is 425 grams and 483 grams with 0.67 ACH (see Threshold Analysis 1a and 1b in Table 8). Additionally, the threshold analysis indicates that window AC units with charge sizes of 125 grams, 195 grams, and 1,000 grams should not be installed in rooms smaller than 12 m[3] (430 ft[3]), 19 m[3] (660 ft[3]), and 96 m[3] (3,400 ft[3]), respectively, assuming an air ventilation rate of 0.11 ACH. As shown in Table 8, these recommended minimum rooms sizes are smaller if the ventilation rate is increased to 0.67 ACH.
Because a window AC units with a charge size of 1,000 grams was modeled in a room size that is much smaller than the size recommended by UL 484 in the reasonable worst-case scenarios, it is not unexpected that the calculated 30-minute TWA exposures for that scenario exceeds the AEGL-1 for propane. These potential exposure exceedances emphasize the importance associated with proper equipment installation, (i.e. matching charge size with room dimensions). To prevent exposure and potential serious side effects during larger releases, EPA proposes the charge size for R-441A window AC units to require compliance with UL 484 and with proposed charge sizes based upon cooling capacity in the proposed rule. Smaller accidental releases of the proposed substitute, however, do not pose a significant risk to end-users.  Thus, risk of toxicological threat is minimal if a window AC unit is installed in a room with volumes in accordance with standards and regulations and/or in enclosed areas with volumes larger than those determined in the threshold analyses. Furthermore, proper ventilation should be used in accordance with the MSDS for R-441A. When these conditions are met, accidental catastrophic releases of the proposed substitute would not pose a significant risk to end-users. 
10.	OCCUPATIONAL EXPOSURE ASSESSMENT
This section assesses potential exposures to workers during manufacture, installation, servicing, and disposal of R-441A in window AC units. As indicated by the submitter, all manufacturing steps will be conducted in closed systems appropriately constructed for safety and elimination of environmental releases and worker exposures. Standard operating procedures and personnel training focus on minimizing such releases and occupational exposures. As a result, exposure to R-441A during manufacturing is not anticipated and is not analyzed further.
To ensure that use of the proposed substitute in window AC units 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 were obtained from the Vintaging Model. To determine the estimated level of occupational exposure for a constituent in the proposed substitute blend, the total anticipated release rate of the refrigerant is multiplied by the weight percent composition of each compound in the blend. For the window AC unit end use, the release per event was conservatively assumed to be 0.4 percent of the equipment charge during installation and servicing and 50 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 window AC units. If venting does occur, it should be done in a well-ventilated area (e.g., outdoors). Therefore, scenarios in which 100 percent of the equipment charge was released during servicing and disposal were also considered. The release rate per event was multiplied by the number of events estimated to occur over a workday. For equipment servicing, the number of events per workday was assumed to equal the maximum number of units anticipated to be serviced in one day (i.e., eight units [A.S. Trust & Holdings, Inc. 2012]) 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. 

10.1	Occupational Exposure at Installation and Servicing 
Window AC units are expected to be serviced rarely, since this type of equipment is hermetically sealed. Generally, in the U.S., these units are replaced rather than serviced if the charge leaks. Nevertheless, the potential occupational exposure for those situations where servicing takes place was analyzed. The possibility of a release during installation was also considered. The maximum 30-minute time-weighted average (TWA) exposure for each component in R-441A was estimated for servicing window AC units charged with 125 grams, 195 grams, and 1,000 grams of R-441A. As summarized in Table 8, occupational exposure to R-441A is anticipated to be significantly below the short-term exposure limits (STEL) with either a 125-gram, 195-gram or 1,000-gram charge size and with a 0.4 percent or 100 percent release during installation and servicing. Installation and servicing activities for window ACs using R-441A are not expected to result in significant worker exposure when certified technicians follow the procedures outlined in the MSDS and maintenance manual, undergo proper training, and wear appropriate PPE (e.g., gloves and safety glasses). Adequate ventilation should always be established during any use, handling, or storage of R-441A. Systems should be installed to ensure leak-free conditions, for instance by following procedures of ASHRAE Standard 147 including conducting leak checks once a system is installed (ASHRAE 2013b). In addition, during servicing events, prior to adding refrigerant, all pipes should be inspected for leakages, and repairs should be performed only after all refrigerant has been recovered from the system. By adhering to the safety guidelines mentioned above, and in Section 6, worker exposure to R-441A during installation and maintenance is unlikely.
             Table 9. Occupational Risk Assessment at Servicing[a]
                               R-441A Component
                   30-minute TWA Occupational Exposure (ppm)
                            Charge size: 125 grams
                   30-minute TWA Occupational Exposure (ppm)
                            Charge size: 195 grams
                   30-minute TWA Occupational Exposure (ppm)
                           Charge size: 1,000 grams
                    30-min Short Term Exposure Limits (ppm)
                                       
                                 0.4% Release
                                 100% Release
                                 0.4% Release
                                 100% Release
                                 0.4% Release
                                 100% Release
                                       
                                    Propane
                                     0.60
                                      150
                                     0.86
                                      214
                                      4.8
                                     1,200
                                   6,900[b]
                                   n-Butane
                                     0.23
                                      57
                                     0.44
                                      106
                                      1.8
                                      450
                                   6,900[b]
                                   Isobutane
                                     0.04
                                      9.5
                                     0.07
                                      18
                                     0.30
                                      76
                                   6,900[b] 
                                    Ethane
                                     0.07
                                      18
                                     0.07
                                      17
                                     0.60
                                      150
                                   3,000[c]
	[a] Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
	[b] AEGL-1; See Table 4 for more information 
	[c] ACGIH (2004)
	
10.2	Occupational Exposure at Disposal
Disposal of the R-441A window AC unit is expected to occur at disposal facilities with limited duration of exposure to the refrigerant. 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 R-441A constituents 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 during the 50 percent release scenario will at no point exceed the long-term exposure limits of any of the individual components during disposal of R-441A for window AC units with a charge size of 125 grams, 195 grams, or 1,000 grams. Under the 100 percent release scenario at disposal of the 1,000-gram window unit, the 8-hour TWA would be exceeded for the propane component of R-441A. However, occupational exposure to the proposed substitute during disposal does not represent a true occupational health hazard because the estimated exposure concentrations of the propane component of R-441A for all scenarios do not exceed the 8-hr AEGL-1 for propane, which is 5,500 ppm. Furthermore, these estimated exposures were derived using conservative assumptions (e.g., no ventilation or use of PPE assumed), and represent a reasonable 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)
                            Charge size: 125 grams
                    8-Hour TWA Occupational Exposure (ppm)
                            Charge size: 195 grams
                    8-Hour TWA Occupational Exposure (ppm)
                           Charge size: 1,000 grams
                    8-Hour Long Term Exposure Limits (ppm)
                                       
                                  50% Release
                                 100% Release
                                  50% Release
                                 100% Release
                                  50% Release
                                 100% Release
                                       
                                    Propane
                                      130
                                      270
                                      190
                                      379
                                     1,060
                                     2,100
                                    1,000b
                                   n-Butane
                                      50
                                      100
                                      94
                                      188
                                      400
                                      800
                                   1,000[c]
                                   Isobutane
                                      8.4
                                      17
                                      16
                                      31
                                      67
                                      130
                                   1,000[c]
                                    Ethane
                                      16
                                      32
                                      15
                                      30
                                      130
                                      260
                                   1,000[c]
   [a] Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
[b] OSHA PEL
[c] ACGIH TLV 

Because anticipated occupational exposures could potentially exceed the exposure limits for each of the components of R-441A during disposal of 1,000-gram window AC units without recovery, 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 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. 2012). 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 window AC units.
11. 	GENERAL POPULATION EXPOSURE ASSESSMENT
R-441A is not expected to cause a concern for human health in the general population when used as a refrigerant in window AC units. 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 propane concentrated). Should air releases during manufacturing operations occur, including filling of AC units, engineering controls could be used (e.g., carbon absorption units or 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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