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: Propane (R-290)
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 report 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 propane as a substitute for HCFC-22 in the residential and light commercial air conditioning (AC) and heat pump end-use, specifically in window AC units. Table 1 details the composition of the proposed substitute, including the maximum estimated concentrations of impurities, which may be present in the proposed substitute, as provided by the submitter (allowable impurity levels per 40 CFR Part 82 or under AHRI Standard 700 may be different).
                       Table 1.  Composition of Propane
                                   Component
                               Chemical Formula
                                  CAS Number
                                 Concentration
                               (Weight Percent)
                              Proposed Substitute
                                    Propane
                                     C3H8
                                    74-98-6
                                     98.9%
                 Potential Impurities (maximum concentration)
                                   Isobutane
                                     C4H10
                                    75-28-5
                                     0.4%
                                   n-Butane
                                     C4H10
                                   106-97-8
                                     0.4%
                                    Ethane
                                     C6H14
                                    74-84-0
                                     0.2%
                                    Propene
                                     C3H6
                                   115-07-1
                                     0.1%

Section 2 of this report summarizes the results of the risk screen for the proposed substitute 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						
Propane 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 air conditioners (PTAC), packaged terminal heat pumps (PTHP), and portable AC units. EPA's risk screen indicates that the use of the proposed substitute 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. Propane is 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 propane in window AC units are not anticipated to contribute significantly to ground level ozone concentrations in the United States. No significant asphyxiation risks to consumers or toxicity risks to workers, consumers, or the general population are expected.  It is expected that procedures identified in the material data safety sheet (MSDS) for propane 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 & Health Administration (OSHA) guidelines will be used during manufacture, installation, servicing, and disposal of window AC units using propane. Because units are to be installed in locations with adequate space and/or ventilation for the unit's charge size in accordance with EPA recommendations and the equipment maintenance manual for propane 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) for propane, 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 484. 


3. 	ATMOSPHERIC ASSESSMENT
This section presents an assessment of the potential risks to the atmosphere posed by the use of propane 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, propane also has a 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 propane 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 Propane 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[a]
                                      3.3
                                    0.03[b]
                                    HCFC-22
                                    0.05[b]
                                    1,810 
                                     12[a]
                                   R-410A[c]
                                     0[a]
                                     2,088
                                     NA[d]
NA = Not Available
[a] IPCC 4th Assessment Report (Forster et al. 2007)
[b] WMO 2010 Scientific Assessment Report (2011)
[c] R-410A is a blend of 50% HFC-32 and 50% HFC-125.
[d] Atmospheric lifetimes are not given for blends, because the components separate in the atmosphere. The ALT for HFC-32 is 4.9 years and the ALT for HFC-125 is 29 years (IPCC 4th Assessment Report [Forster et al. 2007]).
4.	VOLATILE ORGANIC COMPOUND ASSESSMENT
Propane is regulated as a VOC under CAA regulations (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 a number of types of smaller, self-contained refrigeration and room air-conditioning 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 propane 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
Propane has been 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 propane window AC units installed in a room of 41m[3] is 180 grams.  However, the submission states that propane window AC units will have a typical charge size of 300 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 (180 grams, 300 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 with the door closed until the charge is completely released. UL 484 assumes that window AC units and their compressors are installed at a height 1 meter above the ground. Based on this location and because propane is denser than air (specific gravity of propane relative to air is 1.52 [air = 1]), this risk screen assumes that a vertical concentration gradient of propane 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 also consistent with the possibility that, in a bedroom scenario, individuals may be lying close to the floor. Table 3 details the end-use modeling assumptions used throughout this risk screen (i.e., in Sections 7, 8, and 9).

                  Table 3. End-Use Scenario Model Assumptions
Parameter
                                  Assumptions
Room Type
                                    Bedroom
 Size (m[3])
                              41[a] (1,450 ft[3])
 Ventilation Rate (air changes per hour)
                               0.11[b]; 0.67[c]
Refrigeration Unit
                                   Window AC
 Charge Size (g)
                           180[d]; 300[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] .
              [e] Typical charge size (CHEAA 2011).
              [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. To protect consumers from the potential dangers of a catastrophic leak from the refrigeration unit,  ASHRAE Standard 34 determined refrigerant concentration limits (RCLs) 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 in addition to the lower flammability limit, hypoxia No Observed Adverse Effect Level (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 guidelines levels (AEGLs), or an 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 and RCLs of propane and its impurities, 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 Propane and Potential Impurities
                                   Component
                           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[i] 
Potential Impurities
                                   n-Butane
                              1,000b  (ACGIH TLV)
                           6,900[e]  (30 min AEGL-1)
                                   4,000[i]
                                   Isobutane
                             1,000[b]  (ACGIH TLV)
                                   6,900[f] 
                                   4,000[i]
                                    Ethane
                             1,000[b]  (ACGIH TLV)
                     3,000g (30 min ACGIH Excursion Limit)
                           2,900[h] (15-min TEEL-1) 
                                   7,000[i]
                                    Propene
                              500[b] (ACGIH TLV)
                     1,500g (30 min ACGIH Excursion Limit)
                                   1,000[i]
[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/results96.htm
[e] AEGL-1 available at: http://www.epa.gov/oppt/aegl/pubs/rest102.htm
[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] Calculated as three times the TLV-TWA. (ACGIH 2004)
[h] DOE (2008)
[i] ASHRAE (2010b)
         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 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.
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. 

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.

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. 
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 propane may be hazardous if inhalation, skin contact, or eye contact with propane occurs. The most likely pathway of exposure is through inhalation. Propane 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 can act as a narcotic and cause central nervous system depression, including dizziness, drowsiness, and headaches. 
If propane 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 assist victims of exposure to propane without adequate PPE. At a minimum, a self-contained breathing apparatus (SCBA) should be worn. Exposures of propane to the skin may cause frostbite. In the case of dermal exposure, the MSDS for propane recommends that person(s) immediately wash the affected area with water and remove all contaminated clothing; if frostbite occurs, bathe (do not rub) the affected area with lukewarm, not hot, water. If water is not available, cover the affected area with a clean, soft cloth. Alternatively, if the fingers or hands are frostbitten, warm the affected area by placing it in the armpit; gently exercise the affected part while being warmed, and seek medical attention immediately. Exposures of propane to the eyes could cause eye irritation. In case of ocular exposure, the MSDS for propane 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 propane can be minimized by following the exposure guidelines and ventilation and PPE recommendations outlined in the MSDS for propane and this risk screen.
7. 	FLAMMABILITY ASSESSMENT 
ASHRAE Standard 34 classifies propane as a Class A3 refrigerant. Propane is flammable when its concentration in air is in the range of 2.1 percent and 9.5 percent by volume (21,000 ppm to 95,000 ppm). In the presence of an ignition source (e.g., static electricity, a spark resulting from a switch malfunction, or a lit cigarette), an explosion or a fire could occur if the concentration of propane exceeds the lower flammability limit (LFL) of 21,000 ppm.  As such, propane 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
Propane window AC units are currently manufactured by the submitter in China; the manufacturer currently has no plans to manufacture these systems in the United States. If the manufacture of these propane systems occurs in the United States, the submitter indicates that release of or exposure to propane is possible at the charge and sealing steps on the window AC unit production line at the manufacturing site (CHEAA 2013). It is therefore important that all relevant standards be followed during the manufacture of window AC units, such as UL 484. Engineering controls should include normal and local ventilation (e.g., chemical hoods) for standard manufacturing procedures so workers can avoid physical contact with the refrigerant and to limit emissions. In general, use of appropriate PPE consistent with OSHA guidelines is recommended, such as splash goggles, mechanically-resistance gloves when handling cylinders, chemically-resistant gloves when handling the gas mixture (e.g., butyl rubber, chlorinated polyethylene, or neoprene), and protective clothing. 

All propane 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. 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 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 propane. 

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 propane. Both servicing and end-use of propane window AC units are expected to take place in the same location (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 propane immediately following the release of refrigerant were compared to the LFL for propane. As demonstrated in Table 6, the maximum instantaneous concentration in the lower 1 meter of the room at a charge size of 180 grams would be approximately 5,400 ppm, approximately 8,980 ppm for a 300-gram charge size, and approximately 29,930 ppm for a 1,000-gram charge size. The 180-gram charge size proposed by EPA (Reasonable Worst-Case 1) and the 300-gram charge size indicated by the submitter (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) both exceed the proposed substitute's LFL of 21,000 ppm. However, according to UL 484, a window unit with a charge size of 1,000 grams is not intended for installation in a room with a volume as small as that modeled in the worst-case scenario (41 m[3]). The maximum instantaneous concentration in the upper portion in the room for all 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 of the room. 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 180 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
                                      180
                               41 (1,450 ft[3])
                                     5,400
                            Reasonable Worst-Case 2
                                      300
                               41 (1,450 ft[3])
                                     8,980
                            Reasonable Worst-Case 3
                                     1,000
                               41 (1,450 ft[3])
                                    29,930
                       Threshold Analysis 1: Charge Size
                                      700
                               41 (1,450 ft[3])
                                    21,000
                       Threshold Analysis 2a: Room Size
                                      180
                                11 (345 ft[3])
                                       
                       Threshold Analysis 2b: Room Size
                                      300
                                18 (575 ft[3])
                                       
                       Threshold Analysis 2c: Room Size
                                     1,000
                               58 (1,920 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 propane is equal to 21,000 ppm.
    c Values provided in this column refers to the concentration in the lower 1 meter of the room, which presents the most conservative risk as 95 percent of the leaked refrigerant is present in this space. 
  
For the flammability threshold analyses shown in Table 6, the conditions at which a flammability concern would exist (i.e., when the maximum instantaneous concentration in the lower stratum of the bedroom equals the LFL for propane) were determined. Within the reasonable worst-case room size of 41 m[3] (1,450 ft[3]), as shown under Threshold Analysis 1, the charge size of the propane window AC unit would have to be at least 700 grams for a flammability concern to exist, which is greater than EPA's recommended charge size (i.e., 180 grams) and the largest charge size intended by the submitter (i.e., 300 grams). For window AC units with a charge size of 180 grams (see Threshold Analysis 2a in Table 6) the volume of the bedroom would have to be 11 m[3] (345 ft[3]) or smaller for a flammability risk to occur. Using a 300-gram window AC unit, as shown under Threshold Analysis 2b, the volume of the room would have to be 18 m[3] (575 ft[3]) or smaller for a flammability risk to occur. Using a 1,000-gram propane window AC unit, as shown under Threshold Analysis 2c, the volume of the bedroom would have to be 58 m[3] (1,920 ft[3]) or less 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 than those modeled in this assessment and because persons or furniture in the room may reduce the effective volume of the space, window AC units containing propane should not be installed in enclosed areas with effective volumes less than indicated by UL 484 or the Room Air-Conditioners with Flammable Refrigerants Installation and Service Manual provided by the submitter, unless additional steps are taken to protect against a flammability risk (e.g., higher ventilation rates).  According to UL 484, window AC units with charge sizes of 300 grams and 1,000 grams should not be installed in a room less than 120 m[3] (4,300 ft[3])  and 1,360 m[3] (48,100 ft[3]), respectively. According to ASHRAE Standard 34, the RCL for propane (9.5 g/m[3] of propane or 5,300 ppm by volume) should not be exceeded in any room that contains a propane window AC unit. Although the RCL for propane is less conservative than the anticipated release amount of propane under the modeled worst-case scenarios (i.e., 180 grams in a 41m[3] space, or 4.4 g/m[3] and 300 grams in a 41 m[3] space, or 7.3 g/m[3]), the RCL is calculated assuming that refrigerant is evenly mixed in the space, whereas this analysis assumes a vertical concentration gradient due to the higher density of propane to air (propane = 1.52, air = 1). End-users, therefore, should ensure that propane window AC units are installed with an appropriate cooling capacity for the intended cooled space (i.e., avoid installing large window AC units to cool small spaces) that is consistent with manufacturer recommendations and the guidelines of relevant safety standards (e.g., ASHRAE 15 and 34 and UL 484).
The submitter additionally indicates that warning labels are present on the equipment indicating that flammable refrigerants are inside the unit as well as notifying the user to read the equipment use instructions which provide safety guidelines for handling propane. Therefore, these guidelines should be acknowledged and followed to mitigate flammability risk. The installation of leak prevention devices would further protect against the very limited risk of explosion.
In the U.S., window AC units are typically replaced rather than serviced. However, should servicing of window AC units with propane occur, EPA recommends that the ventilation requirements outlined in the MSDS for propane be followed through the use of fans (or other mechanical ventilation devices) and portable refrigerant detectors be used to alert technicians to the presence of flammable gases in order to mitigate the risk of fire or explosion during catastrophic leak.  It is also important that only properly trained and certified technicians handle propane. As a further precaution, certification requirements and training programs for technicians that handle propane should be developed using these guidelines.  
8.	ASPHYXIATION ASSESSMENT
The risk of asphyxiation for the reasonable worst-case scenario (see Section 5) was investigated for propane. 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 and 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)
                          Effective Room Size (m[3])
               Percent Oxygen Concentration in Lower 1 Meter[b] 
                            Reasonable Worst-Case 1
                                      180
                               41 (1,450 ft[3])
                                      21
                            Reasonable Worst-Case 2
                                      300
                               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
                                      180
                               0.40 (14.1 ft[3])
                                      12
                       Threshold Analysis 2b: Room Size
                                      300
                               0.66 (23.5 ft[3])
                                      12
                       Threshold Analysis 2c: Room Size
                                     1,000
                               2.21 (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). 
In order for a risk of asphyxiation to occur, the normal concentration of oxygen in air (21 percent) must be reduced to 12 percent. Based on the worst-case scenario modeling assumptions, propane in window AC units does not present a significant risk of asphyxiation. The concentration of propane 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. Because 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, 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 41m[3] (1,450ft[3]), as shown under Threshold Analysis 1, the charge size of the propane window 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 by UL 484 (i.e., 1,000 grams). Using a 180-gram window AC unit, as shown under Threshold Analysis 2a, the volume of the room would have to be 0.40 m3 (14.1 ft[3]) or smaller for asphyxiation to be of concern. Using a 300-gram window AC unit, as shown under Threshold Analysis 2b, the volume of the room would have to be 0.66 m3 (23.5 ft[3]) or smaller for asphyxiation to be of concern. Using a 1,000-gram window AC unit, as shown under Threshold Analysis 2c, the volume of the room would have to be 2.21 m3 (78.2 ft[3]) or smaller for asphyxiation to be of concern. All of the room sizes modeled in the latter three scenarios are significantly smaller than the reasonable worst-case bedroom size (41 m[3] [1,450 ft[3]]) and 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 34 and UL 484). Additionally, adherence to ASHRAE 34, which provides more conservative concentration limits, will ensure that asphyxiation is not a significant risk. Minimum room sizes according to the RCL stated in ASHRAE 34 and UL 484 can be found in Section 7. Leak prevention, detection, or mitigation devices should be installed and the ventilation requirements outlined in the MSDS for propane should be closely followed. If these guidelines are followed, a catastrophic leak of propane is not anticipated to result in a significant asphyxiation risk. 
9.	END-USE EXPOSURE ASSESSMENT
This section presents estimates of potential consumer exposures to propane and each of its impurities 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 scenarios outlined in Section 5 with charge sizes of 180 grams, 300 grams and 1,000 grams. 
For the end-use exposure assessment scenario, 30-minute TWA exposures for the proposed substitute and each of its impurity constituents 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 limits 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 propane and all of its impurity constituents; however, only the results for propane are presented in Table 8. As propane is approximately 98.9 percent pure, it presents the greatest risk of exceeding the STEL and thus the most conservative assessment. 

                   Table 8. End-Use Exposure Assessment[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
                                      180
                               41 (1,450 ft[3])
                                     0.11
                                     5,247
                           Reasonable Worst-Case 1b
                                       
                                       
                                     0.67
                                     4,602
                           Reasonable Worst-Case 2a 
                                      300
                                       
                                     0.11
                                    8,745 
                           Reasonable Worst-Case 2b
                                       
                                       
                                     0.67
                                     7,670
                           Reasonable Worst-Case 3a
                                     1,000
                                       
                                     0.11
                                    29,151
                           Reasonable Worst-Case 3b
                                       
                                       
                                     0.67
                                    25,566
                      Threshold Analysis 1a: Charge Size
                                      237
                               41 (1,450 ft[3])
                                     0.11
                                     6,900
                      Threshold Analysis 1b: Charge Size
                                      270
                                       
                                     0.67
                                       
                       Threshold Analysis 2a: Room Size
                                      180
                               31 (1,020 ft[3])
                                     0.11
                                       
                       Threshold Analysis 2b: Room Size
                                       
                                27 (890 ft[3])
                                     0.67
                                       
                       Threshold Analysis 3a: Room Size
                                      300
                               52 (1,710 ft[3])
                                     0.11
                                       
                       Threshold Analysis 3b: Room Size
                                       
                               46 (1,510 ft[3])
                                     0.67
                                       
                       Threshold Analysis 4a: Room Size
                                     1,000
                               173 (5,680 ft[3])
                                     0.11
                                       
                       Threshold Analysis 4b: Room Size
                                       
                               152 (5,000 ft[3])
                                     0.67
                                       
                   Threshold Analysis 5a: Air Exchange Rate
                                      180
                               41 (1,450 ft[3])
                                       0
                                       
                   Threshold Analysis 5b: Air Exchange Rate
                                      300
                                       
                                      1.1
                                       
                   Threshold Analysis 5c: Air Exchange Rate
                                     1,000
                                       
                                      8.6
                                       
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 95 percent of the leaked refrigerant in present in this space. 

In the reasonable worst-case scenario, catastrophic releases of window AC units with charge sizes of 180 grams, 300 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 2a, 2b, 3a, and 3b, the 30-minute AEGL-1 for propane of 6,900 ppm is likely to be exceeded (see Table 8). The 30-min TWA exposures 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, exceed the AEGL-2 (17,000 ppm), but not the AEGL-3 (33,000 ppm) for propane. 
A threshold analysis was performed to determine the charge size, room volume, and ventilation rates where window AC units containing propane could be installed to avoid the short-term exposure limit for propane. 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 237 grams and 270 grams with 0.67 ACH. Additionally, the threshold analysis indicates that window AC units with charge sizes of 180 grams, 300 grams and 1,000 grams should not be installed in rooms smaller than 31 m[3] (1,020 ft[3]), 52 m[3] (1,710 ft[3]), and  173 m[3] (5,680 ft[3]), respectively, assuming an air ventilation rate of 0.11 ACH. As shown in Table 8, these recommended minimum room sizes are smaller if the air ventilation rate is increased to 0.67 ACH. 
Because window AC units with charge sizes of 300 grams and 1,000 grams were 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 these scenarios exceed the AEGL-1 for propane. These potential 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 recommends that the charge size for a propane window AC unit does not exceed the RCL (9.5 g/m[3]) and proposes to require compliance with UL 484 in any space containing a window AC unit, unless proper leak protection devises are in place in order to prevent exposures of propane beyond the recommended limits. Smaller accidental releases of the proposed substitute, however, do not pose a significant risk to end-users.
Thus, risk of excessive exposure 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 propane. When these conditions and the proposed use conditions of the rule 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 propane in window AC units. 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 in 2010 were obtained from the Vintaging Model.  To determine the estimated level of occupational exposure for a constituent in proposed substitute blend, the total anticipated release rate of the refrigerant is multiplied by the weight percent composition of each compound and impurity. For the window AC unit end-use, 0.4 percent of the equipment charge was conservatively assumed to be released during manufacture and servicing and 50 percent of the equipment charge was conservatively assumed to be released during disposal. Additionally, EPA is proposing to allow intentional venting or release of propane 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 window AC unit servicing, it was conservatively assumed that eight events of servicing a unit occur in an 8-hour work day. 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 during Manufacture
Propane window AC units are currently manufactured by the submitter in China, and the manufacturer currently has no plans to manufacture these systems in the United States. As indicated by the submitter, release of or exposure to propane is possible at the charge and sealing steps on the window AC unit production line. If the manufacture of these propane systems occurs in the United States, the proposed substitute's MSDS should be referenced and proper engineering controls and PPE should be used. Propane is not expected to pose a risk to workers during manufacture when the engineering controls and PPE recommendations and referenced in the MSDS for propane are followed. Engineering controls should include normal and local ventilation (e.g., chemical hoods) for standard manufacturing procedures so workers can avoid physical contact with the refrigerant and limit emissions. The manufacturing equipment is designed to minimize potential emissions while engineering controls at the manufacturing facility include warning alarms for propane leakage and ventilation systems. Maintenance manuals describe procedures to reduce leakage and prior safety training is required for all personnel who work on the production line. In general, use of appropriate 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), and protective clothing. Because of established equipment design and manufacture practices, exposures to propane will be unlikely. Thus, EPA does not believe that manufacturing of AC units with propane under these workplace conditions presents a concern to workers.
Containers should be stored in cool, dry conditions (maximum storage temperature should be 40C) in well-sealed receptacles and should not be allowed to contact open flames, glowing metal surfaces, or electrical heating elements. EPA believes that when proper handling and disposal guidelines are followed in accordance with both good industrial hygiene and manufacturing practices and the MSDS for propane, there is no significant risk to workers during the manufacture of propane window AC units.

10.2	Occupational Exposure at Installation and Servicing 
Window AC units are expected to be serviced rarely, since this type of equipment is hermetically sealed and in the U.S. is often replaced rather than serviced if the charge leaks. Nevertheless, the potential occupational exposure for those situations where servicing takes place were analyzed. The possibility of a release during installation was also considered. The maximum 30-minute time-weighted average (TWA) exposure for propane and its potential impurities were estimated for servicing window AC units charged with 180 grams, 300 grams and 1,000 grams of refrigerant. As summarized in Table 9, occupational exposure to propane is anticipated to be significantly below the short-term exposure limits (STEL) with a 180-gram, 300-gram or 1,000-gram charge size for both 0.4 percent release and 100 percent release of refrigerant during servicing. Therefore, worker exposure to propane during installation and servicing is not a significant concern. Technicians should 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 propane. Systems should be installed by following procedures of ASHRAE Standard 147 including conducting leak checks once a system is installed (ASHRAE 2013). 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 propane during installation and maintenance is unlikely.
             Table 9. Occupational Risk Assessment at Servicing[a]
                                   Component
                   30-minute TWA Occupational Exposure (ppm)
                            Charge size: 180 grams
                   30-minute TWA Occupational Exposure (ppm)
                            Charge size: 300 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
                                     1.42
                                      356
                                     2.37
                                      593
                                     7.90
                                     1,980
                                   6,900[b]
Potential Impurities
                                   Isobutane
                                     0.004
                                      1.1
                                     0.007
                                      1.8
                                     0.024
                                      6.1
                                   6,900[b]
                                   n-Butane
                                     0.004
                                      1.1
                                     0.007
                                      1.8
                                     0.024
                                      6.1
                                   6,900[b] 
                                    Ethane
                                     0.004
                                      1.1
                                     0.007
                                      1.8
                                     0.023
                                      5.9
                                   3,000[c]
                                    Propene
                                     0.002
                                      0.4
                                     0.003
                                      0.6
                                     0.008
                                      2.1
                                   1,500[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)

10.3	Occupational Exposure at Disposal
Disposal of propane window AC units 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 propane and its impurities during disposal. Based on the assumptions described in the beginning of Section 10, the modeling indicates that 8-hour worker exposure concentrations for propane and its impurities during the 50 percent release scenario will not exceed the long-term exposure limits of any of the individual components during disposal of propane for window AC units with a charge size of 180 grams or 300 grams. Under the 100 percent disposal release scenario for the 300-gram unit and the 50 percent and 100 percent release scenarios for the 1,000-gram unit, the modeling indicates that occupational exposure could exceed the 8-hour long term exposure limits for propane. However, the occupational exposure to the proposed substitute during disposal does not represent a true occupational health hazard because the estimated exposure concentrations for all scenarios do not exceed the 8-hr AEGL-1 for propane, which is 5,500 ppm. Furthermore, these 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]
                                   Component
                    8-Hour TWA Occupational Exposure (ppm)
                            Charge size: 180 grams
                    8-Hour TWA Occupational Exposure (ppm)
                            Charge size: 300 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
                                      315
                                      629
                                      524
                                     1,050
                                     1,748
                                     3,500
                                    1,000b
Potential Impurities
                                   Isobutane
                                     0.97
                                     1.93
                                     1.61
                                     3.22
                                     5.36
                                     10.7
                                   1,000[c]
                                   n-Butane
                                     0.97
                                     1.93
                                     1.61
                                     3.22
                                     5.36
                                     10.7
                                   1,000[c]
                                    Ethane
                                     0.93
                                     1.87
                                     1.56
                                     3.11
                                     5.19
                                     10.3
                                   1,000[c]
                                    Propene
                                     0.33
                                     0.67
                                     0.56
                                     1.11
                                     1.85
                                      3.7
                                    500[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 are above the exposure limits for propane for the 100 percent disposal release scenario for 300g and 1000 g charge sizes, the recommendations for proper engineering controls and PPE in the MSDS for propane should be followed. Adequate ventilation should always be established during any use, handling, storage, or disposal of propane. Engineering controls should include vapor-in air detection systems and local exhaust ventilation during use and disposal of propane to prevent dispersion throughout the work place. In addition, an eye wash and safety shower should be near the manufacturing facility and locations where propane 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). EPA believes that if proper handling and disposal guidelines are followed in accordance with good industrial hygiene and manufacturing practices and the MSDS for propane, there is no significant risk to workers during the manufacturing, installation, servicing, and disposal of propane in window AC units. 
11.	GENERAL POPULATION EXPOSURE ASSESSMENT
Propane is not expected to cause a concern for human health in the general population when manufactured for use and used as a refrigerant in window AC units. At room temperature, propane is a gas and, therefore, releases to ground or surface water are not anticipated, as propane 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 window AC units, engineering controls should be used (e.g., carbon absorption units or scrubbers) to collect propane and prevent the release of propane 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 propane is not expected to pose a significant toxicity risk to the general population.








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