Document ID: EPA-HQ-OAR-2013-0748-0005
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2014-07-09T04:00Z

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: HFC-32 (Difluoromethane)
                                       
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 HFC-32 as a substitute for HCFC-22 in the residential and light commercial air conditioning and heat pump end-use, specifically in room air-conditioning (AC) systems included under Underwriters Laboratory (UL) Standard 484: Room Air Conditioners. These systems are limited to packaged terminal air-conditioners (PTAC), packaged terminal heat pumps (PTHP), and other AC units that include a hermetic refrigerant motor-compressor and are intended for installation in a window, through a wall, or as a console located in or adjacent to the space to be conditioned (e.g., portable AC units), and hereinafter will be referred to collectively as "room AC systems." The scope of UL 484 and this risk screen specifically excludes remote-condenser applications such as a mini-split ductless air conditioner. The proposed substitute, HFC-32, may contain minute quantities of impurities. Table 1 details the composition of the substitute, including the maximum estimated concentration of impurities that may be present, as indicated by the submitter (allowable impurity levels per 40 CFR Part 82 or under AHRI Standard 700 may be different).

                        Table 1. Composition of HFC-32
                              Proposed Substitute
                                 Concentration
                               (Weight Percent)
                                    HFC-32 
                                    99.909
                             Potential Impurities
                    Maximum Concentration (Weight Percent)
                                       
                                       
                                       
                                       

Section 2 of this risk screen 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 Scenarios 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 Assessment
         * Section 12: References
2.	SUMMARY OF RESULTS
HFC-32 is recommended for SNAP approval for residential and light commercial air conditioning and heat pump systems that comply with UL Standard 484: Room Air Conditioners.  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.  In addition, HFC-32 contributions to volatile organic compound (VOC) emissions are not significant, as HFC-32 is exempt under CAA regulations (40 CFR § 51.100(s)). No significant asphyxiation risks to consumers or toxicity risks to workers, consumers, or the general population are expected.  Because units are to be installed in locations with adequate space or ventilation in accordance with the AC maintenance manual for HFC-32, as discussed in greater detail in Section 9, significant toxicity or flammability risk to consumers is unlikely. Given that the MSDS for HFC-32 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 and Health Administration (OSHA) guidelines will be used during manufacture, installation, servicing, and disposal of room AC systems using HFC-32, worker exposure to HFC-32 will be unlikely. Additional safeguards, including specified refrigerant concentration limits (RCL) for HFC-32, 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 UL Standard 484. 
3. 	ATMOSPHERIC ASSESSMENT
This section presents an assessment of the potential risks to the atmosphere posed by the use of HFC-32 in the residential and light commercial air conditioning and heat pumps sector.  The ozone depletion potential (ODP), global warming potential (GWP), and atmospheric lifetime (ALT) of the proposed substitute are presented in Table 2.	As compared to HCFC-22, the proposed substitute is substantially less harmful to the ozone layer, has less climate impact, and has a shorter atmospheric lifetime. HFC-32 does however, have a non-zero GWP, but at 675, this value is generally in the range of  or lower 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 HFC-32 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 R-410A. 
    Table 2.  Atmospheric Impacts of HFC-32 Compared to HCFC-22 and R-410A
                                  Refrigerant
                                      ODP
                                      GWP
                                  ALT (years)
                                    HFC-32
                                     0[a]
                                    675[b]
                                    4.9[b]
                                    HCFC-22
                                    0.04[c]
                                   1,810[b]
                                     12[b]
                                   R-410A[d]
                                       0
                                   2,088[b]
                                     NA[e]
[a] HFC-32 SNAP Submission (Daikin 2011)
[b] IPCC 4th Assessment Report (Forster et al. 2007)
[c] WMO (2011)
[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 HFC-32 is 4.9 years, and the ALT for HFC-125 is 29 years (IPCC 4th Assessment Report [Forster et al. 2007]).
NA = not applicable
4.	VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT
 HFC-32 is exempt from the definition of volatile organic compound (VOC) under CAA regulations (40 CFR § 51.100(s)).  Therefore, environmental impacts from the release of HFC-32 as a VOC are not a significant concern. 
5. 	DISCUSSION OF END-USE SCENARIOS MODELED
HFC-32 has been proposed for use in residential and light commercial air conditioners and heat pumps, including PTACs, PTHPs, and other room AC units that employ hermetic refrigerant motor-compressors and are intended for installation in a window, through a wall, or as a console located in or adjacent to the space to be conditioned. The remainder of this risk screen assesses the risk of PTAC/PTHP systems, which represent a reasonable worst-case scenario for room air conditioning systems (as included under UL 484). These systems consist of a separate, un-encased combination of heating and cooling assemblies mounted through a wall. There is forced ventilation as well as separable outdoor horizontal slats providing air circulation. Models can be designated as "cooling only" or heating can be provided by hot water, steam, or electrical resistance heat (Daikin 2013). In addition, PTAC and PTHP systems are classified as "high probability systems" by ASHRAE Standard 15; if a leak occurs, the entire refrigerant charge of the system has the potential to be released into one room connected to the unit (ASHRAE 2010a). 

For the reasonable worst-case scenario, it was assumed that a PTAC is installed in a small, enclosed dormitory room of 41 m[3] (1,450 ft[3]) and is used to cool only that room. HFC-32 is also proposed for other residential and light commercial uses, including hotel and motel guest rooms, hospitals and assisted living facilities, apartments and military barracks, and offices and similar spaces in a variety of building types and for use in PTHP systems. However, because these spaces are typically larger than small dormitory rooms and have higher ventilation rates, these room types were considered to be less conservative and thus not modeled in this risk screen.  PTAC and PTHP systems have the same charge sizes and operate in the same way, except that PTAC systems provide cooling only while PTHP systems provide heating and cooling. The conservative results of this analysis can be used to assess the use of HFC-32 in PTAC or PTHP systems in all proposed end-use applications. 

Under EPA's proposed charge size limits, for a room AC unit installed in a room of 41 m[3] (with a capacity of 6,500 BTU/hour), the maximum HFC-32 refrigerant charge allowed is 5,350 grams, and 7,960 g is the maximum charge allowed for a room AC installed in any room size. EPA's proposed charge size limits will also restrict the charge size for a PTAC unit installed in a 41 m[3] room (with a capacity of 6,500 BTU/hour) to 1,460 grams, and the maximum charge size for a PTAC in any room size would be 4,650 g. However, the submission states that PTAC and PTHP units will be produced with charge sizes up to 8,500 grams (Daikin 2013). Therefore, this risk screen conservatively evaluates the risk associated with the maximum charge size for a PTAC indicated by the submitter (i.e., 8,500 grams), the maximum charge size for a room AC proposed by EPA (i.e., 7,960 grams), and the maximum charge size for a PTAC proposed by EPA in a small, enclosed dormitory room of 41 m[3] (i.e., 1,460 grams). Under the worst-case scenario, the full charge of the unit is assumed to be emitted over the course of one minute into the dormitory room. It was assumed that an individual is present at the start of the leak and remains in the room until the charge is completely released. A vertical concentration gradient is not assumed since HFC-32 is highly volatile and will likely disperse fairly evenly and immediately upon release. 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
                             Small Dormitory Room
 Size (m[3])
                               41 (1,450 ft[3])
 Ventilation Rate (air changes per hour)
                                    0.25[a]
Refrigeration Unit
                                     PTAC
 Charge Sizes (g)
                            8,500[b]; 7,960; 1,460
 Length of Release (minutes)
                                       1
 Vertical Concentration Gradient
                                      No
              a Background Document (EPA 1994))
              [b] Maximum charge size for PTAC unit (Daikin 2013)
6. 	POTENTIAL HEALTH EFFECTS
To assess potential health risks from exposure to the proposed substitute in room AC systems, 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 a PTAC or other residential and light commercial air-conditioning and heat pump systems, ASHRAE Standard 34 determined refrigerant concentration limits (RCLs) to reduce the risks of acute toxicity, asphyxiation, and flammability hazards in occupied spaces(ASHRAE 2010b). ASHRAE Standard 15 requires 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). The RCL for HFC-32 was referenced throughout this risk screen as an additional, conservative limit to ensure flammability, asphyxiation, and end-use exposure risks do not occur. Table 4 lists the relevant toxicity limits and RCLs of HFC-32 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 HFC-32 and Potential Impurities
                                   Chemical
                         Long-term Workplace Exposure
                                (ppm, 8-hr TWA)
                         Short-term Workplace Exposure
                               (ppm, 15-min TWA)
                               Cardiotoxic NOAEL
                               (ppm, 5-min TWA)
                  Refrigerant Concentration Limit (RCL) (ppm)
                              Proposed Substitute
                                    HFC-32
                                    1,000a
                                    3,000b
                                  350,000[a]
                                    36,000
                             Potential Impurities

      [a] HFC-32 SNAP Submission (Daikin 2011)
      [b] STEL was estimated as three times the PEL; this method of estimating a short-term exposure limit is commonly done by ACGIH.
         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
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. 
NOAEL[b]
No Observed Adverse Effect Level
The highest exposure level at which there are no biologically significant increases in the frequency or severity of adverse effect between the exposed population and its appropriate control; some effects may be produced at this level, but they are not considered adverse or precursors of adverse 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 (2014)

According to the MSDS, exposure to HFC-32 may be hazardous if inhalation, skin contact, eye contact, or ingestion of HFC-32 occurs. The most likely pathway of exposure is through inhalation. When present in concentrations large enough to significantly lower oxygen concentrations below 19.5 percent by volume, HFC-32 can cause symptoms of asphyxiation, such as headaches, ringing in ears, dizziness, drowsiness, nausea, vomiting, depression of all senses, and unconsciousness. Under some circumstances of over-exposure (i.e., oxygen levels fall below 6 percent by volume), death may occur. HFC-32 can also cause cardiac arrhythmia if inhaled in sufficiently great quantities. If HFC-32 is inhaled, person(s) should be immediately removed and exposed to fresh air. Exposures of HFC-32 to the skin may cause frostbite. In the case of dermal exposure, the MSDS for HFC-32 recommends that person(s) immediately wash the affected area with soap and water and remove all contaminated clothing. Exposures of HFC-32 to the eyes could cause eye irritation. In case of ocular exposure, the MSDS for HFC-32 recommends that person(s) immediately flush the eyes, including under the eyelids, with copious amounts of water for 15 minutes. If HFC-32 is ingested, person(s) should consult a doctor. EPA's review of the human health impacts of this proposed substitute is contained in the public docket for this decision. These risks and procedures after exposure are similar for other common refrigerants.
The potential health effects of HFC-32 can be minimized by following the exposure guidelines and ventilation and PPE recommendations outlined in the MSDS for HFC-32 and this risk screen.
7. 		FLAMMABILITY ASSESSMENT
ASHRAE Standard 34 has classified HFC-32 as a Class A2L refrigerant (ASHRAE 2010b), because it has low toxicity, low flammability, and a low burning velocity (approximately 6.7 cm/s) (Takizawa et al. 2005). The proposed substitute is flammable when its concentration in air is in the range of 13.8 percent and 29.9 percent by volume (138,000 ppm to 299,000 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 when the concentration of HFC-32 exceeds its lower flammability limit (LFL) of 138,000 ppmv, posing a significant safety concern for workers and consumers.  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
HFC-32 PTACs are currently manufactured by the submitter outside of the United States; the manufacturer currently has no plans to manufacture these systems in the United States. If the manufacture of these HFC-32 systems occurs in the United States, the submitter indicates that release of or exposure to HFC-32 is possible at the charge and inspection steps on the PTAC production line at the manufacturing site (Daikin 2013). It is therefore important that all relevant standards be followed during the manufacture of PTACs, specifically 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 HFC-32 storage and transport equipment should be installed with safety devices that minimize the likelihood of catastrophic releases. 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 HFC-32. 
6.2	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 HFC-32. Both servicing and end-use of HFC-32 PTACs 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 HFC-32 immediately following the release of refrigerant were compared to the LFL for HFC-32. As demonstrated in Table 6, the maximum instantaneous concentration of HFC-32 in the room under Reasonable Worst Case Scenario 1 is 95,800 ppm, which is approximately 69 percent of the LFL (138,000 ppm). Although Reasonable Worst Case Scenario 1 (i.e., an 8,500-gram PTAC in a small dormitory) does not present a significant flammability concern, according to both UL 484 and ASHRAE Standard 34, a PTAC unit containing a charge size of 8,500 grams of HFC-32 is not intended for installation in a room with a volume as small as that modeled in the Reasonable Worst Case scenario (i.e., 41 m[3]). The other charge sizes analyzed (i.e., 7,960 and 1,460 grams) also did not present a significant flammability concern. The results of the flammability assessment are presented in Table 6.   

                      Table 6. Flammability Assessment[a]
                                   Scenario
                           Room Type/Appliance Type
                                Charge Size (g)
                          Effective Room Size (m[3])
                 Maximum Instantaneous Concentration (ppm) [b]
                            Reasonable Worst-Case 1
                              Dormitory Room/PTAC
                                     8,500
                               41 (1,450 ft[3])
                                    95,800
                            Reasonable Worst-Case 2
                            Dormitory Room/Room AC
                                     7,960
                               41 (1,450 ft[3])
                                    89,700
                            Reasonable Worst-Case 3
                              Dormitory Room/PTAC
                                     1,460
                               41 (1,450 ft[3])
                                    16,500
                       Threshold Analysis 1: Charge Size
                              Dormitory Room/PTAC
                                    12,200
                               41 (1,450 ft[3])
                                    138,000
                        Threshold Analysis 2: Room Size
                              Dormitory Room/PTAC
                                     8,500
                               28 (1,000 ft[3])
                                    138,000
   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 HFC-32 is equal to 138,000 ppm.

For flammability to be of concern in a 41 m[3] (1,450 ft[3]) room (i.e., when the maximum instantaneous concentration in the room equals the LFL for HFC-32), the charge size of the HFC-32 AC unit would have to be at least 12,200 grams (see Threshold Analysis 1 in Table 6), which is 50 percent larger than the maximum size intended for HFC-32 room AC units for any room size, and significantly larger than the maximum charge sizes for a PTAC and for any room AC proposed by EPA for a 41 m[3] room (i.e.,  1,460 grams and 5,350 grams, respectively). For flammability to be of concern with an 8,500-gram HFC-32 PTAC unit, the volume of the dormitory room would have to be decreased to at least 28 m[3] (see Threshold Analysis 2 in Table 6). 

According to the results of this flammability analysis, the risk of fire is minimal if an HFC-32 room AC unit is installed in a room with volumes in accordance with standards and regulations. As dormitory rooms 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, room AC systems containing HFC-32 should not be connected to rooms with an effective volume less than required to maintain maximum concentrations below the LFL, as described below. According to UL 484, the maximum recommended charge size for a HFC-32 PTAC installed in a room with a floor area of 17 m[2], which corresponds to the volume of the enclosed dormitory room volume used in the worst-case scenario (i.e., 41 m[3] or 1,450 ft[3]), is approximately 1,400 g. According to ASHRAE Standard 34, the RCL for HFC-32 (36,000 ppm or 77 g HFC-32/m[3]), which is a more conservative exposure limit than the LFL of HFC-32 (138,000 ppm), should not be exceeded in any room that is connected to an HFC-32 room AC system (e.g., through a vent or a wall-unit). End-users, therefore, should ensure to install PTAC units or other room AC systems with an appropriate cooling capacity and charge size for the intended cooled space (i.e., avoid installing large 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 intends to also manufacture PTAC units with typical charge sizes ranging between 0.5 kg and 1.05 kg, which are more suitable for smaller spaces.

Leak prevention, detection, or mitigation devices should be installed and proper ventilation should be present to further protect against the risk of fire or explosion in small spaces cooled by HFC-32 AC systems. In addition, it is important that only properly trained and EPA Section 608-certified refrigerant technicians handle HFC-32.  Proper ventilation should be maintained at all times during the manufacture, use and servicing of equipment containing HFC-32.  During servicing operations, technicians should ensure that proper ventilation is in place through the use of fans (or other mechanical ventilation devices) and portable refrigerant detectors should be used to alert technicians to the presence of leaked refrigerant in the area.
8. 	ASPHYXIATION ASSESSMENT
The risk of asphyxiation for the reasonable worst-case scenario (see Section 5) was investigated for HFC-32.  In this section, risk of asphyxiation, considered to be when there is less than 12 percent oxygen present in a space, 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 a asphyxiation risk with the charge size specified in the worst-case scenario.  This analysis does not consider other ventilation conditions that are likely to occur that would reduce the exposure levels, such as open doors or windows, fans operating, conditioned airflow (either heated or cooled), or even seepage between the door and door frame.  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 model assumed that nitrogen and oxygen retain the same relative volumes in the rooms with the balance composed entirely of HFC-32 and that the pressure of the room does not increase significantly with the addition of the refrigerant.  Further, the model assumes no stratification of refrigerant.  The results of the asphyxiation assessment are summarized in Table 7 below.

                     Table 7.  Asphyxiation Assessment[a]
                                   Scenario
                           Room Type/Appliance Type
                          Effective Room Size (m[3])
                                Charge Size (g)
                   Percent Oxygen Concentration in Room[b] 
                            Reasonable Worst-Case 1
                             Dormitory Room/ PTAC
                                41 (1450 ft[3])
                                     8,500
                                      19
                            Reasonable Worst-Case 2
                             Dormitory Room/ PTAC
                                41 (1450 ft[3])
                                     7,960
                                      19
                            Reasonable Worst-Case 3
                             Dormitory Room/ PTAC
                                41 (1450 ft[3])
                                     1,460
                                      20
                       Threshold Analysis 1: Charge Size
                             Dormitory Room/ PTAC
                                41 (1450 ft[3])
                                    37,300
                                      12
                        Threshold Analysis 2: Room Size
                             Dormitory Room/ PTAC
                                9.3 (328 ft[3])
                                     8,500
                                      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). 
 applicationsne.  mmended that pens r than the room assumed in the worst case scenario (see Section 4). Under the reasonable, worst-case scenarios (see Reasonable Worst-Case 1-3 in Table 7), an asphyxiation risk will not occur, as the oxygen concentration in the room is between 19 and 20 percent for all charge sizes, well above the 12 percent level of concern. For asphyxiation to be a concern in a 41 m[3] (1,450 ft[3]) room, the charge size of the HFC-32 AC unit would have to be increased to at least 37,300 grams (see Threshold Analysis 1 in Table 7), which is more than 4 times the largest size proposed by EPA for HFC-32 room AC units (i.e., 7,960 grams). For asphyxiation to be of concern with an 8,500-g HFC-32 PTAC unit, the volume of the dormitory room would have to be decreased to 9.4 m[3] (332 ft[3]), with an approximate floor area of 2.0 m x 2.0 m (6.5 ft x 6.5 ft), which is significantly smaller than the reasonable worst-case dormitory room size (41 m[3] [1,450 ft[3]]). In addition, the threshold room volume at which asphyxiation could occur during a catastrophic leak (9.3 m[3] [328 ft[3]]) is smaller than the minimum dormitory room volume typically found in the U.S. 

To further protect against an asphyxiation risk, end-users should ensure PTAC units and other room AC systems are installed with an appropriate cooling capacity for the intended cooled space to be consistent with manufacturer recommendations, EPA regulations, and the guidelines of relevant safety standards (e.g., ASHRAE 15 and 34 and UL 484). Minimum room sizes according to the RCL stated in ASHRAE 34 and UL 484 can be found in Section 6. Leak prevention, detection, or mitigation devices should be installed and the ventilation requirements outlined in the MSDS for HFC-32 should be closely followed. If these guidelines are followed, a catastrophic leak of HFC-32 is not anticipated to result in a significant asphyxiation risk. 
9.	END-USE EXPOSURE ASSESSMENT
This section presents estimates of potential consumer exposure to HFC-32 in PTACs and other room AC systems.  An exposure analysis was performed to examine potential catastrophic release of the proposed substitute in a dormitory room under the reasonable worst-case scenario outlined in Section 5. 

For the scenario, 15- and 30-minute time-weighted average (TWA) exposures for the proposed substitute were calculated using the box model described in the Background Document, which was adapted to estimate concentrations on a minute-by-minute basis.  These exposures were then compared to the standard toxicity limit presented in Table 8 to assess the risk to consumers.  However, the TWA values are fairly conservative as the analysis does not consider opened windows, fans operating, conditioned airflow (either heated or cooled) and other variables that would reduce the levels to which individuals would be exposed. The results of the assessment, which show the end-use exposure levels under the reasonable worst-case scenario in Section 5, are presented in Table 8. 

                   Table 8.  End-Use Exposure Assessment[a]
                            Room Type/Appliance Type
                             HFC-32 Charge Size (g)
                      Modeled 15-minute TWA Exposure (ppm)
                      Modeled 30-minute TWA Exposure (ppm)
                              Cardiotoxic NOAEL, 
                             5-minute TWA (ppm)[b]
                                Dorm Room/PTAC
                                     8,500
                                    95,000
                                    92,100
                                    350,000
                               Dorm Room/Room AC
                                     7,960
                                    89,000
                                    86,000
                                    350,000
                                Dorm Room/PTAC
                                     1,460
                                    16,300
                                    15,800
                                    350,000
Bold font indicates modeling results. 
a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
[b] See Table 4 for more information

The effect of a one-time exposure to a consumer can be accurately evaluated by comparing the exposure concentration to the cardiotoxic NOAEL (350,000 ppm), a conservative upper limit for short-term consumer exposure.  In the case of infrequent consumer exposure (e.g., from  an accidental release), a one-time acute concentration is better represented by the cardiotoxic NOAEL than by an occupational exposure limit, which is more appropriate during scenarios in which workers are exposed to the chemical in question on a daily basis.  The modeled 15-minute and 30-minute TWA exposures for consumers are well below the cardiotoxic NOAEL for HFC-32 for all charge sizes.  

Further, the model used to calculate the exposure concentrations presented in Table 8- relies upon several conservative assumptions.  In an actual catastrophic release, only a portion of the refrigerant charge may be released, and the ventilation rates and mixing ratios may be much higher than those assumed for this analysis.  Moreover, in the event that a highly unusual catastrophic release does occur, the refrigerant may instead leak from the outdoor air conditioning/heat pump unit, potentially causing environmental effects (see Section 11), but eliminating the risk to consumers.

Given that the risk screen process models a highly catastrophic release of the proposed substitute and the calculated 15-minute and 30-minute TWAs of the refrigerant are well below the cardiotoxic NOAEL, the consumer is not likely to be harmed from any accidental releases from equipment containing HFC-32.  Smaller accidental releases of the proposed substitute therefore do not pose a significant risk to consumers. To prevent exposure during larger releases, EPA recommends that the charge size for HFC-32 PTACs and room ACs does not exceed the the RCL given in ASHRAE 34 (77 g/m[3] or 0.005 lb/ft[3]) and proposes to require compliance with UL 484. End-users should only install properly-sized PTAC units based on the size of the room intended to be cooled and ensure that recommended charge size limitations from the manufacturer or relevant safety standards are not exceeded. In addition, proper ventilation should be used in accordance with the MSDS for HFC-32. When these conditions are met, accidental catastrophic releases of the proposed substitute would not pose a significant risk to consumers.
10.	OCCUPATIONAL EXPOSURE ASSESSMENT
This section assesses potential exposures to workers during manufacture, installation, servicing, and disposal of HFC-32 in PTAC and other room AC systems. To ensure that use of the proposed substitute in PTAC 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 to 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 2014 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 PTAC unit end-use, 2 percent of the equipment charge was conservatively assumed to be released during manufacture and servicing and 40 percent of the equipment charge was conservatively assumed to be released during disposal.  The release rate per event was multiplied by the number of events estimated to occur over a workday. For PTAC 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
HFC-32 is currently manufactured by the submitter in Japan, and the manufacturer currently has no plans to manufacture the proposed substitute in the United States. Other companies however manufacture HFC-32 in the U.S. Where manufacture occurs in the United States, the proposed substitute's MSDS should be referenced and proper engineering controls and PPE used. HFC-32 is not expected to pose a risk to workers during manufacture when the engineering controls and PPE recommendations and referenced in the MSDS for HFC-32 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 to achieve emission control. In general, use of PPE consistent with OSHA guidelines is recommended, such as respiratory protection (including a self-contained breathing apparatus [SCBA] in case of insufficient ventilation), tightly sealed goggles, and protective gloves (Daikin 2011). 
As indicated by the submitter, charging of the AC units typically will occur at the manufacturing site. When this occurs, the submitter has indicated that charging equipment is designed to minimize potential emissions and that maintenance manuals describe procedures to reduce leakage and prior safety training is required for all personnel who would be charging units. Because of established equipment design and installation practices, exposures to HFC-32 will be unlikely. Thus, EPA does not believe that manufacturing, including charging, of AC units with HFC-32 presents a concern to workers.
In addition, as for other halogenated refrigerants, there is a risk of generation of toxic degradation products if HFC-32 is exposed to high temperatures or fire. 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 HFC-32, there is no significant risk to workers during the manufacture of HFC-32 and AC units pre-charged with it.
10.2	Occupational Exposure at Installation and Servicing
Installation and servicing activities for PTACs and other room AC systems using HFC-32 are not expected to result in significant worker exposure when certified technicians follow the procedures outlined in the HFC-32 MSDS and maintenance manual, undergo proper training, and wear appropriate PPE (e.g., gloves and safety glasses). Nevertheless, the potential occupational exposure during servicing was analyzed. The possibility of a release during installation was also considered. The maximum 30-minute time-weighted average (TWA) exposure for HFC-32 was estimated for servicing PTAC and room AC units charged with the charge sizes listed in Table 3. As summarized in Table 9, occupational exposure to HFC-32 is anticipated to be significantly below the short-term exposure limits (STEL) for a 2 percent release of refrigerant during servicing for all three charge sizes. In addition, because the proper controls and PPE described in the MSDS for HFC-32 are used and good manufacturing practices and adequate ventilation are established during any use, handling, or storage of HFC-32 indoors, worker exposure during installation and servicing is not likely. 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 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 5, worker exposure to HFC-32 during installation and servicing is not a concern.
     Table 9. Occupational Risk Assessment at Installation or Servicing[a]
                            HFC-32 Charge Size (g)
                   15-minute TWA Occupational Exposure (ppm)
                   30-minute TWA Occupational Exposure (ppm)
                   15-min Short Term Exposure Limits (ppm) b
                                     8,500
                                      220
                                      170
                                     3,000
                                     7,960
                                      200
                                      150
                                     3,000
                                     1,460
                                      37
                                      28
                                     3,000
       Bold font indicates modeling results. 	
       a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
       b STEL was estimated as three times the PEL; this method of estimating a short-term exposure limit is commonly done by ACGIH.

10.3	Occupational Exposure during Disposal
According to the submitter, HFC-32 is intended to be recovered and recycled, pending the development of recovery technology, at disposal of the PTAC unit. The submitter anticipates that disposal procedures for HFC-32 refrigerant will follow the same procedures as for other refrigerants, such as R-410A, and be supplemented with additional technician training related to handling A2L refrigerants. According to the MSDS for HFC-32, technicians should dispose of HFC-32 via incineration. 
Table 10 displays the maximum estimated 8-hour TWA occupational exposure level of HFC-32 during disposal. Based on the assumptions described in the beginning of Section 9, the modeling indicates that 8-hour worker exposure concentrations for HFC-32 assuming 40 percent release at disposal could exceed the long-term exposure limit (i.e., 1,000 ppm) during disposal of HFC-32 for PTACs and room ACs with charge sizes of 8,500 and 7,960 grams, respectively. However, these exposures were derived using conservative assumptions (e.g., no ventilation or use of PPE assumed), and represent a worst-case scenario with a low probability of occurrence. These types of systems are typically disposed of by trained personnel using proper industrial hygiene techniques. 
             Table 10. Occupational Risk Assessment at Disposal[a]
                            HFC-32 Charge Size (g)
                    8-hour TWA Occupational Exposure (ppm)
                    8-hour Long Term Exposure Limits (ppm)
                                     8,500
                                     2,700
                                     1,000
                                     7,960
                                     2,500
                                     1,000
                                     1,460
                                      470
                                     1,000
      Bold font indicates modeling results. 	
      a Cells highlighted in green are the scenarios with acceptable exposure levels given various modeling assumption options.
      
Because anticipated occupational exposures could potentially exceed the exposure limits for larger HFC-32 units (i.e. 8,500 and 7,960 gram units) during disposal, the recommendations for proper engineering controls and PPE in the MSDS for HFC-32 should be followed. Adequate ventilation should always be established during any use, handling, or storage of HFC-32. Engineering controls should include vapor-in air detection systems and local exhaust ventilation during use of HFC-32 to prevent dispersion throughout the work place. 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 HFC-32, there is no significant risk to workers during the manufacturing, installation, servicing, and disposal of HFC-32 in PTACs or room AC units.
11.	GENERAL POPULATION EXPOSURE ASSESSMENT
HFC-32 is not expected to cause a concern for human health in the general population when used as a refrigerant in room AC systems. At room temperature, HFC-32 is a gas and, therefore, releases to ground or surface water are not anticipated. Should air releases during manufacturing operations, including filling of AC units, occur, engineering controls could be used (e.g., carbon absorption units or scrubbers) to collect HFC-32 and prevent the release of HFC-32 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 HFC-32 is not expected to pose a toxicity threat to the general population.
12.	REFERENCES
ASHRAE. 2013.  ASHRAE Standard 147-2013. Reducing the Release of Halogenated Refrigerants from Refrigeration and Air-Conditioning Equipment and Systems. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE 2010a. ASHRAE Standard 15-2010. Safety Standard for Refrigeration Systems. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 

ASHRAE 2010b.  ASHRAE Standard 34-2010 and addenda. Designation and Safety Classification of Refrigerants. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE 2010c.  ASHRAE Standard 62.1-2010. Ventilation for Acceptable Indoor Air Quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Daikin SNAP Submission. 2011. "Significant New Alternatives Policy Program Submission to the United States Environmental Protection Agency," June 2011.

Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland. 2007. Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

ICC. 2012. International residential code for one- and two-family dwellings.  International Code Council. Available at: http://publicecodes.cyberregs.com/icod/irc/2012/index.htm?bu2=undefined. 

ICF. 1997. Physiological Effects of Alternative Fire Protection Agents - Hypoxic Atmospheres Conference. Stephanie Skaggs prepared the proceedings of the conference held May 22, 1997 in New London, CT.

Mackenzie, F.T. and J.A. Mackenzie. 1995. Our changing planet. Prentice-Hall.

Takizawa, Kenji, Akifumi Takahashi, Kazuaki Tokuhashi, Shigeo Kondo, and Akira Sekiya, 2005. Burning velocity measurement of fluorinated compounds by the spherical-vessel method. National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, Japan. http://dx.doi.org/10.1016/j.combustflame.2005.01.009  

UL 484. 2012. Underwriters Laboratories. UL 484 Standard for Safety: Room Air Conditioners. Eighth Edition, revised August 3, 2012.

U.S. EPA. 1994.  "SNAP Technical Background Document:  Risk Screen on the Use of Substitutes for Class I Ozone-depleting Substances: Refrigeration and Air Conditioning."  Stratospheric Protection Division.  March, 1994.

U.S. EPA. 2014. Risk Assessment Glossary. Available online at: http://www.epa.gov/risk_assessment/glossary.htm.

WMO (World Meteorological Organization), 2011. Scientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project -- Report No. 52, 516 pp., Geneva, Switzerland, 2011.