1 May 22, 2009 

## Significant New Alternatives Policy Program Refrigeration and Air Conditioning Sector Risk Screen on Substitutes for CFC - 12 in Household Refrigerators and Household Freezers. Substitute: Isobutane This risk screen contains no Clean Air Act (CAA) Confid ential 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 ove r the past decade, 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, is developing a program to evaluate the human health and environmental risks posed by alternatives to ODS. The main purpose of EPA's program, called the Significant New Alternatives Policy (SNAP) Program, is to identify acceptable and unacceptable substitutes for ODS in specific end uses. EPA’s decision on the accep tability of a substitute is based largely 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 uses within all of the maj or 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 seri es 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) by adding to the list of potential substitutes for specific end

-uses of CFC

- 12 in this sector. Proposed end

-use applications considered in this analysis include new replacements for household refrigerators and household freezers

. The specific proposed CFC

- 12 subs titute examined in this report is isobutane (R600a)

. Table 1 presents the composition of the substitute, including the maximum estimated concentrations of impurities which may be present in the substitute

. Table 1 . Composition of the Substitute. Component Concentration (Weight Percent) Substitute Isobutane  99.5 % Potential Impurities (maximum concentration) Propane and N
- butane 0.5% 1,3
- Butadiene 0.0005% N
- Hexane 0.005% Benzene 0.0001%2 May 22, 2009 Table 1 . Composition of the S ubsti tute (continued) Component Concentration (Weight Percent) Sulfur 0.0001% Liquid phase water 0.0005% Air 0.05% (V/V) The potential risks associated with use of substitute s in residential refrigeration have been examined at length in the Background Doc ument. The reader is referred to this reference for a detailed discussion of the methodologies used to conduct this risk screen. Presently, EPA’s SNAP Program has not approved any hydrocarbon blends as a substitute for CFC

- 12 in residential appliance end uses, such as those intended for this substitute (i.e., household refrigerators and household freezers). Of particular concern are the flammability risks associated with hydrocarbon blends during manufacturing, use, servicing, and disposal of household appliances. Occupational exposure modeling was performed to ensure that use of the proposed substitute in the application listed above did not pose unacceptable risk to workers. Consumer exposure modeling was performed to examine potential catastrophic re leases of the substitute

. Lastly, general population exposure modeling was performed to ensure that the proposed substitute would not pose unacceptable risk to the population at large. Section 2 of this report summarizes the results of the risk screen for the proposed substitute. The remainder of the report is organized into the following sections:

 Section 3: Atmospheric Assessment  Section 4: Flammability Assessment  Section 5: Asphyxiation Assessment  Section 6: Toxicity Assessment  Section 7: Volatile Organic Compound Assessment  Section 8: References 

### 2. SUMMARY OF RESULTS Isobutane is recommended for SNAP approval for household refrigerators and freezers. EPA's risk screen indicates that the use of the proposed substitute and its constituents w ill be less harmful to the atmosphere than the continued use of CFC

- 12. No significant toxicity risks to workers, consumers, or the general population are expected according to occupational and consumer exposure modeling. Flammability models indicate th at risks of explosions are not a concern for consumers, provided the refrigerant is not used in small, poorly ventilated spaces (see Section 4). Caution must be used in manufacturing facilities and by refrigeration technicians to minimize explosion risk, while in the presence of large quantities of the substitute. This includes installation of proper safety equipment during manufacturing , transportation, and storage and providing proper training and certification to technicians. EPA recommends that Ameri can Society of Heating, Refrigerating and Air

- Conditioning Engineers (ASHRAE) Standards 15 and 34 be followed. 

### 3. ATMOSPHERIC MODELING This section presents an assessment of the potential risks to atmospheric integrity posed by the use of isobutane in the residential refrigeration sector. The ODP, GWP, and atmospheric lifetime (ALT) of the proposed substitute are presented in Table 2

. The environmental impacts resulting from use of isobutane are generally in the range of those predicted for other subs titutes examined in the Background Document. The substitute is substantially less harmful3 May 22, 2009 to the ozone layer, has less climate impact, and a shorter atmospheric lifetime compared to CFC

- 12.

Table 2 . Atmospheric Impacts of Isobutan e Compared to CFC - 12. Refrigerant Ozone Depleting Potential (ODP) Global Warming Potential (GWP) Atmospheric Lifetime years (ALT) Isobutane 0 a 8 a <1 b CFC
- 12 1 c 8,100 d 100 c a Isobutane SNAP Submission (GE 2008)

. b Atmospheric lifetime (ALT) not provided in SNAP submission. Calm and Hourahan ( 2007 ) indicate the ALT is 0.019 years, or about one week. c Available at: http://www.epa.gov/ozone/ods.html. d IPCC, Second Assessment Report (1996). 

### 4. FLAMMABILITY ANALYSIS Due to its flammable nature, isobutane could pose a significant safety concern for workers and consumers if it is not handled carefully. In the presence of an ignition source (e.g., static electricity, a spark resulting from a closing door, or a cigarette), an explosion or a fire could o ccur when the concentration of isobutane exceeds its lower flammability limit (LFL) of 18 ,000 ppm. Therefore, it is important to ensure that the levels of isobutane do not exceed 18,000 ppm. In production facilities or other facilities where large quanti ties of the refrigerant will be stored, proper safety precautions should be in place to minimize the risk of explosion. White goods installed with isobutane should be clearly labeled as containing a flammable refrigerant charge and designed to prevent cat astrophic leaks. Furthermore, only refrigerant technicians certified to work with flammable refrigerants should handle these units during manufacturing, installation, servicing, transportation and disposal. To determine whether flammability would be a concern for consumers, a reasonable worst

- case scenario analys i s w as performed to model catastrophic release of the refrigerant. The analysis models the release of charge from a refrigerator into a kitchen

. The kitchen volume is assumed to be 18 m3 (635 ft 3 ) or approximately 2.7 x 2.7 m (8.9 x 8.9 ft) for a square room with 2.4 m (8 ft) ceilings (EPA 1994) . In the analysis, the maximum permissible leak per the standard UL 250 Supplement SA ( 50 g) 1 is assumed to be emitted within one minute and the kitchen is assumed to have an air flow rate of 2.5 air exchanges per hour

. Given these conservative assumptions, the assumed reasonable “worst

- case” scenario is highly unlikely. Horizontal stratification is also assumed since isobutane is denser than air and will settle in higher concentrations closer to the ground. In order to simulate the horizontal concentration gradient that will occur because of the weight differential between the refrigerant and air, it is assumed that 95 percent of the leaked re frigerant mixes evenly into the bottom 0.4 meter of the room, and the rest of the refrigerant mixes evenly in the remaining volume (Kataoka 1999). Under catastrophic release scenarios, the maximum instantaneous concentration of isobutane in the lower stratum of the room would be approximately 37 percent of its LFL for the average room size assumed, as shown in Table 3

. T he maximum instantaneous concentration is lower in the upper stratum of the room, as only five percent of the leaked refrigerant is pres ent in this stratum, and this stratum has a greater volume than the lower stratum

. For flammability to be of concern under the conservative (protective) assumptions described above, the volume of the kitchen would have to b e about 7 m3 (247 ft 3 ). Assumin g a square room with a ceiling height of 2.4 m (8.0 ft), this equates to a 1.7 x 1.7 m (5.6 x 5.6 ft) kitchen.

1 Fifty grams is the maximum permissible leak for refrigerants with limits of flammabi lity and heat of combustion greater than 19,000 kj/kg, such as isobutane, per the standard UL 250 Supplement SA. Per this standard, a larger charge is not prohibited, if the amount of refrigerant leaked during testing does not exceed 50 grams. Therefore , if a charge greater than 50 grams is to be used in these refrigerators, the system should be designed to ensure that a refrigerant leak would not exceed 50 grams.4 May 22, 2009 Very l imited data are available regarding the distribution of kitchen volume s in the United States. However, an analysis by Murray (1997) whi ch aggregated data from over 60 different projects report ed the minimum kitchen volume encountered as 31 m3

. 2 Further, only one percent of houses sampled had a kitchen smaller than 53 m3

. To avoid the risk of fire and explosion, it is recommended that the refrigerators not be installed in small, poorly ventilated spaces such as very small ‘galley ’ kitchen s or storage closets (especially as other equipment or appliances in the space would reduce the effective volume of the room)

. However, based on the available data regarding kitchen volumes, it is not likely that a kitchen would exist which would be small enough for flammability to be a concern , even under a reasonable worst

- case scenari o . F or full

sized kitchens the risk of explosion is minimal. The installation of leak prevention devices would further protect against the very limited risk of explosion. For example, in commercial refrigeration end

-uses, refrigerant leak prevention systems can be used to capture leaked refrigerant in a receiving tank during over pressure events, rather than venting the refrigerant to the atmosphere. 3 Additionally, in motor vehicle air

- conditioning, an outflow prevention device can be used to prevent leakage events when the heat exchanger of a unit is damaged. 4 ICF recommends that similar safety devices ( designed for residential refrigerators and freezers) be installed in units containing isobutane to prevent refrigerant leaks and thereby further reduce the risk of explosion. Table 3 . Flammability Assessment Room Type/Appliance Type Reasonable Worst - Case Scenario Flammability Threshold Scenario

Room Size (m 3 ) Maximum

Instantaneous Concentration (ppm) a,b Room Size (m 3 ) Maximum Instantaneous Concentration (ppm) a,b Kitchen/Refrigerator 18 (635 ft 3 ) 6,647 7 ( 247 ft 3 ) 17 , 006
a Lower Flammability Limit of isobutane is equal to 18 ,000 ppm

. b Values provided in these columns refer to the concentration in the lower stratum of the room. Catastrophic releases of large quantities of re frigerant during servicing and manufacturing, especially in areas where large amounts of refrigerant are stored, could cause an explosion. For this reason, it is important that only properly trained and certified refrigerant technicians handle isobutane

. The submitter has provided information regarding their training program for service technician s . The program includes detailed information regarding proper recovery of the refrigerant prior to service as well as information on servicing the refrigerator and charging the system with isobutane (GE SNAP Submission 2008). This training should be provided for all technicians who will be servicing refrigerators using isobutane. As a further precaution, isobutane storage and transport equipment should b e in stalled with safety devices that minimize the likelihood of catastrophic releases. For example, NFPA 58 Lique fied Petroleum Gas C ode (NFPA 200 8 ) requires the use of overfill protection devices (OPD) on cylinders to minimize the likelihood of leaks. The NPFA 58 Code also contains storage and transportation requirements/guidelines. Similar equipment safety and procedural requirements should be implemented for this substitute

.

2 Murray (1997) uses data from the Brookhaven National Laboratory PFT database. Data regarding kitchen volumes were only available for the LA area and the kitchen volumes are for a “kitchen zone” which may include associated areas, such as utility rooms, dining rooms, living rooms, and family room. The inclusion of these other spaces in the “kitchen zone” volume is realistic, as the presence of adjoining rooms would increase the volume into which the refrigerant could leak. 3 http://www.freepatentsonline.com/5259204.html 4 http://www.freepatentsonline.com/6966365.html5 May 22, 2009 It is important that the strictest standards be followed during manufacturing. Itis recommended that refrigerants be properly stored and caution used within manufacturing facilities to minimize explosion risk and that worker s adhere to the requirements set by OSHA under 29 CFR 1910. OSHA requirements include proper ventilation an d storage practices within manufacturing facilities to prevent fire and explosion. Proper ventilation should be maintained at all times during the manufacture of equipment containing isobutane through adherence to g ood manufacturing p ractices . If refriger ant levels in the air surrounding the equipment rise above one

- fourth of the lower flammability limit , 5 the space should be evacuated and re

- entry should only occur after the space has been properly ventilated. 

### V entilation is also of the utmost importance to mitigate the risk of fire or explosion when servicing equipment using isobutane . During servicing operations, technicians should ensure that proper ventilation is in place through the use of fans (or other mechanical ventilation devices) and portable refrigerant detectors should be used to alert technicians to the presence of flammable gases in the area. 

### 5. ASPHYXIATION The risk of asphyxiation for a reasonable “worst

- case” scenario was investigated for isobutane . This analysis does n ot consider conditions that are likely to occur that would reduce the levels to which individuals would be exposed, such as open doors or windows, fans operating, conditioned airflow (e ither heated or cooled), or even seepage between the door and door frame. T he maximum leak of isobutane necessary to reduce the oxygen levels to 1 2 percent in air , 6 in a kitchen of volume 18 m3 (635 ft 3 ) (EPA 1994) , was calculated, assuming horizontal stratification of the refrigerant and the air. Horizontal stratification is assumed since i sobutane is denser than air and will settle in higher concentrations closer to the ground. Assuming that nitrogen and oxygen retain the same relative volumes in the rooms with the balance composed entirely of isobutane, and that the pre ssure of the room does not increase significantly with the addition of the refrigerant, a leak of approximately 6 2 5 g would be necessary to reach 12 percent oxygen in the lower stratum. This amount is more than twelve times the maximum permissible leak fo r a single isobutane refrigerator or freezer (50 g)

. The size of a leak needed to reach the same effect in the upper strata would be even greater because of the stratum’ s larger volume. For asphyxiation to be of concern with the maximum permissible leak, under the conservative (protective) assumptions described above, the volume of the kitchen would have to be about 1.5 m3 (53 ft 3 ). Assuming a square room with a ceiling height of 2.4 m (8.0 ft), this equates to a 0

. 8 x 0

. 8 m ( 2.6 x 2.6 ft) kitchen. Th e results of the asphyxiation assessment are summarized in Table 4 below. Itis recommended that isobutane refrigerators not be installed in small, poorly ventilated spaces, such as very small ‘galley’ kitchens, to avoid the risk of asphyxiation. However , based on the available data regarding kitchen volumes (see Section 4) , it is not likely that a kitchen would exist which would be small enough for asphyxiation to be a concern, even under a reasonable worst

- case scenario. Therefore, EPA does not believe that the use of isobutane in this end

-use poses a significant risk of asphyxiation or impaired coordination to consumers. Table 4 . Asphyxiation Assessment Room Type/Appliance Type Maximum

Permissible Leak from Appliance (g) a Rea sonable Worst - Case Scenario Asphyxiation Threshold Scenario

Room Size (m 3 ) Leak Size

Causing Impairment (g) b Room Size (m 3 ) Leak Size Causing Impairment (g) b Kitchen/Refrigerator 50 18 (635 ft 3 ) 625 1.5 ( 53 ft 3 ) 50

5 OSHA regulation 29 CFR 1 910.110 considers ventilation adequate “when the concentration of the gas in a gas

- air mixture does not exceed 25 percent of the lower flammable limit.” 6 Twelve percent oxygen in air is the No Observed Adverse Effect Level (NOAEL) for hypoxia (ICF 1997).6 May 22, 2009 a Fifty grams is the maximum permiss ible refrigerant leak per the standard UL 250 Supplement SA. b Values provided in these columns refer to the leak size required to cause impairment in the lower stratum of the room. 

### 6. TOXICITY REFERENCE VALUES FOR SUBSTITUTES To assess potential health risks from exposure to this substitute in the residential refrigeration sector, EPA identified the relevant toxicity threshold values for comparison to modeled exposure concentrations for different scenarios. For the occupational exposure analysis, po tential risks from chronic and acute worker exposure were evaluated by comparing exposure concentrations to available occupational exposure limits. Occupational exposure limits are typically established for either an eight

-hour or ten
- hour time period for long

- term exposure, such as the Workplace Guidance Levels (WGLs), or for a 10 to 30

- minute period for short

- term exposure, such as the Emergency Guidance Levels (EGLs), as shown in Table 5

. Because they are designed to assess risks from acute exposure, e mergency guidance levels are used to assess risks from short

- term consumer exposures. Reference concentrations (RfCs) are used to assess risks to the general population from exposure to ambient air releases and to assess potential risks associated with chronic consumer exposures. A list of the relevant toxicity limits is shown in Table 5

. Table 6 provides definitions of the acronyms used in Table 5

. EPA’s approach for identifying or developing these values is discussed in Chapter 3 of the Background Doc ument.

Table 5 . Toxicity Levels of Isobutane and Potential Impurities Long - term Exposure ppm Short - term Exposure ppm Reference Concentration (RfC) mg/m 3 Substitute Isobutane 800 a (NIOSH REL) 18000 b (NOAEL) 0.95 c Potential I mpurities Propane 1000 d

(OSHA PEL/NIOSH REL) 2100 d (IDLH) 0.9 c
n - Butane 800 e (NIOSH REL) NA 0.95 c 1,3
- Butadiene 1 f (OSHA PEL) 5 f (OSHA PEL
- STEL) 670 g (10 minute interim AEGL
- 1) 2 x 10
- 3 h N
- Hexane 50 I (NIOSH REL) 1100 i (IDLH) 0.7 j Benzene 0.1 k (NIOSH REL) 1 k (NIOSH STEL) 500 k (IDLH) 3 x 10
- 2 l Sulfur NA NA NA NA = Not Available a http://www.cdc.gov/niosh/npg/npgd0350.html b OSHA (2004) notes the following regarding isobutane: “OSHA does not have a PEL for isobutane, which is affirme d as "generally recognized as safe" as a direct human food ingredient (21 CFR 184.1165). No toxic effects reported below 18,000 ppm.” c SNAP Refrigerant Background Document (EPA 1994). d http://www.cdc.gov/Niosh/npg/npgd0524.html e http://www.cdc.gov/niosh /npg/npgd0068.html f http://www.cdc.gov/niosh/npg/npgd0067.html g http://www.epa.gov/opptintr/aegl/pubs/rest148.htm h http://www.epa.gov/ncea/iris/subst/0139.htm#refinhal i http://www.cdc.gov/niosh/npg/npgd0322.html j http://www.epa.gov/ncea/iris/subst/048 6.htm#refinhal k http://www.cdc.gov/niosh/npg/npgd0049.html l http://www.epa.gov/iris/subst/0276.htm#refinhal7 May 22, 2009 Table 6 . Explanation of Toxicity- Related Acronyms a Organization Definition OSHA Occupational Safety and Health Adminis tration NIOSH National Institute for Occupational Safety and Health Exposure Limit Definition Explanation AEGL
- 1 Acute Exposure Guideline Level The AEGL
- 1 “is the airborne concentration... 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” (EPA 2008 a ). 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. NOAEL No Observed Adverse Effect Limit “ T he 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.” b PEL Permissible Exposure Limit This is an 8
- hour time
- weighted average exposure limit set by OSHA. PEL
- STEL Permissible Exposure Limit
- Short
term exposure limit. This is a 15
- minute time
- weighted average expos ure limit set by OSHA. REL Recommended Exposure Limit This is a 10
- hour time
- weighted average exposure limit set by NIOSH. RfC Reference Concentration A concentration “ designed to protect the general population against adverse systemic (i.e., noncancer) effects.”
aAll information in this table taken from EPA (1994) , except where noted otherwise. b From http://www.epa.gov/riskassessment/glossary.htm#n 6.1 OCCUPATIONAL EXPOSURE Occupational exposure modeling was performed for the proposed substitute to ensure that use of the substitute does not pose an unacceptable risk to workers. The methodology used for this screening assessment is based on the one used in the occupational exposure and hazard analysis described in Chapter 5 of the Background Document. A box

- model approach was used to evaluate potential worker exposure to alternative refrigerants. This approach has been widely used for many years to estimate probable exposures of worke rs to hazardous airborne materials, and has been described in detail by the National Institute for Occupational Safety and Health (NIOSH) . This model takes into consideration the duration and magnitude of the resulting exposure which is influenced by 1) d uration and intensity of the release, 2) rate at which contaminated air is dilute d with uncontaminated air, 3) proximity of the worker to the source of the release, and 4) the length of time the worker remains in the affected space. Estimates of refrige rant release per event for various release scenarios and data on number of events were obtained from the Vintaging Model. 7 T he release per event was conservatively assumed to be 1 percent of the equipment charge during manufacturing and 3 percent of the equipment charge during disposal. 8 The release rate per event was multiplied by the number of events estimated to occur over a workday. For

7 ICF International maintains the Vintaging Model for EPA in order to simulate the aggregate impacts of the ODS phaseout on the use and emissions of various fluorocarbons and their substitutes over a period of several years across more than 40 different a pplications. The model tracks the use and emissions of various compounds for the annual vintages of new equipment that enter service in each end

- use. The vintage of each type of equipment determines such factors as leak rate, charge size, number of units in operation, and the initial ODS substance that the equipment contained. 8 During disposal it is assumed that only 90 percent of the refrigerant charge remains in the unit.8 May 22, 2009 equipment manufacturing, the number of events per workday was assumed to equal the number of units containing the substitute produced per plant per year divided by 365 workdays per year. 9 For the purposes of this model, the isobutane market penetration rate was estimated using data from the SNAP submission and the Vintagin g Model (version 4.3_2.16.09) and one production facility was assumed to be in operation. These assumptions result in approximately 44 events/manufacturing facility/day. For disposal, it was conservatively assumed that 100 units are disposed during an 8

- hour work day. The maximum time weighted average (TWA) exposure was estimated for each exposure scenario, and this value compared to the Workplace Guidance Levels (WGLs) for isobutane and the potential impurities in the substitute

. The modeling results indicate that b oth the short

- term (15

- minute and 30

- minute) and long

- term (8

-hour) worker exposure concentrations at no point exceed 2 percent of the WGLs. Table 7 displays the maximum estimated 15

- minute TWA occupational exposure level s of isobutane and the potential impurities in the substitute

. Even these maximum estimated short

- term occupational level s are significantly lower than the 8

-hour or 10

-hour long

- term WGL s , and therefore occupational exposure to isobutane and the potential impurities is not considered a toxicity threat. Table 7 . Occupational Risk Assessment

Maximum 15 - minute TWA Occupational Exposure Levels (ppm) Workplace

Guidance Levels (ppm) a Workplace

Guidance Levels Time Period Substitute Isobutane 10.16 800 10
- hour TWA Potential Impurities Prop ane and Butane b 5.8 x 10
- 2 1000 (propane) 800 (butane) 10
- hour TWAc 1,3
- butadiene 5.5 x 10
- 5 1 8
- hour TWA n - Hexane 3.4 x 10
- 4 50 10
- hour TWA Benzene 7.6 x 10
- 6 0.1 10
- hour TWA Sulfur 1.9 x 10
- 5 NA NA NA = Not Available a. See Table 5 for more inform ation. b. Propane and Butane weight percentage in substitute presented as one single value in submission. Exposure level is well below the WGL for either constituent. c. The WGL for Propane is set as a 1000 ppm 8
- hr TWA by OSHA and a 10
- hr TWA by NIOSH. The Butane value is a 10
- hr TWA. 6.2 CONSUMER EXPOSURE This section presents estimates of potential consumer exposures to isobutane in home appliances. A consumer exposure analysis was performed to examine potential catastrophic release of the substitute under a reasonable “worst

- case” scenario . Estimates for acute/short

- term consumer exposures resulting from catastrophic leakage of refrigerant from residential refrigerators were examined. The analysis was undertaken to determine the 15

- and 30

- minute T WA for the substitute , which were then compared to the standard toxicity limits presented in Tab l e 5 to assess the risk to consumers. However, the TWA values are fairly conservative as the analysis does not consider opened windows, fans operating, conditi oned airflow (either heated or cooled) and other variables that would reduce the levels to which individuals would be exposed. The model involves a refrigerant leak from a refrigerator into an enclosed kitchen of volume 18 m3 (635 ft 3 ). The model assume s that the individual is present at the start of the leak and the individual remains in

9 Submission indicates this is the maximum number of days per year that manu facturing will occur.9 May 22, 2009 the room while the refrigerant is released. It is also assumed that horizontal stratification causes most of the refrigerant to settle in higher concentrations closer to the ground. Considering the horizontal stratification is important because children, a particularly vulnerable segment of the population, breathe air that is closer to the ground. In order to simulate the horizontal concentration gradient that will occur because of the weight differential between the refrigerant and air, it is assumed that 95 percent of the leaked refrigerant mixes evenly into the bottom 0.4 meter of the room, and the rest of the refrigerant mixes evenly in the remaining volume (Kataoka 1 999). Exposure concentrations were calculated using the box model described in the Background Document, which was adapted to estimate concentrations on a minute

-by

- minute basis. It was assumed that the maximum permissible leak per the standard UL 250 Sup plement SA (50 g) would be released during a time span of 1 minute, at which time the concentration of isobutane will peak, and then steadily decline onwards. Refrigerant concentrations were modeled under two air change scenarios believed to represent the range of potential flow rates for a home, assuming flow rates of 2.5 and 4.5 air changes per hour (ACH) (Sheldon 1989). The highest concentrations of the refrigerant occur in the lower stratum of the room and when assuming 2.5 ACH. The highest expect ed levels of consumer exposure based on this analysis are presented in Table 8 below. Table 8 . Consumer Exposure Assessment 15 - minute TWA Consumer Exposure (ppm) 30 - minute TWA

Consumer Exposure (ppm) Substitute Isobutane 5,025 3 ,844

Potential Impurities Propane and Butane a 29 22 1,3
- butadiene 0.03 0.02 n - Hexane 0.17 0.13 Benzene 0.004 0.003 Sulfur 0.009 0.007 TWA = Time Weighted Average a. Propane and Butane weight percentage in substitute presented as one single value in submission. Exposure level is well below the exposure limits for either constituent. OSHA (2004) states no toxic effects are reported with exposures to isobutane below 18,000 ppm. Even under the very conservative assumptions used in the consumer exposu re modeling, both the estimated 15

- minute and 30

- minute consumer exposures to isobutane are lower than this level and thus should not pose a toxicity threat. The exposure levels of the impurities are also lower than their respective short

- term toxicity l evels (see Table 5 ) and thus should not pose a toxicity threat. 6.3 GENERAL POPULATION EXPOSURE In the SNAP Background document for refrigerants (EPA 1994) , the RfC value for i sobutane is 0.95 m/m3

. We compared this RfC to estimated factory releases and on - site releases. This gives a ratio of exposure concentration to RfC that varies between 1 .3 x 10 - 5 to 1. 7 x 10 - 1 , depending on the type of release scenario. 10 Ratios of exposure concentration to RfC for the substitute’s impurities were even lower. Since the exposure concentrations for the substance s are lower than the RfC value s , the substitute is not expected to pose a toxicity threat to the general population.

10 Release scenarios include factory, on

- site and recycling/salvage yard releases, with and without recycling of the refrigerant.10 May 22, 2009 

### 7. VOLATILE ORGANIC COMPOUND (VOC) ANALYSIS Isobutane ha s not been exempt ed as a VOC under the CAA ( 40 CFR 51.000) . However, through regulations and standard industry practices, VOC emissions should be controlled. Chapter 8 of the Background Document shows that potential emissions of VOCs from all substitutes for all end uses in the refrigeration and air conditioning sector are likely to be insignificant relative to VOCs from all other sources (i.e., other industries, mobile sources, and biogenic sources ). Additional analysis sh ows that e ven if all refrigerators produced by GE in one year wer e to leak the maximum permissible leak per the standard UL 250 Supplement SA over the course of the year (extremely unlikely), the resulting annual VOC emissions would be less than 1 x10 - 5 percent of all annual anthropogenic VOC emissions

. 11 Further , the c alculated potential VOC emissions due to use of isobutane in household refrigerators is less than 1 x10 - 4 percent of annual residential wood combustion emissions. 12 As these emissions of isobutane are several orders of magnitude less than other anthropogen ic emissions , including other residential emissions (i.e., residential wood combustion) , the environmental impacts of these VOCs are not considered a threat. 

### 8. REFERENCES Calm, J.M. and G.C. Hourahan. 2007. “Refrigerant Data Update.” Heating and Refri gerant Data Update. 79(1):50

- 64. January 2007. EPA 2008 a . Acute Exposure Guideline Levels: Definitions. Accessed 27 February 2009. Available at: <http://www.epa.gov/opptintr/aegl/pubs/define.htm>. EPA 2008b. Volatile Organic Compounds

– National Summary of VOC Emissions

. Last updated 21 October 2008. Accessed 4 March 2009. Available at <http://www.epa.gov/air/emissions/voc.htm>. EPA 1994. Significant New Alternatives Policy 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. GE SNAP Submission. 2008. Significant New Alternatives Policy Program Submission to the United States Environmental Protection Agency , October 2008. 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. Kataoka. 1999. “Allowable Charge Li mit of Flammable Refrigerants and Ventilation Requirements.” Draft Proposal. O. Kataoka/Daikin/Japan, June, 1999. Murray, D.M. 1997. “Residential House and Zone Volumes in the United States: Empirical and Estimated Parametric Distributions.” Risk Anal ysis . 17(4): 439

- 446. NFPA. 2008. NFPA 58: Liquefied Petroleum Gas Code. National Fire Protection Agency. OSHA. 2004. “Safety and Health Topics: Isobutane.” February 2004. Available online at: <http://www.osha.gov/dts/chemicalsampling/data/CH_2478 40.html>. Sheldon, L.S., et al. 1989. "An Investigation of Infiltration and Indoor Air Quality." New York State Energy Research & Development Authority, Report 90

- 11.

11 This figure determined using 2002 annual VOC emissions data from EPA (2008b) and expected annual produc tion levels from the GE SNAP Submission (2008). 12 This figure determined using 2002 annual VOC emissions data from EPA (2008b). Residential wood combustion is the only residential source included in the EPA (2008b) analysis.