MEMORANDUM

To:	Margaret Sheppard, U.S. EPA

CC:	Bella Maranion, Melissa Fiffer, and Carolyn Hayek, U.S. EPA

From:	Rebecca Ferenchiak, Jenny Tanphanich, Neha Mukhi, and Mark Wagner,
ICF International 

Date:	August 1, 2011 

Re:	Additional End-Use Modeling for Household Refrigerators and Freezers

(EPA Contract Number EP-W-10-031 Task Order 005, Task 01)



ICF has reviewed the public comment submitted by Honeywell
(EPA-HQ-OAR-2009-0286-0170.1) in response to EPA’s proposed SNAP
ruling which approves the use of hydrocarbon refrigerants in
refrigerators ([EPA-HQ-OAR-2009-0286; FRL-9147-9] RIN 2060-AP54). In the
comment, Honeywell specifically notes that in EPA’s risk screen for
isobutane in household refrigerators and freezers, the flammability risk
for isobutane is underestimated. To support this notion, Honeywell
performed leak testing of an isobutane refrigerator and provided the
test results in their comment. In this memorandum, ICF examines the
impact of using more conservative assumptions in the flammability
assessment for isobutane and R-441A to determine whether a flammability
risk exists.

Please contact Mark Wagner at 202-862-1155 with any questions or
comments.

Background

In Comment EPA-HQ-OAR-2009-0286-0170.1(FRL-9147-9, RIN 2060-AP54),
Honeywell states that EPA underestimated the flammability risks
associated with the use of isobutane as a refrigerant in household
refrigerators and freezers. Consequently, ICF, at the request of EPA,
has revisited the end-use modeling performed for both substitutes
proposed for use in household refrigeration, isobutane and R-441A, and
performed an additional flammability analysis and threshold analysis. 

Discussion of End-Use Scenarios Modeled

ICF reviewed the assumptions made in the original risk screens for
isobutane and R-441A (formerly known as HCR-188C1), dated May 22, 2009
and November 6, 2009 respectively, to determine whether they were
sufficiently conservative to represent a reasonable worst-case scenario.
 The assumptions used in the original risk screens for worst-case
scenario modeling are summarized in Table 1.  

Table 1. Worst-Case Scenario Model Assumptions in Risk Screen

Parameter	Risk Screen Assumptions: Isobutane	Risk Screen Assumptions: 

R-441A

Appliance	Household Refrigerator	Household Refrigerator

Room	Household Kitchen	Household Kitchen

Charge size (g)	50	40

Percentage of Charge Leaked 	100%	100%

Length of release (minutes)	1	1

Room size (volume - m3)	18	18

Room ventilation (air changes per hour)	2.5	2.5

Horizontal stratification	95% in bottom 0.4 m (~16 in) of room	95% in
bottom 0.4 m (~16 in) of room



Charge Size

The charge sizes originally modeled for isobutane and R-441A were 50g
and 40g, respectively.  These values were chosen for modeling based on
statements in the SNAP submissions for these substitutes that indicated
the intended charge sizes to be used in appliances.  

There is the potential to be more conservative in the setting of this
parameter for additional flammability analysis, since EPA’s proposed
rule allows a household refrigerator to have a charge size of up to 57g.
 The proposed rule also effectively requires that the charge size be
consistent with the standard UL 250 Supplement SA, which calls for a
maximum leak amount of 50 grams for refrigerants with flammability
limits and a heat of combustion greater than 19,000 kJ/kg, such as
isobutane or R-441A. However, the test to determine leak amounts is not
documented in the UL 250 Standard and could potentially be administered
incorrectly.  As a result, in the additional flammability analysis
(described in the following section) ICF uses a leak amount of 57g as a
more conservative assumption for purposes of additional flammability
analysis.

Room Size

In the original risk screen analysis, a kitchen with a floor area of 7.4
m2 and a ceiling height of 2.4 m was assumed (EPA, 1994).  This is
equivalent to a volume of 18 m3. Although very limited data are
available regarding the distribution of kitchen volumes in the United
States, an analysis by Murray (1997) which aggregated data from over 60
different projects reported the minimum kitchen volume encountered as 31
m3.  Further, only one percent of houses sampled had a kitchen smaller
than 53 m3.  Therefore, ICF does not believe there is a need to be more
conservative in the setting of this parameter for the purpose of the
additional flammability analysis.

Room ventilation

The range of potential flow rates for a residential kitchen is believed
to be 2.5 to 4.5 air changes per hour (ACH) (Sheldon 1989).  The more
conservative rate of 2.5 ACH was used in the analyses, and ICF does not
believe there is a need to be more conservative in the setting of this
parameter for the purpose of additional flammability analysis.

Horizontal Stratification

In the original risk screen, it was assumed that horizontal
stratification will occur since both isobutane and R-441A are denser
than air and as a result, 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, ICF assumed that 95 percent of the leaked refrigerant mixes
evenly into the bottom 0.4 meters of the room, and the remainder of the
refrigerant mixes evenly in the remaining volume (Kataoka 1999).  

There is the potential to be more conservative in the setting of this
parameter for additional flammability analysis, since the release point
for a refrigerant may vary with the type of appliance in use.  To
capture the scenario of a bottom-freezer refrigerator, which would
likely have the lowest release point, this flammability analysis will
assume that 95 percent of the leaked refrigerant mixes evenly into the
bottom 0.22 meters (~ 9 inches) of the room, and the remainder of the
refrigerant mixes evenly in the remaining volume.

Additional Flammability Analysis and Results

Table 2 details the assumptions that will be used for the additional
analyses of flammability risks associated with the use of isobutane or
R-441A in the household refrigeration end-use.  

Table 2. Assumptions for the Additional Worst-Case Scenario Flammability
Analysis

Parameter	New Assumption

Refrigeration Unit	Household Refrigerator

Room	Household Kitchen

Leak Amount (g)	57*

Length of release (minutes)	1

Room size (volume - m3)	18

Room ventilation (air changes per hour)	2.5

Horizontal stratification	95% in bottom 0.22 m (~9 in) of room*

*More conservative than the assumption used in the original risk
screens.

Based on the re-analysis, assumptions are the same as those modeled in
the original risk screen, with the exception of the charge size
(increased to 57g) and the stratification level assumptions (95% of the
refrigerant will settle into the bottom 0.22 m [~9 in.] of the room). 
The results of this secondary analysis for isobutane and R-441A compared
to the results of the original analysis are shown in Table 3. 

Table 3. Maximum Concentrations in Lower Compartment of Kitchen

Proposed Substitute	Maximim Concentration: Original Assumptionsa (ppm)
Maximum Concentration:

 Conservative Assumptionsb (ppm)

Isobutanec	6,647	13,778

R-441Ad	6,236	16,153

a See Table 1

b See Table 2

c Isobutane LFL is 18,000 ppm

d R-441A LFL is 16,800 ppm

Although the concentrations in the lower compartment of the kitchen
increased for both isobutane and R-441A after using more conservative
charge size and stratification assumptions, the maximum concentrations
remained below the LFL for both compounds. The maximum concentration for
R-441A is within 95% of the LFL (16,800 ppm); however, it is unlikely
that concentrations would reach these levels using either refrigerant in
a real-life leak situation, due to the conservative nature of the
assumptions. As noted previously, it is unlikely that a kitchen size
would be 18 m3 and that the entire 57 gram charge would leak.

Threshold Analysis and Results

A threshold analysis was also performed to assess the impact of
differences in room volume and leak amount and to determine the needed
parameter values for leaked concentrations to reach the LFL for
isobutane and R-441A.  One of the two assumptions in the revised
flammability analysis (i.e., room size and leak amount) was changed
while the other assumptions remained constant (see Table 2) to determine
the value at which concentrations in the lower compartment of the
kitchen would reach the LFL for isobutane and R-441A.  The results of
the threshold analysis are shown in Table 4.

Table 4.  Room volumes and leak amounts necessary to reach LFL 

Refrigerant a,b	Room Size (Volume)	Leak Amount

Isobutane	18 m3	75 g

Isobutane	13.8 m3	57g

R-441A	18 m3	59 g

R-441A	17.3 m3	57g

a Lower Flammability Limit of isobutane is equal to 18,000 ppm.

b Lower Flammability Limit of R-441A is equal to 16,800 ppm..

Assuming a room volume of 18 m3, the charge sizes required for the
concentration in the lower compartment of the kitchen to reach the LFL
for isobutane and R-441A were 75 grams and 59 grams, respectively. Based
on the proposed SNAP ruling, the charge sizes required to reach the LFL
would not be allowed for household refrigerators. Further, although a
charge size of 59 grams for R-441A is close to the allowable 57 gram
charge size, the UL Standard 250 requires that if a charge size of 57
grams is used, engineering controls must be in place to ensure that only
50 grams (or approximately 88%) can leak from the system. 

If the charge size of 57 grams was held constant, kitchen volumes of
13.8 m3 (487 ft3) and 17.3 m3 (611 ft3) would be necessary for isobutane
and R-441A concentrations, respectively, in the lower compartment of the
kitchen to reach the LFL. Both threshold kitchen volumes are lower than
the original assumed kitchen volume of 18 m3. However, as noted
previously, it is highly unlikely that a kitchen would exist at such
small volumes—only one percent of houses sampled in more than 60
different projects had a kitchen smaller than 53 m3 (Murray 1997). 

Additional Discussion

Depending on the mixing conditions, it is still possible that in certain
locations at floor-level, or in restricted areas such as a space between
a refrigerator and a wall, the concentrations of isobutane or R-441A
could reach their LFLs for a few minutes, posing a threat in the
presence of a spark. However, the annual probability of an external leak
occurring over the course of minutes and an ignition source being
present simultaneously is approximately 5.0 x 10-7 (i.e., 0.5 in one
million) (A.D. Little 1991). 

To avoid the risk of fire and explosion, it is recommended that
refrigerators containing isobutane or R-441A not be installed in small,
poorly ventilated spaces such as very small enclosed ‘galley’
kitchens or storage closets (especially as other equipment or appliances
in the space would reduce the effective volume of the room).  For
full-sized kitchens and for kitchens with typical ventilation levels,
the risk of fire and explosion is minimal.

 

References

A.D. Little 1991.  Risk Assessment of Flammable Refrigerants for Use in
Home Appliances. Arthur D. Little, Inc. for EPA, Climate Change
Division.  September 10, 1991.  Docket item EPA-HQ-OAR-2009-0286-0023.

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.

EPA 2009. Risk Screen on Substitutes for CFC-12 in Household
Refrigerators and Freezers: Isobutane. Stratospheric Protection
Division. Prepared by ICF International. March 2009.  

Honeywell 2010. Honeywell International, Inc. Comment on EPA Proposed
Rule. Protection of Stratospheric Ozone: Listing of Substitutes for
Ozone-Depleting Substances-Hydrocarbon Refrigerants.
EPA-HQ-OAR-2009-0286; FRL-9147-9. July, 2010.

Kataoka.  1999.  “Allowable Charge Limit 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
Analysis.  17(4): 439-446.  

Sheldon, L.S., et al.  1989. "An Investigation of Infiltration and
Indoor Air Quality."  New York State Energy Research & Development
Authority, Report 90-11.

UL. 2000. UL 250: Standard for Household Refrigerators and Freezers.
Underwriters Laboratory. 

 Murray (1997) uses data from the Brookhaven National Laboratory PFT
database.  Data regarding kitchen volumes were only available for the
Los Angeles 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.

 This value is consistent with the location for a potential leak from
the condenser-compressor department for a bottom freezer depicted in
comment EPA-HQ-OAR-2009-0286-0170.1.

 Enclosed galley kitchens are kitchens that are not open to the rest of
the dwelling, generally have two (or occasionally three) sides, and have
a pass way or doorway entrance, but no door.

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