Calculating EtO commercial sterilizer emissions for the 2017 AirToxScreen
assessment
The table below summarizes the average emission factors for ethylene oxide (EtO) from specific
areas/equipment within a sterilizer facility as a percentage of the annual EtO usage. (In one
case - Indoor EtO Storage - the percentage is not reported because the information is claimed
as Confidential Business Information or CBI.) The percentage values were calculated using
industry responses from a December 2019 Information Collection Request (ICR) collected under
Section 114 of the Clean Air Act, available performance test data, and other data provided by
facilities, and are a simple arithmetic mean of the facilities' data.
Industry avg
# of facilities'
Emission Process Group
percentage of
data used for
EtO Use
average*
Aeration Room Vent
4%
15
Chamber Exhaust Vent
1%
18
Indoor EtO Storage
CBI
N/A
EtO Dispensing
0.1%
3
Vacuum Pump Operation
0.2%
5
Pre-Aeration Handling Sterilized Material
0.2%
1
Post-Aeration Handling Sterilized Material
0.3%
15
Non-oxidizer APCD Area
0.08%
1
This column shows the number of facilities whose data were used to calculate each value. These facilities' data
came from the December 2019 questionnaire for ethylene oxide emissions from commercial sterilizers. These
values will likely change when data from a subsequent 2021 information collection request are incorporated into
the calculations.
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Example Calculation: Centurion Medical Products in Salisbury NC
Basic breakdown of emissions based on company-provided data as part of the 2019 questionnaire:
Emission Process Group
(EPG)
Stack or
Fugitive?
% EtO use
going to
this EPG (a)
Control
Device
Removal
efficiency
Removal
efficiency
(source)
Emissions
(pounds
per year)
Sterilization Chamber
Stack
93.59%
99.991%
6/11/15 state
3.4
Vent
permit application
Aeration Room Vent
Stack
4%
99.995%
6/27/19 state
inspection (2013
performance test)
0.08
Chamber Exhaust Vent
Stack
1%
99.995%
6/27/19 state
inspection (2013
performance test)
0.02
EtO storage/Sterilizer
Uncontrolled
0.07%
0%
N/A
28.5
Room
Vent
(Vacuum Pump
Operation + EtO
Dispensing + Pre-
Aeration Handling
Sterilized Material)
QC area/back
Fugitive
0.13%
0.%
N/A
50.5
warehouse (and half
hall)
(Post-Aeration Handling
Sterilized Material)
Front warehouse (and
Fugitive
0.21%
0%
N/A
85.2
half hall)
(Post-Aeration Handling
Sterilized Material)
(a) When calculating emissions for a particular year, the emission factor calculated from reported data is
used and applied to the year-specific EtO throughput to calculate emissions for the process group.
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Estimating Fugitive Emissions
Emission Process Group
Room
floor area
(A, sqft)
Room
height
(h, ft)
# Air
changes
per hour
(n)
Summer
Temp
(Ts, F)
Winter
Temp
(Tw, F)
Spring/Fall
Temp
(Ti, F)
EtO
Concentration
(C, ppm)
EtO storage/Sterilizer
Room
1260
12.9
15.5
105.0
105.0
105.0
0.1209
QC area/back warehouse
(and half hall)
14600
20.1
1.9
98.0
68.0
73.0
0.0921
Front warehouse (and
half hall)
50850
14.3
2.0
98.0
68.0
73.0
0.0599
The annual operating hours for this facility (t) = 8,760. This information can be plugged into the
equation below (derived from the ideal gas law) to get the amount of EtO being emitted from each
room area in pounds per year:
44x^lxCx/ixn
0.73 X 106
1 x ('
t h- 4
¦ +
t H- 4
+ ¦
t -H 2
¦7V + 459.69 Tw + 459.69 T, + 459.69
T)
i
3
The molecular weight of EtO is 44 Ib/lb-mol, 0.73 is the ideal gas constant for these units (ft , R, atm,
and lb-mol), and 459.69 is used to convert the temperatures to Rankine (an absolute
scale of thermodynamic temperature). ) If we assume all other inputs are constant, the only variable
that will impact the amount of EtO being emitted is the temperature, which is reflected in the equation.
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