MEMORANDUM

October 12, 2018

To:

Honorable Daniel Lipinski
Attention: Dr. Joel Creswell

From:

Kate C. Shouse, Analyst in Environmental Policy, kshouse@crs.loc.gov, 7-1181

Subject:

History of federal air emission regulations for ethylene oxide at commercial
sterilization facilities

This memorandum responds to your request for information about federal air emission regulations for
ethylene oxide at commercial sterilization facilities. In particular, you asked CRS to summarize the
history of the National Emission Standards for Hazardous Air Pollutants (NESHAP) for ethylene oxide
from commercial sterilization and fumigation operations, including changes that the U.S. Environmental
Protection Agency (EPA) promulgated with respect to control of the chamber exhaust (i.e., backvent).
In sum, EPA promulgated the ethylene oxide NESHAP for commercial sterilization and fumigation
operations in 1994 (hereinafter, “ethylene oxide sterilization NESHAP”).1 These standards required
control of three emission points, including chamber exhaust vent emissions. However, in 2001, EPA
removed the requirement to control the chamber exhaust vent emissions based on its determination that
such controls posed a safety hazard.2 EPA affirmed this decision in 2006, when it completed the risk and
technology review of the ethylene oxide sterilization NESHAP.3 Currently, the federal ethylene oxide
sterilization NESHAP does not require control of the chamber exhaust. According to EPA, however, at
least one state—California—requires control of the chamber exhaust.4
Please note that information in this memorandum may be used in other CRS products. Your
confidentiality as a requester will be preserved in any case.

EPA, “National Emission Standards for Hazardous Air Pollutants for Ethylene Oxide Commercial Sterilization and Fumigation
Operations,” 59 Federal Register 29823, December 6, 1994, https://www.gpo.gov/fdsys/pkg/FR-1994-12-06/html/94-29823.htm.
2 EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 66 Federal Register 55577, November 2, 2001.
Hereinafter, “EPA 2001 Final Rule.”
3 In 2006, EPA determined no additional control requirements were warranted and therefore did not revise the ethylene oxide
NESHAP for commercial sterilization facilities. EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 71
Federal Register 17712, April 7, 2006. Hereinafter, “EPA 2006 Final Rule.”
4 Memorandum from David Markwordt, EPA’s Policy, Planning, and Standards Group, to Laura McKelvey, Group Leader,
EPA’s Policy, Planning, and Standards Group, September 21, 2005, https://www.regulations.gov/document?D=EPA-HQ-OAR2003-0197-0027, p. 6. Hereinafter, “EPA 2005 Memorandum.”
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Background
The Clean Air Act (CAA) directs EPA to promulgate emission standards—known generally as National
Emission Standards for Hazardous Air Pollutants (NESHAPs)—for sources of the 187 hazardous air
pollutants listed in Section 112(b).5 The CAA directs EPA to set technology-based NESHAPs, which
require major sources6 to use Maximum Achievable Control Technology (MACT).7 Section 112 also
directs EPA to specify categories of sources subject to the emission standards. EPA is to “review, and
revise as necessary” the emission standards promulgated under Section 112(d) at least every eight years.8
For additional information about these and other requirements under CAA Section 112, see CRS Report
RL30853, Clean Air Act: A Summary of the Act and Its Major Requirements, by James E. McCarthy.
Ethylene oxide is one of the hazardous air pollutants listed in CAA Section 112(b). Chemical
manufacturers use this flammable, colorless gas to make products such as antifreeze, textiles, plastics,
detergents and adhesives.9 Ethylene oxide is also used to sterilize “heat or moisture-sensitive materials,”
such as medical equipment, and to control microorganisms or insects.10
Long-term exposure to ethylene oxide can cause adverse health effects.11 EPA’s most recent assessment
concluded that ethylene oxide is carcinogenic to humans.12 The National Air Toxics Assessment (NATA)
estimated that ethylene oxide “significantly contributes to potential elevated cancer risks” in some areas
of the country.13 In addition, exposure to ethylene oxide can irritate the eyes, skin, nose, throat, and lungs
as well as damage the brain and nervous system.14

5

42 U.S.C. §7412. The 1990 Clean Air Act Amendments specified 189 pollutants, but P.L. 102-187, enacted on December 4,
1991, deleted hydrogen sulfide from the list of toxic pollutants, leaving only 188. On December 19, 2005, EPA removed methyl
ethyl ketone (MEK) from the list of toxic air pollutants. The total number of listed air toxics is now 187.
6 CAA Section 112(a) defines a major source as “any stationary source or group of stationary sources located within a contiguous
area and under common control that emits or has the potential to emit considering controls, in the aggregate, 10 tons per year or
more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air pollutants.” 42 U.S.C.
§7412(a)(1).
7 42 U.S.C. §7412(d). For information about litigation related to EPA’s interpretations under Section 112, see CRS Report
R43699, Key Historical Court Decisions Shaping EPA’s Program Under the Clean Air Act, by Linda Tsang.
8 42 U.S.C. §7412(d)(6).
9 EPA, Background Information on Ethylene Oxide, https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/backgroundinformation-ethylene-oxide#main-content.
10 EPA, Final Air Toxics Rule for Controlling Ethylene Oxide Emissions from Commercial Sterilization and Fumigation
Operations (Fact Sheet), November 1994, https://www.epa.gov/sites/production/files/201506/documents/ethylene_oxide_1994_factsheet.pdf.
11EPA, Fact Sheet: Ethylene Oxide, December 2017, https://www.epa.gov/sites/production/files/2016-09/documents/ethyleneoxide.pdf. Hereinafter, “EPA 2017 Ethylene Oxide Fact Sheet.”
12 EPA, Evaluation of the Inhalation Carcinogenicity of Ethylene Oxide, In Support of Summary Information on the Integrated
Risk Information System (IRIS), December 2016, pp. 3-1,
https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf.
13 EPA, Background Information on Ethylene Oxide, https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/backgroundinformation-ethylene-oxide#main-content. Hereinafter, “EPA Background on Ethylene Oxide.”
14 EPA 2017 Ethylene Oxide Fact Sheet.

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History of the Ethylene Oxide Sterilization NESHAP
Under Clean Air Act Section 112,15 EPA promulgated the ethylene oxide sterilization NESHAP in 1994.16
EPA based the rulemaking on its determination that commercial sterilization and fumigation operations
emit ethylene oxide, one of the hazardous air pollutants listed in Section 112(b).17 The final rule
established technology-based standards for three emissions points, namely the three emission vents
associated with the sterilization and fumigation process: (1) the sterilization chamber vent; (2) the
aeration room vent; and (3) chamber exhaust vent.18 The rule required facilities that emit over 10 tons of
ethylene oxide per year to use a control device that reduced ethylene oxide emissions by 99% from each
of the three emission points.19 Technologies used to control ethylene oxide emissions include scrubbers,
combusters, dry-bed absorbers, or some combination of these devices.20
Subsequent to the 1994 rulemaking, explosions occurred at some ethylene oxide sterilization and
fumigation facilities.21 In July 1997, EPA reported explosions had occurred at three different ethylene
oxide plants and noted that these plants were “not the only ones which have had explosions since the
promulgation” of the 1994 ethylene oxide sterilization NESHAP.22 EPA stated that while “the causes of
these explosions are not yet precisely known, these facilities were using combustion control units to
control emissions” and that such units “could be a factor” in the explosions.23 EPA therefore
recommended that regional agency staff “inform the facilities that if they have a safety concern they may
disconnect the control units immediately in the short term.”24 EPA also suspended the ethylene oxide rule
for one year—until December 1998—to investigate the explosions.25
The Ethylene Oxide Sterilization Association (EOSA) and EPA conducted separate investigations of the
explosions. EOSA concluded, among other things, that ‘‘improperly overfeeding the oxidizer system from
the chamber backvent was the primary safety concern.’’26 EPA investigated the accidents as well, stating
15

42 U.S.C. §7412.
EPA, “National Emission Standards for Hazardous Air Pollutants for Ethylene Oxide Commercial Sterilization and Fumigation
Operations,” 59 Federal Register 29823, December 6, 1994, https://www.gpo.gov/fdsys/pkg/FR-1994-12-06/html/94-29823.htm.
Hereinafter, “EPA 1994 Final Rule.” The standards are codified at 40 C.F.R. Part 63, Subpart O, see
https://www.gpo.gov/fdsys/pkg/CFR-2015-title40-vol10/pdf/CFR-2015-title40-vol10-part63-subpartO.pdf.
17 42 U.S.C. §7412(b).
18 EPA 1994 Final Rule, Table 1. To view the general layout of a sterilization facility and sterilization chamber as well as
photographs of the associated vents and equipment, see Ali Reza and Erik Christiansen, “A Case Study of an Ethylene Oxide
Explosion in a Sterilization Facility,” Chemical Engineering Transactions, vol. 31 (2013), pp. 465-66,
http://www.aidic.it/cet/13/31/078.pdf.
19 EPA also established standards for smaller sources. EPA 1994 Final Rule, Table 1.
20 EPA 2005 Memorandum, p. 6.
21 According to one retrospective case study, after 1994, “ten explosions occurred in sterilization facilities using ethylene oxide,
causing several injuries and one fatality.” See Ali Reza and Erik Christiansen, “A Case Study of an Ethylene Oxide Explosion in
a Sterilization Facility,” Chemical Engineering Transactions, vol. 31 (2013), p. 464, http://www.aidic.it/cet/13/31/078.pdf.
22 Memorandum from John Seitz, Director, EPA’s Office of Air Quality Planning and Standards, to EPA Regional Air Division
Directors and Regional Air Toxics Contacts, July 18, 1997, https://www3.epa.gov/ttn/emc/news/etoseitz.txt. Hereinafter, “EPA
1997 memorandum.”
23 EPA 1997 memorandum.
24 EPA 1997 memorandum.
25 EPA, “National Emissions Standards for Hazardous Air Pollutants for Ethylene Oxide Commercial Sterilization and
Fumigation Operations,” 62 Federal Register 64736, December 9, 1997, https://www.gpo.gov/fdsys/pkg/FR-1997-12-09/pdf/9732328.pdf.
26 EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 66 Federal Register 13465, March 6, 2001.
Hereinafter, “EPA 2001 Proposed Rule.”
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that it “reviewed reports prepared by EPA Regional Offices and by EOSA member sterilization companies
and, based on that investigation and review, concurred with the industry conclusion and
recommendation.”27 Specifically, EPA “agreed with industry that, in the cases where explosions occurred,
the catalytic oxidizer units were overfed with ethylene oxide in concentrations above the safe operations
limit due to abnormal activation of the chamber.”28 Consistent with EOSA’s recommendation, EPA
extended the compliance deadline for aeration vent and chamber exhaust emissions one more year, to
December 1999. EPA noted that these aeration vent and chamber exhaust emissions represented about 3%
and 1%, respectively, of uncontrolled ethylene oxide emission from the sterilization and fumigation
operations.29 In June 1999, EOSA recommended that EPA eliminate the requirements for chamber exhaust
vent controls.30
In December 1999, EPA suspended the aeration room vent emission standards for one year and suspended
the control requirements for chamber exhaust vent emissions for two years.31 EPA did not identify safety
concerns about the pollution control technology in the aeration room itself. The agency, however,
suspended the requirement for this emissions point because many facilities had routed chamber exhaust
emissions to the pollution control device used for the aeration room vents.32 EPA based the two-year
suspension of the chamber exhaust vent emissions on the estimated time that it would take the agency to
reconsider the Maximum Achievable Control Technology (MACT) requirements for this emissions point
and to propose and promulgate any changes through the rulemaking process.33
In March 2001, EPA proposed to eliminate the MACT requirements for chamber exhaust vents34 and
finalized this elimination in November 2001.35 EPA observed that the MACT standards for chamber
exhaust vents promulgated in 1994 “apparently involved safety hazards not known at that time” and
determined that “solutions to the safety problems have not been developed, and there is no indication that
resolution of the safety issues is forthcoming.”36
EPA affirmed this decision in 2006, when it completed the risk and technology review of the ethylene
oxide sterilization NESHAP.37 EPA retained the control requirements for the sterilization chamber vent
emissions and the aeration room vent emissions. Specifically, EPA determined no additional control
requirements were warranted and therefore did not revise the ethylene oxide sterilization NESHAP.
Regarding the 2001 removal of the chamber exhaust vent requirements, EPA stated that it “continues to
believe that the action taken in 2001 is reasonable and [the agency has] found no safe way to impose
controls on the chamber exhaust vents.” 38 EPA determined that it would “not impose controls on chamber
exhaust emissions for either new or existing facilities.”39 The 2006 decision is the most recently
completed risk and technology review for the ethylene oxide sterilization NESHAP.
I hope this information is helpful. Please feel free to contact me if you have additional questions.
27

EPA 2001 Proposed Rule, p. 13465.
EPA 2001 Final Rule, p. 55578.
29 EPA 2001 Final Rule, p. 55578.
30 EPA 2001 Final Rule, p. 55578.
31 EPA 2001 Final Rule, p. 55578.
32 EPA 2001 Final Rule, p. 55578.
33 EPA 2001 Final Rule, p. 55578.
34 EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 66 Federal Register 13464, March 6, 2001.
35 EPA 2001 Final Rule, p. 55577.
36 EPA 2001 Final Rule, p. 55577.
37 EPA 2006 Final Rule, p. 17712.
38 EPA 2006 Final Rule, p. 17717.
39 EPA 2006 Final Rule, p. 17717.
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