U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

ALERT

EPA EOSA

Preventing Worker Injuries and

Deaths from Explosions in 

Industrial Ethylene Oxide

Sterilization Facilities

Revised Edition
ORDERING INFORMATION

To receive NIOSH documents or for more information about occupational safety and 

health topics, contact:

1–800–CDC–INFO (1–800–232–4636) 

Text telephone (TTY): 1–888–232–6348 

E-mail: cdcinfo@cdc.gov

or visit the NIOSH Web site at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov/niosh/eNews.

DHHS (NIOSH) Publication No. 2007–164 (supersedes 2000–119)

EPA Publication No. 550–F–99–018

This document was prepared jointly by the National Institute for Occupational 

Safety and Health (NIOSH), the U.S. Environmental Protection Agency (EPA), 

and the Ethylene Oxide Sterilization Association (EOSA). The document is in the 

public domain and may be freely copied or reprinted.

Disclaimer: Mention of any company or product does not constitute endorsement 

by NIOSH, EPA, or EOSA.
ATTENTION WORKERS!

Explosions may result from improper venting of 

ethylene oxide into oxidizing emission control devices (OECDs).

Workers should take the following steps to protect 

themselves while working in ethylene oxide (EtO) 

sterilization facilities:

Prevent overfeeding of the OECD

• Make sure that all interlocks and other safeguards are in place before sterilization begins.

• Periodically wash or vent sterilized products

that sit idle in a sterilizer or aeration room to

prevent EtO buildup.

• Monitor EtO concentrations in the sterilizer before the back vents are activated to avoid venting high EtO concentrations to the oxidizing

emission control device (OECD).

• Vent confined spaces such as the sterilizer and 

the aeration room to the outisde after a power

loss.

• Do not purge EtO lines to an OECD.

• Perform regular preventive maintenance.

• Obtain management approval before changing

the process or safety interlocks.

Store and handle EtO properly

• Store EtO in tightly closed cylinders or tanks in

a cool, shaded, well-ventilated, explosion-proof

area.

• Do not smoke at work.

• Do not use electrical devices or create open

flames where EtO is handled, used, or stored.

• Use nonsparking tools when opening or closing

metal containers of EtO or whenever EtO might

be present.

• Keep containers individually bonded and grounded to the earth when liquid EtO is poured or transferred.

Deal with leaks and spills

• Leave a leak or spill area immediately.

• If a catastrophic or large release of EtO occurs,

do not enter the area. Evacuate the building

and notify the fire department immediately. 

• Do not enter an area where there is a small EtO

leak until you have put on personal protective

equipment (PPE), including a self-contained

breathing apparatus (SCBA) that has a full facepiece and is operated in a pressure-demand or

other positive-pressure mode.

• Do not use an SCBA unless you have received proper training and are current on its 

safe use. 

Be prepared for rescue

• Know emergency rescue steps and where emergency equipment is located.

• Do not participate in emergency response 

without an SCBA and proper training. If you

do not have an SCBA and proper training, let

the local fire department conduct the rescue. 

• Before rescuing anyone in a leak or spill area,

notify another person and put on an SCBA. Do

not use a canister-type respirator for emergency

response.

Please tear out and post. Distribute copies to workers. See back of sheet to order complete Alert.

Preventing Worker Injuries and Deaths From Explosions in 

Industrial Ethylene Oxide Sterilization Facilities

EPA EOSA

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

ALERT

EPA EOSA

Preventing Worker Injuries and

Deaths from Explosions in 

Industrial Ethylene Oxide

Sterilization Facilities
• If someone stops breathing because of EtO inhalation, immediately remove the person from

the exposure area and perform cardiopulmonary resuscitation (CPR) while someone else

calls for medical help. Keep the victim warm.

Prevent skin and eye contact

• If liquid EtO contacts your skin, rinse it immediately under a heavy shower. Remove any contaminated clothing. Get medical attention.

• If EtO gets into your eyes, flush them immediately with a steady stream of water for at least

15 minutes. Lift the upper and lower eyelids

and direct the stream of water under the eyelids. Get medical attention.

• Do not wear contact lenses in an area where

EtO exposure might occur.

Use respiratory protection and other 

PPE

• Use the respiratory protection recommended in

the complete Alert during emergencies, maintenance work, vessel cleaning, and whenever

engineering controls cannot be implemented.

(See ordering information for the Alert at the

bottom of this sheet.)

• Use PPE such as chemical-resistant gloves,

eye-splash protection, and liquid-tight protective clothing whenever liquid EtO might be

present.

For additional information, see NIOSH Alert: Preventing Worker Injuries 

and Deaths From Explosions in Industrial Ethylene Oxide Sterilization 

Facilities [DHHS (NIOSH) Publication 2007–164 (supersedes 2000–119)].

Single copies of the Alert are available free from the following:

1–800–CDC–INFO (1–800–232–4636)

Text telephone (TTY): 1–888–232–6348

E-mail: cdcinfo@cdc.gov

or visit the NIOSH Web site at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to

NIOSH eNews by visiting www.cdc.gov/niosh/eNews.

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Preventing Worker Injuries and Deaths From Explosions 

in Industrial Ethylene Oxide Sterilization Facilities

ATTENTION EMPLOYERS!

Explosions may result from improper venting of 

ethylene oxide into oxidizing emission control devices (OECDs).

Employers should take the following steps to 

prevent ethylene oxide (EtO) explosions:*

Analyze and develop written procedures

•	 Conduct a process hazard analysis that emphasizes safety procedures for the entire sterilization system.

•	 Establish written procedures to cover all steps

of EtO sterilization.

•	 Evaluate the advantages and disadvantages of

each control technology.

Prevent overfeeding of the OECD

•	 Make sure that all interlocks and other safeguards are in place before sterilization begins.

•	 Periodically wash or vent sterilized products

that sit idle in a sterilizer or aeration room to

prevent EtO buildup.

•	 Monitor EtO concentrations in the sterilizer before the back vents are activated to avoid venting high EtO concentrations to the oxidizing

emission control device (OECD).

• Install an OECD bypass for emergency use

if allowed by State or local environmental

regulations.

•	 Vent confined spaces such as the sterilizer and

the aeration room to the outside after a power

loss.

•	 Do not purge EtO lines to an OECD.

•	 Perform regular preventive maintenance.

Store and handle EtO properly

•	 Store EtO in tightly closed cylinders or tanks in

a cool, shaded, well-ventilated, explosion-proof

area.

•	 Do not permit smoking, use of electrical devices, or open flames where EtO is handled, used,

or stored.

•	 Use nonsparking tools when opening or closing

metal containers of EtO or whenever EtO might

be present.

•	 Keep containers individually bonded and

grounded to the earth when liquid EtO is poured

or transferred.

Deal with leaks and spills

•	 Make sure that all workers leave a leak or spill

area immediately.

•	 If a catastrophic or large release of EtO occurs,

do not permit workers to enter the area. Evacuate the building and notify the fire department

immediately.

• If a small leak occurs, do not permit workers to

enter the area until they have put on personal

protective equipment (PPE), including a

self-contained breathing apparatus (SCBA).

• Do not permit workers to use SCBAs unless 

they have received proper training and are 

current on their safe use. 

Please tear out and post. Distribute copies to workers. See back of sheet to order complete Alert.

*

This list is not all-inclusive and may not be equally applicable to all sterilization and repackaging facilities.

Employers should identify and use the controls and procedures that are relevant to their facilities. They should

also be aware that no fail-safe control technique exists

to guarantee that fires and explosions will not occur at

their facilities.

EPA EOSA

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

ALERT

EPA EOSA

Preventing Worker Injuries and

Deaths from Explosions in 

Industrial Ethylene Oxide

Sterilization Facilities
Implement engineering controls

• Provide an abort cycle (with diluent) in the sterilizer control system.

• Establish and follow a cycle approval process

for all test cycles.

• Provide limited access to override controls.

• Eliminate back vents through appropriate equipment and cycle design.

• Interlock the sterilizer door to prevent opening

before the cycle is complete.

• Interlock the gas inlet (shut-off) valve.

• Make sure that regular preventive maintenance

is performed.

• Install a flow-limiting device on the vacuum

pump inlet (controls or orifice).

• Install valve position sensors on critical valves.

• Install real-time area monitors that will alert

workers to unsafe EtO concentrations.

• Use redundancies or other safeguards on all

critical valves.

• Use damage control devices in the EtO supply

lines and the OECD feed lines to limit explosion

damage.

• Make sure that all other equipment has proper

safety controls.

Install emergency equipment

• Equip the facility with a type 2, 3 carbon dioxide

or dry chemical fire extinguisher. Train workers

annually in their safe use.

• Provide emergency eye-wash facilities.

Provide respiratory protection and PPE

• Provide workers with the respiratory protection recommended in the complete Alert during

emergencies, maintenance work, vessel cleaning, and whenever engineering controls cannot

be implemented. (See ordering information for

the Alert at the bottom of this sheet.)

• Provide workers with chemical-resistant gloves,

eye-splash protection, and liquid-tight protective

clothing whenever liquid EtO might be present.

Provide training

• Fully train all operations, maintenance, and engineering workers in the dangers of EtO-rich

evacuations to an OECD.

• Train all workers who will be responding to

emergencies (including managers and supervisors) in the proper use of safety equipment

and in emergency procedures for all EtO plant

operations.

Prepare workers for rescue

• Make sure that workers know emergency rescue steps and where emergency equipment is

located. Be sure that they comply with Occupational Safety and Health (OSHA) regulations.

• Do not permit workers to participate in 

emergency response without SCBAs and 

proper training. If workers do not have SCBAs

and proper training, let the local fire department

conduct the rescue.

• Design, develop, and practice emergency evacuation and rescue procedures.

For additional information, see NIOSH Alert: Preventing Worker Injuries and 

Deaths From Explosions in Industrial Ethylene Oxide Sterilization Facilities [DHHS (NIOSH) Publication 2007–164 (supersedes 2000–119)]. Single

copies of the Alert are available free from the following:

1–800–CDC–INFO (1–800–232–4636)

Text telephone (TTY): 1–888–232–6348

E-mail: cdcinfo@cdc.gov

or visit the NIOSH Web site at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to

NIOSH eNews by visiting www.cdc.gov/niosh/eNews.

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
WARNING!

Explosions may result from improper venting of 

ethylene oxide into oxidizing emission control devices (OECDs).

The National Institute for Occupational 

Safety and Health (NIOSH), the U.S. Environmental Protection Agency (EPA), 

and the Ethylene Oxide Sterilization 

Association (EOSA) request assistance 

in preventing explosions at industrial 

ethylene oxide (EtO) sterilization facilities and EtO repackaging plants. EtO 

is a flammable gas. During sterilization 

procedures, EtO can easily form explosive mixtures when it is vented to certain types of emission control devices 

such as catalytic oxidizers.

Between 1994 and 1998, EtO was involved in 10 explosions at industrial 

EtO sterilization facilities and EtO repackaging plants. One of these explosions caused 1 death and 59 injuries 

among workers. All of these incidents 

caused damage to the plants, most of 

which used catalytic oxidizers to control EtO emissions.

This Alert informs owners, managers, 

supervisors, engineers, safety professionals, and workers about the explosions, injuries, and deaths that may 

occur at industrial EtO sterilization facilities and repackaging plants. Steps 

are recommended for preventing these 

explosions.

BACKGROUND

According to EPA, EtO is among the top 

3% of high-volume chemicals produced in 

the United States. Less than 1% of all EtO 

produced in the United States is used as 

an industrial sterilant or fumigant [LaMontagne et al. 2007]. For sterilization applications, EtO is supplied in cylinders as a 

pure liquid under pressure or mixed with 

other carriers.

Industry has long recognized the value of 

safe, effective, and efficient sterilization using EtO. The health care and food industries 

depend on the EtO sterilization industry for 

sterile products. More than 50% of all sterile medical devices sold are sterilized using 

EtO [Kroschwitz and Howe-Grant 1994].

Oxidizing emission control devices (OECDs) 

are integrated into some sterilization 

systems. They remove or destroy small 

amounts of EtO remaining in a vent stream 

through oxidation or burning. In most cases, OECDs replace acidified wet scrubber 

systems that are slightly less efficient in 

controlling low-concentration EtO emissions (see Appendix B). However, the use 

of OECDs alone increases the potential for 

fire and explosion. Most recent explosions 

Preventing Worker Injuries and Deaths From Explosions in 

Industrial Ethylene Oxide Sterilization Facilities

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

ALERT

EPA EOSA

Preventing Worker Injuries and

Deaths from Explosions in 

Industrial Ethylene Oxide

Sterilization Facilities
EtO

in the EtO sterilization industry are associated with OECDs. Since EtO vapors are 

highly flammable and explosive, the EtO 

concentration in the vent stream to the 

OECD must remain well below the flammable or explosive range because thermal or catalytic OECDs provide a source 

of ignition that could trigger an explosion 

in the vent system.

Nearly all such explosions are associated 

with overfeeding of the system. Such overfeeding occurs when

a back vent is opened while a 

high concentration of EtO is in the 

sterilizer, 

no valve is used to control the flow 

rate of EtO to the OECD, and 

an EtO-rich stream reaches the 

device. 

Overfeeding the OECD usually involves 

one or more of the following: (1) opening 

a sterilizer door that triggers back vent operation, (2) using a manual switch to trigger back vent operation, or (3) triggering 

back vent operation through a sterilizer 

controller (see Appendices C and D for 

more information about overfeeding). The 

high flow rate of the back vent exhausts 

could emit EtO at a rate that exceeds the 

safe design limits of the OECD if a valve 

or orifice is not used to control the flow of 

EtO or the EtO concentration sent to the 

OECD.

Properties of EtO

EtO (C2H4O, epoxyethane, oxirane) is a 

colorless gas at room temperature with 

an ether-like odor at concentrations above 

500 to 700 parts per million (ppm). The 

—

—

—

odor threshold for EtO is 260 ppm. EtO 

has a vapor density of 1.49 and is thus 

approximately 1.5 times heavier than air 

[Clayton and Clayton 1993]. The boiling 

point of EtO is 51 °F, and the liquid has 

a flash point of 0 °F. The gas has an autoignition temperature of 805 °F. The vapor pressure of EtO is 1,095 mm Hg. EtO 

is soluble in water and reacts with acidified water to produce ethylene glycol. This 

process is one method for controlling EtO 

emissions. EtO is reactive with strong acids, alkalis and oxidizers, chlorides of iron, 

aluminum or tin, and oxides of iron and 

aluminum [Lewis 1996]. Highly flammable, 

EtO poses a dangerous fire and explosion 

risk. The flammability limits in air are 3% 

(30,000 ppm) to 100% [Lewis 1996]. Pure 

EtO can be ignited in the absence of air. 

EtO is more dangerous than hydrogen 

and should be treated with the same care 

as hydrogen and acetylene. Once ignited, 

it can flash back to the fuel source with velocities of 1,800 to 2,400 m/sec.

EtO Health Effects

EtO irritates the eyes and skin; it may also 

irritate mucous membranes and cause a 

strange taste in the mouth. EtO may cause 

allergies, adverse reproductive effects, 

and possibly asthma. At high concentrations, it can cause nausea and vomiting 

[LaMontagne et al. 2007; LaMontagne and 

Kelsey 1998]. EtO can be detected by 

odor only when it has already reached the 

dangerous concentration of 260 ppm. Olfactory fatigue may limit a persons ability 

to smell EtO, but perception at concentrations below the odor threshold may occur because of mucous membrane irritation and a peculiar taste in the mouth. In 

1984, the Occupational Safety and Health 

Administration (OSHA) classified EtO as 

a carcinogen and regulated it as such 
EtO 

[29 CFR* 1910.1047]. In 1994, the International Agency for Research on Cancer 

(IARC) classified EtO as a Group 1 human 

carcinogen [IARC 1994].I

INDUSTRIAL 

STERILIZATION PROCESS

Although the sterilization process and 

emission controls vary greatly among facilities, most industrial sterilization processes involve placing the products to be 

sterilized in a large chamber, injecting the 

chamber with EtO, flushing the EtO out of 

the chamber, and removing the sterilized 

products. Steps include product conditioning (preconditioning), sterilization, and 

sterilant gas removal (aeration). The sterilization stage consists of an initial purge, 

sterilant injection, sterilant gas dwell, and 

post-sterilization purge. Stages vary with 

the type of products to be sterilized and 

the equipment used.

In the typical process, EtO vapors from the 

sterilizer chamber and other areas of the 

facility are sent to an acidified wet scrubber 

before emission to the air. However, the 

scrubber may not keep the EtO concentration low enough to meet the emissions 

standard. Furthermore, sterilizer operators 

are left with ethylene glycol solutions for 

disposal. Consequently, sterilizer operators 

have added OECDs either after or in place 

of the wet scrubber. In OECD systems, 

EtO vent streams are mixed with dilution 

air to ensure that the EtO concentration 

that reaches the OECD is kept below 7,500 

ppm (one-fourth of the 30,000-ppm lower 

flammability limit) or the manufacturers 

specification under normal operating conditions. A key factor in sterilizer operation 

is ensuring that workers are not exposed 

to toxic concentrations of EtO.

One feature of the sterilizer chamber is a 

back vent, which consists of a large diameter valve and a blower at the back of the 

sterilizer chamber. The blower creates a 

large-volume air flow through the chamber 

when the chamber door is opened at the 

end of a sterilization cycle. When this door 

is opened, the valve in the back vent automatically opens, and the OECD unit throttles 

up to capture and destroy EtO. This process 

keeps EtO concentrations below the OSHA 

permissible exposure limit (PEL) for workers who must enter the chamber to remove sterilized products. Figures 1 and 2 

depict the typical process and emissions 

flow of industrial EtO sterilization facilities 

with and without an OECD.

SAFETY CONCERNS†

Overfeeding increases the risk of EtO explosion. Possible causes for various types 

of overfeeding are listed here.

A. Overfeeding the OECD from back 

vents containing high concentrations 

of EtO

Causes:

1. The back vent was turned on with 

EtO-rich gas present because 

safety interlocks were bypassed, 

the EtO valve leaked, 

—

—

*

Code of Federal Regulations. See CFR in references. †

See also Appendix D.
EtO
EtO

the product degassed too long 

in the sterilizer after cycle completion, or 

the computer system, controller, or instrumentation failed. 

2. The product was not adequately 

washed or flushed of EtO before the 

door was opened. 

3. The incorrect cycle was used for the 

product. 

4. The lower flammability limit sensors 

and the flow sensors had slow response times. 

5. Test cycles that explored process 

capability limits (resulting in an unexpected EtO-rich environment). 

B. Overfeeding from vacuum pumps

Causes:

1. Too many vacuum pumps were operating. 

2. Discharges were misdirected. 

3. Incoming flows were not interlocked 

or controlled. 

4.EtO feed valves failed or malfunctioned. 

5.Safety interlocks were bypassed. 

C. Overfeeding from lack of adequate 

dilution air

Causes:

1.Aeration exhaust or dilution source 

was lost. 

—

—

2. Makeup dilution was lost. 

D. Overfeeding from other sources

Causes:

1.Spills or drum leaks occurred near 

vents to the OECD. 

2. No interlock was present between 

the EtO valve and the sterilizer. 

3. The air in-bleed valve failed or malfunctioned. 

4.Valves became stuck and resulted in 

misdirected flow. 

5.EtO cylinders were purged with EtO 

delivery valves in the wrong position. 

6. The upstream scrubber was operated improperly. 

7. The sterilizer control system was inadequate. 

8. Cabinet locks were not present, allowing easy access to the manual 

sterilizer switches. 

CURRENT STANDARDS

NIOSH

The NIOSH recommended exposure limit 

(REL) for EtO is 0.1 ppm as an 8-hr timeweighted average (TWA) with a 10-min 

ceiling limit of 5 ppm [NIOSH 1983]. NIOSH 

has determined that 800 ppm is the EtO 

concentration that is immediately dangerous to life and health (IDLH) [NIOSH 1994, 

1997].
EtO

OSHA

The OSHA PEL for EtO is 1 ppm as an 

8-hr TWA with a 15-min excursion limit of 

5 ppm [29 CFR 1910.1047]. Because of 

OSHA regulations, back vents were installed to reduce worker exposure to EtO.

EPA

EPA has developed acute exposure 

guideline levels (AEGLs) for high-priority, 

acutely toxic chemicals. The AEGL is the 

concentration at or above which the general population could experience serious, 

long-lasting health effects or impaired ability to escape (because of health effects). 

The AEGL for EtO is 110 ppm for 1 hr [62 

Fed. Reg.‡ 58839 (1997)].

On December 6, 1994, EPA promulgated 

its final standard under the Clean Air Act 

(Subpart O—Ethylene Oxide Emissions 

Standards for Sterilization Facilities [40 

CFR 63.360]). Because of public health 

concerns about EtO emissions to the air, 

this standard required that by December 6, 

1997, all sterilization and fumigation facilities using more than 10 tons of EtO per 

year increase emission removal efficiency from 95% to 99% and add controls to 

certain vent streams. Many facilities selected and installed OECDs to meet these 

requirements (see Appendix B for more 

information about emission control devices). When several facilities using EtO 

and OECDs experienced explosions, EPA 

delayed the compliance deadline for 3 

consecutive years so that facilities could 

reassess the safety of their processes and 

emission control systems.

ACGIH

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends for EtO a threshold limit value (TLV) 

of 1 ppm as an 8-hr TWA [ACGIH 1999].

AIHA

The American Industrial Hygiene Association (AIHA) writes emergency response 

planning guidelines (ERPGs) for toxic 

chemicals involved in emergency situations such as releases to the community. 

The ERPG-2 for EtO is 50 ppm—the concentration below which nearly all persons 

can be exposed for up to 1 hour without 

experiencing irreversible or other serious 

health effects [AIHA 1998]. The ERPG-3 for 

EtO is 500 ppm—the concentration below 

which nearly all persons can be exposed 

for up to 1 hour without experiencing lifethreatening health effects [AIHA 1998].

CASE REPORTS

The following case reports briefly describe 

the EtO explosions at sterilization or repackaging facilities.

Case 1

At an EtO sterilization facility, an operator noted an overfeed of EtO in one of the 

chambers during sterilization. The operator tried to correct the problem by adding 

dilution air and bringing the chamber to 

atmospheric pressure. When the front 

door of the sterilizer was opened, a valve 

opened at the back of the sterilizer (the 

back vent), causing EtO to bypass the wet 

scrubbers and go directly to the OECD. 

An ignition occurred in the OECD on the ‡Federal Register. See Fed. Reg. in references. 
EtO

roof of the facility. EtO gas in the ductwork 

flashed back and over-pressured the ductwork and the sterilizer. As a result, the roof 

of the building, walls, ductwork, and OECD 

were severely damaged. No workers were 

injured, and no chemicals were released 

to the environment [EPA 1997a].

Case 2

An explosion occurred recently at a commercial EtO sterilization facility. This facility 

handles the bulk sterilization of medical kits 

using 100% EtO. The sterilization chambers are connected to two 400-lb EtO cylinders. Before the incident, the facility had 

replaced an acidified wet scrubber system 

with a new OECD to control EtO emissions. 

During a test run of the OECD at Chamber 

1, an explosion occurred following primary evacuation of the chamber—about 15 

sec after the back vent fan exhausted the 

chamber. Later it was determined that the 

ignition had occurred at the OECD. The ensuing explosion caused a flame front from 

the oxidizer back to the mixing plenum, 

completely destroying the plenum box. 

The explosion continued upstream toward 

the sterilizer, blowing out 14-gauge steel 

ducting along the way. The door blew off 

the sterilizer and shot through the building, 

damaging the de-gas room. The 50,000-lb 

chamber was moved 3ft off its foundation. 

About 7% EtO (15 to 20 lb) was in the sterilizer at the time of the explosion. No worker 

injuries were reported [EPA 1997b].

Case 3

At an EtO repackaging facility, an explosion 

occurred during a test run on the inside 

of a thermal oxidizer. Testing probes had 

been placed at the inlet and outlet sides 

of the thermal oxidizer. At the beginning 

of the test, the inlet concentration was in 

the expected range of 1,000 ppm EtO. 

But just before the explosion, the inlet EtO 

concentration rose to 35,000 ppm. Within 

16 sec, the explosion occurred in the thermal oxidizer. The thermal oxidizer bed and 

production equipment were damaged, and 

the filling room was destroyed. No worker 

injuries were reported [EPA 1998].

CONCLUSIONS

All incidents described in the case reports occurred during operations in which 

an OECD was used as the only emission control device (that is, when acidified wet scrubbers were not used or were 

bypassed). Sterilization facilities using an 

OECD typically have the chamber door interlocked with the back vent system to protect workers from EtO exposure when they 

are loading or unloading products. When 

the back vent system is activated, it vents 

a high-volume flow directly to the OECD. 

The intention is to activate the back vent 

only when the concentration of EtO in the 

chamber is well below the lower flammability limit (3% or 30,000 ppm EtO)—­typically 

in the range of several hundred parts per 

million. OECDs are designed to operate at 

concentrations well below the lower flammability limit to avoid igniting the sterilant 

gas. Some EtO explosions have been 

caused by incomplete evacuation cycles, 

and others have been caused by improper 

operation. In all cases, overfeeding resulted when a high concentration of EtO 

was inadvertently sent to the OECD.

Investigation and analysis of the incidents 

described here and a review of the sterilization process by EOSA and EPA resulted 

in the following conclusions:
EtO

1. Fires and explosions result when sterilizer OECDs are overfed with high concentrations of EtO. 

2. Current procedures for aborting the 

EtO sterilizer cycle are deficient when 

OECDs are used. 

3. Current safety systems for EtO sterilization processes are deficient when 

OECDs are used. 

4. When OECDs are used as the only 

emission control device (that is, when 

acidified wet scrubbers are not used or 

are bypassed), the risk of fire and explosion is greatly increased. 

RECOMMENDATIONS

Workers

Workers should take the following steps to 

prevent EtO explosions:

1.	 Prevent overfeeding of the OECD

• Make sure that all interlocks, safeguards, and other preventive measures are in place before a sterilization cycle begins. 

• Periodically wash or vent sterilized 

products that sit idle in a sterilizer or 

aeration room to prevent EtO buildup. 

• Monitor EtO concentrations in the 

sterilizer before the back vents are 

activated to avoid exhausting high 

concentrations of EtO through the 

back vent to the OECD. 

• Vent confined spaces such as the 

sterilizer and the aeration room to 

the outside after a power loss to prevent EtO buildup and overfeeding of 

the OECD. 

• Do not purge EtO lines to an OECD: 

an incorrect valve lineup or a leak in 

the storage area is likely to lead to 

overfeeding. 

• Perform regular preventive maintenance. 

• Obtain management approval before 

changing the process or safety interlocks. 

See Appendix C for more details about 

steps to prevent overfeeding of the OECD.

2.	 Store and handle EtO properly

• Store EtO in tightly closed cylinders 

or tanks in a cool, shaded, wellventilated, explosion-proof area. Store 

cylinders or tanks away from heat, 

sparks, flames, strong oxidizers, alkalines, acids, and acetylide-forming 

metals such as copper, silver, mercury, and their alloys. The storage room 

should be explosion-proof according 

to the definition of the National Fire 

Protection Association (NFPA 560) 

[NFPA 1995]. 

• Do not smoke, use electrical devices, 

or create open flames where EtO is 

handled, used, or stored. 

• Use nonsparking tools when opening 

or closing metal containers of EtO or 

whenever EtO might be present. 

• Keep containers individually bonded 

and grounded to the earth when liquid EtO is poured or transferred. 

3.	 Deal with leaks and spills

• Leave a leak or spill area immediately. 

• If a catastrophic or large release of 

EtO occurs, do not enter the area. 

Evacuate the building and notify the 
EtO

fire department immediately. Note: A 

large release of EtO is any release other 

than the type of small leak that would occur (for example) from a loose connection or valve. A catastrophic release is 

one that would occur if (for example) a 

forklift pierced a 400-lb EtO cylinder. 

• Do not enter an area where there is a 

small EtO leak until you have put on 

personal protective equipment (PPE), 

including a self-contained breathing 

apparatus (SCBA) that has a full facepiece and is operated in a pressuredemand or other positive-pressure 

mode. 

• Do not use an SCBA unless you 

have received proper training and 

are current on its safe use. 

4.	 Be prepared for rescue

• Know emergency rescue steps and 

where emergency equipment is located. Be sure that you comply with OSHA 

regulations regarding emergency response, PPE, and rescue in confined 

spaces [29 CFR 1910.38, 1910.120(q), 

1910.132138, 1910.146]. 

• Do not participate in emergency 

response without an SCBA and 

proper training. If you do not have an 

SCBA and proper training, let the local 

fire department conduct the rescue. 

• Before rescuing anyone in a leak 

or spill area, notify another person 

and put on an SCBA. Do not use a 

canister-type respirator for emergency response; such respirators provide no protection in case of leaks or 

spills. 

• If someone stops breathing because 

of EtO inhalation, immediately remove the person from the exposure 

area and perform cardiopulmonary 

resuscitation (CPR) while someone 

else calls for medical help. Keep the 

victim warm. 

5.	 Prevent skin and eye contact

• If liquid EtO contacts your skin, rinse 

it immediately under a heavy shower. 

Remove any contaminated clothing. 

Get medical attention. 

• If EtO gets into your eyes, flush them 

immediately with a steady stream of 

water for at least 15 min. Lift the upper and lower eyelids and direct the 

stream of water under the eyelids. 

Get medical attention. 

• Do not wear contact lenses in an area 

where EtO exposure might occur. 

6.	 Use respiratory protection and other

PPE

• Use appropriate respiratory protection§

 during emergencies, maintenance 

work, vessel cleaning, and whenever 

engineering controls cannot be implemented. At a minimum, such protection 

must comply with OSHA requirements 

in 29 CFR 1910.1047 and 1910.134. 

• Use PPE such as chemical-resistant 

gloves, eye-splash protection, and 

liquid-tight protective clothing whenever liquid EtO might be present. At 

a minimum, such equipment must 

comply with OSHA requirements [29 

CFR 1910.1047]. 

§

For detailed information about respiratory protection for workers exposed to EtO, see NIOSH Current Intelligence Bulletin 52: Ethylene Oxide Sterilizers in Health Care Facilities [DHHS (NIOSH) 

Publication Number 89–115]. 
10 EtO

Employers

The following list of recommendations presents engineering controls and safety procedures for preventing fires and explosions at 

EtO sterilization and repackaging facilities. 

This list was identified by the EOSA Safety 

Committee and was revised by NIOSH. The 

list is not all-inclusive and may not be equally applicable to all sterilization and repackaging facilities. Employers should identify 

and use the controls and procedures that 

are relevant to their facilities. They should 

also be aware that no fail-safe control technique exists to guarantee that fires and explosions will not occur at their facilities.

1.	 Analyze and develop written procedures

• Conduct a process hazard analysis 

that emphasizes safety procedures for 

the entire sterilization system (chambers, aeration rooms, EtO delivery 

and evacuation, and emission control). This analysis will minimize the 

possibility that flammable concentrations of EtO will enter the oxidizer 

(see Appendix E). 

• Establish written procedures to cover 

all steps of EtO sterilization. 

• Evaluate the advantages and disadvantages of each control technology. 

2.	 Prevent overfeeding of the OECD

• Prevent overfeeding of the OECD by 

following the steps listed on page 8. 

• Install an OECD bypass for emergency use if allowed by State or local 

environmental regulations. 

3.	 Store and handle EtO properly

• Store EtO in tightly closed cylinders or 

tanks in a cool, shaded, well-­ventilated, 

explosion-proof area. Store cylinders or 

tanks away from heat, sparks, flames, 

strong oxidizers, alkalines, acids, and 

acetylide-forming metals such as copper, silver, mercury, and their alloys. 

Make sure that the storage 

room is explosion-proof according to the definition of the National Fire Protection Association (NFPA 560) [NFPA 1995]. 

Make sure that the storage 

room meets National Electrical 

Code requirements to prevent 

ignition and explosion. 

• Do not permit smoking, use of electrical devices, or open flames where 

EtO is handled, used, or stored. 

• Use nonsparking tools when opening 

or closing metal containers of EtO or 

whenever EtO might be present. 

• Keep containers individually bonded 

and grounded to the earth when liquid EtO is poured or transferred. 

4.	 Deal with leaks and spills

• Make sure that all workers leave a 

leak or spill area immediately. 

• If a catastrophic or large release of 

EtO occurs, do not permit workers to 

enter the area. Evacuate the building 

and notify the fire department immediately. Note: A large release of EtO is 

any release other than the type of small 

leak that could occur (for example) from 

a loose connection or valve. A catastrophic release is one that would occur if (for 

example) a forklift pierced a 400-lb EtO 

cylinder. 

• If a small leak occurs, do not permit 

any worker to enter the area until he 

—

—
EtO 11

**For detailed information about respiratory protection for workers exposed to EtO, see NIOSH Current Intelligence Bulletin 52: Ethylene Oxide Sterilizers in Health Care Facilities [DHHS (NIOSH) 

Publication Number 89–115]. 

or she has put on PPE, including an 

SCBA that has a full facepiece and 

is operated in a pressure-demand or 

other positive-pressure mode. 

• Do not permit workers to use SCBAs 

unless they have received proper 

training and are current on their safe 

use. 

5.	 Implement engineering controls

• Provide an abort cycle (with diluent) 

in the sterilizer control system. 

• Establish and follow a cycle approval 

process for all test cycles. 

• Provide limited access to override 

controls. 

• Eliminate back vents through appropriate equipment and cycle design. 

• Interlock the sterilizer door to prevent 

opening before the cycle is complete. 

• Interlock the gas inlet (shut-off) valve. 

• Make sure that regular preventive 

maintenance is performed. 

• Install a flow-limiting device on the 

vacuum pump inlet (controls or orifice). 

• Install valve position sensors on critical valves. 

• Install real-time area monitors that 

will alert workers to unsafe EtO 

concentrations. 

• Use redundancies or other safeguards on all critical valves. For 

example, install redundant control 

valves on the EtO line (use doubleblock valves with leak check). 

• Use damage control devices to limit 

explosion damage: 

install flow-control check valves 

in the EtO supply lines. 

install flame arresters and check 

valves in OECD feed lines from 

the vacuum pumps to eliminate 

flame propagation back into 

and throughout the system. 

• Make sure that all other equipment 

has proper safety controls. 

6.	 Install emergency equipment

• Equip the facility with a type 2, 3 carbon dioxide or dry chemical fire extinguisher. Train workers annually in 

their safe use. 

• Provide emergency eye-wash facilities. 

7.	 Provide respiratory protection and

PPE

• Provide workers with appropriate respiratory protection** for use during 

emergencies, maintenance work, vessel cleaning, and whenever engineering controls cannot be implemented. 

At a minimum, such protection must 

comply with OSHA requirements in 

29 CFR 1910.1047 and 1910.134. 

• Provide workers with chemicalresistant gloves, eye-splash protection, and liquid-tight protective clothing 

whenever liquid EtO might be present. 

At a minimum, such equipment must 

—

—
12 EtO

comply with OSHA requirements [29 

CFR 1910.1047]. 

8.	 Provide training

• Fully train all operations, maintenance, and engineering workers in 

the dangers of EtO-rich evacuations 

to an OECD. 

• Train all workers who will be responding to emergencies (including managers and supervisors) in the proper use 

of safety equipment and in emergency procedures for all EtO plant operations. Training should include 

instruction about spill and control procedures, 

information about the OSHA hazard communication standard [29 

CFR 1910.1200], 

training in the use of SCBAs 

and other PPE, and 

instructions in following OSHA 

requirements for preventing EtO 

exposure and for decontamination [29 CFR 1910.1047]. 

9.	 Prepare workers for rescue

• Make sure that workers know emergency rescue steps and where emergency equipment is located. Be sure 

that they comply with OSHA regulations regarding emergency response, 

PPE, and rescue in confined spaces [29 CFR 1910.38, 1910.120(q), 

1910.132138, and 1910.146]. Note:

29 CFR 1910.119 applies if a facility possesses 5,000 lb EtO or more at any given 

time. 

—

—

—

—

• Do not permit workers to participate in emergency response without SCBAs and proper training. 

If workers do not have SCBAs and 

proper training, let the local fire department conduct the rescue. 

• Design, develop, and practice emergency evacuation and rescue procedures. 

Manufacturers

Manufacturers should develop reliable, 

high-speed EtO monitoring sensors to be 

installed and integrated into the EtO sterilization process.

ACKNOWLEDGMENTS

The principal contributors to this Alert were 

John Palassis (NIOSH, Education and Information Division), Craig Matthiessen 

(EPA, Chemical Emergency Preparedness 

and Prevention Office), Armando Santiago 

(U.S. Chemical Safety and Hazard Investigation Board), Joseph Hadley (EOSA), 

Anthony D. LaMontagne, Sc.D. (the University of Melbourne, School of Population 

Health), and Arthur Harris (Chicago Sterilization Services). NIOSH staff who provided critical review of this document were 

Stephen Berardinelli, Ph.D.; Robert Chaiken, Ph.D.; Jerome Flesch; Charles Lazzara, Ph.D.; Michael Sapko; Marie Haring Sweeney, Ph.D.; David Votaw; Isaac 

Zlochower, Ph.D.; and Ralph Zumwalde. 

Editorial services were provided by Anne 

Hamilton, Susan Feldmann, and Jane 

Weber. Susan Kaelin and Vanessa Becks 

provided layout and design.

We also acknowledge the contributions 

of the following reviewers: Janice Bradley 

(Industrial Safety Equipment Association), 

Marthe Kent (OSHA), Richard J. Kruse 
EtO 13

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing 

Office, Office of the Federal Register.

Clayton GD, Clayton FE, eds. [1993]. Pattys industrial hygiene and toxicology. Vol. 

II, Part A. 4th ed. New York: John Wiley 

and Sons, Inc., pp. 338–348.

EPA [1997a]. Chemical accident investigation report. Boston, MA: U.S. Environmental Protection Agency, Chemical Emergency Preparedness and Prevention Office.

EPA [1997b]. Chemical accident investigation report. Philadelphia, PA: U.S. Environmental Protection Agency, Chemical 

Emergency Preparedness and Prevention 

Office.

EPA [1998]. Chemical accident investigation report. Chicago, IL: U.S. Environmental Protection Agency, Chemical Emergency Preparedness and Prevention Office.

62 Fed. Reg. 58839 [1997]. U.S. Environmental Protection Agency: National Advisory Committee for Acute Exposure Guideline 

Levels for Hazardous Substances; notice.

IARC [1994]. Some industrial compounds: 

ethylene oxide. IARC Monograph 60. Lyon, 

France: World Health Organization, International Agency for Research on Cancer, 

pp.73–159.

Kroschwitz JI, Howe-Grant M, eds. [1994]. 

Ethylene oxide. In: Kirk-Othmer encyclopedia of chemical technology. Vol.9. 4th 

ed. New York: John Wiley and Sons, Inc., 

pp. 915–959.

LaMontagne AD, Steenland NK, Kelsey 

KT [2007]. Ethylene oxide. In: Rom WN, 

Markowitz SB, eds. Environmental and 

(Advanced Air Technologies, Inc.), Joseph 

Rose (Taunton, MA, Fire Department), 

Michael Sprinker (International Chemical 

Workers Union and Council/United Food 

and Commercial Workers), and Katherine 

Svedman (American Hospital Association).

Please direct any comments, questions, 

or requests for additional information to 

the following:

Dr. Paul A. Schulte

Director, Education and Information Division

National Institute for Occupational

 Safety and Health

4676 Columbia Parkway

Cincinnati, OH 45226–1998 

Telephone: 513–533–8302;

or call 1–800–356–4674. 

We greatly appreciate your assistance in 

protecting the health of U.S. workers.

John Howard, M.D.

Director, National Institute for 

 Occupational Safety and Health 

Centers for Disease Control and

 Prevention

REFERENCES CITED

ACGIH [1999]. 1999 TLVs® and BEIs®. 

Cincinnati, OH: American Conference of 

Governmental Industrial Hygienists.

AIHA [1998]. The AIHA 1998 emergency 

response planning guidelines and workplace environmental exposure level guides 

handbook. Fairfax, VA: American Industrial Hygiene Association, AIHA Press.
14 EtO

occupational medicine. 4th ed.Philadelphia, 

PA: Lippincott, Williams, & Wilkins, pp. 

1144–1157.

LaMontagne AD, Kelsey KT [1998]. 

OSHA’s renewed mandate for regulatory 

flexibility review: in support of the 1984 

ethylene oxide standard. Am J Ind Med 

34(2):95–104.

Lewis JL [1996]. Sax’s dangerous properties of industrial materials. 9th ed. New 

York: Van Nostrand Reinhold Publishers, 

pp. 1554–1555.

NFPA [1995]. NFPA 560: Standard for the 

storage, handling, and use of ethylene oxide for sterilization and fumigation. Quincy, 

MA: National Fire Protection Association.

NIOSH [1983]. NIOSH testimony on the 

Occupational Safety and Health Administration’s proposed rule on occupational 

exposure to ethylene oxide, July 20, 1983. 

NIOSH policy statements. Cincinnati, OH: 

U.S. Department of Health and Human 

Services, Public Health Service, Centers 

for Disease Control, National Institute for 

Occupational Safety and Health, NTIS No. 

PB–84–182–039.

NIOSH [1994]. Documentation for IDLH 

concentrations (IDLHs). Washington, DC: 

U.S. Department of Health and Human 

Services, Public Health Service, Centers 

for Disease Control and Prevention, National Institute for Occupational Safety and 

Health, NTIS No. PB–94–195047.

NIOSH [1997]. NIOSH pocket guide to 

chemical hazards. Washington, DC: U.S. 

Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 

DHHS (NIOSH) Publication No.97–140.

BIBLIOGRAPHY

40 CFR 68, Risk management program 

standard.

40 CFR 355, Emergency release notification.

40 CFR 370, Hazardous chemical reporting.

40 CFR 372, Toxic chemical release 

inventory.

Clean Air Act. 42 USC 7401 et seq. (1970).

Comprehensive Environmental Response, 

Compensation, and Liability Act. 42 USC 

9601 et seq. (1980).

Emergency Planning and Community 

Right-to-Know Act. 42 USC 1101 et seq. 

(1986).

EOSA Safety Committee [1998]. EOSA 

safety considerations for ethylene oxide 

sterilization. Washington, DC: The Ethylene Oxide Sterilization Association.

Kletz TA [1993]. The unforseen side effects of improving the environment. Process Safety Progress 12(3):147–150.

LaMontagne AD, Kelsey, KT [1997]. Evaluating OSHA’s ethylene oxide standard: 

employer exposure monitoring activities in 

Massachusetts hospitals from 1985 through 

1993. Am J Public Health 87(7):1119–1125.

National Fire Protection Association (NFPA) 

68 Standard on explosion protection by 

deflagration venting.

NFPA 69 Standard for explosion prevention 

systems.

NFPA 86 Standard for ovens and furnaces.
EtO 15

NFPA 560 Standard for storage, handling, 

and use of ethylene oxide for sterilizations 

and fumigation.

NIOSH [1989a]. Control technology for ethylene oxide sterilization in hospitals. Cincinnati, OH: U.S. Department of Health and 

Human Services, Public Health Servvice, 

Centers for Disease Control, National Institute for Occupational Safety and Health, 

DHHS (NIOSH) Publication No. 89–120.

NIOSH [1989b]. Current Intelligence Bulletin 52: ethylene oxide sterilizers in health 

care facilities: engineering controls and 

work practices. Cincinnati, OH: U.S. Department of Health and Human Services, 

Public Health Service, Centers for Disease 

Control, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication No. 89–115.

Occupational Health Service, Massachusetts Respiratory Hospital [1990]. Ethylene oxide health and fact sheet number 

9: precautions for changers and personnel 

servicing EtO sterilizers. Braintree, MA: 

Massachusetts Respiratory Hospital, Occupational Health Service.

Regulations to the Clean Air Act. Title I, 

Part A, Section 112(r). Prevention of accidental releases.

SOURCES OF ADDITIONAL 

INFORMATION

Organizations

The Center for Chemical Process Safety 

 (CCPS) of the American Institute of 

 Chemical Engineers (AIChE)

3 Park Avenue, 19th Floor

New York, NY 10016

Telephone: 212–591–7237

The Ethylene Oxide Sterilization 

 Association, Inc. (EOSA)

Washington, DC

Telephone: 202–296–6300 

ISEA—The Safety Equipment Association

Arlington, VA

Telephone: 703–525–1695 

National Fire Protection Association 

 (NFPA)

1 Batterymarch Park

Quincy, MA, 02169 

Telephone: 617–770–3000

National Institute for Occupational Safety

 and Health (NIOSH)

Cincinnati, OH

Telephone: 1–800–CDC–INFO

(1–800–232–4636) 

U.S. Environmental Protection Agency (EPA)

Chemical Emergency Preparedness and 

 Prevention Office

Washington, DC

Telephone: 202–260–9781 

U.S. Chemical Safety and Hazard 

 Investigation Board

Washington, DC

Telephone: 202–261–7600 

Internet Resources

AIChe–CCPS Web site: 

www.aiche.org/CCPS/

EOSA Web site: www.eosa.org
16 EtO

EPA Chemical Emergency Preparedness 

and Prevention Office Web site: www.

epa.gov/ceppo

ISEA Web site: www.safetycentral.org/isea

NIOSH Web site: www.cdc.gov/niosh

NFPA Web site: www.nfpa.org

OSHA Web site: www.osha.gov

OSHA Regulations for Ethylene Oxide 

(29 CFR 1910.1047) Web site: www.

osha-slc.gov/OshStd_data/1910_1047.

htm

Right-to-Know Web site: www.rtknet.org

U.S. Chemical Safety and Hazard Investigation Board Web site: 

www.chemsafety.gov or www.csb.gov
EtO 17

Abbreviations

ACGIH American Conference of Governmental Industrial Hygienists

AEGL acute exposure guideline level

AIHA American Industrial Hygiene Association

Btu British thermal unit

CFR Code of Federal Regulations

CPR cardiopulmonary resuscitation

EOSA The Ethylene Oxide Sterilization Association

EPA U.S. Environmental Protection Agency

ERPG emergency response planning guideline

EtO ethylene oxide

°F degrees Fahrenheit

Fed. Reg. Federal Register

ft foot (feet)

HAZOP hazardous operational study

hr hour(s)

IARC International Agency for Research on Cancer

IDLH immediately dangerous to life and health

L liter(s)

lb pound(s)

m meter(s)

mg milligram(s)

min minute(s)

mm Hg millimeters of mercury

NESHAP National Emission Standards for Hazardous Air Pollutants

NFPA National Fire Protection Association

APPENDIX A

ABBREVIATIONS AND GLOSSARY
18 EtO

NIOSH National Institute for Occupational Safety and Health

OECD oxidizing emission control device

OSHA Occupational Safety and Health Administration

PEL permissible exposure limit

PPE personal protective equipment

ppm parts per million

REL recommended exposure limit

SCBA self-contained breathing apparatus

scfm standard cubic feet per minute

sec second(s)

STEL short-term exposure limit

TLV threshold limit value

TWA time-weighted average

% percentage
EtO 19

Glossary

Algorithm: The “logic” programmed into 

a computer that controls the process on 

the basis of inputs from sensors, switches, 

or other devices. A typical algorithm may 

control how many pumps can be operating or when a valve is turned on or off or is 

repositioned.

Back vent: A large-diameter valve and 

blower at the back of the sterilizer. The 

vent creates a high-volume evacuation of 

the sterilizer when the sterilizer entrance 

door is opened to reduce operator EtO exposure during unloading. Most back vents 

pull in air at a rate equal to one sterilizer 

volume per minute. Most back vents are 

automatically triggered when an operator 

opens or attempts to open the sterilizer 

door, regardless of conditions within the 

chamber.

Cycle: Treatment of a product with EtO in 

a sterilizer designed to render the product free of all forms of viable microorganisms. EtO concentrations in the sterilizer range between 100 and 800 mg/L 

or between 5.5% and 44.4%. The cycle 

includes removing air from the sterilizer, 

conditioning with temperature and humidity (if used), injecting EtO, exposing the 

product to EtO, removing EtO, and flushing the sterilizer. A diluent gas (such as 

nitrogen) is generally injected and evacuated as part of air removal at the beginning of the cycle and during flushing after 

EtO exposure. These diluent injections 

and evacuations have become prominent 

safety additions for OECD operation because they decrease the flammability of 

the environment within the sterilizer. After completion of the cycle, the back vent 

is run before unloading. (Note: Cycle parameters vary widely among facilities. Most 

facilities operate several different cycles, depending on customer needs.)

Emission control device and OECD: A 

device designed to reduce the EtO content 

in the exhaust stream (source). Generally, 

OECD refers to an oxidizing emission control device (catalytic or thermal) (see also 

Appendix B).

Exhaust stream: The sum of all gases 

exiting from the facility (source) that is directed to the inlet of the emission control 

device or OECD.

Gas delivery system: The system that 

delivers EtO from its protective storage 

drum through automated valves into a vaporizer. The vaporizer converts the liquid 

EtO to gas as it is injected into the sterilizer. The correct amount of EtO injected 

may be determined by measuring the 

change in weight of the EtO tank, by measuring the change in pressure within the 

sterilizer, or both.

Interlock: A mechanical device or computer algorithm that ties one action into 

another action (response). An interlock 

may be as simple as a mechanical limit 

switch that is tied to a motor starter, or it 

may be a computer program that electrically or mechanically “locks out” a valve 

or motor until certain conditions have been 

met. Effective interlocks provide a safer, 

but not foolproof, method of assuring that 

an objective or procedure is met before an 

action is taken. A complete review of all 

normal and abnormal operating conditions 

(using a hazard analysis) is necessary 

when assessing an interlock’s effectiveness. Startup and testing of safety-related 

interlocks is important and requires extreme caution.
20 EtO

Lower flammability limit: The lowest 

concentration of a substance in air that will 

sustain combustion when elevated to its ignition temperature. The lower flammability 

limit for EtO is about 3% or 30,000 ppm at 

standard conditions. This limit can be lower 

under elevated temperature or pressure. 

Note that EtO is also flammable at 100%, 

indicating that oxygen is not required to 

have a flammable event.

Manual intervention: The ability of an 

operator to manually override the sterilizer 

controller by (1) accessing the sterilizer 

controller and manually initiating an action before completion of a cycle step or 

(2) opening the sterilizer door (and thus 

triggering the operation of a back vent) 

before completion of the cycle.

Operator: A person who is responsible to 

initiate, monitor, and control a cycle. The 

operator may manually intervene and may 

also load and unload product from the 

sterilizer.

Overfeeding: Introducing EtO to an emission control device or OECD at a rate 

greater than the manufacturers design 

limitation.

Sterilizer: A sealed chamber in which 

a product is subjected to a cycle that 

renders it free of all forms of viable microorganisms. A sterilizer generally consists 

of a chamber with one or more doors, a 

vacuum pump, a back vent valve with a 

blower, a heating system, a gas delivery 

system, a sterilizer controller, and various 

parameter gauges and instruments.

Sterilizer controller: A computer system 

that controls and monitors the cycle. The 

system controls (1) the appropriate valves, 

pumps, blowers, and heaters according 

to a planned sequence (algorithm) and 

(2) rates of pressure changes to achieve 

the desired environment within the sterilizer. The system monitors sterilizer pressure, sterilizer temperature, possibly EtO 

cylinder weight and EtO temperature, 

evacuation rates, and vacuum depths. 

Redundant sensors or methods contribute 

to increased reliability of operating parameters.

Vacuum pump: A device that withdraws 

gases from a sealed sterilizer. It generally consists of a liquid ring pump capable 

of pulling a vacuum in a sealed sterilizer. 

Vacuum pumps are rated in cubic feet 

per minute at the pump inlet. Most pumps 

have a rated capacity between 0.1 and 

0.25 sterilizer volumes per minute.
EtO 21

The following describes the different technologies used to treat EtO emissions and 

the common ranges of operation for these 

control devices.

Wet Scrubbers

Wet scrubbers have been installed on many 

sterilizer primary vacuum pump discharges. 

A wet scrubber absorbs EtO into a recirculating water-acid solution, converting the 

EtO to ethylene glycol. It operates effectively 

with higher concentrations of EtO in air or nitrogen. The most common size for sterilizer 

primary discharges (vacuum pumps) is between 200 and 400 standard cubic feet per 

minute (scfm) (600 to 600,000 ppm EtO). 

Wet scrubbers can have capacities of up to 

20,000 scfm, though these are generally for 

lower EtO concentrations (50 to 8,000 ppm). 

Wet scrubbers operate at ambient temperature. Overfeeding generally results in recovery efficiencies below the required 99% 

NESHAP†† but is generally not detrimental 

to the system.

Catalytic OECDs

Catalytic OECDs operate by oxidizing or 

burning EtO to form the end products of 

carbon dioxide, water, and heat. The inlet 

gas is preheated to the needed activation 

temperature of the catalyst, about 300 °F. 

The preheating is generally accomplished 

with a direct-fired burner, indirect-fired 

burner, steam coil, or electric element. 

The oxidation causes the temperature in 

the catalyst to rise. EtO has a fuel value of about 12,000 British thermal units 

(Btu)/lb. Catalytic OECDs can have up to 

30,000 scfm rated flow capacity. The most 

common sizes currently in use fall between 

6,000 and 14,000 scfm. The maximum inlet concentration of EtO should be limited 

to 3,000 to 6,000 ppm or to the manufacturers specification.

Overfeeding produces even higher temperatures in the catalyst and gas stream, 

potentially damaging the catalyst or shortening its useful life. If the inlet gas has an 

EtO concentration greater than the explosive limit, an explosion can result. If the 

inlet gas has a concentration above the 

explosive limit, an explosion can result either from the high temperature of the catalyst or from the direct-fire burner. Exhaust 

gases containing EtO should never be 

passed through a catalytic OECD under 

cold conditions, because the catalyst will 

adsorb and destroy the EtO. The exothermic EtO destruction will increase the temperature of the system and an explosion 

may result.

††National Emission Standards for Hazardous Air 

Pollutants 

APPENDIX B

TYPES OF EMISSION CONTROL DEVICES
22 EtO

Thermal OECDs

Thermal OECDs operate with the same 

end result as the catalytic OECDs. They 

operate without a catalyst at a higher 

temperature than catalytic OECDs and 

generally have a higher EtO concentration limit. Inlet concentration limits vary 

by manufacturer. Recuperative thermal OECDs and regenerative thermal 

OECDs provide heat recovery for facility uses. Recuperative and regenerative 

thermal OECDs have flow rates of up to 

20,000 and 100,000 scfm, respectively. Thermal OECDs provide an ignition 

source for vapor containing concentrations greater than the lower flammability 

limit of EtO.

Dry-Bed Reactors

Dry-bed reactors eliminate EtO by causing 

it to bind permanently to the reactant. They 

operate at ambient temperatures and do not 

require preheating of the exhaust gas. They 

are most commonly used for removing low 

concentrations of EtO from high-volume exhaust streams. Occasionally, they are used 

for emergency containment of a catastrophic event (emergency responses) where they 

handle a short burst with a high concentration of EtO. Dry-bed systems can be furnished for any flow capacity. Typical operating concentrations vary from 5 to 300 ppm 

with spikes up to 10,000 ppm. Overfeeding 

these reactors increases the temperature 

and may cause a fire or explosion.
EtO 23

The EOSA Safety Committee has identified the following preventive measures and 

safety considerations for the sterilization 

process. The list was revised by NIOSH.

A. Interlock the sterilizer door and gas 

valve.

Mechanically or electrically lock the gas 

valve out of operation if the sterilizer door 

is opened. This measure prevents an EtOrich environment from entering a sterilizer 

while a cycle is not running.

B. Use interlocks to prevent the opening of a sterilizer door before a cycle 

is complete.

Be sure interlocks, safeguards, or other 

preventive measures are in place to prevent the opening of a sterilizer door during 

a sterilization cycle. Since several sterilizer installations have the back vent interlocked with the sterilizer door for worker 

safety considerations, the door must remain shut when EtO-rich concentrations 

are present in the chamber.

C. Wash or vent periodically while the 

sterilizer is idle with the product.

If a sterilized product sits idle in a sterilizer 

or aeration room, wash or vent it periodically to prevent buildup of EtO.

D. Monitor the EtO concentration in the 

sterilizer before back vents are activated.

Use direct analysis of the sterilizer gas 

content in conjunction with lockout of the 

back vent to prevent exhausting high concentrations through the back vent. Direct 

analysis and the air-flow rate of the back 

vent and vacuum pump provide real-time 

information that can be used to limit EtO 

flow to the OECD below design limits. Selection of EtO process monitors should 

ensure that the safety, accuracy, reliability, 

calibration, and response time of the instrument are suitable for indicating whether EtO concentrations are below 25% of 

the EtO LEL before venting sterilizer gas 

to oxidizing emission control devices, in 

accordance with NFPA 560 chapters 8.2.1 

and 11.5.3 (2002 edition). Selection, engineering, installation, testing, turnover, and 

maintenance and repair of process monitoring instrumentation should be done by 

a person who is qualified in chemical engineering, process safety, and/or fire prevention, to ensure that monitors are properly 

integrated into EtO process safety control 

systems under normal or abnormal conditions, emergencies, and maintenance operations.

APPENDIX C

PREVENTIVE MEASURES AND SAFETY CONSIDERATIONS
24 EtO

E. Use redundant control valves (double-block, with leak check) on the 

EtO line.

Use redundant control valves on the EtO 

line to prevent overfeeding if one valve 

fails or develops a leak.

F. Install valve position sensors on 

critical valves.

Valve position sensors provide continuous feedback of a valve’s open or closed 

status. Consider the types of position indicators installed and whether they can be 

used as a mechanical, electrical, or software interlock with the OECD.

G. Install a flow-limiting device on the 

vacuum pump inlet (controls or orifice).

Install software or mechanical flow-limiting 

devices on vacuum pump inlets to prevent 

overfeeding of the OECDs.

H. In an emergency, disconnect the 

back vents and bypass the OECD (if 

legally allowed).

In an emergency, removal of the back 

vents from the OECD can eliminate this 

stream as a source of overfeeding. However, this measure may be illegal because 

of the environmental impact.

I. Use redundancies or other safeguards for all critical valves.

Redundant valves, sensors, or systems 

prevent overfeeding if one valve fails or 

develops a leak.

J. Vent confined spaces to the outside 

atmosphere after a power loss.

Since high-EtO concentrations can accumulate in a confined space after a power 

loss, vent the confined space to the outside 

atmosphere to prevent buildup of EtO concentrations and overfeeding of the OECD.

K. Do not purge EtO lines to an OECD.

Avoid purging EtO drums or venting EtO 

storage systems to an OECD, since an incorrect valve lineup or a serious leak in the 

storage area is likely to lead to overfeeding. Do not install a vent in the gas storage 

or charging area that feeds the OECD. Instead, consider using spring-closed valves.

L. Assure proper controls of other 

equipment.

Systematically evaluate the integration of 

the OECD into the facility under all operating conditions during a process hazard 

analysis. The OECD relies on the correct 

operation of other sterilization equipment 

that may fail periodically. Failure of any 

single piece of equipment should not result in the unsafe operation of the OECD.

M. Provide limited access to override 

controls.

Avoid overriding or bypassing safeguards 

or interlocks. Overrides of safety interlocks should not be allowed without proper 

review of their consequences by qualified 

personnel.

N. Provide an abort cycle (with diluent) 

in the sterilizer control system.

If the sterilization cycle is aborted after EtO 

gas has been injected into the chamber, 
EtO 25

the sterilizer controller should automatically run an abort cycle. The abort cycle 

typically consists of evacuations and diluent washes to bring the gas content of 

the chamber below the lower flammability 

limit.

O. Fully train all operations, maintenance, and engineering personnel 

on the dangers of EtO-rich evacuations to an OECD.

Proper safety training is essential for all 

workers involved in operating the sterilization equipment.

P. Follow a cycle approval process for 

all test cycles.

When testing is performed using sterilization equipment or the OECD, an administrative approval process is recommended 

to ensure safe operation. During testing, 

the design limits of systems are often approached and safeguards are bypassed.

Q. Perform regular preventive maintenance.

A sound preventive maintenance program 

reduces the number of failures of critical 

equipment and therefore reduces the risk 

associated with operating the sterilization 

equipment.

R. Eliminate back vents through appropriate equipment and cycle design.

Through appropriate equipment and cycle 

design, back vents may be eliminated as 

an input stream to the OECD. Worker safety issues should be fully assessed when 

this preventive measure is implemented to 

ensure a safe working environment.

S. Obtain management and administrative approvals.

Proper management and administrative 

approvals are also needed before any 

changes are made to the process or safety 

interlocks. This approval process needs to 

include proper review of the consequences associated with any changes.

T. Use damage control devices.

Incorporate safety engineering devices 

such as flame or detonation arresters and 

explosion vents to minimize equipment 

and facility damage. Install the flame arresters or detonation arresters and check 

the valves in the EtO supply lines. Also, 

install flame arresters and check valves 

in the OECD feed lines from the vacuum 

pumps to eliminate flame propagation 

back into and throughout the system.
26 EtO

The EOSA Safety Committee has identified the safety concerns and good engineering design for the catalytic and 

thermal emission control devices listed 

in this appendix. Most of the recent explosion incidents in the EtO sterilization 

industry are associated with the use of 

OECDs, and nearly all are associated 

with opening a back vent. The following 

section provides information to consider 

in the design and integration of an OECD 

with a sterilizer. This section does not replace a typical process hazard analysis 

that should be conducted on the entire 

sterilization process before installing an 

OECD. Nor should this section replace 

the normal good engineering guidelines 

that should be used in the design of the 

equipment. The purpose of this section is 

to provide each facility with ideas for the 

process design and operation.

Good Engineering Design

Good engineering practice requires that 

the designer use proper engineering 

guidelines and codes in the design and 

operation of the sterilizer and associated 

equipment (including the OECD equipment). This includes adherence to proper 

electrical and mechanical codes throughout the sterilization system. Furthermore, 

the designer needs to ensure that the 

equipment can safely accommodate maximum operating conditions (including EtO 

feed rates, temperature, pressure, etc.). 

Any startup, shutdown, or abnormal operating condition must be reviewed before 

the system is installed.

The designer should look at EtO inventories at every step of the process and 

determine the minimum and maximum 

rates (including EtO rate), minimum and 

maximum temperatures, minimum and 

maximum pressures, and other operating conditions. Good engineering practice 

should also include the review of all failure modes (such as a sticking EtO feed 

valve or smart valve failure) to see if the 

equipment selected can safely handle the 

resulting flow conditions. If more than one 

sterilizer is used, this review must include 

all possibilities of “simultaneous” sources 

to ensure that the entire system is within 

the design limits. For safety concerns, the 

designer should look at atmospheric venting for emergency conditions (such as 

vessel over pressure). Good engineering 

practice should include redundant instrumentation of critical operating parameters 

(such as flow rates, EtO weights, etc.). In 

addition, position indicator sensors should 

be included on any valves that are critical 

to the process and safe operation of the 

system. The control algorithm should include checking the alarm and sensor operation and its integrity during both normal 

and abnormal operating conditions.

APPENDIX D

SAFETY CONSIDERATIONS FOR 

THE INTEGRATION OF OECDs
EtO 27

Other good engineering practices include 

installing manual valves for equipment 

isolation. A dual path may be desirable 

because it allows connection of a backup 

pump or sensor until a broken item can be 

repaired. Safety must be considered in the 

design of engineering equipment.

Integration of Emission Control 

Device with the Sterilization 

Process

If an OECD is used, it needs to be properly 

integrated with the sterilization process, 

possibly with a scrubber system. The design and operation of both the OECD and 

the sterilization system must be considered, as the two processes are connected. 

All operating conditions of the sterilization 

process, including those during startup, 

shutdown, and test phases, must be analyzed for potential failure points. Abnormal 

process conditions pose the most serious 

safety challenges.

Only after the OECD limitations have been 

established can the entire operating and 

control system be devised and reviewed 

to ensure that these limitations cannot be 

exceeded under any circumstance. EtO 

concentrations in the explosive range must 

never be allowed to enter the device that 

can create a temperature rise sufficient to 

ignite the gas stream. The design of the 

emission control system must take into account the potential for release of EtO from 

all EtO sources in the facility. The design 

may vary substantially, depending on the 

limitations of the control device selected. 

Since the gas that is initially discharged 

from the sterilizer by the vacuum pump is 

always concentrated, dilution is necessary.

Safety Concerns Associated with 

Catalytic or Thermal OECDs

Most emission control devices have two 

limitations: (1) the maximum volumetric 

flow capacity (commonly expressed in 

cubic feet per minute), and (2) the maximum quantity of EtO it can process (commonly expressed in pounds per minute). 

However, if the system has a variable flow 

capacity, it will most likely have a variable 

EtO capacity, which will be expressed as a 

concentration limit—commonly, ppm.

The most immediate safety concern associated with catalytic or thermal OECDs 

is to prevent overfeeding the system. The 

most severe result of overfeeding occurs 

when a quantity of EtO is released that is 

greater than the lower flammability limit. In 

this case, the exhaust stream can be ignited by the burner flame (if the OECD has 

a burner) or by an increase in the catalyst 

temperature. This would cause an explosion throughout the OECD, the exhaust 

ducting, and connected sterilizers.

The following four conditions might overfeed an OECD and cause an explosion. 

Included are references to preventive 

measures from Appendix C.

1. Overfeeding the OECD from back

vents containing high concentrations of EtO

Nearly all of the known explosions associated with OECDs occurred when a 

sterilizer back vent was opened while a 

high concentration of EtO was in a sterilizer. This condition generally involves a 

worker’s (a) opening a sterilizer door that 

triggers back vent operation, (b) using a 

manual switch to trigger back vent operation, or (c) triggering back vent operation 
28 EtO

through a sterilizer controller. The high 

flow rate of the back vent exhausts could 

send EtO at a rate that exceeds the safe 

design limitation of the OECD. An explosion could result.

Each sterilization facility should be examined to determine every condition in which 

a back vent could be opened while a sterilizer contains an EtO-rich mixture. Appropriate measures should then be taken to 

prevent opening of the back vent when 

these conditions exist. Employee error has 

been a significant cause of overfeeding 

events. Errors have resulted from allowable procedure changes, test conditions, 

use of improper procedures, and inadequate process control systems. Since EtO 

operators can make mistakes, the process 

hazard analysis must address possible human errors and identify safeguards to protect against and prevent them. Bypassing 

interlocks should never be allowed without 

specific permission based on extensive 

evaluation and knowledge of the possible 

consequences by designated, qualified 

personnel.

Sterilization requires an EtO-rich environment during part of the overall cycle. The 

EtO-rich gas is removed from the sterilizer 

by the vacuum pump (see item 2 on page 

28). A normal cycle includes post-vacuum flushing or purges that successively 

dilute the EtO concentration in the sterilizer before opening the back vent. In all 

cases, the normal number of post-vacuum 

purges should be completed before initiating the back vent. If operations do not go 

as planned, back vents may be activated 

during the following unplanned situations:

• Sterilizer back vent turned on with 

EtO-rich gas present—This situation 

may be caused by the following:

► Bypassing safety interlocks—Even in 

the best engineered systems, bypassing of safety interlocks by operators or maintenance personnel 

can result in overfeeding an OECD 

through the back vent. Aborting 

cycles after EtO gas is added without adequate diluent washes is an 

example of improper bypassing of 

safety interlocks (review preventive 

measures A, B, C, D, H, and N in 

Appendix C). 

► EtO valve leak—This condition involves a leak of EtO into the sterilizer anytime before a back vent 

operation. While a pressure rise 

would generally be observed during the sterilization control portion 

of a cycle, a person could misdiagnose the cause of the pressure 

rise. When a cycle is not running, a 

leak could also fill a sterilizer before 

a door is opened, triggering back 

vent operation (review preventive 

measures A, B, C, D, E, F, H, and 

Q in Appendix C). 

► Product degasses too long in sterilizer 

after cycle completion—Significant 

degassing can occur as a load sits 

in a nonvented sterilizer, resulting 

in an EtO-rich environment (review 

preventive measures C, D, H, and J 

in Appendix C). 

► Computer system/controller failure—

Computer systems or controllers 

that directly interface with the sterilization process or OECD control 

can fail from power bumps, age, 

software bugs, etc. Since these 

systems are critical to interlock 
EtO 29

mechanical equipment properly, 

their failure can result in an EtOrich environment in a sterilizer (review preventive measures A, B, D, 

H, J, and Q in Appendix C). 

► Instrumentation failure—The sterilizer controller relies on signals from 

sensors and transmitters to control 

and monitor the cycle, and these 

can fail. In addition, lower flammability limit sensors are considered 

unreliable for use in EtO environments and should not be relied on 

for quantitative decisions in controllers associated with OECDs (review preventive measures H and Q 

in Appendix C). 

• Inadequate washing before opening 

the door—Cycle design that does not 

provide for a sufficient number of diluent 

washes after EtO exposure generally results in an EtO-rich environment before 

back vent operation (review preventive 

measures D and H in Appendix C). 

• Incorrect cycle used for product—

Because of variable absorption and 

desorption rates by different products, 

a cycle that does not finish with an EtOrich environment for one product may 

finish with an EtO-rich environment for 

other products (review preventive measures D, H, O, and P in Appendix C). 

• Slow response time—Some lower 

flammability limit and flow sensors 

could have slow response times that 

would not properly identify an EtO-rich 

stream going to the OECD (review preventive measures D, H, I, and R in Appendix C). 

• Test cycles—Test cycles often explore 

process capability limits, and unexpected EtO-rich environments can result 

(review preventives measures A, B, C, 

D, H, O, and P in Appendix C). 

2. Overfeeding from vacuum pumps

Unless an OECD is sized to accept the 

peak flow of every system exhausting to 

it, a control algorithm will be necessary to 

sequence (queue) the number of vacuum 

pumps evacuating to the OECD. The algorithm may have to monitor what point in 

the cycle every sterilizer is operating. The 

control can be very complex and must be 

thoroughly evaluated. OECD manufacturers rely on the facility personnel to control the maximum amount of EtO flow to 

OECD. The following are ways design limits can be exceeded:

• Too many vacuum pumps operating (design and control issue)—An 

expanding facility can exceed design 

limits by (1) adding sterilizers, aeration 

rooms, or an EtO-rich cycle to a sterilizer not previously considered in the 

design of the queue controller, or (2) 

incorrectly computing EtO concentrations being evacuated (review preventive measures G, H, I, L, and O in Appendix C). 

• Misdirecting discharges—­Directing an 

EtO-rich exhaust stream into a duct 

system faster than the duct can move 

it to the OECD can deliver EtO-rich 

gas to another idled sterilizer or aeration room. This situation creates a 

“temporary inventory” that is later sent 

unknowingly to the OECD (review preventive measures D, G, H, I, J, and L in 

Appendix C). 
30 EtO

• Failure to interlock or control incoming flows—Proper queue control 

of all flows must be considered to prevent overfeeding the OECD. Inaccuracies or failures in the queue controller 

could allow evacuations at a flow rate 

exceeding the limits of the OECD. Although OECD manufacturers generally 

have safety cut-off systems that react 

to some overfeeding conditions, the reaction is generally too late to prevent 

an explosion if the exhaust stream is 

above the lower flammability limit (review preventive measures G and I in 

Appendix C). 

• Failure or malfunction of the EtO 

feed valves—Failure of an EtO feed 

valve can result in an unexpected EtOrich environment in a sterilizer. When 

the vacuum pump is activated, it delivers more EtO than planned (review 

preventive measures E, F, G, I, and Q 

in Appendix C). 

• Bypassing safety interlocks—Even 

on the best-engineered systems, bypassing safety interlocks by operations, 

maintenance, or engineering personnel can result in a back overfeeding of 

the OECD by the back vent. Aborting 

cycles after EtO gassing without adequate diluent washes is an example of 

improper bypassing of safety interlocks 

(review preventive measures A, B, C, 

D, H, M, N, and O in Appendix C). 

3. Overfeeding from lack of adequate

dilution air

• Loss of the aeration exhaust or dilution source—Some OECD installations rely on the aeration room exhaust 

to dilute the high concentrations from 

EtO-rich sources to a safe concentration (review preventive measures I and 

Q in Appendix C). 

• Loss of make-up dilution—OECDs 

generally have one or more fans, various valves, one or more filters, a diffuser, and a catalyst bed. The failure 

or plugging of any of these items decreases the flow of air. Discharging an 

otherwise acceptable EtO-rich stream 

may cause overfeeding because of 

insufficient dilution (review preventive 

measures I and Q in Appendix C). 

4. Overfeeding from other sources

• Spills or drum leaks near vents to 

OECD—Spills or drum leaks near any 

vent flowing to an OECD can result in 

an unplanned EtO-rich flow delivered 

to an OECD. Spills most generally occur from a leaky valve or damage to an 

EtO line (review preventive measures 

E, K, O, and Q in Appendix C). 

• Lack of interlock between EtO valve 

and sterilizer—Most chamber installations do not have interlocks preventing 

the opening of a sterilizer door when 

the EtO valve is open. If the back vent 

is interlocked to trigger when the chamber door is opened, an EtO-rich mixture 

can be delivered to an oxidizer (review 

preventive measures A, B, D, H, O, and 

M in Appendix C). 

• Failure or malfunction of the air 

in-bleed valve—Failure of the air 

in-bleed valve can cause a nonflammable cycle to change to an EtO-rich 

flammable cycle that might exceed 

an OECD’s safe operating conditions 
EtO 31

(­review preventive measures D, F, and 

Q in Appendix C). 

• Sticking valves that result in misdirected flow—A multiport control valve 

designed to send exhaust either to an 

OECD or to the atmosphere can fail, allowing the operator to deliver EtO-rich 

gas to the OECD rather than to the atmosphere (review preventive measures 

F and Q in Appendix C). 

• Purging EtO cylinders with EtO delivery valves in wrong position—If an 

EtO delivery system is piped to allow 

purging of EtO cylinders to an OECD, an 

operator could empty an entire cylinder 

into the OECD line when valves are left 

in the wrong position (review preventive 

measures G, K, L, and O in Appendix C). 

• Improper operation of upstream 

scrubber—If an OECD relies on an 

upstream scrubber to reduce EtO 

concentrations, malfunction of the upstream system can overfeed the OECD. 

A scrubber can be considered a safeguard ONLY when operating properly 

(review preventive measures I, L, and 

Q in Appendix C). 

• Sterilizer control systems inadequate—Older sterilizer controllers 

may not support the safe operation of 

an OECD. Systems requiring periodic 

manual intervention are of particular 

concern (review preventive measure L 

in Appendix C). 

• Lack of cabinet locks—Many older 

sterilizer control systems allow easy 

access to the manual sterilizer switches. If manual intervention is allowed, 

there is high danger that a person will 

trigger a wrong switch and send an 

EtO-rich flow to an OECD (review preventive measures G, L, M, and O in 

Appendix C). 
32 EtO

Background and Regulatory 

Requirements

A process hazard analysis is an effective 

tool that provides a systematic analysis 

of hazards associated with the sterilization process and the integration of environmental controls with this process. The 

chemical industry has been using process 

hazard analyses successfully for the past 

several years to identify and correct hazards associated with their processes. The 

sterilization industry should also use a 

process hazard analysis as a risk assessment tool to identify and correct hazards 

associated with EtO and their equipment.

Recent regulations from OSHA and EPA 

may require the industry to conduct such 

process hazard analyses on a regular basis. In 1992, OSHA promulgated the process safety management regulation that 

requires companies to establish a process safety management system for any 

process that contains more than 5,000 lb 

of EtO. The process safety management 

system includes several key elements 

(e.g., procedures, training, maintenance, 

and management of change) and requires 

that process hazard analyses be conducted and updated or revalidated on a regular 

basis. All process hazard analyses were 

to have been completed by May 1997; 

several sterilization facilities are subject 

to these requirements. In June 1996, EPA 

promulgated its risk management program 

regulation, which requires any company 

that handles more than 10,000 lb of EtO 

to implement a risk management program 

and prepare a risk management plan. The 

risk management program builds on the 

OSHA process safety management standard (compliance with the OSHA process 

safety management standard will basically meet EPA requirements as long as offsite consequences are included). The risk 

management program also requires process hazard analyses or hazard reviews 

as part of an accident prevention program. 

Information about the program is documented in a risk management plan that 

must be submitted to EPA in June 1999. 

Finally, the Clean Air Act Amendments of 

1990 include a general duty clause that 

states that “any facility handling any extremely hazardous substance must identify hazards using appropriate hazard assessment techniques, design and maintain 

a safe facility taking such steps as necessary to prevent accidental releases and 

minimize the consequences of accidental 

releases that do occur.”

Several different process hazard analysis 

methodologies are available to help assess 

the hazards associated with the sterilization process. The above regulations do not 

APPENDIX E

PROCESS HAZARD ANALYSIS
EtO 33

specify the process hazard analysis methodology to use, but they do have process 

hazard analysis requirements. These process hazard analysis requirements stipulate that a multifunctional team familiar with 

the process must be used for a process 

hazard analysis. Also, the process hazard 

analysis leader must be knowledgeable in 

the particular methodology being used for 

the analysis. They also require that workers 

be involved and made aware of this study 

and its recommendations.

The company must select the proper process hazard analysis methodology for the 

sterilization process and their analysis goals. 

The methodology selected should allow the 

process hazard analysis team to adequately review the failure modes of all equipment 

and instrumentation, potential operator errors, adequacy of the control system and 

interlocks, previous industry incidents, and 

any other process hazard. For an overall 

review of the hazards associated with the 

entire sterilization process, a gross hazard 

analysis (including what-if) or hazardous 

operability study (HAZOP) is probably the 

most appropriate methodology type. Other 

methodology types may be used for other 

analysis purposes (such as accident investigation or quantitative reviews).

General guidance on process hazard 

analysis and generic process design and 

control methods is available in publications from the Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AlChE),

3 Park Avenue, 19th Floor, New York, NY 

10016, Telephone: 212–591–7237.

For more information, see Safe Design 

and Operation of Process Vents and Emission Control Systems, Center for Chemical Process Safety, AlChE (John Wiley & 

Sons, Hoboken, N.J., 2006).
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