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ETO Background Information


ETO Exposure Patterns
    Potential Sources of Large Accidental ETO Releases
    Routine Sources with Potentially High ETO Emissions
    Sources of Low Exposure
Regulatory Analysis
    Permissible Exposure Limits
    Monitoring Requirements
Rules Governing Monitoring
Regulated Areas
Compliance Methods
Personal Protective Equipment
Medical Surveillance
Hazard Communication
Record Keeping
ETO Occupational Exposure Control

    Personal Monitoring
    Leak Inspection and Detection
Work Practice Controls

    Changing Cylinders
    Sterilizer Operation
    Cleaning Sterilizers
The Chlorofluorocarbon Problem
    Environmental Protection
Federal Regulations
    State Regulations


The National Institute for Occupational Safety and Health (NIOSH) has classified EtO emissions from the sterilizer process into three groups according to the potential seriousness of releases.

Those with potential for creating EtO exposures of 1,000 ppm or more as the result of an accident: "The EtO supply container for the sterilizer, whether it is a large cylinder or single-use cartridge, may release from one hundred to several thousand grams of EtO.... Leaks or failure of any of the connections or the cylinders themselves could cause the contents of the entire cylinder to be discharged into the workroom atmosphere. It is known that EtO cylinders have leaked before being connected to the supply line and while in service, and that the entire contents of supply cylinders have been accidentally discharged due to human error. And even if the exposures in front of the sterilizer are controlled, the maintenance worker who changes the cylinder or supply line filters could be acutely exposed."

Routine emissions that may create exposures in excess of 5 ppm: "These sterilizers [12/88 sterilizers] are pressurized to approximately 10 psig during the sterilization dwell period. Over pressurization of the chamber could result if the gas supply valve malfunctioned and was open when it was supposed to be closed. To counteract this, the chamber is fitted with an overpressure relief valve which could cause local concentrations of several hundred ppm in the indoor atmosphere if not properly vented, depending on the size of the sterilizer and the nature of the malfunction."

Those sources that may result in exposures of a few ppm or less: "The sterilizer door gasket may develop leaks. This is especially true for the pressurized 12/88 sterilizers. Again, depending on the size of the sterilizer, the nature of the leak, and the effectiveness of the ventilation, local concentrations as high as several hundred ppm could develop."


The first group of potentially hazardous, although infrequent, emissions includes three sources:
Leaks or failures in the supply cartridges or cylinders Because single-use cartridges of pure EtO are punctured automatically inside the sterilizer unit, they eliminate the risks associated with piping leaks and cylinder changes. The likelihood of a 100% EtO cartridge rupture outside the sterilizer is much less than a cylinder failure or piping leak in an EtO 12/88 system. Cylinder failure can result in a sudden and complete discharge into the workroom atmosphere. Maintenance workers responsible for changing cylinders and supply line filters are the most likely to be exposed by such a catastrophic release.

Overpressurization of the sterilizer In EtO 12/88 sterilizers, a malfunctioning gas-supply valve could result in overpressurization of the chamber, with the potential release of several hundred ppm of EtO to the area if the overpressure-relief valve is not properly vented.

Leaks that develop in the sterilizer door gasket Again, this source is generally associated with pressurized sterilizers using the EtO 12/88 gas mixture. Local EtO concentrations as high as several hundred ppm could develop, depending on the size of the sterilizer, nature of the leak, and local exhaust ventilation system effectiveness.


Three routine emission sources probably account for most of the EtO released into breathing space.
Antisiphon air gap
Spent EtO is evacuated from 12/88 units through a water-sealed vacuum pump. It is estimated that 60% to 80% of the EtO in the sterilization chamber is dissolved in the pump discharge water. Water and EtO are released to a sewer drain; however, most plumbing codes require an antisiphon air gap between the discharge point of the pump and the sewer drain to prevent the siphoning of liquid from the drain. EtO can be released through the antisiphon air gap. Depending on the ventilation control at the drain air gap, this may be the most significant routine source of EtO emission to workplace air.

Fugitive emissions
Residual EtO in the sterilizer chamber after completion of the sterilization cycle can be released when the sterilizer door is opened, exposing workers to brief but relatively high concentrations.

Residual EtO is gradually released when workers transfer loads from the sterilization chamber to the aerator.

Research suggests that, of all these potential exposures, the greatest source of actual exposure is opening the sterilizer door after sterilization is complete. Even when all other sources of exposure are eliminated, opening the sterilizer door and removing the sterile items still present significant risks.


NIOSH identified opening the aerator door and cleaning the interior of the sterilization chamber as the two most common sources of potential low-level exposure to EtO. The sterilizer may contain residual EtO even after the load is removed, especially if the door is closed after each use. Chamber cleaning often requires that the worker insert his or her head and upper body into the chamber to reach back surfaces; if cleaning is done soon after a sterilization cycle, exposure could occur.


OSHA has a substance-specific standard for EtO, 29 CFR 1910.1047, based on the determination that EtO presents a carcinogenic, mutagenic, genotoxic, reproductive, neurologic, and sensitization hazard to workers. EPA, under authority of the Federal Insecticide, Fungicide, and Rodenticide Act, regulates EtO as a pesticide. In addition, EtO is a priority pollutant under the Clean Air Act Amendments of 1990.


The OSHA PEL (Permissible Exposure Limit) for EtO is 1 ppm as an 8-hour time-weighted average. The EL (Excursion Limit) is 5 ppm averaged over a 15-minute time period. The AL (action level) of 0.5 ppm is the exposure limit above which employers must initiate compliance actions.


The compliance requirements depend on monitoring results. Different measured exposure levels trigger different actions:

OSHA Requirements Triggered by Exposures above the AL:
Implement semiannual employee exposure monitoring for all employees exposed at or above the AL. Implement an employee training program in accordance with the requirements of the OSHA standard. Implement a medical surveillance program for all employees exposed at or above the AL.

OSHA Requirements Triggered by Exposures above the PEL:
Immediately cease all sterilization activity, or provide employees in the work area with appropriate respiratory protection until controls are implemented to reduce EtO levels below the PEL. If respirators are used, establish a respirator program as required in section (g) of the standard and compliant with the OSHA Respiratory Protection Standard, 1910.134. Institute engineering controls and work practices to reduce and maintain exposure below the PEL. Considering the serious health consequences of both acute and chronic EtO exposure and the liabilities attendant on exposure, it is recommended that exposure be reduced to the lowest possible level. Perform representative employee exposure monitoring at least every three months. Implement an employee training program. Implement a medical surveillance program for all employees exposed over the AL. Establish regulated areas demarcating the locations where there is known or potential exposure above the PEL or the EL. Implement a written program to reduce employee exposure to or below the PEL by means of engineering and work practice controls. The program must include periodic leak surveys.

OSHA Requirements Triggered by Exposures above the EL:
Immediately cease all sterilization activity, or provide employees in the work area with appropriate respiratory protection until controls are implemented to reduce EtO levels below the EL.
If respirators are used, establish a respirator program as required in section (g) of the standard and compliant with the OSHA Respiratory Protection Standard, 1910.134. Institute engineering controls and work practices to reduce and maintain exposure below the TWA. Considering the serious health consequences of both acute and chronic EtO exposure and the liabilities attendant on exposure, it is recommended that exposure be reduced to the lowest possible level. Perform short-term monitoring at least every three months.
Implement an employee training program. Establish regulated areas demarcating the locations where there is known or potential exposure above the PEL or the EL. Implement a written program to reduce employee exposure to or below the EL by means of engineering controls and work practices. The program must include periodic leak surveys.

Other OSHA Requirements in Effect Regardless of Exposure Level:
Label all containers of EtO with appropriate warnings.
Maintain all exposure measurement records, survey reports, and other relevant information for at least 30 years.
Provide employees with monitoring results within 15 days of receipt of results. Have a written emergency plan compliant with the OSHA Emergency Plan Standard, 1910.38., which includes respiratory protection for anyone who must respond to an emergency. Establish regulated areas demarcating the locations where there is known or potential exposure above the PEL or the EL. Label all regulated areas with labels prescribed by the standard.
Provide protective equipment wherever skin or eye contact with EtO can occur.


Exposure monitoring is personal monitoring, and samples must represent air in the breathing zone of the representative employees. Area monitoring using infrared detectors or continuous gas chromatographs is not exposure monitoring. For the proper use of area monitoring, see below, "Leak Inspection and Detection."

It is important to note that initial and periodic monitoring can be of representative workers rather than all workers. However, that representation extends only to those workers in similar exposure situations. For example, personal monitoring of workers who unload sterilizers would not be representative for workers who change EtO cylinders because the potential exposure scenarios are significantly different.

Monitoring must be conducted again when processes, procedures, or equipment are changed and when personnel engage in significantly different activities.

The employer must permit affected employees or their designated representatives to observe the monitoring procedure.

Monitoring must be conducted by a method that is accurate to a 95% confidence level to plus or minus 25% for the PEL and plus or minus 35% for the AL and the EL.

Using one of the methods published by OSHA or NIOSH is recommended; unproven methods run the risk of providing inaccurate data. Worker health could be jeopardized, and OSHA could find the facility in violation if the employer uses an inaccurate method.

Employees must be notified of monitoring results in writing within 15 days after the employer receives the results. If monitoring results show exposure above the PEL and/or EL, the written notification must also include the employer's plans to reduce exposure below the PEL and/or EL.


The employer must establish a regulated area wherever occupational exposure to EtO might exceed the PEL or EL. The restricted area should be delimited in such a way as to minimize the number of persons working within it. Access must be limited to authorized persons.

Technically, the regulated area is defined by the distance from the EtO source at which exposure is potentially above the PEL. According to OSHA that determination does not necessarily presuppose an enclosed, isolated area (which might not be practicable in a chemical plant, for instance). In the hospital setting the entire EtO area, consisting of the mechanical access room and the sterilizer workroom, should be regulated. Moreover, rather than performing complicated monitoring to establish the effective limit of exposure, it is much easier to define the regulated area by installing walls and a door that isolate the regulated area from non-regulated areas. Access through the door will then be restricted to trained personnel.


As with most OSHA standards, engineering controls and work practices are required where feasible. Respiratory protection can be substituted only when other controls are infeasible or while other controls are being installed. Current sterilizer technology reduces the potential for exposure through design features such as vacuum purging. Other steps, discussed below, will reduce exposure even further. When exposure exceeds the PEL or EL, employers are required to have written exposure reduction program detailing engineering and work practice controls. The plan must contain:
A schedule for leak inspection.

Emergency plans and procedures. The emergency plan must specifically provide for respiratory protection for those who respond to emergencies.

The use of respiratory protection for situations in which engineering controls are not feasible.

Employers should be aware that rotating employees for purposes of achieving exposure control is prohibited.


Respirators must be supplied by the employer for maintenance and repair work and for emergencies. Respirators supplied must be approved by NIOSH, and the employer must institute a respirator program in accord with 29 CFR 1910.134. The EtO respirator selection chart is included with the full text of 29 CFR 1910.1047.

If there is a risk of eye and skin contact with EtO, the employer must also provide appropriate protection in accord with 29 CFR 1910.132 and 1910.133:

Eye protection must be vapor proof for those potentially exposed to EtO release from the sterilizer. For employees changing cylinders or performing maintenance, eye protection should be splash proof.

Gloves provided must be resistant to EtO. NIOSH recommends nitrile or butyl rubber, which provides protection against liquid EtO. Gloves used for removing items from sterilizers must also be heat proof. Examination and surgical gloves of any composition are not acceptable for protection against contact with EtO.


Medical surveillance by or under the supervision of licensed physician at the employer's expense must be instituted for all employees potentially exposed to EtO at or above the AL for at least 30 days per year. Respiratory protection does not eliminate the requirement for medical surveillance. Medical surveillance includes:

Examination of employees who have been exposed in an emergency.
Regular consultation with and examination by a physician according to the following schedule:
Before employment in a potential exposure position, and
At least annually for all employees exposed at or above the AL for 30 days per year.
At termination of employment or reassignment.
As soon as possible if an employee develops signs or symptoms of exposure or if the employee desires consultation on the relation of exposure to childbearing.
If the examining physician determines that examinations should be performed more often.

The medical examination must include:

Medical and work history with emphasis on pulmonary, hematologic, neurologic, and reproductive systems, as well as eyes and skin.
A physical examination emphasizing the same systems and features as above.
A complete blood count, including differential cell count, red cell count, hematocrit, and hemoglobin.
Any other tests the physician deems necessary.
Pregnancy or fertility testing if the physician deems it appropriate.

The employer must provide all relevant information to the physician, including:

A copy of the EtO standard. Exposure monitoring data. The employee's work and medical history. A description of personal protective equipment (PPE) used.

The physician must provide a written statement of the results of the medical examination containing recommendations for continued work or the use of respirators. The opinion must not reveal findings unrelated to EtO exposure, and a written copy must be provided to the employee within 15 days of receipt by the employer.


All aspects of OSHA's Hazard Communication Standard are applicable to EtO, with these special features:

Legible signs must be posted demarcating regulated EtO areas. The signs must contain the words "cancer and reproductive hazard" and must warn unauthorized personnel not to enter.
Hospitals have been cited for posting signs that were not large enough to permit easy legibility from a distance. while the meaning of "easy" might be open to interpretation, signs should be large enough to be read from at least 20 feet away by most persons.
All containers of EtO must be labeled "cancer and reproductive hazard" and must contain a warning against breathing EtO.
Material safety data sheets (MSDSs) are required.
Employees must be trained according to the requirements of the Hazard Communication Standard. If monitoring reveals exposure above the AL, employees must also be trained in the EtO standard itself.


Employers must keep complete records for 30 years on employees exposed to EtO. Records must include:

Exposure measurements, including the date, the operations monitored, the analytic method used, the number and duration of samples taken, the type of protective devices worn, and the names of the monitored employees.
Medical surveillance, including all written physician opinions.
On request, the employer must make all records available to employees or their representatives.


The first step in the development of an EtO control plan is to conduct initial exposure monitoring to determine if there is an exposure problem and, if so, how severe it is. If there is a problem, hospitals must institute corrective actions: facility engineering should evaluate the current sterilizer design and ventilation characteristics, and central services should evaluate work practices and procedures.


It is recommended that initial monitoring be performed by an industrial hygienist using the most accurate methods available, while passive dosimeters use an OSHA-accepted method, it is prudent for hospitals to use active sampling according to OSHA Method 50 or NIOSH Method 3072 for monitoring, with samples analyzed by a laboratory accredited by the American Industrial Hygiene Association (AIHA). Monitoring should be conducted again when significant changes in equipment or personnel functions are instituted. Significant changes in a typical hospital sterilization operation might include:

Installation of new or rebuilt sterilizers or aerators.
Installation of new or upgraded ventilation systems.
Installation of new piping arrangements.
New exposure situations for employees, such as increased sterilization process duties.

Because the purpose of periodic monitoring is to evaluate the success of controls, continued monitoring is the best way to ensure continued exposure containment, protect employee health, and reduce potential liability.


NIOSH and the Association for the Advancement of Medical Instrumentation (AAMI) recommend that leak inspection be performed every two weeks. All leak detection should be carefully documented in a logbook. The most likely places for leaks are at piping connections, at valves, and at sterilizer door seals. Door seals can also be inspected visually for cracks and decayed material. There are two ways to conduct leak testing:

For EtO 12/88 sterilizers, pressurize the entire system with Freon and check for leaks with a Freon meter. Special attention should be paid to the solenoid valve that controls EtO flow by checking the gas entrance port in the sterilizer. OSHA recommends that such inspections be conducted every two weeks.

Perform sampling of potential leak sites with various types of devices (e.g., infrared analyzers) that measure EtO ambient room concentrations. Sampling should be conducted by a trained, experienced industrial hygienist, and samples should be analyzed by an AIHA-accredited laboratory. Area monitoring will detect leaks from 100% EtO, as well as EtO 12/88, sterilizers. Area monitoring is not a substitute for Personal monitoring.

ALARMS    Index

OSHA requires that a means be provided to alert employees promptly in the event of a catastrophic release of EtO. OSHA defines an emergency as "any occurrence such as, but not limited to, equipment failure, rupture of containers, or failure of control equipment that is likely to or does result in an unexpected significant release of EtO."

While OSHA claims that continuous monitors against emergencies are not required, no alternative method of warning makes sense. The EtO standard references the requirements for emergency plans (29 CFR 1910.38), which in turn reference the requirements for employee alarm systems (29 CFR 1910.165). Requirement 1910.165 states that:

The employee alarm system shall provide warning for necessary emergency action as called for in the emergency action plan or for reaction time for safe escape of employees from the work place or the immediate work area, or both.

The employee alarm system shall be capable of being perceived above the ambient noise or light levels by all employees in the affected portions of the workplace.

The alarm shall be distinctive and recognizable as a signal to evacuate the work area or to perform actions designated under the emergency action plan.

Continuous monitoring makes sense according to the following principles:

Install continuous monitors that utilize electro-chemical or solid-state detection. Continuous gas chromatographs are far too expensive.

Monitors should be set at a level high enough to avoid interferences from other chemicals.

Three sensors are sufficient. Sensors should be placed at breathing level and as close to the cylinders as possible in the mechanical access room, above the sterilizer door, and above the door to the regulated area. If the regulated area contains more than one sterilizer, it is suggested that maximum protection be provided by placing a sensor above each sterilizer door.

Alarms can be visible or audible, but having both is the best practice.

During training, employees should see and/or hear the actual alarms so that they can recognize them.

Alarms should be maintained and tested according to Requirement 1910.165:

The employer shall ensure that all employee alarm systems are maintained in operating condition except when undergoing repair or maintenance.

The employer shall ensure that a test of the reliability and adequacy of non supervised employee alarm systems is made every two months. A different activation device shall be used in each test of a multiactuation device system so that no individual device is used for two consecutive tests.

The employer shall maintain or replace power supplies as often as is necessary to ensure a fully operational condition. Backup means of alarm, such as employee runners or telephones, shall be provided when systems are out of service.

The employer shall ensure that employee alarm circuitry installed after January 1,1981, that is capable of being supervised is supervised and that it will provide positive notification to assigned personnel whenever a deficiency exists in the system. The employer shall ensure that all supervised employee alarm systems are tested at least annually for reliability and adequacy.

The employer shall ensure that the servicing, maintenance, and testing of employee alarms are done by persons trained in the designed operation and functions necessary for reliable and safe operation of the system.


Correct work practices can significantly decrease EtO exposure. All employees working with EtO should be instructed in proper procedures for all aspects of EtO sterilization processes, including gas cylinder changing, the sterilization cycle, and sterilized item handling.


Changing cylinders and supply-line filters represents the maximum potential exposure scenario. Although rare, valve failure, resulting from expansion of liquid EtO trapped when the valve is shut off or the tendency of EtO to polymerize and clog valves and feed lines, does happen and can expose workers to both liquid and gaseous EtO. The following PPE be worn during cylinder changing:

Heavy neoprene, nitrile, or butyl rubber gloves to protect skin.
Tyvek full-body suits with shoe coverings to protect clothing and shoes (EtO contamination cannot be removed from leather).
Splash-proof/vapor-proof face shield or goggles.
A respirator with an EtO-specific canister.

The recommended PPE will provide employees with escape time should there be a catastrophic release. It will not provide adequate protection for entering contaminated atmospheres of higher or unknown concentrations. The canister respirator is acceptable for concentrations only up to 50 ppm, which should be adequate to evacuate the regulated area.


Work procedures should be designed to minimize exposure at every step. The following practices are recommended:

Prepare items for sterilization outside the regulated area. Place them in trays or baskets for quick and easy loading of the sterilizer chamber.

At the conclusion of a sterilization cycle, crack the sterilizer door open two inches (or according to the manufacture's instructions) and vacate the area for at least 15 minutes before unloading. Door cracking allows residual EtO to rise and be scavenged by the LEV above the door. The door should not be cracked open wider than the capture area of the overdoor exhaust vent.

Transfer items from the sterilizer to the aerator as quickly as possible. Wear chemical and heat-resistant gloves to prevent contact with EtO on sterilized items or basket handles.

Do not push transfer carts from behind. Pull them from the front so that residual EtO will drift away from the breathing zone.

Remove items from the aerators and finish processing outside the regulated area.

Do not remain in the regulated area any longer than necessary to complete loading, transfer, or unloading.


Employees who must put their upper bodies into the sterilization chamber to clean it should wear canister respirators, Tyvek shirts and caps, and face and eye protection.


Employees should be trained to evacuate the regulated area as soon as the warning system indicates a catastrophic release. In almost all cases, employees can leave the area much more quickly than they can put on respirators. As soon as they have evacuated the regulated area, employees should call the hospital emergency response number and remain outside the regulated area to prevent others from entering and to provide information to emergency response personnel.


The gas used in hospital sterilizers has most often been diluted by a chlorofluorocarbon (CFC) to 12% EtO and 88% CFC to reduce the flammability of EtO. Under the Clean Air Act Amendments of 1990, no CFCs will be produced after 1995, and 12/88 EtO will become prohibitively expensive. Consequently, sterilizer manufacturers and gas suppliers have had to come up with ways to surmount the lack of CFCs. There are currently three ways to compensate for the loss of CFCs:

100% EtO. Sterilizers using pure EtO have been around for a long time. But now sterilizer makers are looking to manufacture 100% EtO sterilizers with capacities equal to 12/88 sterilizers.

Carbon Dioxide (C02). Using C02 as the dilutent for EtO is not a new idea. C02 reduces EtO flammability and is relatively inexpensive compared to other available dilutents. However, C02 is not an ideal dilutent because the EtO and C02 tend to separate in the cylinder and because sterilizers using the EtO/C02 mixture must run at a higher pressure. Higher pressures increase the hazard when there is a failure of the pressure relief-valve or the evacuation system.

Hydrochlorofluorocarbons (HCFCs). HCFCs are similar to CFCs in many ways, but they are friendlier to the ozone layer because they contain fewer ozone-eating chlorine atoms and because they tend to break down before they reach the stratosphere. Several companies are now offering EtO/HCFC mixtures.


EtO is one of the 189 substances listed as hazardous air pollutants in the original Clean Air Act of 1970. This list was retained in the 1990 Clean Air Act Amendments; Congress mandated EPA to draft a National Emission Standard for Hazardous Air Pollutants (NESHAP) for all 189 pollutants and specifically identified EtO as a priority pollutant in 1990.


On March 7,1994, EPA published a proposed NESHAP for EtO emitted from those point source defined as commercial sterilization and fumigation operations, defined by EPA as a source category that "consists of commercial operations that use EO [EPA uses "EO" instead of "EtO"] in the sterilization of medical equipment supplies and in miscellaneous operations as a sterilant for heat- or moisture-sensitive materials or as a fumigant to control microorganisms or insects. A variety of materials are sterilized or fumigated with EO including medical equipment, pharmaceuticals, cosmetics, spices, books, artifacts, and beehives" (Fed Regist 59[44]:10592).

Lest there be any confusion about whether hospital sterilizers are "commercial sterilizers" in the EPA's mind, EPA adds that there are approximately 180 facilities in the EtO commercial sterilization/fumigation source category. Of these, only about 68 will actually come under the NESHAP; the others have already abated emissions or are too small to fit the appropriate regulatory definitions.


However, hospitals are not completely off the hook because state and even local agencies can require abatement of EtO emissions from hospital sterilizers if they find it necessary to meet ambient air quality standards as defined in the Clean Air Act Amendments or in state laws. This has already happened in California, Wisconsin, Michigan, Texas, New York, and the Puget Sound Basin in Washington. These states generally require a 95% to 99.9% reduction in emissions. The California rules are instructive. They require all hospitals, except those using 25 pounds or less of EtO per year, to meet the following criteria:

There is no discharge of the sterilizer exhaust vacuum pump working fluid to wastewater streams.

There are no leaks in the exhaust system, including all piping and ducts, fittings, valves, and flanges through which EtO-contaminated air passes from the sterilizer and aerator to the emissions control system.

Facilities using more than 600 pounds of EtO per year must duct the back-draft valve to the emissions control device for the aerator exhaust stream.

Facilities using more than 5,000 pounds of EtO per year (this requirement should not apply to hospitals) must duct the sterilizer and aerator door hoods to the emissions control device.

In addition, hospitals must report on a regular basis the number of sterilizer cycles and pounds of EtO used per cycle for each sterilizer or the total pounds of EtO purchased, used, and returned each year.

Regulations similar to those adopted in California are likely to be adopted for hospital sterilizers in large metropolitan areas that are not in compliance with the Clean Air Act Amendments' limits on ozone in ambient air. Hospitals should contact their state environmental department and local environmental agencies to find out if EtO sterilizer emission limitations are currently being considered.