Workers may be at risk of death or serious injury from explosions if safe operating procedures are not established and followed in large-scale industrial processes that use ethylene oxide gas (EtO) for sterilizing medical devices and other products, the National Institute for Occupational Safety and Health (NIOSH) warns in a new NIOSH Alert.

In these processes, products are placed in bulk in a closed, semitrailer-sized chamber, and EtO is injected into the chamber. Once sterilization is completed, EtO is vented at a controlled rate through closed ductwork to an emissions control device. There, to meet environmental emissions limits, the EtO is either burned off or converted to water and carbon dioxide through heat and catalytic conversion.

If EtO is inadvertently "overfed" into the emissions control device at rates or concentrations higher than the device safely can handle, concentrations of the gas may reach flammable levels. If that occurs, heat sources in the emissions control device may trigger an explosion.

To prevent overfeeding or other problems, procedures should be specified and followed for maintaining equipment, venting safely, and, in general, storing and handling EtO properly, NIOSH recommends.

"If ignited from overfeeding in industrial sterilization processes, EtO can explode with enough force to lift a 50,000 pound sterilization chamber three feet off its foundation, and blow out steel ductwork," noted NIOSH Director Linda Rosenstock, M.D., M.P.H. "It is important to treat it with care."

Between 1994 and 1998, EtO was associated with 10 explosions at industrial sterilization facilities and also at EtO repackaging plants where EtO is transferred from large drums to small tubes or canisters for later use in small sterilization units at hospitals. In one such explosion, a worker was killed and 59 others were injured.

NIOSH prepared the Alert in partnership with the Ethylene Oxide Sterilization Association and the U.S. Environmental Protection Agency.

In addition to safety recommendations for employers and workers, the Alert also includes extensive discussion of potential hazards, descriptions of three case studies, and lists of resources for additional information.

To avoid overfeeding EtO from sterilization chambers, NIOSH recommends that:

• On the basis of a process hazard analysis that emphasizes the safe operation of the entire sterilization system, employers should establish written safety procedures to cover all steps of EtO sterilization.

• All interlocks, safeguards, and other hazard-prevention measures should be in place before a sterilization cycle begins.

• If, after sterilization is completed, a sterilized product sits idle in a sterilization chamber or an aeration room before being removed, the chamber or room should be periodically vented to avoid EtO buildup. Packaged sterilized products are sometimes placed in an aeration room to allow any EtO trapped in the package to escape. Any EtO released in the room is also routed to the emissions control device.

• EtO concentrations in the sterilization chamber should be monitored before back vents are activated, exhausting EtO in the chamber to the emissions control device. Monitoring is needed to avoid exhausting high concentrations of EtO inadvertently.

• After a power loss, a sterilization chamber or an aeration room should be vented to the outside to prevent overfeeding of the emissions control device.

• Precautions should be taken to avoid an incorrect valve lineup or a leak in the EtO storage area that may result in high concentrations of EtO being fed to the emissions control device.

• Regular preventive maintenance of equipment should be performed.

"NIOSH Alert: Preventing Worker Injuries and Deaths from Explosions in Industrial Ethylene Oxide Sterilization Facilities," DHHS (NIOSH) Publication No. 2000-119, is available on the NIOSH Web Page at http://www.cdc.gov/niosh/2000119.html. Copies also are available through the toll-free NIOSH information number, 1-800-35-NIOSH (1-800-356-4674). Additional information on NIOSH research is also available from the toll-free number and from the NIOSH Web Page at www.cdc.gov/niosh.