Health and Safety

The focus of this article is ethylene oxide (abbreviated as EtO or less commonly EO), a frequently used and potentially dangerous sterilizing agent. EtO has been in use for decades. More than 30 years ago, in 1977, the National Institute for Occupational Safety and Health (NIOSH) estimated 75,000 workers nationwide were potentially exposed with more than 10,000 sterilizers in use.¹ Further, during the period 1994 to 1998, EtO was associated with ten explosions causing major property damage, scores of injuries, and at least one fatality.² In August 2004, Sterigenics, a major contract sterilization company, had an explosion in their Ontario, CA facility injuring four employees and shutting down the plant.³

Ethylene oxide is used for sterilization in many veterinary and animal surgical facilities because it is efficient and performed at low temperatures compared to steam sterilization. The sterility assurance level (SAL) for EtO sterilizers is 10-6 meaning there is only a one in a million chance that a live microbe survived the sterilization cycle.Also, EtO is very compatible with the polymer-based single use medical devices, procedure kits and surgical trays, as well as most surgical instruments. The average animal research facility most likely uses the small-chamber counter-top self contained sterilizing cabinets. For larger volume demand, contract companies have sterilizing units as large as semi-tractor trailers. In the small batch sterilizers used in animal surgical units, EtO is usually delivered as a gas or from a small cartridge or ampule that is opened and allowed to vaporize for each batch run. However, ethylene oxide is not without its drawbacks. EtO is very toxic and highly flammable. Ethylene oxide sterilizer use requires precise installation, rigorous maintenance, and employee protections.

Hazard Recognition – The Dangerous Properties
Ethylene oxide is a gas at room temperature with a boiling point of 10.7 oC (51 oF). EtO is also highly flammable. The flammable limits in air are from 3% to 100%, a very wide range. The vapor density is 1.5 (air=1.0) and, if left uncontrolled, the vapors will tend to sink to the floor (or lowest available levels) and accumulate, spreading to the nearest ignition source.

In addition, EtO is a serious health hazard. It is colorless with a characteristic sweet ether-like odor, but if you can smell it you are breathing a toxic concentration hundreds of times greater than the exposure limit. The OSHA occupational permissible exposure limit is only 1 ppm for a regular eight hour work shift. However, the reported odor threshold is between 500 and 700 ppm. Therefore, odor is a very poor warning property for EtO.

Exposures can occur by inhalation or skin absorption and can have severe results. Inhalation exposure symptoms include eye pain, sore throat, blurred vision, difficult breathing, dizziness, and convulsions. Acute effects may lead to central nervous system depression, pulmonary edema, respiratory distress, and coma.

Liquid EtO can produce irritation or blistering of the skin or frostbite from rapid evaporation and consequent cooling. In some persons, ethylene oxide exposure may result in allergic sensitization, and future exposure may cause hives or a life-threatening allergic reaction.

Ethylene oxide is designated as a suspected human carcinogen that may cause leukemia and other cancers. EtO is also linked to spontaneous abortion, genetic damage, nerve damage muscle weakness, and peripheral paralysis.