Disinfection is serious business, especially now during the COVID-19 global pandemic, when the need to disinfect and sterilize everything from offices to ventilators is so important. This article is about ethylene oxide, a frequently used but potentially hazardous sterilizing agent.
Ethylene oxide has been used for decades. In fact, in 1977, the National Institute for Occupational Safety and Health (NIOSH) estimated that with more than 10,000 sterilizers in use, 75,000 workers nationwide were potentially exposed. However, during the period 1994 to 1998, ethylene oxide was associated with 10 explosions causing major property damage and scores of injuries, including at least one fatality. As recently as August 2004, a major contract sterilization company had an explosion in their facility, injuring four employees and shutting down the plant.
Abbreviated as EtO (or less commonly EO), ethylene oxide is used for sterilization in many medical, dental, veterinary, and animal surgical facilities. This is because it is efficient and performs at low temperatures compared to steam sterilization. In addition, EtO is very compatible with the polymer-based single use medical devices, procedure kits, and surgical trays, as well as most surgical instruments.
The most common use is the small-chamber countertop, self-contained sterilizing cabinets. In these small-batch sterilizers, 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 very toxic and highly flammable. Ethylene oxide sterilizer use requires precise installation, rigorous maintenance, and employee protections.
Recognizing the dangers
Ethylene oxide is a gas at room temperature with a boiling point of 10.7°C (51°F) and flammable limits in air from three to 100 percent, a very wide range. The vapor density is one and a half times that of air, therefore the vapors will tend to sink to the floor (or lowest available levels) and accumulate, spreading to the nearest ignition source.
EtO is also a serious health hazard. It is colorless with a characteristic sweet, ether-like odor. However, be warned—if you can smell it, you are breathing a toxic concentration hundreds of times greater than the exposure limit, given the OSHA occupational permissible exposure limit is only 1 ppm for a regular eight-hour work shift and the reported odor threshold is between 500 and 700 ppm. Therefore, odor is a very poor warning property for EtO.
Exposures occur by inhalation or skin absorption and can have severe results. Inhalation exposure symptoms include eye pain, sore throat, blurred vision, difficulty 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 resultant cooling. EtO exposure may also produce allergic sensitization, with future exposure causing hives or life-threatening allergic reactions.
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.
Evaluating the hazards
Occupational use of ethylene oxide is regulated by the OSHA standard, 29CFR1910.1047. Employers must perform initial monitoring in each area where EtO is used to accurately determine the airborne concentrations to which employees might be exposed. For employees exposed at or above the PEL, monitoring is required every three months.
The established action level (AL) is 0.5 ppm based on an eight-hour time weighted average (TWA). If the action level threshold is exceeded, then additional requirements for routine personal monitoring, medical examinations, training, and record keeping would trigger. For example, if the AL is exceeded, then employers must conduct periodic monitoring every six months.
It is recommended that a qualified industrial hygienist (IH) perform the hazard evaluation and all required sampling. The IH should also evaluate hazard controls, especially exhaust and ventilation systems.
Hazard control—preventing overexposure
Good engineering controls are our primary defense to prevent potential exposures. Measure supply and exhaust flows and conduct a ventilation test and balance. For general ventilation, make sure the room is on dedicated single-pass air without recirculation. Ensure the sterilizer area is balanced slightly negative relative to adjacent spaces. Check that the supply flow is adequate and volumes are as designed.
Next we want to ensure equipment is properly installed and exhausted and that there are no leaks. Check for leaks from the sterilizer, gas cylinder, and supply lines (if so equipped). Are the door gaskets in place and in good condition? Is the sterilizer exhausted properly according to the manufacturer’s recommendations? Is the exhaust working? How are ethylene oxide gas cylinders handled? Are associated piping, hoses, valves, regulators, and filters inspected and leak-checked regularly?
After the equipment is checked and the facility ventilation is verified, ensure all employees using the system have comprehensive training, including operator training. Observe work practices and the technician’s operation of a complete sterilization cycle. Pay special attention when the sterilizer is unloaded. Is a purge cycle used? How are the sterilized materials vented and handled? It is best to get all these things in order before spending money on expensive monitoring.
Uncontrolled releases and exposures are most common during the venting and off-gassing of sterilized materials. We have found significant EtO levels can remain up to 30 minutes in the packages after removal from the sterilizer. Therefore, an additional purge cycle or transferring materials to a hood or other exhausted enclosure for a short period to allow final off-gassing is recommended prior to further handling.
Additional assistance is available from the EtO Sterilization Association (http://www.eosa.org/) as well as the NIOSH and OSHA websites. The key to working with hazardous materials is first to recognize the hazards, followed by evaluation of any potential exposures and ending with design and implementation of proper controls. Where EtO is used, we must ensure proper equipment installation and sufficient facility HVAC supply and exhaust, safe cylinder/material handling, and routine leak-check procedures. Finally, ensure that periodic monitoring of the engineering systems and air concentrations is conducted.