Safe Ethylene Oxide Sterlization
This column will focus on ethylene oxide, a frequently used and potentially dangerous sterilizing agent. Also known as EtO or EO, it is highly compatible with today’s polymer-based single-use medical devices, procedure kits, surgical trays, etc., and is commonly used for sterilization in many veterinary and animal surgical facilities. Although it typically is used in small-batch countertop cabinets, contract companies have units as large as semi tractor trailers. In the smallbatch sterilizers, EtO is usually delivered as a gas or in a small capsule of liquid that is opened and allowed to vaporize for each batch run. Sounds simple. But ethylene oxide at normal room temperatures is a colorless, highly flammable, toxic gas, and improper or careless use can cause serious problems. We will now take a closer look at the hazards of EtO and how to safely use this common sterilizing agent.
Recognizing the hazard
EtO has been in use for many years. In 1977, the National Institute for Occupational Safety and Health (NIOSH) estimated that there were more than 10,000 sterilizers in use and 75,000 workers nationwide were potentially exposed.1 It’s probably safe to assume that these numbers have increased in the interim. In addition, during the period from 1994 to 1998, EtO was associated with 10 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 its Ontario, Calif., facility that injured three employees and shut down the plant.3 With these facts in mind, let’s begin with understanding the physical and chemical properties of EtO.
As mentioned above, EtO is a gas at room temperature, with a boiling point of 10.7°C (51°F). It is colorless, with a characteristic sweet odor; however, if you smell it, you are breathing a concentration hundreds of times greater than the exposure limit. The OSHA permissible exposure limit is only 1 ppm, while the reported odor threshold is between 500 and 700 ppm. Therefore, odor is a very poor warning property for EtO.
EtO is also a highly flammable gas. The flammable limits in air are three percent to 100 percent, a very wide range. The vapor density is 1.5 (air=1.0), and if uncontrolled, the vapors will tend to sink to the floor (or lowest available levels) and accumulate, spreading to the nearest ignition source.
In addition to its dangerous physical properties, EtO is a serious health hazard. Exposures usually occur by inhalation or skin absorption. Exposures to either the liquid or vapors can have severe results. Liquid EtO can produce irritation or blistering of the skin or frostbite from rapid evaporation and consequent cooling. In some people, ethylene oxide exposure may result in allergic sensitization and future exposure may cause hives or a life-threatening allergic reaction.
Symptoms of inhalation exposure can include headache, nausea, vomiting, diarrhea, shortness of breath and cyanosis (blue or purple coloring of the skin). Acute effects may lead to central nervous system depression, pulmonary edema, respiratory distress and coma.
Finally, if the facts above are not reason enough for caution, ethylene oxide is designated as a suspected human carcinogen with links to reproductive effects, mutagenic changes and neurotoxicity.
Evaluating the hazard
Ethylene oxide has its own specific OSHA standard, 29CFR1910.1047. This standard covers all occupational exposures to EtO and outlines the requirements for monitoring, medical examinations, training and record keeping. Under the standard, OSHA has established an action level of 0.5 ppm and a permissible exposure limit (PEL) of 1.0 ppm, both based on eight-hour timeweighted averages. There is also a short-term exposure limit of 5.0 ppm, and a 15-minute average that employees should never exceed. Periodic monitoring is conducted every six months for employees exposed at or above the action level and every three months for those exposed at or above the PEL. The appendices to the standard contain useful information on health and safety data, sampling and analytical methods, and workplace design and practices.
If ethylene oxide is used in your facility, potential exposures should be evaluated. First, take a close look at your equipment and how it is set up. Is the room or area appropriate, with proper ventilation and exhaust and without conflicting uses? For general ventilation, is the room on dedicated single-pass air without recirculation? Is the air pressure in the area slightly negative relative to adjacent spaces? Are there sufficient room air changes (normally expressed as air changes per hour (ACH)? ACH is calculated based on room volume and the cubic feet per minute of supplied conditioned air.
Examine the sterilizer equipment thoroughly. 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 gas cylinders handled? Are associated piping, hoses, valves, regulators and filters inspected and checked for leaks regularly?
Next, scrutinize the technician’s operation of a complete sterilization cycle. Pay special attention to unloading of the sterilizer. Is a purge cycle used? How are the sterilized materials vented and handled?
Controlling the hazard
After you have completed the comprehensive hazard evaluation above, move on to implementing and verifying the needed controls. Measure supply and exhaust flows and calculate the balance, then check physically with simple smoke tubes. Ensure that equipment is exhausted and that there are no leaks. Check for leaks from the sterilizer, gas cylinder and supply lines (if so equipped) while you are at it.
We have observed significant potential for exposures from the venting and off-gassing of sterilized materials. Considerable EtO levels can remain for up to 30 minutes after removal from the sterilizer. Think about incorporating an additional purge cycle or transferring materials to a hood or other exhausted enclosure prior to further handling.
The final step is to conduct exposure monitoring to validate that all the above systems and procedures are in fact preventing any exposures. Have your industrial hygienist conduct personal exposure monitoring with appropriate media and air-sampling pumps, followed by analysis by an accredited laboratory. Portable infrared analyzers and direct-read instruments can provide real-time data and are useful for leak detection.
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 ethylene oxide (and any hazardous material) is first to recognize the hazards, then evaluate the potential exposures, and then design and implement proper controls. In areas where EtO is used, ensure ample exhaust, sufficient room air changes, safe cylinder/material handling and routine leak-check procedures. Finally, conduct periodic monitoring of the engineering systems and air concentrations.
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