P2 for Hospital Sterilizers: Background and OverviewPrint Friendly Page
"Hospital Sterilizers" = EtO for the purposes of this topic hub
A variety of public health products is used to control the different microorganisms infectious to humans. This section describes the breadth of products used based on their abilities to kill potentially hazardous microorganisms. Ethylene Oxide is included in the most potent of the product categories, sterilizers. Only one sterilizer is included under the "hospital sterilizer" category specified in the Clean Air Act section 112(c) regulating toxic air pollutants. This sterilizer is ethylene oxide or EtO.
The more commonly used public health antimicrobial products include the following:
Sterilizers (Sporicides): Used to destroy or eliminate all forms of microbial life including fungi, viruses, and all forms of bacteria and their spores. Spores are considered the most difficult form of microorganism to destroy. Therefore, EPA considers the term Sporicide to be synonymous with "Sterilizer." Sterilization is critical to infection control and is widely used in hospitals for medical and surgical instruments and equipment. Types of sterilizers include steam under pressure (autoclaving), chemiclaving, dry heat ovens, low temperature gas (ethylene oxide), and liquid chemical sterilants. Gaseous and dry heat sterilizers are used primarily for sterilization of medical instruments.
High Level Disinfectants: These are primarily in liquid form, such as the aldehydes (e.g. glutaraldehyde, formaldehyde) and are used for delicate instruments that cannot withstand high temperature and gases, for example andescopes. Although these are sometimes called "liquid sterilants", they are not considered strong enough to kill spores, and so are not considered to be sterilizers.
Disinfectants: Used on hard inanimate surfaces and objects to destroy or irreversibly inactivate infectious fungi and bacteria but not necessarily their spores. Disinfectant products are divided into two major types: hospital and general use. Hospital type disinfectants are the most critical to infection control and are used on medical and dental instruments, floors, walls, bed linens, toilet seats, and other surfaces. General disinfectants are the major source of products used in households, swimming pools, and water purifiers.
Sanitizers: Used to reduce, but not necessarily eliminate, microorganisms from the inanimate environment to levels considered safe as determined by public health codes or regulations. Sanitizers include food contact and non-food contact products. Sanitizing rinses for surfaces such as dishes and cooking utensils, as well as equipment and utensils found in dairies, food-processing plants, and eating and drinking establishments comprise the food contact Sanitizers. These products are important because they are used on sites where consumable food products are placed and stored. Non-food contact surface sanitizers include carpet sanitizers, air sanitizers, laundry additives, and in-tank toilet bowl sanitizers.
Antiseptics and Germicides: Used to prevent infection and decay by inhibiting the growth of microorganisms. Because these products are used in or on living humans or animals, they are considered drugs and are thus approved and regulated by the Food and Drug Administration (FDA).
EtO is an extremely effective biocide and is considered to be one of the most universally applicable sterilizers since it can be used for such a wide variety of sterilization purposes. Many other methods of sterilization have limitations. EtO is a cold sterilizer, so can be used where heat and steam might damage fragile materials. EtO gas also penetrates the narrow channels and small-diameter tubes and cavities characteristic of many devices that hospitals use. Unlike some of the substitutes, EtO is generally compatible with packaging, so that integrity of the product is not affected by the use of EtO.
Both the healthcare industry as well as the food industry have long recognized the value of safe, effective, and efficient sterilization using EtO, and have depended on the EtO sterilization industry for sterile products.
EtO Regulatory History
Unfortunately, EtO represents a serious occupational exposure hazard: it is toxic (central nervous system depression, eye and mucous membrane irritations), a reproductive hazard for both genders, and a probable human carcinogen. EtO is regulated by OSHA, the FDA, the EPA and many states have additional restrictions on its use. Under the Clean Air Act Amendments of 1990, EtO is a listed hazardous air pollutant, with control technology requirements pertaining in many cases.
Characteristics of EtO use have changed along with discovery and discloser of its hazards. Until the 1990s, most EtO gas sterilization machines used a mixture of 12% EtO and 88% CFC (as a stabilizing agent). Sterilization using "12/88" machines was conducted at two atmospheres of pressure. The spent mixture was vented to outside air. Release of CFCs is now banned; newer devices use 100% EtO at partial atmospheric pressure, or an alternative stabilizing gas.
EtO was regulated for large air polluters by a National Emission Standard for Hazardous Air Pollutant (NESHAP) rule for commercial sterilizers in 1994. The NESHAP regulation also applies to many smaller "area sources", however historically there has been an exemption for hospital use. "Area sources" are those that emit less than 10 tons annually of a single hazardous air pollutant or less than 25 tons annually of a combination of hazardous air pollutants, with major sources emitting greater than those quantities. Previously area sources were not regulated since individually they are small emitters, however together they represent a significant contribution to the emission of many hazardous air pollutants. Figure 1 shows that as a category, area sources are more important than any of the other sources and were responsible for 30% of hazardous air emissions in 2002. Hospital sterilizers are only one of 70 area sources that fall into the category and are responsible for only a small fraction of the total air pollution represented in this graph.
Figure 1 Hazardous Air Pollution Sources for 2002
Almost 100% of all hospitals fall into the category of being an area source rather than a major source of air pollution. Currently however, the EPA is drafting an area source rule that targets hospital EtO emissions.
Both the health care and food industries depend on EtO for sterile products. As of 1994, more than 50% of all sterile medical devices sold were sterilized using EtO. In 1999, 26% of total EtO emissions were generated from hospital sterilizers with 34% coming from consumer and products use.
Voluntary Reduction of Use
Since the early 1990's many hospitals have reduced their use of EtO voluntarily or to comply with their state regulations. This follows the declaration of EtO as a known human carcinogen, teratogen and neurotoxin. In 1990, the estimated total EtO emitted by hospitals in the U.S. was about 1000 tons/year. At that time, almost all of this use was uncontrolled, with emissions released into sewers or into the air. By 2005, use has dropped to about 135 tons/year with an estimated 50% of the use being controlled. Controlled emissions are neutralized through proper procedures and pollution abatement equipment and result in little hazardous releases into the environment. The estimated average emissions for a hospital using EtO is about 400 lbs/year, with the maximum for a large user being about 1000 lbs/year. Based on the tremendous voluntary use reduction, the EPA may decide to allow hospital EtO use to remain without further regulation, or issue a new area source restriction by October 2007.
Properties of EtO
EtO (C2H4O, epoxyethane, oxirane) is a colorless gas at room temperature with an ether-like odor at concentrations above 500 to 700 parts per million (ppm). For sterilization applications, EtO is supplied in cylinders as a pure liquid under pressure or mixed with other carriers. The odor threshold for EtO is 260 ppm. EtO has a vapor density of 1.49 and is thus approximately 1.5 times heavier than air. The boiling point of EtO is 51 �F, and the liquid has a flash point of 0 �F. The gas has an auto ignition temperature of 805 �F. The vapor pressure of EtO is 1,095 mm Hg.
EtO is soluble in water and reacts with acidified water to produce ethylene glycol. This process is one method for controlling EtO emissions. EtO is reactive with strong acids, alkalis and oxidizers, chlorides of iron, aluminum or tin, and oxides of iron and aluminum. Highly flammable, EtO poses a dangerous fire and explosion risk. The flammability limits in air are 3% (30,000ppm) to 100%. Pure EtO can be ignited in the absence of air. EtO is more dangerous than hydrogen and should be treated with the same care as hydrogen and acetylene. Once ignited, it can flash back to the fuel source with velocities of 1,800 to 2,400 m/sec.