(d) Timing of each cycle must be adjusted for differences in materials
and size of load that makes it subject to human error.
a. Ethylene oxide gas is used to sterilize items that are heat or moisture
sensitive. Ethylene oxide is a chemical agent that kills microorganisms, including
spores. Used in its gaseous state, ethylene oxide gas must have direct contact with the
microorganisms in or on items to sterilize. Ethylene oxide sterilization is dependent
upon EO gas concentration, temperature, humidity, and exposure time. Since pure
ethylene oxide is highly flammable and explosive in air, it is mixed with an inert gas for
use in sterilizers.
b. Gas sterilizers usually operate at 120 to 140 F (49 to 60C). Temperature
influences the destruction of microorganisms and the permeability of EO through the
packaging material. As temperature increases, exposure time can be decreased.
Moisture is also essential in achieving sterility with EO gas so relative humidity of 40 to
80 percent in the sterilizer is required. Exposure time is lengthy; three to six hours may be
required. The aeration time is also very lengthy. Newer equipment uses less exposure
time. The standard set by the American Association of Medical Institutions (AAMI) for
gas sterilizers is 2 hours exposure time. Gas use has also changed; 12 percent EO, 88
percent freon is recommended by AMSCO. However, manufacturers have different
exposure time for their products. Gas use has also changed. Because of quality air
standards, 3M uses strictly fluorocarbons.
c. Aeration time is the time it takes for the EO gas to diffuse (evaporate) from
the items sterilized. Ethylene oxide is not only flammable but is also very toxic and can
cause serious chemical burn in case of prolonged contact. Aeration can be
accomplished with ambient (room) air or in an aerator chamber designed for this
purpose. Only in unusual circumstances will ambient aeration be used. Mechanical
aerators are generally available in the CMS today. The nature of the item, the
temperature, and the airflow in the aerator influence aeration. Table 3-1 illustrates
aeration time for articles sterilized by ethylene oxide gas.
d. The advantages with EO sterilization are:
It is effective against all types of microorganisms.
It is noncorrosive.
It completely permeates all porous materials.
It leaves no film.
It is easily obtainable.