The Principles of Medical Device Decontamination

EO is a toxic gas and so sterilizers are normally located in their own specially constructed rooms which will ensure at least 10 air changes per hour, ventilated using special spark proof fan systems designed to prevent fires. The ventilation exit points must be located away from public areas, usually on a roof, so that free air flow dilutes any emissions to very low levels. Similarly, the effluent from the sterilizer at the end of the sterilization cycle must be vented to a safe place to allow free air flow dilution or preferably passed through an abatement system such as a catalytic converter which will convert the EO to carbon Dioxide (CO 2 ) and water.

Low Temperature Steam with Formaldehyde

Once very common in the UK but rarely found today. The LTSF process takes place in a sealed chamber and uses saturated steam at ca 60 to 80 o C under low pressure (ca 200 to 500mB absolute) mixed with formaldehyde vapour at a concentration of ca 15mg/L. The process variables are temperature, time, vapour concentration in the presence of moisture (as saturated steam). The process is complex. After evacuation of the chamber, steam is admitted to heat and humidify the load. This is followed by introduction of formaldehyde vapour, vaporised from formalin which is contained within a reservoir tank. A series of formaldehyde and steam pulses are injected into the chamber in order to drive the formaldehyde into the load. After the formaldehyde exposure phase further pulses of steam and air are injected into the chamber in order to remove the formaldehyde from the chamber and allow desorption from the load. Formaldehyde is a toxic vapour and must therefore be handled carefully to avoid operator exposure. Loads should not smell of formaldehyde when removed from the chamber. Generally thermally labile medical devices which will not tolerate high temperatures but will tolerate exposure to steam can be sterilized by LTSF. Care must be taken to ensure complex shapes, cavities and lumen are exposed for sufficient time to allow formaldehyde penetration.

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