The Principles of Medical Device Decontamination

In these types of processes, the steam entering the chamber behaves as a heat transfer medium transferring energy through the container walls and into the aqueous fluid contained within the container. Such processes also have three phases in which the load is heated to a predetermined temperature, held for a predetermined time and then cooled back to ambient temperature. It is also possible to include air within the chamber to act as a ballasting overpressure to prevent flexible containers bursting as a result of the high pressures which can develop during sterilization. It is vital that any such air-steam mixtures are intimately mixed so as to avoid separation and stratification in the chamber which could give rise to dangerous cold spots. Sterilizers Saturated steam sterilizers can fall into one of two categories. There are small steam sterilizers often used in dental or GP surgeries and large steam sterilizers found in hospital settings. The difference between the two is related to chamber size. A sterilizer less than 60L and unable to accommodate a sterilization module measuring 30 x 30 x 60cm can be categorised as a small sterilizer. Any sterilizer with a chamber larger than 60L is a large steam sterilizer and these can be of any size up to several cubic metres. In a hospital, large sterilizers between 750 and 1000L are typically found. Whilst fundamentally the same i.e. they use saturated steam at high temperature and pressure in a sealed pressure vessel to effect sterilization, the requirements for small and large sterilizers differs as prescribed in published standards (see Table 10.1).

Physical Methods - High Temperature - Dry Heat

Dry heat sterilization is carried out in the absence of moisture. The process stages involve heating the load to the sterilization temperature (typically 160 o C) and holding it there (e.g. for 2 hours) followed by a cooling period. Heating and cooling the load can take a considerably long time if bulky items are being sterilized. Dry heat is used for the sterilization of non-aqueous pharmaceutical powders, oils, waxes and glassware but rarely used in hospital SSD’s. Great care must be taken to ensure homogenous thermal distribution in loads. Hot and cold spots can easily occur, and this is why hot air fan assisted ovens are common.

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