One of the processes forming part of the validation procedure of a sterilizer (autoclave). Revalidation of each sterilizer should be undertaken quarterly to ensure the sterilizer is functioning correctly. A suitably qualified person should undertake this process and each sterilizer should be validated independently during annual tests. Revalidation should also be undertaken after sterilizer relocation, repair work, control function modifications, or when key component parts of the sterilizer are replaced or altered. On completion of each sterilization cycle parametric inspection must be undertaken to verify that the cycle has completed within defined, validated critical parameters e.g. 134°C to 137°C for 3 minutes. Most autoclaves can display or record key sterilization cycle parameters such as temperature, pressure, and time. Ideally, all sterilizers should be fitted with a recorder or a process evaluation system (EN 13060; EN 17665 ; EN 285 ). These systems provide a permanent record of daily tests and all production cycles, reduce time spent in performing daily tests, generate a unique cycle number that can be entered in the patients' notes to assist traceability, and eliminate the possibility of transcription errors. The recorder printout should be kept securely in the sterilizer logbook. Some types of cycle printouts (e.g. from thermal recorders) fade quickly and therefore special action may be required to preserve these records (e.g. photocopying). Many modern sterilizers can record cycle parameters in an electronic archive. A variety of other indicators can be used including chemical indicators and biological indicators. Chemical indicators should meet the requirements of appropriate standards (e.g. BS EN 867, ISO 11140) and should be used only for the process specified by the manufacturer. The manufacturer's instructions for use and storage should be followed. There are three main types, none of which prove that an autoclaved item is sterile. The first type (process indicator) is often printed on dental instrument sterilization pouches and bags and on autoclave tape. These sterilization indicator marks change colour (typically they darken in colour) when exposed to steam and serve only to distinguish processed items from unprocessed items. The second type of chemical indicator ( performance indicator) are used as indicators for specific tests such as Bowie and Dick steam penetration indicators used to monitor steam penetration into a test pack or a process challenge device. The third type of chemical indicator includes integrating indicators and emulating indicators. These indicators are intended to monitor the attainment of two or more critical variables in the sterilization process, either by a graduated response or a defined end point reaction.
Biological indicators are designed to show by the survival of a test micro-organism whether specified sterilization conditions have been attained. The most commonly used test micro-organisms are heat-resistant spores of the bacterium Geobacillus stearothermophilius. Biological indicators must meet the requirements of BS EN ISO 11138–1:2006. They are of limited value in routine sterilization process control because of the delay before the results are available and are restricted to a few special applications (e.g. in process validation) where they should always be regarded as additional to the measurement of temperature, pressure, and time.