SUMMARY The performance of autoclaves in 27 laboratories, operated in accordance with the normal routine of local practice, has been monitored using thermometric equipment. Sterilising performance was unsatisfactory on 10 of 62 occasions, and cooling was inadequate on 52 of 60 occasions.As part of the general concern over safety standards, laboratories in the Public Health Laboratory Service (PHLS) were encouraged to obtain thermometric equipment to monitor the performance of their autoclaves. This provided an opportunity to discover whether, when the autoclaves were operated in accordance with the normal practices in use in those laboratories at the time of acquisition of the equipment, sterilising performance was satisfactory and cooling of the loads was adequate to allow the autoclaves to be opened safely. The results of a survey of these aspects of autoclaving practice in 27 laboratories are reported here.
Survey material LABORATORIES AND AUTOCLAVESIn all, 46 downward-displacement autoclaves in 27 laboratories were tested. Twenty-four of the autoclaves were vertical and cylindrical, and 22 were horizontal. Some were the responsibility of the PHLS Board, some of Area Health Authorities and, in one case, of a university department.Twenty-three of the laboratories were engaged, to a varying extent, in clinical microbiology and four were reference laboratories in special microbiology.
MethodTests were made when the autoclaves were loaded, operated, and unloaded in their normal manner according to local custom and practice. Most temperature measurements were made with copper/ constantan thermocouples (02 mm diameter) insulated with polytetrafluoroethylene (PTFE) but unsheathed. Usually these could be led into the autoclave chamber between the door and the seal. They were inserted at those points in the load where experience had shown that performance was likely to be unsatisfactory as regards either sterilising or subsequent cooling. For example, when testing the processing of discarded cultures, a thermocouple was placed inside one of the cultures making up the load, and this was placed at the centre and about one-third of the way up the discard container. Similarly, when observing cooling times, thermocouples were placed in the largest units of volume making up the load since it was in these that cooling was likely to be most prolonged.Thermocouple signals were recorded on a suitable instrument; these were checked at intervals against a mercury-in-glass thermometer which had been certified by the National Physical Laboratory.Not surprisingly, the choice of sterilising temperatures or times among the laboratories was not uniform, thus making comparison difficult. Furthermore, distinction has to be drawn between the treatment given to discarded cultures and other materials that have to be sterilised to make them safe, and that accorded to culture media which require to be heated to the minimum temperature and for the time which experience will have shown 418