An autoclave is essentially a sophisticated steam, or pressure cooker. The increase in pressure also pushes temperatures up. It would take two hours of 160 °C air sterilization to achieve what 134 °C steam can do in three minutes. At 15lb per square inch, the steam will reach 121°C. If this is maintained for over 15 minutes, bacterial and fungal spores cannot survive.
Autoclaves are used by dentists, doctors, podiatrists, vets and tattooists to sterilize needles and other equipment. But that’s not all. The electronics industry obtains its synthetic quartz crystals by growing them in autoclaves. Rubber is vulcanized in autoclaves. Aerospace industries use huge autoclaves, as do hospital laundries and other places where medical waste is treated prior to disposal.
In order for sterilisation to be effective, the instruments placed in the autoclave must not be touching: the steam must come into contact with every part of the instrument being sterilized.
For safety’s sake, an autoclave’s sterility/function should be monitored and tested regularly. Physical, chemical or biological indicators can be used.
Chemical autoclave tape changes colour when the correct conditions of temperature and pressure are met, but does not detect pathogens. Bowie-Dick devices put the chemical indicator in the centre of a wad of compressed paper – which can demonstrate that the conditions for sterilization lasted long enough. A biological indicator contains spores of heat-resistant bacterium. If these manage to germinate and change the colour of a pH sensitive agent, then the autoclave isn’t effective enough. Physical indicators consist of an alloy that should melt under the correct conditions.