Autoclaves work by allowing steam to enter, and maintaining pressure at 15 psi. This causes the steam to reach 121°C, and this is maintained for at least 15 minutes.
The high pressure means autoclaves are constructed of strong metal, and are shut very tightly and securely.
Autoclaves are found in hospitals, microbiology labs, and other places that need to ensure sterility of an object.
Because damp heat is used, heat labile products (such as plastics) cannot be sterilised this way or they will melt. Some paper, or other products that may be damaged by the steam, should also be sterilised another way.
Chemical indicators, can be found on medical packaging and autoclave tape, and these change colour once the correct conditions have been met. This indicates that the object inside the package, or under the tape, has been autoclaved sufficiently.
Biological indicators include Attest devices. These contain spores of a heat resistant bacterium. If the autoclave did not reach the right temperature, the spores will germinate, and their metabolism will change the colour of a pH-sensitive chemical.
Physical indicators often consist of an alloy designed to melt only after being subjected to 121°C for 15 minutes. If the metal has melted, the change will be visible.
As well as these separate indicators, autoclaves have temperature and pressure gauges visible from the outside.Autoclave quality assurance
There are physical, chemical and biological indicators that can be used to ensure an autoclave reached the correct temperature for the correct amount of time.