Autoclaves
Autoclaves
An autoclave is a pressurized device designed to heat aqueous solutions above their boiling point at normal atmospheric pressure to achieve sterilization. It was invented by Charles Chamberland in 1879.The term autoclave is also used to describe an industrial machine in which elevated temperature and pressure are used in processing materials.
Under ordinary circumstances (at standard pressure), liquid water cannot be heated above approximately 100 °C/212 °F (99.99 °C at 101.325 kPa, 99.62 °C at 100 kPa) in an open vessel. Further heating results in boiling, which is the transition from liquid to gas, but does not raise the temperature of the liquid water. However, when water is heated in a pressurized vessel such as an autoclave, it is possible to heat liquid water to a much higher temperature. As the container is heated the pressure rises due to the constant volume of the container. The boiling point of the water is raised because the amount of energy needed to form steam against the higher pressure is increased.
A medical autoclave is a device that uses steam to sterilize equipment and other objects. This means that all bacteria, viruses, fungi, and spores are inactivated. However, prions, like those associated with Creutzfeldt-Jakob disease, may not be destroyed by autoclaving at the typical 121°C for 15 minutes or 134°C for 3 minutes, but can be destroyed with a longer sterilization cycle of 134°C for 18 minutes.
Also, some recently-discovered organisms, such as Strain 121, can survive at temperatures above 121°C.
Autoclaves are found in many medical settings and other places that need to ensure sterility of an object. Many procedures today use single-use items rather than sterilized, reusable items. This first happened with needles, but today many surgical instruments (such as forceps, needle holders, and scalpel handles) are commonly single-use items rather than reusable.
Because damp heat is used, heat-labile products (such as some plastics) cannot be sterilized this way or they will melt. Some paper or other products that may be damaged by the steam must also be sterilized another way. In all autoclaves, items should always be separated to allow the steam to penetrate the load evenly.
Autoclaving is often used to sterilize medical waste prior to disposal in the standard municipal solid waste stream. This application has grown as an alternative to incineration due to environmental and health concerns raised by combustion byproducts from incinerators, especially from the small units which were commonly operated at individual hospitals. Incineration or a similar thermal oxidation process is still generally mandated for pathological waste and other very toxic and/or infectious medical wastes.