An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different from ambient air pressure. Autoclaves are used in medical applications to perform sterilization and in the food and chemical industries. They are also used in industrial applications.
Many autoclaves are used to sterilize equipment and supplies by subjecting them to high-pressure saturated steam at 121 °C (249 °F) for around 15–20 minutes depending on the size of the load and the contents. The autoclave was invented by Charles Chamberland in 1879, although a precursor known as the steam digester was created by Denis Papin in 1679. The name comes from Greek auto-, ultimately meaning self, and Latin clavis meaning key, thus a self-locking device.
Sterilization autoclaves are widely used in microbiology, medicine, podiatry, tattooing, body piercing, food industry, veterinary medicine, mycology, funeral homes, dentistry, and prosthetics fabrication. They vary in size and function depending on the media to be sterilized.
Typical loads include laboratory glassware, other equipment and waste, surgical instruments, and medical waste.
A notable recent and increasingly popular application of autoclaves is the pre-disposal treatment and sterilization of waste material, such as pathogenic hospital waste. Machines in this category largely operate under the same principles as conventional autoclaves in that they are able to neutralize potentially infectious agents by using pressurized steam and superheated water. A new generation of waste converters is capable of achieving the same effect without a pressure vessel to sterilize culture media, rubber material, gowns, dressings, gloves, etc. It is particularly useful for materials which cannot withstand the higher temperature of a hot air oven.
Autoclaves are also widely used to cure composites and in the vulcanization of rubber. The high heat and pressure that autoclaves allow help to ensure that the best possible physical properties are repeatable. The aerospace industry and sparmakers (for sailboats in particular) have autoclaves well over 50 feet (15 m) long, some over 10 feet (3.0 m) wide.
Other types of autoclave are used to grow crystals under high temperatures and pressures. Synthetic quartz crystals used in the electronic industry are grown in autoclaves. Packing of parachutes for specialist applications may be performed under vacuum in an autoclave which allows the be warmed and inserted into the minimum volume.
It is very important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a very poor medium for achieving sterility. Steam at 134 °C can achieve in three minutes the same sterility that hot air at 160 °C can take two hours to achieve. Methods of air removal include:
Downward displacement (or gravity-type): As steam enters the chamber, it fills the upper areas first as it is less dense than air. This process compresses the air to the bottom, forcing it out through a drain which often contains a temperature sensor. Only when air evacuation is complete does the discharge stop. Flow is usually controlled by a steam trapor a solenoid valve, but bleed holes are sometimes used, often in conjunction with a solenoid valve. As the steam and air mix, it is also possible to force out the mixture from locations in the chamber other than the bottom.
Steam pulsing: air dilution by using a series of steam pulses, in which the chamber is alternately pressurized and then depressurized to near atmospheric pressure.
Vacuum pumps: a vacuum pump sucks air or air/steam mixtures from the chamber.
Superatmospheric cycles: achieved with a vacuum pump. It starts with a vacuum followed by a steam pulse followed by a vacuum followed by a steam pulse. The number of pulses depends on the particular autoclave and cycle chosen.
Subatmospheric cycles: similar to the superatmospheric cycles, but chamber pressure never exceeds atmospheric pressure until they pressurize up to the sterilizing temperature.