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Laboratory autoclaves

Laboratory autoclaves


An autoclave is essentially a heavy steel chamber which is used to sterilize equipment using pressurized steam. It is thought to have been invented by Charles Chamerberland in the late nineteenth century. He was a biochemist working with Louis Pasteur and is also thought to have accidentally made a vaccine against chicken cholera.  There are many different types of autoclave available for use, from small bench-top models to huge industrial equipment dealing with several loads daily. It is an invaluable piece of equipment for any laboratory.

Early models use the downwards displacement of air by steam to generate the necessary pressure inside. Steam enters through a vent at the top of the chamber. This forces the air out of a controlled drain towards the base. This is called a downward displacement autoclave. The replacement of air by the same volume of steam creates a lowered internal pressure which allows the steam to become superheated. Autoclaves therefore have heavy metal doors which are closed using a secure locking mechanism.

Vacuum pump models can pump the air out directly before steam enters. The pressure inside allows a temperature of 121oC to be reached. This is the most effective way of sterilising laboratory equipment and is known to effectively destroy most, if not all micro-organisms. The value of a vacuum purged autoclave is that it can also be used to remove the steam at the end of the cycle which can present an explosion hazard if not dealt with adequately. This also facilitates rapid drying of the contents.

On an industrial scale, huge, continuous sterilizers exist which have an internal conveyor belt assembly. These are towers up to 20m high which contain three compartments. A preheating chamber brings the temperature of the contents up to the required level. The next compartment is a steam sterilisation chamber, and then a water cooling chamber. The items to be sterilised are held within large buckets and slowly moved up through the different chambers. They can be held for the required amount of time within each to ensure that sterilisation is complete.

A 15-20 minute cycle of steam sterilisation is usually enough to completely sterilise equipment for laboratory use. Autoclaves are also routinely used in medical environments to sterilise waste materials prior to their safe disposal. The autoclave is simple and cost effective. The simple use of steam far outweighs the alternatives of chemical or radiation sterilisation in a routine environment.