Autoclave definition and how it works
An autoclave, sometimes referred to as a sterilizer, is a device that is used in laboratories to sterilize equipment. An autoclave sterilizes equipment by exposing them to pressurized steam heated at 121 ͦC for about 15-20 minutes. This device was invented by Charles Chamberland in 1879. Today, autoclave definition has been extended to cover various applications in medicine, microbiology, dentistry, podiatry, veterinary science, mycology, body piercing, tattooing and prosthetic fabrication. Autoclaves come in different sizes and have varying functionalities and the choice of an autoclave is usually determined by the device to be stabilized.
How autoclaves work
Any effective autoclave uses saturated steam to create the desired sterilization temperatures inside the autoclave chamber. This is achieved by removing air in the chamber and the load. Low surface area materials with little or no air pockets require little air removal and the air in them is usually removed by automatic air purging. The air removed from the chambers of these items leaves through a vent while high pressure saturated steam enters the chamber from an integral source or an external supply. Effective removal of air is achieved by leaving the vent open for several minutes. The pressurized steam forces the air out of the item and the autoclave. Items that have many air pockets e.g. fabrics and wrapped instruments require a more effective air removal method.
Vacuum air removal system is very effective in removing air from the autoclave and the items to be sterilized. In this method, a vacuum is first created in the chamber before the steam is introduced. When all air is removed from the chamber and the material, the pressurized steam is introduced and which makes the temperature and pressure inside the vessel to rise up to when the set temperature is reached. The recommended sterilization temperature is 121 ͦC or more and this temperature can only be achieved when the steam is pressurized to at least 1.1 Bar G. This high pressure can only be sustained by autoclaves that are designed to the set engineering standards.
The required sterilization temperature within the chamber is achieved in the following ways:
1. For laboratories that have a direct steam source, steam is directly injected to the chamber until the desired temperature is achieved
2. Laboratories that do not have an internal steam supply usually use steam from external sources e.g. a stainless steel steam generator. The steam generators can be fitted within the autoclave cabinets or put externally especially for Larger autoclaves.
3. Some autoclaves are fitted with heaters at the base of the chamber which heat the water to the required temperature to generate steam.
Steam generators are preferred because they ensure that steam is immediately available for sterilization as compared to some basic autoclaves that generate steam from water. These basic autoclaves require water to be manually topped up or pumped to the vessel which is quite involving.
When the required temperature inside the chamber is reached, the steam supply is turned off and the temperature and pressure inside gradually drops. When the items need to be dried, the steam is pumped out of the chamber using a fitted vacuum pump.
Autoclave definition however varies depending on the intended area of application and the manner of operation of the device.
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