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AUTOCLAVE.
Autoclaving is the most effective method of sterilizing the lab equipment especially for liquid handling products to kill harmful bacteria, viruses, fungi, and spores.
The autoclaving process takes advantage of the phenomenon that the boiling point of water (or steam) increases when it is under high pressure.
Autoclaving or steam sterilizer is used in several industries including medicine, dentistry, microbiology and veterinary science.
| It is performed in a machine known as the Autoclave where high pressure is applied with a recommended temperature of 250°F (121°C) for 15-20 minutes to sterilize the equipment |
MAIN COMPONENTS
- Heating Elements
- Temperature Controller
- Pressure Sensor
- Chamber
- Door gasket
- Safety valve
- Water level Sensor
PHASES OF A STERILIZATION
AUTOCLAVE PRINCIPLE/ WORKING
- The autoclave works on the principle of moist heat sterilization where steam under pressure is used to sterilize the material present inside the chamber.
- The high pressure increases the boiling point of water and thus helps achieve a higher temperature for sterilization.
- Water usually boils at 100°C under normal atmospheric pressure (760 mm of Hg); however, the boiling point of water increases if the pressure is to be increased.
- Similarly, the high pressure also facilitates the rapid penetration of heat into deeper parts of the material, and moisture present in the steam causes the coagulation of proteins causing an irreversible loss of function and activity of microbes.
- This principle is employed in an autoclave where the water boils at 121°C at the pressure of 15 psi or 775 mm of Hg.
- When this steam comes in contact with the surface, it kills the microbes by giving off latent heat.
- The condensed liquid ensures the moist killing of the microbes.
- Once the sterilization phase is completed (which depends on the level of contamination of material inside), the pressure is released from the inside of the chamber through the whistle.
- The pressure inside the chamber is then restored back to the ambient pressure while the components inside remain hot for some time.
ADVANTAGES
- Economical or cheap
- Short procedure time
- Provides good penetration on all surfaces
- No additional chemicals or disposables required
DISADVANTAGES
- Moisture retention
- Carbon steel can get damaged due to moisture exposure
- Only stainless steel instruments and plastics which can bear the heat be sterilized
TYPES OF AUTOCLAVE
There are different types of autoclaves present in the market, some of which are:
- Pressure cooker type/ Laboratory bench autoclaves (N-type)
- These, as domestic pressure cookers, are still in use in many parts of the world.
- The more modern type has a metal chamber with a secure metal lid that can be fastened and sealed with a rubber gasket.
- It has an air and steam discharge tap, pressure gauge, and safety valve. There is an electric immersion heater at the bottom of the chamber.
- Gravity displacement type autoclave
- This is the common type of autoclave used in laboratories.
- In this type of autoclave, the steam is created inside the chamber via the heating unit, which then moves around the chamber for sterilization.
- This type of autoclave is comparatively cheaper than other types.
- Positive pressure displacement type (B-type)
- In this type of autoclave, the steam is generated in a separate steam generator which is then passed into the autoclave.
- This autoclave is faster as the steam can be generated within seconds.
- This type of autoclave is an improvement over the gravity displacement type.
- Negative pressure displacement type (S-type)
- This is another type of autoclave that contains both the steam generator as well as a vacuum generator.
- Here, the vacuum generator pulls out all the air from inside the autoclave while the steam generator creates steam.
- The steam is then passed into the autoclave.
- This is the most recommended type of autoclave as it is very accurate and achieves a high sterility assurance level.
- This is also the most expensive type of autoclave.
