AUTOCALVE

An autoclave is a machine that provides a physical method of sterilization by killing bacteria, viruses, and even spores present in the material put inside the vessel using steam under pressure.

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 increased.
• Similarly, the high pressure also facilitates the rapid penetration of heat into deeper parts of the material, and the 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 to the ambient pressure while the components inside remain hot for some time.

Autoclave Parts/ Components:

Pressure Chamber:

• The pressure chamber is the main component of a steam autoclave, consisting of an inner chamber and an outer jacket.
• The inner chamber is made up of stainless steel or gunmetal.
• The size of the pressure chamber ranges from 100 L to 3000 L.

 Lid/ Door:

• The purpose of the lid is to seal off the outside atmosphere and create a sterilized condition on ht inside of the autoclave.
• The lid is made airtight via the screw clamps and asbestos washer.

Pressure gauge: A pressure gauge is present on the lid of the autoclave to indicate the pressure created in the autoclave during sterilization.

Pressure releasing unit/ Whistle:

• A safety valve is present on the lid of the autoclave, which is crucial in cases where the autoclave fails to perform its action or the pressure inside increases uncontrollably.
• The valve has a thin layer of rubber that bursts to release the pressure and to avoid the danger of explosion.

 Steam generator/ Electrical heater: An electrical steam generator or boiler is present underneath the chamber that uses an electric heating system to heat the water and generate steam in the inner and outer chambers.

Wastewater cooler

• Many autoclaves are provided with a system to cool the effluent before it enters the draining pipes.
• This system prevents any damage to the drainage pipe due to the boiling water being sent out of the autoclave.

Procedure for running an autoclave:

1.  Check the working condition of the instrument for any defects or malfunctions.

2.  Sufficient amount of water is added to the chamber.

3. The materials are kept inside the chamber to be sterilized.

4. The lid and screw are tightly closed to create pressure inside the chamber and the instrument if switched on.

5. The safety valves are adjusted to maintain the pressure.

6. The water starts to boil and produces a huge amount of steam inside, which builds up the pressure.

7. Once the pressure is reached, the whistles blow out the extra pressure out.

8. After the whistle, the autoclave is kept for the required time period 15 minutes.

9. The instrument is turned off till all the pressure is released by the valve's outlet.

10. After the pressure is released, the lids and screws are released, and the materials are taken out.

Types of Autoclaves:

Pressure cooker type/ Laboratory bench autoclaves (N-type): 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: In this type of autoclave, the steam is created inside the chamber via the heating unit, which then moves around the chamber for sterilization.

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.

Negative pressure displacement type (S-type);

• autoclave that contains both the steam generator as well as a vacuum generator.
• The vacuum generator pulls out all the air from inside the autoclave while the steam generator creates steam.

Uses of Autoclave:

• They are used to decontaminate specific biological waste and sterilize media, instruments, and labware.
• Regulated medical waste that might contain bacteria, viruses, and other biological materials is recommended to be inactivated by autoclaving before disposal.
• In medical labs, autoclaves are used to sterilize medical equipment, glassware, surgical equipment, and medical wastes.
• Similarly, autoclaves are used for the sterilization of culture media, autoclavable containers, plastic tubes, and pipette tips.