Autoclave Working Principles


An autoclave is a sterilization device that is widely used in in hospitals, Pharmaceutical industries and laboratories. Sterilization is critical within the pharmaceutical and medical industries.

How do Autoclave works :

An autoclave is a device that works on the principle of moist heat sterilisation, wherein saturated steam is generated under pressure in order to kill microorganisms such as bacteria, viruses, and even heat-resistant endospores from various types of instruments. This is done by heating the instruments within the device to temperatures surpassing the boiling point of water.

This process is also embodied by gas laws, which basically states that the higher the pressure is within the device, the higher the temperature increases. In other words, pressure and temperature are directly proportional to each other.

It is also important to note that it is the temperature that kills the microorganisms, not pressure. Rather, higher pressures are capable of increasing the boiling point of water, which thus increases the temperature of sterilization. High pressure also helps heat to rapidly spread within the material.

Autoclaves typically yield a temperature of about 121 degrees Celsius, taking about 15-20 minutes to complete the sterilization process. However, autoclave cycles may be adjusted accordingly by the working technician. 

Autoclaves are grounded on three factors, namely: pressure, temperature, and time. These three factors all work together to create saturated steam, within a particular time frame, that can kill all signs of microbial life, whether they are in vegetative or spore form.

What is The Operating Procedure of Autoclave :

1). Check if there are previous instruments, Glass, stainless steel, cultures etc contained within the chamber.

2). Put water in the chamber and make sure it is the right amount.

3). Place the instruments, Glass, stainless steel, cultures etc inside the chamber which are required to be sterilized.

4). Close the lid and tighten the screws then switch on the electric heater.

5). Adjust the safety valves to maintain the required pressure level within the chamber.

6). Once the water within the chamber begins to boil, the air-water mixture can escape through the discharge tube in order to displace all the air inside. Complete displacement is evident when no more water bubbles come out from the pipe.

7). Close the drainage pipe and let the steam reach the desired level.

8). Once the pressure level has been reached, blow the whistle to remove all the excess pressure within the chamber.

9). Let the autoclave run for the set time period after the whistle.

10). Switch off the electric heater and let the autoclave cool until the pressure within the chamber has lowered down to the atmospheric pressure.

11). Open the discharge pipe to allow air from outside the autoclave to enter. 

12). Open the lid and remove the instruments from the chamber.

The Stages of Autoclave Sterilization :

The sterilization process includes different phases

  1. Purge Phase : During this phase steam displaces air within the autoclave chamber and both temperature and pressure begin to increase
  2. Sterilization Phase : The exhaust remains closed, allowing the temperature and press to rapidly rise to the desired values. It is during this phase that autoclaves harsh conditions destroy bacteria, spores and other pathogens.
  3. Exhaust Phase : Pressure is released from chamber, but temperature remain high. Operator or microbiologist should take care when removing hot contents from autoclave.

Autoclave Compatible and Incompatible Materials

Compatible Materials Incompatible Materials
Biological cultures and stocksMaterials containing solvents, volatile or corrosive, or flammable chemicals
Culture dishes and related materialsMaterial contaminated with chemotherapeutic agents or cytotoxic drugs
Contaminated solid items (i.e. pipette tips, gloves, Petri dishes, etc.)Material containing Bleach*
Discarded live (including attenuated) viruses/vaccinesCarcinogens or mutagens (i.e. ethidium bromide)
Polypropylene (PP) and polycarbonate (PC) plasticsPhenol and Trizol
Borosilicate glassPolystyrene (PS), polyethylene (PE), and high-density polyethylene (HDPE) plastics
Stainless steelHoushold glassware

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