Laboratory Autoclave- Definition, Principle, Parts, Types, Uses

An autoclave is a machine that uses the physical method of sterilization that not only sterilizes the surface of the material but also the constituents present in it, thereby, killing all different types of bacteria, viruses, fungi, and even spores using steam under pressure. It sterilizes the material inside the chamber by applying high temperatures for a particular period. It is also known as a steam sterilizer which is required in healthcare facilities and industries for different purposes. This method of sterilization is the most effective method out of all the methods because it is based on moist heat sterilization.

Laboratory Autoclave
Figure: Laboratory Autoclave. Image Source (Right): Labster.

History of Laboratory Autoclave

  • Denis Papin:

British physicist born in French invented the steam digester in 1967. The cooking instrument that he invented is now commonly known as a pressure cooker, which later, developed into an autoclave.

  • M. Lemare:

He made modifications to the Papin’s steam digester and created a better version of it in 1820. He also claimed that his cooking vessel can cook meat for half an hour only. The only drawback, of his steam digester, has that there were lots of injuries that took place because of it. 

  • Charles Chamberland:

He transformed the cooking steam digester into a fully functional autoclave in 1879, that started using inn medical and scientific industries. He was a microbiologist who worked under Louis Pasteur. This invention of his started to known as an autoclave sterilizer. 

Principle of Laboratory Autoclave

An autoclave is based on the principle of moist heat sterilization which efficiently kills all the microorganisms including the spores which are highly resistant to Endospores and can escape all sterilization procedures except autoclaving. It uses the ability pressure which builds inside the chamber due to the presence of steam, which has higher penetration power than normal heating temperature.

Figure: Principle of Laboratory Autoclave. Image Source: Orbit Biotech.

The commonly used temperature-pressure combination is 121 degrees Celsius at 15 psi for 15-20 minutes. This temperature is suitable to eliminate all kinds of microbial spores present in sterilizing medium. Extended time is required to sterilize the large volume vessels because they take longer to reach the temperature of sterilization.

Components/ Parts of Laboratory Autoclave

Pressure cooker types and laboratory bench autoclaves are the simplest type of autoclaves. The different parts of the autoclave are:

1. Pressure chamber

  • The main component of an autoclave consists of an inner chamber and an outer jacket.
  • The outer part of the chamber is made up of iron and the inner part is made up of stainless steel or gunmetal.
  • There is an additional presence of an outer jacket in autoclaves used in healthcare laboratories which efficiently reduces the time of sterilization.
  • Material to be sterilized is kept inside the chamber of the autoclave.
  • Vessel Size ranges from 100L-3000L.

2. Lid/Door

  • Most important component.
  • Lead is used to seal the chamber, and thus allow it to build the required pressure and temperature.
  • It is specifically made airtight via screw clamps and an asbestos washer.
  • The lid has various other parts such as:
  1. Pressure gauge:
  • It is used to indicate the pressure that is built inside the autoclave during sterilization.
  • Ensure safety by sealing the chamber 
  1. Pressure releasing unit/whistle:
  • Function the same as the whistle of a pressure cooker, in which it is used to release the steam through holes in the whistle when the pressure inside the cooker increases above a certain level.
  1. Safety valve:
  • Curcial most component
  • The safety valve checks on the proper working of the autoclave, in a way that when the autoclave fails to perform its function and inside pressure increases uncontrollably, the safety valve prevents damage from happening.

3. Steam generator

  • The electric heating system is used by this generator to generate heat to bring the water to its steam form and it helps in generating steam in the inner and outer chambers.
  • The most important thing to keep in mind is the level of water, is that it should cover the heating system but it should not be up to the point where the tray is, which is used to keep the material to be sterilized.

4. Vacuum generator

  • It is optional and present in only a few types of autoclaves.
  • A separate vacuum generator is required which creates a vacuum inside the chamber by sucking out the air present in it.
  • Because there is air left inside the chamber, then it will support the growth of aerobic bacteria of a different kind. And also, it will interfere with pressure generation as it will create air pockets between steam molecules. That is why it is better to have an external vacuum generator to make sure the proper functioning of the autoclave.

5. Wastewater cooler

  • Before the hot effluent enters the draining pipes for discard, is cooled using a wastewater cooler.
  • It makes sure that draining pipes won’t get damaged because of the high temperature of effluent.

Types of Laboratory Autoclave

Based on the method of air replacement

One of the major factors that define the efficiency of the sterilization procedure in the absence and proper removal of cold is present in the chamber with that of steam. So, on the basis of replacement of this cold air, the autoclave is of two types.

a. Gravity displacement autoclave:

  • A most common type of autoclave
  • The presence of an exhaust valve allows the passage for the cold air to escape the chamber gradually as the steam starts rising inside the chamber. 
  • Simple in design
  • Easy to operate
  • Low cost
  • Suitable for materials that do not require deep steam penetration. Example: plasticware, glassware, liquid medium, etc.

b. Vacuum displacement autoclave:

  • Using the pumping system, a vacuum is created inside the chamber to allow the steam to cover all the space.
  • Complex mechanism and designing
  • Comparatively expensive
  • Suitable for porous and hard-to-reach materials such as cotton, fabrics wrapped in surgical kits, etc.

Based on class

a. Class N autoclave

Same as gravity displacement autoclave.

b. Class S autoclave: 

  • Immediate type of N and B class
  • Type of vacuum displacement autoclave.
  • A single pre-vacuum system is allowed only.
  • Effectively less than class B.

c. Class B autoclave

  • Most advanced form 
  • The function of the fractioned pre-vacuum system.
  • Has vacuum drying property as well.
  • Application in tattoo studios and dentistry etc.

Based on design

  1. Pressure cooker type autoclave
  2. Horizontal autoclave
  3. Vertical autoclave
  4. Benchtop autoclave

Procedure of Running a Laboratory Autoclave

  1. Fill the pressure chamber with a sufficient amount of water that should be below the plate to which the material is to be kept and the heating tray should be fully submerged in it.
  2. Place the material to be sterilized on the tray above the heating pad.
  3. Close the lid of the autoclave and switch on the electrical heater.
  4. The safety valve is now adjusted up to the pressure that is required.
  5. Allow the stream of hot air to escape through the air outlet valve after the water boils and at this point, air should be displaced by the steam built inside the chamber.
  6. One way to check the displacement of air with steam is by passing it from the discharge tap into a pail of water and passing it through a connecting rubber tube. The air bubble will start to appear and when it stops, it indicates that air is displaced by steam. 
  7. Now, close the discharge tap.
  8. As the steam pressure starts building, and one gets the desired pressure, the safety valve opens and excess steam should escape the chamber.
  9. Set the time for which you want to autoclave the material, which is 15-25 mins in most cases.
  10. Now when the set time is complete, the electrical heater must be stopped and the autoclave chamber should be left untouched to cool.
  11. Open the chamber and carefully take out all the sterilized materials kept initially. 

Uses and Applications of Laboratory Autoclave

Some of the applications and major uses of autoclaves in different industries for sterilization are:

  • In the scientific research laboratory
  • To sterilize autoclavable glassware and plasticware in microbiology, and pharmaceuticals laboratories for both research and academic purpose.
  • Sterilization of biohazardous material before disposal in laboratories is done using autoclaves.
  • Use to sterilize surgical equipment, blades, etc in hospitals and the medical industry. Can also be used to sterilize aprons, gowns, etc of health workers.
  • Culture media sterilization in laboratories.
  • Uses in automobiles and agricultural industries.

Limitations of Laboratory Autoclave

  1. Cannot be used for temperature-sensitive material that cannot withhold high-temperature conditions and get damaged.
  2. Since it follows the principle of moist heat sterilization, thus sterilized material becomes wet.
  3. Waterproof material such as oil, grease, etc or gloved powders cannot be sterilized, since they require dry heat.
  4. Materials that are prone to corrosion cannot be sterilized.
  5. Since low-quality glassware and plasticware cannot sustain high temperatures, thus they cannot be sterilized.
  6. Limitation of space inside the autoclaving chamber.
  7. Liquid enclosed in the closed vessel cannot be sterilized, because vaporization of liquid for a long period can damage the vessel.
  8. Effectiveness of sterilization reducing with the rapping of glassware with aluminum foil and plastic covers.

Precautions while using Laboratory Autoclave

  1. Autoclaving should be done separately for waste and clean items.
  2. The use of polythene trays should be avoided since they will melt and damage the autoclaving chamber.
  3. Material kept in the autoclave should not touch the sides and upper portion of the chamber.
  4. Overloading of material should be avoided, since the penetration rate of steam will vary in all the items, resulting in poor sterilization efficiency.
  5. Wrapping with aluminum foil should be avoided in order to increase the efficiency of sterilization and wrapping with material that allows penetration should be encouraged.
  6. Autoclaving chamber should be filled with a sufficient amount of water that should be below the plate on which the material is to be kept and the heating tray should be fully submerged in it.
  7. The air inside the chamber should completely be replaced with steam.


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