Autoclaves: Explained

25 Sep

What is an Autoclave?

An autoclave is a machine that uses steam under pressure to kill harmful bacteria, viruses, fungi, and spores on items that are placed inside a pressure vessel. The items are heated to an appropriate sterilization temperature for a given amount of time. The moisture in the steam efficiently transfers heat to the items to destroy the protein structure of the bacteria and spores.

An autoclave is used to sterilize surgical equipment, laboratory glassware and instruments, pharmaceutical items, and other materials. It can sterilize solids, liquids, hollows, and instruments of various shapes and sizes.

Autoclaves vary in size, shape, and functionality. A very basic autoclave is like a pressure cooker; both use the power of steam to kill bacteria, spores, and germs resistant to boiling water and powerful detergents.

Most of our Life Sciences clients use autoclaves in their laboratories. Sterilizing harmful pathogens, growth media or material before disposal makes them safer for transport or storage.

How do Autoclaves Work?

There are three phases to the process:

  1. Conditioning Phase: Air inhibits sterilization and must be removed from the chamber during the first phase of the sterilization cycle known as conditioning. In dynamic air removal-type steam sterilizers, the air can be removed from the chamber using a vacuum system.
  2. Exposure Phase: After the air is removed, the sterilizer drain closes and steam is continuously admitted into the chamber, rapidly increasing the pressure and temperature inside to a predetermined level. The cycle enters the exposure phase and items are held at the sterilization temperature for a fixed amount of time required to sterilize them.
  3. Exhaust Phase: During the final phase of the cycle, exhaust, the sterilizer drain is opened, and steam is removed, depressurizing the vessel, and allowing the items in the load to dry.

What are the different types of autoclaves?

Different types of autoclaves are present according to your needs. It includes:

  • Pressure Cooker Type / Laboratory Bench Autoclaves (N-type): It's a domestic pressure cooker that is a perfect fit for tissue culture.
  • Gravity Displacement Type Autoclave: It's the most common type of autoclave used in research laboratories. In this autoclave, steam displaces air in the chamber by gravity through a drain port.
  • Positive Pressure Displacement Type (B-type): This is an advanced autoclave, in which steam is generated in a separate steam generator, which is then passed into the autoclave for sterilization of equipment.
  • Negative Pressure Displacement Type (S-type): This is the most expensive type of autoclave. It comes with a vacuum generator and steam generator that works efficiently to achieve complete sterilization of equipment.

Some of the cautions whilst using Autoclaves

  • Do not sterilize waterproof or water-resistant materials like oil or powders.
  • Do not overcrowd the autoclave with the vessel and equipment.
  • Only use autoclavable bags to autoclave packages wastes.
  • Use autoclavable bags to sterilize your equipment. Do not use aluminum foils.
  • Do not fill the autoclave chamber up to the lid.
  • Never attempt to open the autoclave while it's operating.
  • Tightly close the lid to ensure the completely closed condition of the autoclave for proper sterilization.
  • Do not use regular plastics or trays in the autoclave.
  • Never autoclave flammable, reactive, corrosive, toxic, or radioactive materials, household bleach, or paraffin-embedded tissue.
  • Fill the water in the steam generator up to the volume where it touches the end of the vessel or chamber of the autoclave.

Depending on the type of autoclave used by our clients, the Bulb scientific and technical services team will allow adequate space and services (Power, drainage, ventilation) for autoclaves at the design stage.

At Bulb, we are happy to assist with your bespoke laboratory design, process flow, equipment selection, and placement to achieve required compliance. Get in touch today at or call 0118 988 9200.

Ravi Kalsi

Laboratory Specialist

07719 064995

Get in touch

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