Laboratory autoclave

🏾 Content :

🏾 Definition

The autoclave is a steam sterilizer, it uses moist heat in the form of saturated steam under pressure to reach a temperature above the boiling point, up to 135-137°C, to destroy microorganisms such as bacteria, viruses, fungi and spores.

Steam sterilization is non-toxic, inexpensive, rapidly microbicidal, sporicidal, and rapidly heats and penetrates tissue

With variable size, shape and functionality, the autoclave can sterilize liquids, solids, cavities, surgical materials and laboratory instruments of different shapes and sizes, it is suitable for different scientific and industrial applications.



🏾 Principle of the autoclave

◉ The basic principle of autoclave sterilization is to expose each object to direct contact with steam at the required temperature and pressure for the specified time. Thus, there are four steam sterilization parameters: steam, pressure, temperature, and time.

  • The ideal steam for sterilization is dry saturated steam and entrained water.
  • The pressure serves as a means to achieve the high temperatures necessary to rapidly kill microorganisms.
  • Specific temperatures must be achieved to ensure microbicidal activity. The two common steam sterilization temperatures are 121°C (250°F) and 132°C (270°F).
  • These temperatures must be maintained for a minimum of time to kill microorganisms. Sterilization times vary depending on the type of item (eg, metal vs. rubber, plastic), whether the item is wrapped or unwrapped, and the type of sterilizer.

Autoclaves operate mainly by gravity or by vacuum-induced or pre-vacuum (pre vac) sterilization methods. Although some types of autoclaves combine both methods to sterilize :

🏾 How does the autoclave destroy bacteria?

The oldest and most recognized agent for the inactivation of microorganisms is heat. Moist heat destroys microorganisms through the irreversible coagulation and denaturation of enzymes and structural proteins.

🏾 Compatible/incompatible materials for the autoclave

🏾 Types and classes of autoclaves

When choosing an autoclave, it is possible to choose between three different types.

Class B autoclaves

Class B autoclaves are the most advanced steam sterilizers. In this type of autoclave, steam is generated, rapidly in seconds, in a separate steam generator which is then sent into the autoclave. Post-sterilization vacuum drying ensures complete drying of all loads after the sterilization process is complete.

Class B autoclaves are certified autoclaves (NF EN13060) used in hospitals, dental offices, laboratories, tattoo studios etc. They also meet all sanitary and epidemiological requirements.

Class N autoclaves

The class N autoclave is the lowest class device. Only instruments with a solid structure can be sterilized in such a device. It is not possible to sterilize hollow or porous cartridges or to sterilize items in wrappers.

It has an air and steam vent valve, it does not guarantee 100% air removal nor does it have an effective drying option.

Class S autoclaves

The class S autoclave is an intermediate class between N and B. Class S allows the sterilization of single-wrapped, multi-layered and more massive instruments, which cannot be sterilized in class N autoclaves.

Autoclaves of this class have a vacuum pump, which allows the air to be completely removed from the chamber before starting the sterilization process (less efficient than class B autoclaves).

🏾 Factors Affecting Sterilization Effectiveness


  1. CDC - Guideline for Disinfection and Sterilization in Healthcare Facilities
  2. CDC - Factors affecting the efficacy of sterilization
  3. S. Martin, E. Duncan, in Implantable Sensor Systems for Medical Applications, 2013
  4. Office of Laboratory Safety - Autoclave Use