How Does Autoclave Sterilization Work?

Grainger Editorial Staff

An autoclave is used in medical and laboratory settings to sterilize lab equipment and waste. Autoclave sterilization works by using heat to kill microorganisms such as bacteria and spores. The heat is delivered by pressurized steam. Pressurization allows the steam to reach the high temperatures that are required for sterilization.

According to Centers for Disease Control (CDC) Guidelines for Disinfection and Sterilization of Healthcare Facilities, pressurized steam is the most widely used and dependable method of sterilization. It’s nontoxic and inexpensive, it kills microbes and spores rapidly, and it quickly heats and penetrates fabrics.

According to manufacturer Tuttnauer, medical clinics and dental offices typically use tabletop autoclaves, which are about the size of a microwave oven, while hospitals use much larger units that can sterilize many instruments at once.

To work effectively, an autoclave must remove all the air in and around the object that’s being sterilized, forcing steam to penetrate its surfaces, according to Healthcare Purchasing News. There are two basic ways that an autoclave can remove the air and force in steam:

  • Gravity displacement autoclaves, also called gravity autoclaves, inject steam into the autoclave chamber and then rely on that steam, which is heavier than air, to force the air to leave the chamber through the drain vent at the bottom, according to the CDC.
  • Prevacuum or prevac autoclaves use a vacuum pump to remove air from the chamber before steam is admitted to it, which means that steam penetrates even porous objects almost instantly.

What Type of Autoclave Do I Need?

Gravity autoclaves have a simpler design and are recommended for most uses, according to manufacturer TOMY. They are suitable for common laboratory media including type I borosilicate glassware or other autoclavable labware, steel lab utensils, and biohazardous waste. On the other hand, prevac autoclaves are more effective at sterilizing objects that are large or porous, including wrapped objects such as surgical kits; objects made from high-density polyethylene, such as pipette tips and syringes; and animal cages and bedding.

How does autoclaving kill bacteria?

The heat that an autoclave delivers via pressurized steam kills bacteria and other microorganisms by causing the organisms' structural proteins and enzymes to lose their shape in an irreversible way, denaturing and coagulating them and making them nonfunctional.

What is the temperature for autoclave sterilization?

The most common temperature for autoclave sterilization is 121°C, but many autoclaves allow cycles at higher temperatures, such as 132°C and 134°C.

How long does it take an autoclave to sterilize?

The time required to sterilize something depends on what that object is made of, whether it's wrapped or unwrapped, and what type of autoclave is being used, according to the CDC. To sterilize a large volume of media or materials may require a longer sterilization cycle to allow the steam heat to penetrate the media fully , according to "Microbiology" by Daniel Lim.

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The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.


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