How Does an Autoclave Work?

Tuttnauer 3870EA AutoclaveI have seen SO MUCH confusion about how autoclaves work, I hope to boil it down in this article.  It is simple: pressure, heat in the steam, and time are used to kill all the microbes in the chamber.

I’m  going to call autoclaves “steam sterilizers” through this article, too… a heads up on that.

The fundamentals of how an autoclave works are simple.  There are microorganisms on the stuff that we want to sterilize.  This microscopic shit isn’t safe on things like surgical instruments, dental instruments, tattoo needles, etc.  It carries disease and infectious bugs!

First, there is the cleaning and decontaminating of the dirty instruments, or whatever you are using.  Then, it is washed, dried, and wrapped, depending on the size and contents.

The newly decontaminated gear is loaded into the chamber of the autoclave.  There must be room for the steam to get around everything in the chamber during the sterilization process.

The Similarities of Most Autoclaves

Most autoclaves are built around the chamber that can withstand high temperature and pressure.  These forces must be caged to prevent a catastrophic explosion in an extreme case.  But for the most part, the chamber is where your items are loaded and is what fills up with steam.

A vacuum is created by a machine pump right before the sterilization cycle begins, in most up to date autoclaves.  This allows the steam to forcefully penetrate all surface areas in the chamber.

Most sterilizer machines have electronic gauges and automatic shutoffs built into them.  It makes them very safe and precise in their control of pressure and temperature.  There are very strict standards about the times, pressures, and temperatures that are acceptable for sterilization.  Be sure to research the ones that apply to where you live.

After the sterilization cycle, some automatic autoclaves have a drying cycle.  This speeds up the total time that it takes to process that sterile load.  Others don’t and you need to crack the door for a bit on some benchtop steam sterilizers.

So, I kind of rambled and don’t know if I answered “how autoclaves work”.  In a nut shell:

  1. Autoclave is cleaned and turned on, water added to proper level, test run done if needed.  In general: the electric autoclave heats water to make steam and sterilize items in its chamber.  This chamber is the main working area of the autoclave.  Pressure, time, and temperature NEED to be monitored.
  2. Items to be sterilized are disinfected, dried, packaged, given an indicator, and labeled with the needed info.
  3. Autoclave is loaded with prepared gear, giving room for the steam to penetrate all areas of the chamber.  Door is securely shut.  Correct cycle is chosen and run.
  4. The sensors and gauges do their work.  The pump may have made a vacuum in the autoclave chamber before injecting the steam.  Anyway, the steam is injected.  The temperature is the main way that pressure is controlled, either by the machine in an automatic autoclave, or by a person in a manual sterilizer.
  5. After sterilization cycle, either there is a drying cycle, or the door of the autoclave must be cracked to allow for drying.  Wetness contaminates any newly sterile gear, so please keep that in mind!

The combo of pressure, temperature, and time is agreed to be the best way of killing microorganisms.  The test to see if the “autoclaving succeeded” is called a biological test.

It’s a “tough to kill” fungus strain that you run in the morning.  Then, you put it in an incubator device.  If the strain grows, an alarm goes off, saying that a sterilizer may need more tests and a closer look.

Since it is tough to kill, the assumption is that the other microorganisms are dead, too.  It’s strange to think that we depend so much on assumptions, even today.

Okay, that’s my broad overview of how an autoclave works.  I still feel like some of you may not be satisfied with this answer, so leave a comment to speak your mind and I will make this article better, and/or create some videos about the way(s) that steam sterilizers exist to protect all of us from diseases and infections.

It’s all about safety and effectiveness here at!  Have a good one, focus on the positive.  Leave those comments… I feel a video series being born!