How Autoclaves Work: Simple (…and Professional) Answer

Tuttnauer 3870EA AutoclaveThere is some confusion about how autoclaves work, so I hope to clear it up in this article.  Autoclaves are also called “steam sterilizers”. These machines decontaminate and sterilize instruments or gear that are needed for different uses such as: surgery, dental procedures, tattoos, and even mushroom growing!

The whole process is called the “sterilization process”, and it consists of the autoclaves creating: pressure, heat, steam.

Over the decades of research, specific times, temperatures, pressures, and packaging practices have been found to ensure all the microbes and fungus on something is killed through the sterilization process.

As in most articles here, I’m going to use the terms “autoclave” and “steam sterilizer” to mean the same thing (because they are).

The fundamentals of how an autoclave works are simple.  There are microorganisms on the stuff that we want to sterilize.  When an open wound is being exposed to something, we take these enormous precaustions to prevent contamintation.

One of these precautions comes from steam sterilizers processing things like surgical instruments, dental instruments, veterinary instruments, tattoo needles, etc.  The diseases, viruses, and fungus must be ELIMINATED AT ALL COSTS!!

Steps for Decontamination are First…

There is an initial step in sterilization called decontamination.  This is the cleaning, decontaminating, and washing of the dirty instruments, or whatever it may be. In the operating room, decontamination is done in the sterile processing department.

The workers wear massive amounts of protective gear: scrubs, gowns, gloves, face shields, boots, everything!  After the heavy contamination is scrubbed and rinsed, it goes through a large washer machine.

The gear to be sterilized comes through the other end, to sterile processing.  It is considered “clean” or “decontaminated” now on the sterile side.  The decontaminated gear is allowed to dry, then counted, put in the proper sets, and made ready for the autoclave.

Keep in mind, this is for a full operating room in a hospital, so the autoclaves are ten feet tall, built into a wall sometimes.  I’m giving you this sterilization run-down since offices of all sizes go through this process to some extent.  It is not on the scale, but the process should alway be there.

The dirty (used) instruments are decontaminated, washed, dried, prepared and wrapped, then cycled through the steam sterilizer.  It doens’t matter if it is the hospital, dentist’s office, tattoo artist, or dog groomer. The sequence is going to be similar.

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.  Here are the main points of sterilizer operations:

The Basics of How Autoclaves Work

  1. In the morning, the 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 to ensure sterilization.
  2. Items to be sterilized are disinfected (as mentioned above), dried, packaged, given an indicator, and labeled with the needed info such as: initials of worker, date, and name of item (if it’s a weird shaped one).
  3. The steam sterilizer is loaded with the decontaminated gear.  We allow room for the steam to penetrate all areas of the chamber.  In other words, it’s not packed completely tight.  The door is securely shut, lathed, or locked.  The correct sterilization cycle is selected (or the dials are turned) and it is run.
  4. The sensors and gauges do their work to monitor pressures, temps, and times.  The pump in the autoclave makes a vacuum in the autoclave chamber before injecting it with steam.  The explanation is that if there is no pressure in the chamber, when the steam is injected, it will fully penetrate the items inside to sterilize the entire surface area.  We want every crack and crevice to be sterile since microbes reproduce exponentially.
  5. The temperature is the main way that pressure is controlled, either by the machine in an automatic autoclave, or by a person using a manual sterilizer.
  6. After the sterilization cycle, either there is a drying cycle, or the door of the autoclave must be cracked to allow for drying (depending on the sterilizer).  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.

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.

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!

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