What is an Autoclave and How Does it Work?

Nov 13th 2018

Autoclaves have become a standard piece of medical equipment found in most labs, dental and medical facilities today. But what is an autoclave and what is it used for? In this article we will not only detail the purpose and functionality of an autoclave, but the different types of autoclaves and sterilizers available.

What is an autoclave?

As you might imagine, a couple hundred years ago, sterilization of medical and surgical tools was not at its best. In the 1800s researchers started to understand that sterile surgery was important and they began to search for better sterilization methods. Thanks to a man named Charles Chamberland, in 1884, the first autoclave sterilizer was invented. Today the autoclave is a key medical device found in every hospital, dental office, and laboratory.

What is an autoclave used for?

In short, an autoclave is used to sterilize pharmaceutical, dental, lab, and medical equipment. They vary in size, shape, and functionality depending upon the needs of the user and the materials that require sterilization. An autoclave’s function is to sterilize liquids, solids, waste, and even biochemical hazards in safety labs.

At its basic function, an autoclave acts like a giant pressure cooker utilizing steam to kill the germs and bacteria that cleaning products or boiling water simply cannot. However, autoclaves outperform pressure cookers by creating extra autoclave pressure to raise the temperature of the water to above boiling point producing more heat effectively killing germs.

The other key to an autoclave is time. A lengthy high pressure steam sterilization is far more effective than a quick wash with detergent.

Why do autoclaves require steam?

Easily created and transferrable, steam is one of the most powerful methods of sterilization. However, not all steam is created equal. According to Tuttnauer, the optimal composition of steam within an autoclave is 3% liquid and 97% gas. Any change in the percentage of moisture increases or decreases sterilization time.

If the steam is too wet, its heat transfer efficiency is lowered and won’t properly sterilize wrapped tools or pouches. Additionally, the moisture created by the steam can corrode products over time and produce bacteria.

If the steam is too hot, it will turn the sterilizer into a dry heat sterilizer, this is known as superheated steam. Superheated steam is less efficient in killing germs and requires a longer sterilization process.

How do you use an autoclave?

Now that we understand what an autoclave is, we will discuss how they are used.

Autoclave chambers are where you load your materials and the sterilization process takes place. Once the chamber is sealed, a vacuum pump or the process of pumping in steam removes all of the air.

Sterilization Phase:

Steam is then pumped through the chamber until it reaches an above boiling point temperature, 121-140 celsius. Depending upon the size and power of the autoclave and the size of the load, sterilization times can vary between 3-20 minutes in order to properly kill microorganisms.

Cool Down Phase:

Once the sterilization process is completed, there is a cool down phase. Remember, an autoclave uses high pressure, high temperature steam so allowing a proper cool down period before opening is crucial. A sudden release of this pressure could result in a steam explosion and cause injury.

What can’t be sterilized in an autoclave?

While an autoclave is used to sterilize a wide variety of medical equipment and tools, there are some materials that you shouldn't put into an autoclave.

  • Heat labile products
  • Radioactive elements
  • Volatile materials
  • Chlorinated compounds
  • Corrosive chemicals
  • Articles contaminated with chemotherapeutic agents
  • Certain plastics
  • Articles that can be destroyed under the steam.

Types of Autoclaves

Autoclaves vary in size and shape depending upon the need of the clinician or facility. For example, smaller microwave sized automatic sterilizers and autoclaves are common in dental offices or medical facilities that don’t require large equipment sterilization. In hospitals, larger autoclaves, also known as horizontal autoclaves, are common. These larger autoclaves are meant to handle larger load sizes and equipment based on the needs of the hospital.

Horizontal or Downward Displacement Autoclave

In a Downward Displacement Autoclave, also known as a horizontal or gravity displacement unit, cold air escapes through the bottom of the chamber as steam displaces it from above.

This type of sterilizer uses a heating elements to heat up the water and produce steam. The steam then forces the air inside the sterilization chamber to move downward and eventually the air is forced out through the drain of the sterilization chamber. Once the temperature within the chamber is sufficient, the sterilization process begins.

Vacuum Assisted Autoclave

In a vacuum assisted autoclave, there is a vacuum pump to remove air from the sterilization chamber and steam is created in a second, separate chamber. Air is quickly forced out from the sterilizing chamber at the beginning of the cycle while steam pulses in creating a vacuum. This way, steam is able to penetrate materials very quickly. There is another vacuum within the autoclave that withdraws moisture after sterilization, allowing a quicker drying process.

Classification of Autoclaves

Autoclaves can be classified as a type “N” or type “B” unit. The main difference is type B autoclaves use a vacuum pump to remove air from the chamber and type N autoclaves don’t.

Type “B” autoclaves are best used for wrapped and hollow instruments such as products in pouches and textiles. A class B autoclave is able to provide more complete air removal before the sterilization process begins due to the vacuum pump. The vacuum pump allows better penetration of steam into difficult load types.

Type “N” autoclaves are best for solid, unwrapped instruments due to the method of air removal. This method uses steam to eliminate air, but depending upon the method used, complete air removal from hollow or porous materials isn’t as efficient as a type “B” autoclave.

How do you choose the best autoclave?

As we discussed above, not all autoclaves are the same, so how do you choose the best autoclave for your needs? Before you choose an autoclave, you first need to determine the following factors.

How large are the sterilization loads?

When considering an autoclave, the most important factor is to determine if it’s large enough to fit all of the materials you want to sterilize. You want to be sure you know the chamber dimensions, how it’s designed, and how many racks fit into the chamber. You should also find out what each cycle’s capacity is.

What type of materials need to be sterilized?

When discussing the difference between type “N” and type “B” autoclaves, the major difference is the type of materials in need of sterilization. Are your materials often prepackaged and hollow and porous or are they smaller and unwrapped? In order to make the best decision for your materials, you should understand the difference between gravity and vacuum autoclaves mentioned above.

How much space do I have for an autoclave?

Do you work in a small dental office with limited space or a hospital with a sufficient area for sterilization purposes? Autoclaves come in many shapes and sizes. The best autoclave should be sufficient enough to properly sterilize the materials you need without occupying more space than necessary.

Autoclave Maintenance and Technical Support

Due to the necessity of autoclaves, there are many suppliers and brands to choose from. An autoclave requires regular maintenance for safety and regulatory standards. Talk with potential suppliers and find out if they offer warranties and what their maintenance policy is. Do they offer technical support?

Certain parts of the autoclave need replacement from time to time such as chamber lid gaskets, you should double check pricing for these parts and the replacement policy put in place by your supplier.

So what is an autoclave and how does it work? We hope that this article not only answered these basic questions but explained the different types of autoclaves available, and the key factors that are most important for your business. Whether you operate a small lab, dental clinic, or large medical facility a good autoclave is key to providing the best services, procedures, and patient care possible.

Here at Predictable Surgical Technologies, we provide the best quality automatic autoclaves from top brands like Midmark and Tuttnauer. Many of our autoclaves come with a comprehensive 2 year parts and labor warranty and a 10 year chamber warranty. We also offer free shipping and provide outstanding customer service.