For many years, there have been concerns over the hygiene of medical tools and scientific instruments. These instruments cannot be cleaned with water or wiped with a normal brush or piece of cloth. They need to be cleaned very thoroughly as microorganisms and germs are resilient and cannot be cleaned using normal cleaning methods. They cannot be wiped, but you still need to kill the germs to make the tool clean and safe for use on a patient without contamination. So the best way to kill these microorganisms is by exposing them to harsh environments, and this is where an autoclave comes in.


What is an autoclave?

The autoclave was introduced in the late ’80s, and this is when medical experts and researches started to understand the importance of sterile surgery. Doctors used to rely on open flaming as a way of killing the microorganisms, but this was not very reliable. Soon after its introduction, the benefits of using an autoclave were so evident, it is no surprise to see many hospitals now adopting this method of cleaning and sterilising medical tools and equipment.

The autoclave is generally used to disinfect anything that needs to be free of microorganisms. It can decontaminate solids, liquids, hollow items and instruments of varying shapes depending on the type of autoclave and its size. A typical one resembles a pressure cooker in shape and functionality as it uses the power of steam to kill these microorganisms that are resistant to detergents. Over time, the autoclave has developed into a sophisticated device owing to the diverse applications that one can be used for. This way, designers are challenged with coming up with one that is suited for a specific application such as in medical clinics and biological laboratories.


How an Autoclave Works?

Autoclaves use a combination of steam and high pressure to transfer heat from the machine to the items inside it. Over the years, they’ve undergone a number of iterations and technological improvements. There are still basic mechanical models available today, but it’s also possible to get a fully computerized machine.

A basic autoclave cycle looks something like this:

  1. Boil water to generate steam that enters the chamber. As the steam comes in, the air is removed, and as the steam expands, it continues to be pushed out. Air is removed using either a vacuum process, seen in larger autoclaves, or by displacement, which is an option seen in smaller tabletop models.
  2. After all the air is removed, close the chamber’s exhaust valve to increase pressure and temperature. Continue to add steam to the chamber. Temperature and pressure continue to rise to the level necessary for sterilization. Generally, this is 121°C (250 °F) or 134°C  (273°F).
  3. The sterilization process begins. Also known as holding time or sterilization time, materials may be in this cycle anywhere from three to 20 minutes, depending on the contents and size of the load.
  4. Open the exhaust valve and release steam to reduce pressure. This helps to cool the load.
  5. Finally, cool down the load so that it is safe to touch upon opening the autoclave.

Ultimately, the sterilization cycle length varies depending on what materials are being autoclaved, and how many of them there are in the load.


Importance of Autoclaves in the Medical Field

Hospitals, laboratories and nursing homes cannot work without professional autoclaves; the need to sterilize instruments in such environments is continuous and critical.

Some equipment such as injectors, blades and forceps are intended for singular use while others are designed for reuse. For such equipment, autoclaves are the only way to ensure people interacting with the medical equipment are not at risk of infection. In third-world countries, the chances of re-using equipment are higher, making autoclaves very important in ensuring safe treatment and care giving.

Medical waste should also be sterilized before disposal to ensure no one else gets infected after disposal. In this case, autoclaving is used as a sterilization method. It has become very popular because it is environmentally friendly in application.

These pieces of equipment are readily available in the current market. You can purchase autoclaves from the laboratory equipment website


Different Types of Autoclaves


This is known as gravity displacement autoclaving. It is the most basic form of autoclave sterilization and is suitable for most laboratory equipment and supplies. This type of autoclave is useful because it’s simple and doesn’t depend on additional peripheral mechanisms to displace the air with steam. This lack of dependency also helps keep the costs low. Gravity autoclaves are the most common type available on the market and are recommended for most uses.

These autoclaves are best for non-porous items, that is, anything with a hard surface, including:

  • Biohazard waste
  • Most metals – stainless steel lab utensils and surgical instruments
  • Unwrapped goods
  • Type I borosilicate glassware

Gravity autoclaves are available in front-loading and top-loading configurations. Top-loading units provide maximum loading space, yet minimal floor space. You do not need any building steam connection because the vertical chamber allows water to rest at the bottom, which turns to steam thanks to a heating element located at the bottom.

This type of autoclave is also useful in high altitude geographic areas and in places with high humidity because they constantly maintain the relationship between heat and pressure in the chamber and can accommodate changes in boiling point with adjustments to the exhaust valve.

Smaller benchtop autoclaves are available for dental offices and tattoo studios, but larger units are available for labs with plenty of counter space and limited floor space.


Also known as pre-vacuum autoclaving, this type of autoclaving is best for situations where air cannot easily be removed from the objects to be sterilized. For example, sterilizing animal bedding and cages or wrapped surgical instruments cannot happen without all of the air being removed. The vacuum function ensures the ambient air is removed and allows high-temperature steam to access areas where ambient air would normally be. This approach can also be more efficient at sterilizing things with hard-to-reach areas.

The type of autoclave you choose depends mostly on the media you intend to sterilize regularly. In general, steam sterilization is effective, dependable, quick, and non-toxic. It provides an inexpensive method to heat and penetrate the chamber’s contents, including liquids that have been appropriately contained. This method, however, only works with moisture-resistant goods and cannot be used to sterilize oils or powders.

These autoclaves are best for sterilizing porous or large items, including:

  • Wrapped items
  • Pipette tips and other high-density polyethylene products
  • Solutions stored in appropriate containers, such as tissue culture flasks
  • Animal cages and bedding

 A few common questions about the autoclave

What makes up a sterilization cycle?

Each sterilization cycle has various parameters associated with it. These are typically based around a specific load configuration or material type. The parameters the autoclave uses are: pressure, temperature, and time.

How long does an autoclave take to sterilize?

In general, each cycle will take between 60 to 90 minutes. The sterilization duration varies, but is typically around 30 minutes, and the remaining cycle time is split between heating up and cooling down the chamber.

On what is an autoclave effective?

The sterilization process kills bacteria, viruses and bacterial spores. Biological indicators and lethality calculations can be used to validate a cycle for an autoclave.

Can the process fail?

 It can, for a variety of reasons. Read on to learn why and what to do in such a circumstance.

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