What is an "autoclave" and how does it work? We will focus on the autoclave sterilization cycle process and guide you through the different autoclave cycle stages. After reading all the material in this series, you will understand how an autoclave works. Knowledge is power, and an autoclave user, technician or operator will be more effective if they understand the different stages of the sterilization process.
This series will cover all aspects of autoclaving, including:
Steam generators and steam supplies
True** and after vacuum of sterilization cycle
Autoclave jacket
cooling process
Autoclave control system
Before reading further, you may also be interested in the Learn the Basics of Autoclave Sterilization series, which discusses topics related to autoclave sterilizers and sterilization.
What is an autoclave?
The invention of the autoclave originated from Charles Chamberland in 1879. By then, researchers were beginning to understand the advantages of sterile surgery, and doctors needed a more reliable method of sterilization than an open flame. The benefits of the autoclave were quickly apparent and it became an essential part of every clinic and hospital.
A reactor is used to sterilize surgical equipment, laboratory instruments, pharmaceutical items, and other materials. It can sterilize solids, liquids, hollows and instruments of all shapes and sizes. Autoclaves vary in size, shape, and functionality. A very basic pressure cooker is similar to a pressure cooker. Both use the power of steam to kill germs, spores and germs that are resistant to boiling water and strong detergents.
A very basic pressure cooker similar to a pressure cooker
Although their basic functions are similar, the most advanced autoclaves are no match for pressure cookers
What is the purpose of an autoclave?
An autoclave sterilizes medical or laboratory instruments by heating them above the boiling point. Most clinics have a benchtop autoclave that is similar in size to a microwave oven. Hospitals use large autoclaves, also called horizontal autoclaves. They are typically located in Central Sterile Services Departments (CSSDs) and can handle large numbers of surgical instruments in a single sterilization cycle, thereby meeting the ongoing demand for sterile equipment in operating rooms and emergency rooms.
Small autoclaves, also called tabletop autoclaves, can be found in dental offices
Steam generation and steam quality
Steam is the sterilizing agent in autoclaves. In this "Sterilization Methods" series, we explain the physics of steam and why it's perfect for destroying microorganisms like bacteria and spores. Part 1 of this article will explain how to generate steam for autoclaving purposes. Part 2 of this series will discuss the various types of autoclave steam supply and generation and when to use them.
Back to the source
ANSI/AAMI sterilization standards state:
There are two common sources of steam for sterile processing: hospital steam boiler systems and stand-alone electric boilers. In both cases, treated water must be used to remove total dissolved solids (TDS). Each system should be designed, monitored and maintained to ensure that the quality, purity and quantity of steam provided are suitable for effective aseptic processing
Tuttnauer offers autoclaves connected to a building or hospital steam supply, as well as models equipped with a self-contained steam generator. Other Tuttnauer autoclaves are available with a dual steam option (the ability to change the steam supply source according to the building's steam supply) to suit user requirements. Autoclave steam generators can be built-in or stand-alone, depending on the size of the reaction chamber.
High pressure steam quality
When it comes to delivering large amounts of energy to an object that needs to be sterilized, nothing is more powerful than steam. After all, steam engines propelled ships and trains. Even the Titanic was powered by steam.
We discuss steam quality in our detailed article on sterilization methods, but let's review the factors that determine this steam quality, as it is critical to proper autoclave function and the entire sterilization process. The two parameters are the most important:
Levels of non-condensable gases
Moisture content
The optimal composition of steam in an autoclave is 3% liquid and 97% gas. Any change in moisture percentage will increase or decrease sterilization time. In practice, sterilization time is calculated based on optimal steam conditions and the ability of steam to transfer energy to non-sterilizing loads prior to sterilization. After all, one of the most important benefits of a steam autoclave is that it requires much less time and heat than a dry heat sterilizer due to steam's ability to transfer energy.
Dry steam? Wet steam? Not in the autoclave
Humidities below 3% produce so-called dry steam or superheated steam. This steam increases sterilization time because it reduces energy transfer capabilities. The superheated steam reduces the humidity to approximately 0%, turning the autoclave into a dry-heat oven. Energy transfer is reduced, taking three minutes in the autoclave at 134°C compared to two hours at 160°C and 30 minutes at 180°C!
However, humidity above 3% will produce saturated steam or wet steam, which requires higher sterilization pressure and temperature. Wet steam also prolongs the drying time at the end of the sterilization process. When the packed packaging is not intended for immediate use, dry packaging is required at the end of the process.
Sterilization standards and directives for autoclaves allow for some flexibility in steam moisture levels, as it is almost impossible to provide accurate steam at a consistent flow rate. Even if conditions are nearly optimal, many variables can affect the steam when it is transferred to the autoclave. Chief among them: weather conditions and temperature; pipe quality, length and construction; drainage stations; and the availability of high-quality steam traps.
Receive steam
Now that we understand how steam works, we can examine how steam is generated and fed into the autoclave.
