What are the different types of autoclaves and how they work?

What are the different types of autoclaves and how they work?

Did you know “autoclave” means “self-locking device”? We commonly associate autoclaves with steam sterilisers but over time technology has improved and a large range of autoclaves have been developed to suit all sterilisation needs.

But what are the different types of autoclaves and how do they work? In this article, we will cover the difference between industrial and medical autoclaves, and we will dive more into details about the different types depending on the use.

What’s an autoclave?

Also called “steam steriliser”, commonly an autoclave is a machine used for the sterilisation of materials and supplies. In industrial applications it is used for the manufacturing of composites, using the air vacuum property of autoclaves. In most cases, it uses a combination of high temperature and a saturated steam atmosphere to sterilise.

On average, the process takes from 30 to 60 minutes and removes or inactivates all bacteria, viruses, fungi and spores. The temperature reach between 121°C and 135°C.

They vary in size and function depending on what needs to be sterilised such as laboratory glassware, surgical instruments or medical waste.


Industrial autoclaves vs. Medical autoclaves

Industrial autoclaves can be used in the food & drink, pharmaceutical and life-science industries, sailboat manufacturing, or even aeronautical sectors. These autoclaves can be very large to cater for large loads and the manufacturer would have flexible design options to fit the industry requirements. Regulation depends on the specific industry but for manufacturing, autoclaves can be only used for their air vacuum functionality thus the type used is not regulated. For small usage, autoclaves can have a manual part where the operator is required to manually activate the pulsing of steam at the required pressure.

In healthcare, there are international standards ISO, European norms and local codes of practice from the HSE regarding the re-processing of medical instruments. After use, medical instruments need to be cleaned, disinfected, sterilised and stored. Autoclaves are used for the sterilisation process. Their installation, calibration and validation are highly regulated. These autoclaves are automatic and follow specific programmes. The usage and cycles are tracked with multiple captors (via “traceability” software), and regular tests need to be performed to ensure it is functioning correctly at all times.


Different technologies of sterilisation for autoclaves

Low temperature

Low temperatures also called plasma sterilisation autoclaves are used for medical instruments or scientific devices that cannot withstand high temperatures or moisture. The process uses liquid hydrogen peroxide (H2O2) heated to the point of turning into gas and then plasma. The plasma is dispersed in the steriliser chamber and deactivates all microorganism present on the load by a chemical reaction called oxidation. Examples of instruments loaded in low-temperature autoclaves are defibrillator paddles, laser probes or surgical power drills.

Steam steriliser – gravity displacement

This type of autoclave produces hot steam that will saturate the chamber and naturally evacuate ambient air through a disposal valve. Items inside the autoclaves are sterilised due to the high temperature and pressurised steam atmosphere. These are suitable for common medical items that are non-porous and where steam has easy access to all surfaces. Examples of instruments loaded are steel utensils, glassware, liquid and biohazard waste.

Steam steriliser – high-speed pre-vacuum

Also called vacuum-induced autoclaves, they are used for items with spaces that are harder to reach or for porous items. A vacuum pump removes all the ambient air and then hot steam is produced, forced to fill every space in the chamber. This allows for the sterilisation of fabrics and wrapped pouches that contain instruments and polyethylene syringes.

Steam steriliser – combined gravity and vacuum

Most modern autoclaves use a combination of pulses of steam and air vacuum with different cycle routines.

Gamma radiation

Less commonly used, these autoclaves use gamma-ray radiation to sterilise. Gamma rays are created by the decomposition of an atom. The gamma-ray damages genetic material, inactivating any virus, bacteria etc… on the items. The atom used is Cobalt-60 (the only one used for sterilisation) because the gamma irradiation doesn’t have sufficient energy to cause the items on the load to become radioactive. Thanks to its high penetration property, the absence of heat or moisture it can be used to sterilise versatile loads from human tissue grafts, food, archives, cosmetics, medical devices or packaging.


Medical autoclaves type depending on the usage

Stovetop autoclaves,

Also known as “pressure cookers” these are the simplest autoclaves which only need to be plugged in. The process is manual by adding water, setting the temperature and ending the cycle. These are not common in Occident where more modern and automatic autoclaves are the norm.

Benchtop autoclaves

As the name says, its particularity is its small size, allowing to be disposed on top of a benchtop. These are preferred in small practices such as dental, veterinary or small laboratories that don’t require a large volume of instruments to be sterilised.

Sterile services (CSSD) autoclaves

These autoclaves are designed for hospital sterile services with pass through-door system. The autoclaves are loaded in the “clean room” and unloaded after the cycle in the “sterilised or cooling room”. They are made specifically to sterilise instruments disposed into wrap paper and pouches. It uses the pre-vacuum technology mentioned above.

Life-science and laboratory autoclaves

Also called “research-grade” autoclaves, they are frequently tailored to the need of the facility. They are optimised for ease of use and design features such as door, user interface and chamber size are modular. They also have specific functionality and technology to cater for high content of pathogens.

Waste autoclave

As an alternative to incinerators, waste autoclaves are commonly used for medical waste prior to disposal in the municipal solid waste stream. They are used for contaminated materials, culture waste, textiles from patient care and surgery wastes. These autoclaves are pretty large and can cater for an entire trolley to be loaded. Some are compact units including a shredder to reduce waste size.


Classification for small autoclaves

Class N sterilisation

Class N stand for Naked Solid Products, these autoclaves use the gravity displacement process and can only be used for sterilising items that are not porous, not in pouches or wraps and don’t have complex cavities.

Class B sterilisation

Class B stand for Big Small Steriliser, these autoclaves use a vacuum pump to remove ambient air before injecting steam. These can be used for any type of load and follow the European standard EN 13060 Norm dedicated to small steam sterilisers.

Class S sterilisation

Includes all other types of autoclaves not defined by any standards. Instead, their characteristics are defined by the supplier.


“Green” autoclaves – the quest for energy savings

As you’ve read throughout this article, most autoclaves use water and electricity as resources. It is also important to note that the vacuum pump uses water as a sealing method. For these reasons the same way programmes for your domestic washing machine have been improved over time to save water, programmes and technology for autoclaves have been improved too.

These are not a specific types of autoclaves, but it is worth noting that some manufacturers have heavily invested in research and development to offer advanced energy-saving features in their machines. For example, at Manepa we have a range of autoclaves from Cisa which include a vacuum pump called AQUAZERO® that doesn’t require water to function. With this pump installed, you can save up to 400L per cycle, a major saving over time.


Key takeaway

Since their invention autoclaves have been used in industrial, scientific and medical processes. Mainly using air vacuum and pressurised hot steam, autoclaves cater for a variety of use such as high-level disinfection in healthcare and material assembling in manufacturing. New technologies for sterilisation have come into place using plasma or gamma rays.  They allow more fragile, bulky, or electronic loads to be sterilised. Autoclaves’ size and design vary depending on the application, from large waste autoclaves to sterile service autoclaves and small tabletop autoclaves. However, it is important to note, medical autoclaves are highly regulated.


At Manepa we have 50 years of experience in decontamination and sterilisation equipment. Our team is fully qualified and experienced to design, install, validate and service any piece of decontamination equipment for hospitals, life-science, and community healthcare sectors.  Have a question regarding a tabletop autoclave you have? Have a specific challenge in your sterile service department? Just get in touch, our team will be happy to help.


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