Top Loading Autoclave: Pros and Cons

Originally, an autoclave is a container whose lid slides inside the envelope of the container. The lid is closed hermetically under the effect of the internal pressure of the vapor. A top loading autoclave is a vertical container that can accommodate bioreactors, the tallest flasks and fermenters.

Furthermore, a top loading autoclave makes it possible to exceed atmospheric pressure, and therefore to carry liquid water beyond 100 ° C. Subsequently, other types of containers allowing this action have taken this name as well.

In other words, a top loading autoclave is a container with thick walls and hermetic closure. It is designed to carry out under pressure (from a few bars); either an industrial reaction, or cooking or steam sterilization.

In fact, for a material to be considered sterile, the theoretical probability of isolating a germ must be less than 1 per 1 million. This is the sterility assurance level (NAS) regulated by the EN 556 standard.

The history

Denis Papin invented the principle of the autoclave in 1679 . On April 9, 1820, Pierre-Alexandre Lemare deposits a patent on the autoclave pot. Nicolas Appert then improved his patent. His successor and continuator, Raymond Chevallier-Appert, patented the sterilization practice under the title autoclave with special pressure gauge on December 28, 1852. It was the ancestor of the current steam sterilizer. In 1879, Charles Chamberland improved the process for medical purposes.

Principle of sterilization

The sterilizing agent is the saturated water vapor under pressure or the super-heated water. The heat associated with humidity causes the destruction of germs by denaturing proteins by partial hydrolysis of peptide chains. Generally, most of the hospitals use steam sterilization to sterilize materials and instruments.

Important points

• The quality of the steam (for saturated steam autoclaves), which must be saturated and homogeneous.
• The temperature, which must be regulated as close as possible to the scale.
• Pressure according to Regnault’s law.
• The quality of the water, the presence of suspended substances may lead to an alteration of the load to be sterilized; just as the presence of chlorine in the water can damage the stainless steel irreparably.

Other than many advantages and special features that a top loading autoclave offers; it is worth mentioning that you can purchase a top loading autoclave at one-third the price of a comparable front-loading autoclave.

Furthermore, top loading autoclaves and also other types of them offers an extensive range of application in different fields. Below, you may find some of the most important ones.

Top loading autoclave in biology

The principle of top loading autoclaves in biology is generally to achieve microbiological sterility.

Top loading autoclave in chemistry

Chemistry autoclaves (top loading and other types) working under high pressure are subject to the PED (European Pressure Directive). They are most often fitted with a rupture disc (bursting disc) which is similar to a pressurized fuse.

In chemistry, an autoclave makes it possible to carry out reactions under pressure, such as hydrogenation, polymerization and etc. Chemistry or research autoclaves make it possible to work at pressures up to 5,000 bar and temperatures up to 900 ° C. Autoclaves can be equipped with a stirring system which will be magnetically driven in order to isolate them from the pressure and create a uniform vortex inside the reactor. Thus, numerous research manipulations and laboratory experiments are carried out using autoclaves (pharmaceutical, chemical, petroleum research, etc.).

For process improvements or basic research, the volume of top loading autoclaves varies inversely proportional to the pressure they have to withstand. Thus, a top loading autoclave with a small volume (50 to 300 cubic centimetres) will support pressure more easily than an autoclave with a larger volume (5 to 10 liters).

High pressure autoclaves (or research reactors more commonly known as laboratory bombs) are exclusively made of metallic materials which offer resistance to pressure. The most commonly used manufacturing material for autoclaves is stainless steel in grade 316 SS. Other metals such as Hastelloy C276 or Inconel 600 are used for corrosive or very high temperature applications (Example: 900 ° C).

Use of top loading autoclave in a medical environment

As mentioned earlier, most of the hospitals use steam sterilization to sterilize materials and instruments. It is necessary for the sterilization of any sterile medical device which is not designed for single use. Depending on the product and the packaging (glass bottle, PVC bags, PP bag, syringe), different heat treatments by autoclaves can be applied.

The use of a type B autoclave is compulsory and ensures protection for patients, but also for health professionals and doctors against possible risks of infection or cross-contamination between them.

The prion cycle is the one that is most often used in hospitals. It is the most effective cycle and has been recommended by the Directorate General for Health since 2001.

A medical device must be used extemporaneously after the opening of the sterilization chamber or then kept in a specific packaging which will have been used for sterilization.

Types of autoclaves

Autoclave comes in different types. Small steam sterilizers are defined by a useful volume of less than 60 liters, or cannot contain a sterilization unit. They are described in standard NF EN 13060, which distinguishes three types of devices:

Class B

The only real sterilizers! It carries out a cycle comprising a pre-treatment with alternating voids and steam injections, a stage of sterilization tray, and a phase of drying under vacuum. Class B autoclaves are the only ones recommended by standard NF EN 13060 for the sterilization of medical devices.

Type N

Water vapor disinfectors, dealing with unpackaged devices.

Type S

Tote class whose indications are fixed by the manufacturer.

Large sterilizers, over 60 liters, meet standard NF EN 285. There is only one type performing cycles of the same type as the B cycles of small sterilizers.