Steam sterilisation in an autoclave

Steam sterilisation is conducted inside of a pressure device – steam autoclave equipped with a thermostat, a manometer, and suitable safety valves.

The sterilising agent during steam sterilisation process is saturated steam under pressure in temperature 121°C (steam pressure around 2 bar) or in temperature 134°C (steam pressure around 3 bar). In order to achieve the full effect of steam sterilisation the sterilised material needs to be exposed to saturated steam under pressure for a certain time. All the surfaces of sterilised materials need to be in contact with the steam, therefore the sterilisation time depends on the size of the load and the type and density of sterilised material and takes between 20-30 minutes.

According to the European norm the sterilisation process needs to provide sterility assurance level SAL=10"6. This indicates that the risk of obtaining a non-sterile product is 1: 1000000.

The sterilisation process is a technological process composed of several tasks which lead to obtaining a sterile product. The process is performed so that each sterilisation results in a product of identical quality. Therefore the sterilisation process should be validated and routinely monitored and the autoclaves should be maintained in full operation.

Steam sterilisation is a universal, sure, fast, non-toxic and economic method.

Steam sterilisation process is composed of the following stages :

• The rise time – the interior of the autoclave is vented i.e. the air is removed and entirely replaced by saturated steam.
• The compensation time - after this period, the article to be sterilised has reached the required temperature at every point.
• The sterilisation phase - the duration is dependent on the sterilisation temperature and the microorganisms to be destroyed.
• The cool-down phase – the time needed for the pressure inside of autoclave to fall until it is the same as the atmospheric pressure.

Autoclave

Definition : An autoclave is a hermetically closed container used to perform sterilisation with saturated steam under high pressure and in high temperature. The device is widely used to perform sterilisation of instruments, containers and fluids, sterilisation of waste material, treatment of culture media in microbiology, quality control in the food industry and materials testing .

A simple autoclave steriliser is composed of a thick-walled container capable of withstanding high pressure, a lockable solid lid, a manometer which measures the pressure inside of the autoclave, and a pressure valve which function is to protect the device from explosion in case of too high pressure. 

 

The first autoclave prototype - the steam digester - was created by Denis Papin, a French physicist and inventor, in 1679. In 1879 the invention of the first autoclave was ascribed to a French microbiologist Charles Chamberland.

Modern autoclaves are often automatic, fed with distilled water with the possibility of connecting them to the water supply. They are equipped with a steam heater, they are controlled by a microprocessor, and they allow for fractioned venting.

The state of the art autoclave models available for sale have the option of optical and acoustic display for controlling the processes and an interface for PC connection.

Many of today's modern autoclaves have software primarily aimed at improving equipment operation, increasing their efficiency, speed and safety at work. The main difference, however, between different autoclave models is the temperature and pressure with which they work, their use and their size.

The European Norms for autoclaves are defined in EN 13060 introduced in Europe in 2004, which include a description of the ideal technical solutions to increase the level of effectiveness of sterilization in small steam sterilizers.

A good example of a simple modern autoclave is the EL autoclave model from CertoClav – one of the oldest autoclave manufacturers in Europe. It is a compact benchtop autoclave designed for professional laboratory use. It is available in two sizes – 12 l and 18 l. It is used for sterilisation of solid instruments, liquids (culture media) bottles and devices and for waste sterilisation. 
The safety system of CertoClav EL consists of an excess pressure valve, a pressure valve, a safety cover locking device against opening under pressure and an overpressure safety recess. The autoclave contains a valve for pressure control, a thermostat for temperature control, a precision manometer with drag pointer. No additional water connection is required. The electric heater is integrated in the base of the device.

CertoClav EL autoclave

An example of a modern automatic autoclave is CertoClav Multicontrol Autoclave model. This model is designed for use in sterilisation, materials testing and research. It is an industrial quality autoclave with a precision manometer with drag pointer, an electronic temperature display, an LCD display for process progress and process parameters. It also contains a data interface.

This automatic autoclave is equipped with the serial interface for PC connection, electronic comfort and safety controls for temperature and time, nine programmes for the autoclaving process (two fixed and seven freely programmable). In addition, it allows for running temperature ramps as required in various EU standards during materials testing.

CertoClav Multicontrol autoclave