Disinfection normally refers to the inactivation of pathogenic microorganisms and reduction in number of pathogens by at least five log levels. This means no more than 10 colony forming units (CFUs) out of 1,000,000 can survive the disinfection process. By contrast, sterilisation is a process to remove all living microorganisms such as bacteria, fungi or viruses and their dormant phases from substances, objects and equipment. Accordingly, the goal of sterilisation is the complete removal of all pathogens including reproductive microorganisms from anything classed as sterile. Sterilisation is used for reprocessing medical apparatus, decontaminating infectious laboratory waste and for manufacturing sterile dosage forms and sterile disposable items for laboratory and clinical use.

In hospitals, medical centres, laboratories and manufacturing facilities in the food industry, it is important that certain areas and instruments are not only clean, but also absolutely sterile and therefore pathogen-free. Physical, physical-chemical and mechanical processes can be used to achieve this. Steam sterilisers, dry heat sterilisers and radiation sterilisers are used in physical sterilisation processes. The material that needs to be sterilised is what determines the correct choice of sterilisation process: are the items that need to be sterilised thermostable or thermolabile? While anything in a dry heat steriliser has to withstand dry heat up to 200 Celsius, the steam steriliser works at up to just 130 Celsius using moist heat. Radiation sterilisers work using gamma, UV or X-rays and are therefore suitable for any substances which cannot be exposed to high temperatures.

Steam sterilisers use steam to kill pathogens. Steam sterilisers are therefore used in medicine and in biotechnology in particular, to sterilise or disinfect medical instruments, liquid nutrient media or glassware. Steam sterilisation is a reliable method for making heat-resistant plastic, rubber, metal, ceramics, glass or linen totally sterile within a relatively short period of time. This works using saturated and superheated steam. This is done in steam sterilisation using a vacuum process (for example a Varioklav® GreenLine device or a Varioklav® BlueLine autoclave with vacuum module), to generate an initial vacuum, so that air present in the sterilisation chamber is totally evacuated. The water is then heated until the steam pressure in the autoclave reaches 2 bar at 121 degrees and saturated steam is produced. Autoclaves are traditionally used in the fields of medicine, biotechnology and the manufacturing sector, for processing medical apparatus, such as in central sterile supply departments (CSSD) or medical apparatus processing departments, as well as in the production of medication or solutions in pharmacies.

The term autoclave can be used interchangeably with steam steriliser and generally refers to a gas-tight, sealable pressure vessel used for thermal treatment of substances under high pressure. When it comes to sterilisation in the medical technology, pharmaceutical and biotechnology sectors, a basic distinction is made between two sterilisation processes: the vacuum process and the flow or gravity process. In both cases, the total volume of the items or substances that need to be sterilised is specified in sterilisation units (StU), with one sterilisation unit corresponding to 54 litres. This unit is used to distinguish autoclaves as large steam sterilisers and small steam sterilisers: Large steam sterilisers refers to all autoclaves with a capacity greater than or equal to one sterilisation unit as defined in DIN EN 285. Large autoclaves usually work using the vacuum process and are therefore suitable for the sterilisation and preparation of packed or unpacked, solid or porous medical apparatus with and without cavities. With large sterilisers, steam is usually generated by integrated electrical steam generators (internal steam source) or by an external wall steam system (external steam source). As defined in DIN EN 13060, the definition of small steam sterilisers covers all autoclaves with a capacity below one sterilisation unit. Small steam sterilisers use one of three different types of sterilisation cycle: Small steam sterilisers with class N sterilisation Class N autoclaves work using the flow or gravity method. Air in the sterilisation chamber is displaced from the chamber by the steam flowing in. Due to the lack of vacuum, class N sterilisation cycles are only suitable for solid medical instruments out of their packaging, such as probes or forceps. Overall, class N sterilisers should only be used for non-critical medical apparatus where sterilisation is not a legal requirement. Following a class N sterilisation cycle, the sterile items are not suitable for transport or prolonged storage, but are only sterile for immediate use. Small steam sterilisers with class S (specified) sterilisation Class S autoclaves are suitable for reprocessing particular medical apparatus listed by the autoclave manufacturer in the cycle table. The properties of a class S steriliser must be tested by its manufacturer, and defined, validated and approved for each relevant application. Type S autoclaves can also be used to sterilise solid intruments out of their packaging which are not used for surgical procedures. Small steam sterilisers with class B (big) sterilisation The class B sterilisation cycle is generally considered to be the safest method of sterilisation and ensures that the widest variety of sterile items are sterilised and reprocessed as appropriate for clinical applications. With regard to cycle selection, class B sterilisers – unlike classes N and S – do not require any separate staff training.