General Introductions of Methods of Sterilisation As per Ph. Eur. General Chapters 5.1.1 Part -2

Steam Steriliser

Sterilisation may be carried out by one of the methods described hereafter. Modifications to, or combinations of, these methods may be used, provided that the chosen procedure is validated with respect both to its effectiveness and to the integrity of the product including its container. For all sterilisation methods, the critical parameters of the procedure are monitored in order to confirm that any previously determined requirements or conditions are respected throughout the batch during the entire sterilisation process. This applies in all cases, including those where the reference conditions are used. Guidance concerning validation of a steam sterilisation process using the F0 concept is described in general chapter 5.1.5. Biological indicators of sterilisation are used to develop and validate sterilisation processes and also to monitor gas sterilisation processes. Guidance on the use of biological indicators is provided in general chapter 5.1.2.

Precautions shall be taken to prevent contamination of the sterilised articles after the sterilisation phase.



Steam sterilisation is achieved by heat transfer during condensation of water from a saturated vapour phase on the surfaces of the sterilised items. Where items (open or wrapped) are sterilised in direct contact with steam, the hydrating effect of the condensate adds to the sterilising effect. For direct steam exposure, it is essential that the items are fully penetrated by saturated steam, i.e. free of air and other non-condensable gases. Where items are sterilised in closed-containers, the chamber of the steriliser serves as a steam jacket. Condensation on the surface of the containers still serves as a highly effective mechanism for energy transfer, but has no additional sterilising effect on its own. In closed-container sterilisation, the sterilising effect is determined by the conditions reached within the closed containers, where sterilisation must be achieved in the product itself and in the head-space.


Steam sterilisation is performed in autoclaves, i.e. pressure vessels designed to admit or generate steam continuously and to remove condensate from the chamber to maintain the pressure and temperature at controlled levels.

For equipment used to perform direct steam exposure cycles, the supply of saturated steam, free of non-condensable gases, is assured. In autoclaves intended for the sterilisation of closed containers, steam-air mixtures or a superheated water spray can be used to achieve heat transfer. Suitable autoclaves are qualified to achieve homogeneous conditions within the chamber and the load. The principles of operation are appropriate for the items to be sterilised and the loading configuration. The suitability of the equipment for the items to be sterilised and its performance in the chosen cycle is demonstrated in autoclave performance qualification studies. Temperature profiles in the slowest-to-heat items are recorded.

Suitable autoclaves are equipped with temperature and pressure sensors of appropriate sensitivity that are placed in relevant positions to ensure effective process control. Chamber temperature and pressure profiles are recorded for each cycle. There is at least 1 independent thermal probe that controls the load temperature at the slowest-to-heat position or in the slowest-to-heat closed container of the load.

Cooling water sprayed into the chamber at the end of a sterilisation process for closed containers is of sufficient quality not to impact negatively the sterility of the sterilised items.

Sterilisation cycle

Suitable sterilisation cycles are chosen to be compatible with the items to be sterilised and the loading configuration. Where air is displaced from the chamber by gravity, the items to be autoclaved are designed to allow the removal of air and are arranged within the autoclave to prevent the formation of inaccessible air pockets. Where air is removed by vacuum cycles followed by steam pulses, it is assured that the items are not affected by the evacuation process. For pressure-sensitive products in closed containers, saturated steam sterilisation may not be possible. Steam-air mixtures may be applied to the chamber in order to balance pressure conditions inside the closed containers. Steam penetration is assured by choosing suitable cycles to remove air from porous loads or hollow bodies. Steam penetration is verified during cycle development by, for example, the use of physical/chemical indicators, while the biological effectiveness of the cycle is verified by the use of biological indicators (5.1.2). Appropriate loading patterns are specified.

Cycle effectiveness

The reference cycle for steam sterilisation is 15 min at 121 °C in saturated steam determined in the coldest position of the chamber. Product- and load-specific cycles, e.g. applying another combination of time and temperature, may be adopted based on cycle development and validation. The minimum temperature acceptable for a steam sterilisation process is 110 °C. The minimum F0, calculated in the slowest-to-heat position of the load is not less than 8 min. The calculation of sterilisation effectiveness by the F0 concept is performed according to general chapter 5.1.5.

Calculated effectiveness from physical parameters (Fphys) is correlated with biological effectiveness (Fbio). Fbioexpresses the lethality, in minutes, provided by the process in terms of destruction of the biological indicators used. Fbio is calculated by the following equation:


D121 is the D-value of the biological indicator at an exposure temperature of 121 °C, N0 is the number of viable micro-organisms in the biological indicator before exposure, and N is the number of viable micro-organisms in the biological indicator after exposure.

In cycle validation, the relevant positions in the load that are the most difficult to sterilise are determined and adequate biological effectiveness is verified by exposure of biological indicators (5.1.2) in these positions or products, whichever is relevant. Protection of spores from the sterilising effect (e.g. by physical occlusion of steam or by the protective properties of the product) are suitably addressed. The Fbio determined for the most-difficult-to-sterilise position is used to define the parameters necessary to achieve reliably the required SAL equal to or less than 10– 6 for the chosen cycle.

Routine control

Autoclave cycles are monitored by physical determination of chamber pressure and temperature profiles, at a minimum, in the coldest position of the chamber. For each cycle, pressure, time and temperature are recorded and, if possible, F0 is calculated and recorded.

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