Dry heat sterilisation is a terminal sterilisation method based on the transfer of heat to the articles to be sterilised. Heat may be transferred by means of convection, radiation or direct transfer.
Dry heat sterilisation is carried out in an oven with forced air circulation or using other equipment specifically designed for this purpose, e.g. a tunnel.
The steriliser is loaded in such a way that the specified or required temperature is achieved throughout the load. Knowledge of the temperature within the steriliser during the sterilisation cycle is obtained by means of temperature-sensing elements suitably placed in or on representative items situated in the coolest part (as previously established) of the loaded steriliser. The time and temperature throughout each cycle is suitably recorded.
The reference conditions for this method of sterilisation are a minimum of 160 °C for at least 2 h. Other combinations of time and temperature may be used if it has been satisfactorily demonstrated that the process chosen delivers an adequate and reproducible level of lethality when operated within the established tolerances. The procedures and precautions employed are such as to achieve an SAL equal to or less than 10– 6. Dry heat sterilisation processes are validated using a combination of temperature mapping and biological indicator studies (5.1.2).
Dry heat at temperatures greater than 220 °C, for a validated time, is frequently used for depyrogenation of glassware. In this case, demonstration of a 3 log10 reduction in heat-resistant endotoxin can be used as validation criteria and biological indicators will not be needed.
Dry heat sterilisation cycles are monitored by determination of temperature profiles, at a minimum, in the coldest position of the chamber. Time and temperature are recorded for each cycle.