Steam sterilizer design

The relationship between temperature and pressure holds true only in the presence of pure steam adulteration with air contributes to a partial pressure but not to the temperature of the steam. Thus, in the presence of air the temperature achieved will reflect the contribution made by the steam and will be lower than that normally attributed to the total pressure recorded. Addition of further steam will raise the temperature but residual air surrounding articles may delay heat penetration or, if a large amount of air is present, it may collect at the bottom of the sterilizer, completely altering the temperature profile of the sterilizer chamber. It is for these reasons that efficient air removal is a major aim in the design and operation of a boiler-fed steam sterilizer. 

Steam sterilizers, or autoclaves as they are sometimes known, are stainless steel vessels designed to withstand the steam pressures employed in sterilization. They can be (i)... 

The F-value concept which was developed for steam sterilization processes has an equivalent in dry heat sterilization although its application has been limited. The Fh designation describes the lethality of a dry heat process in terms of the equivalent number of minutes exposure at 170°C, and in this case a z value of 20°C has been found empirically to be appropriate for calculation purposes this contrast with the value of 10°C which is typically employed to describe moist heat resistance. 

The third critical part in a steam-sterilized plant is the valve between the chamber and condenser. Its design should influence the flow of water vapor from the chamber to the condenser as little as possible, and its component must be easily cleaned and sterilized. Several technical solutions are offered for this problem. In Fig. 2.48.1 a design is shown in which the valve plate is moved back-and-forth by a hydraulic cylinder. This fulfils the two requirements ... 

Tanks with vent hlters must be designed for pressures of -20 kPa and +100 kPa and must be equipped with a rupture disk. Tanks for hot loop and steam sterilizable line must be designed to withstand steam sterilization (121°C). A steam jacketed sterile vent hlter must be used to avoid condensation in the hlter and the vent hlter housing temperature controlled. The tank for hot storage is steam jacketed and insulated for temperature maintenance. Minimum instrumentation shall include level indication, temperature recording controller, pressure gauge, and pressure relief valve. 

The condenser housing is round and horizontal with vacuum- and pressure-resistant design for the freeze-drying and steam sterilization processes. The condenser is slanted toward the drain ports. 

The freeze dryer is designed for steam sterilization of the chamber and condenser, as well as defrosting of the condenser with steam. The steam sterilization is carried out at an overpressure of 1 (provide value) bar. 

The final step in steam sterilization validation is the establishment of a monitoring program to ensure that the validated cycle remains essentially unchanged in the future. Cycle monitoring usually involves the use of thermocouples to measure heat penetration at the cool spot location and to verify that the design F0 value has been reached. 

Fig. 2.12. Rectangular chamber, steam-sterilized, with a small loading door in the main door, which can be designed to open either...

The steam sterilization system (see Figures 5-9) used by S.G.D. Serail is designed with autoclave -type vessel construction to resist sterilization pressure combined with a control system permitting the validation of the sterilization cycles and eventual determination of the experimental FO sterilization value. 

Steam sterilizers, or autoclaves as they are also known, are stainless steel vessels designed to withstand the steam pressures employed in sterilization. They can be (i) portable sterilizers, where they generally have internal electric heaters to produce steam and are used for small pilot or laboratory-scale sterilization and for the treatment of instruments and utensils or (ii) large-scale sterilizers for routine hospital or industrial use, operating on dry saturated steam from a separate boiler (Fig. 20.6). Because of their widespread use within pharmacy this latter type will be considered in greatest detail. 

An empirical rule-of-thumb is often used in the design of sterilisation processes which uses the principle of substantial overkill to design a readily validated make-safe process. The MRC Working Party reports on pressure-steam sterilizers are often quoted as the intellectual source of the much-used sterilisation standard of saturated steam at 121.1 °C for 15 minutes. This treatment is widely regarded as giving a sufficient margin of safety in yielding a sterile product irrespective of the type and initial... 

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