The F0 value of a saturated steam sterilisation process is the lethality expressed in terms of the equivalent time in minutes at a temperature of 121 °C delivered by the process to the product in its final container with reference to micro-organisms possessing a Z-value of 10. The total F0 of a process takes account of the heating up and cooling down phases of the cycle and can be calculated by integration of lethal rates with respect to time at discrete temperature intervals. When a steam sterilisation cycle is chosen on the basis of the F0 concept, great care must be taken to ensure that an adequate assurance of sterility is consistently achieved. In addition to validating the process, it may also be necessary to perform continuous, rigorous microbiological monitoring during routine production to demonstrate that the microbiological parameters are within the established tolerances so as to give an SAL of 10^−6 or better. In connection with sterilisation by steam, the Z-value relates the heat resistance of a micro-organism to changes in temperature.
The Z-value is the change in temperature required to alter the D-value by a factor of 10. The D-value (or decimal reduction value) is the value of a parameter of sterilisation (duration or absorbed dose) required to reduce the number of viable organisms to 10 per cent of the original number. It is only of significance under precisely defined experimental conditions.
The Z-value is the change in temperature required to alter the D-value by a factor of 10. The D-value (or decimal reduction value) is the value of a parameter of sterilisation (duration or absorbed dose) required to reduce the number of viable organisms to 10 per cent of the original number. It is only of significance under precisely defined experimental conditions.
Reference:
1. Validation of steam sterilizer cycle: PDA Technical Monograph No.1 (1978).
2. Sterilization of Madical Device – Validation and Routine Control of Sterilization by Moist Heat: European Standard EN 554 (1994)
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