UNDERSTANDING Fphy OR EQUIVALENT EXPOSURE TIME AT 121°C

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 load in its container with reference to micro-organisms possessing a theoretical Z-value of 10.

——-     Equation 1.0

Lethality rate (L) = 10^(T-Tref)/z                                                                                             ——-     Equation 2.0

T= Temperature of load article

T_ref = Set sterilization temperature 121° C

Z Value = 10 (if not known for challenge organism)

Fphy or/ F_physical  = Time interval (Δt) × Accumulated Lethality (ΣL)                          ——-     Equation 3.0

To demonstrate over kill approach Fphy must be > 12. Lower F0 can be acceptable for product specific approach based on the detailed knowledge of bioburden.