Appendix G: F Sub Zero Sterilisation; The Significance Of F0 - Honeywell X Series User Manual

Appendix G: F sub zero Sterilisation

The significance of F
The F
A brief summary is included here to give the essence of the meaning of the terms used.
When items are subjected to sterilisation by heating, the rate at which micro-organisms are
killed is dependent on the temperature.
Traditionally items were sterilised by holding them at 250 ºF (= 121.11 ºC), and the F
for a sterilisation is simply the equivalent time at this temperature that would produce the
same effect. For many "average" micro-organisms each minute at 121.11 ºC reduces the
number present by a factor of 10, so a 15-minute hold at this temperature would reduce the
number by a factor of 10
Figure 1
If it were possible to heat a sample from ambient to 121.11 ºC in 1 second, hold it there for
15 minutes, and then cool it back to ambient in 1 second, the temperature / time profile
would look something like the trace in
15, representing 15 minutes at 121.11 ºC.
In practice, of course, to reach this temperature the object would have to be subject to an
initial heating period up to that temperature, and later a cooling period back down again to
ambient temperature, more like the profile shown in
this heating up, holding at temperature, and subsequent cooling, micro-organisms are being
killed at different rates, and the F
perature (provided it is over some defined starting temperature - see below).
This calculation is performed by using the expression, where T is the temperature in ºC and
Δ
perature coefficient for the destruction of micro-organisms, and is the increase in tempera-
ture, in ºC, that produces a 10-fold increase in sterilisation rate.
This summation is only performed once the sample temperature has reached some speci-
fied starting temperature. For example in
ture has been set to 100 ºC (a common value) then the F
minutes when the temperature first reaches this value.
43-TV-25-30 Iss.6 GLO Aug 07 UK
value is used in the pharmaceutical and related industries in the sterilisation of items.
0
15
t is the time spent at that temperature. The z factor that appears in this equation is the tem-
0
.
Figure 1 on page 297
value is calculated by summing the effect at each tem-
0
Figure 2
Figure 2
and the F value would be
0
Figure 2 on page 297. During all
on page 297 if this starting tempera-
summation would begin at t = 8
0
value
0
297