CALCULATION OF F0 VALUE AND TEN’S POWER
F0 Value (Equivalent Exposure Time)
F0 value is the
equivalent exposure time at 121.1°C to that of the actual exposure time at a
variable temperature calculated with a temperature coefficient of the
destruction of 10°C.
F0
Value Definition
where,
Δt – the time interval between two temperature readings
T – the temperature at time t of the product under sterilization
z – temperature coefficient (assumed as 10°C)
The term next to Δt in
equation (2) is called Lethality Rate. You can calculate it individually or by
averaging complete sterile hold data, the result will be equivalent.
Testing F0 Value And Its Meaning
Consider sterilization
hold time of 30 min. at constant 121.1°C.
Put this in equation
(2),
Solving we get, F0 =
30 min. (This is an ideal condition for steam sterilization)
But what if the
temperature is increased or decreased from 121°C (ideal condition)? Let us find
out…
Example 1 (Below Ideal Condition)
Consider sterilization
hold time of 30 minutes at constant 110°C instead of 121.1°C, in a similar
manner as above,
Solving we get,
F0=2.33 min.
Hence, 30 minutes of
sterilization at 110°C is lethally equivalent to 2.33 min. of sterilization at
121.1°C. (Compare this sentence with the definition of F0 value for easy
understanding)
The crux of the
example is,
121.1°C → 30 min.
(Expected condition)
110°C → 2.33 min.
(Actual condition compared to the expected condition)
Compared to the expected condition, the effective sterilization cycle time was
only 2.33 instead of 30 minutes because of the lowered temperature of 110°C.
Now, let us understand
“how long will it take to complete the sterilization?” for this condition.
Meaning, if we maintain temperature 110°C constantly, how much hold time is
required to achieve an F0 value of 30 min.
By reverse calculation, we can do this. Let us fix the F0 value to 30 minutes.
The unknown part then would be Δt.
Data we have now is F0=30 minutes and Temperature T=110°C
Putting these values in equation (2),
Solving we get, Δt=386
min.
When the temperature of the system under sterilization is
maintained at a constant 110°C, the time of 386 min. (i.e. Sterile Hold Time)
would be required to achieve the lethal effect of 121.1°C at 30 min.
Example 2 (Above Ideal Condition)
Consider sterilization
hold time of 30 minutes at constant 125°C instead of 121.1°C, in a similar
manner as above,
Solving we get,
F0=73.64 min.
Hence, 30 minutes of
sterilization at 125°C is lethally equivalent to 73.64 min. of sterilization at
121.1°C. (Compare this sentence with the definition of F0 value for easy
understanding)
Simply put,
121.1°C → 30 min.
(Expected condition)
125°C → 73.64 min.
(Actual condition compared to the expected condition)
Compared to the expected condition, the effective sterilization cycle time was
73.64 instead of 30 minutes because of the elevated temperature of 125°C.
Let us understand “how
long will it take to complete the sterilization?” for this condition. Meaning,
if we maintain temperature 125°C constantly, how much hold time is required to
achieve an F0 value of 30 minutes.
By reverse calculation, we can do this. Let’s fix the F0 value to 30 min. The
unknown part then would be Δt.
Data we have now is F0=30 minutes and Temperature T=125°C
Putting these values in equation (2),
Solving we get, Δt =
12.24 min.
When the temperature of the system under sterilization is
maintained at a constant 125°C, the time of 12.24 min (i.e. Sterile Hold Time) would
be required to achieve the lethal effect of 121.1°C at 30 min.
You may use this F0 Value Calculator to explore the different steam sterilization scenarios.
CALCULATION OF TEN’S POWER BY CALCULATOR
For Example if we have to
know 100.6 then
Comments
Post a Comment