# Fh value of sterilizing tunnel depyrogenation

Dear all,

This is my first visit and I have a question about Fh value of sterilizing tunnel depyrogenation.

According to “Validation of Pharmaceutical Processes:Sterile products, 2nd edition, by Frederick J.Carleton” p504,
Fh value is 30.0 if we assume a cylce of 250℃ for 30min and z-value 46.4.

Then what if I calculate Fh value at 300℃ for 25min using this references?

As i calculated Fh value using FH=ΔT Σ10^(T-250)/Z, Fh value is about 298.
I think this value is too much so i`d like to ask your helps.

It might be that you are not dividing each instantaneous calculation by the interval. For example, if each temperature is collected at 15 second intervals, then your instantaneous Fh, must be multiplied by 15/60 (or 1/4). If the interval is 30 seconds, then each result will be 1/2.

But your value might be correct. It seems like your base temperature is 250, but your depyro is running at 300. You have 50 C extra temperature of kill. (T-250)/Z becomes (300-250)/46.4, or 50/46.4 or approximately 1. So 10^1 is 10. So you would get 10 minutes of effective kill, for every minute of cycle time. So a 25 minute cycle is the equivalent of 250 (25 cycle minutes x 10 effective minutes / cycle minutes). And 250 is close to 298, so yes, your calculations are correct.

Question: Is there a discussion around your cycle time/temperature (300 C and 30 minutes)? The reference I use lists a common historically acceptable depyrogenation oven cycle as being 250 C for 30 minutes.

If we run 250℃ for 30min, sterilization will not be run 250℃ for 30min because it needs to be heated from 25℃.
(ex. it needs 10min to be heated from 25℃ to 250℃, then it only runs 250℃ for 20min. Therefore Fh value will be under 30) So we decided to run at 300℃ for 25min overkill cycle.

I thought if we run 250℃ for 30min, Fh will be about 298, so our collected Fh data must be over 298.

However I think i was wrong.
Fh(250℃ with z-value 46.4℃) value at 300℃ for 1min is 11.939 (Δ1* Σ10^(300-250)/46.4 = 11.939)
it means 300℃ for 1min = 250℃ for 11.939min.
therefore 300℃ for 30min will be satisfied with the minimum Fh value (250℃ with z-value 46.4℃)

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TAEMIN,

When discussing sterilization time, regulatory agencies discuss sterilization time as the sterile hold/soak time when the sterilization temperature has been reached, not the total cycle time (including ramp-up times).

Also, when calculating sterilization Fh, it is best practice to only include Fh for times when the temperature has reached the target set-point temperature. The reason for this, is that ramp times can change between cycles, and the ramp temperature profile can also change between runs. Whereas, the temperature during the hold time is very repeatable. The last thing you want is to get a Fh during one cycle, and a different Fh then next time you run the cycle, just because there were changes in ramp conditions.