Before using the Fh value calculator, let’s clear some basics. The F0 value calculator we’ve seen earlier, helped us to understand the comparison between the ideal and actual exposure times. Therefore, named Equivalent Exposure Time (F0). Likewise, in dry heat sterilization, it is named in terms of heat i.e. Heat Penetration Factor denoted as Fh.
Using any of them provides assurance that the components are sterile i.e. free from viable microorganisms. However, their application is different in terms of sterilization, tabulated further.
In pharma-related manufacturing, few commonly practiced sterilization techniques include Steam Sterilization, Dry Heat Sterilization, Ethylene Oxide Sterilization, etc. However, here we’re dealing with the Fh value in parallel to the F0 value.
Remember? the z-value we assumed in the F0 concept was 10°C. For the Fh value, it is assumed as 20°C, but obvious when we don’t know the specific micro-organism we’re dealing with. You can read the theory behind the F0 value, D-value, and z-value in the earlier article F0 Value in Steam Sterilization.
To understand the calculations involved in the Fh value, it’s better to know the F0 value first. Despite the different purposes, their structuring is alike.
The following formula is used to calculate the Fh value in dry heat sterilization.
Δt – Sterilization Hold Time in Minutes
T – Average Temperature of all probes during a sterile hold in °C
z – Temperature Coefficient in °C
The term next to Δt is called lethality rate.
The Fh Value Calculator
At this point of time, it’ll be better to differentiate the two i.e. F0 and Fh values.
|F0 Value||Fh Value|
|Used to evaluate the effectiveness of Steam Sterilization||Used to evaluate the effectiveness of Dry Heat Sterilization|
|The assumed z-value is 10°C for sterilization range of 100 to 130°C||The assumed z-value is 20°C for sterilization range of 160 to 200°C|
121.1°C @ 30 min. of sterile hold time
170°C @ 32 min. of sterile hold time
|Targetted to mitigate micro-organisms especially living endospores||Targetted to remove the bacterial endotoxins|
|Much more complicated because of steam quality requirements||Lethality of the microbes is less than that of F0 at the same temperature|
When it comes to moisture-sensitive items, steam sterilization is not appropriate and may damage the accessories proposed to be in contact with the drug product. In such cases, Dry Heat Sterilization is the best suitable option to consider provided that the materials can tolerate higher temperatures than steam sterilization.
When we talk about Dry Heat Sterilization, we must not assume it as Depyrogenation where the temperature is even more than Dry Heat Sterilization and Fh value is then replaced by Fd.
The theoretical requirement for Depyrogenation is 250°C @ 30 min. Another difference is that the z-value assumed as 20°C for Dry Heat Sterilization, whereas for Depyrogenation it is 46.4°C. This means, 170 in the above formula would be replaced by 250, and the z-value of 20 would be replaced by 46.4.
Practical conditions may vary depending upon the type of bacteria being targetted and the physicochemical dynamics. However, these base values are enough to guide us in the evaluation.
Using this you can establish the clear resemblance between the theoretical requirement vs. actual results in terms of your dry heat sterilization cycles. Rather, this article was mainly focused on delivering you the Fh value calculator and not the detailed theory.
Before closing, I have few questions for you. How do you evaluate the performance of your Dry Heat Sterilization cycles? Do you find this Fh value calculator helpful for that? How do you perform your calculations for each cycle? Comment below and I’ll revert you promptly.