# Fh Value Calculator Useful In Dry Heat Sterilization

Page Contents

## Introduction

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.

## Formula Used

Where,

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

## The Difference

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 |

Theoretical Requirement 121.1°C @ 30 min. of sterile hold time | Theoretical Requirement 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 |

## General Considerations

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.

## Conclusion

This article mostly covered the correlation of the Fh value with the earlier learned F0 value. Also, we’ve seen and used the Fh value calculator just like the F0 value calculator.

The definitions and concepts behind the scenes such as D-value, z-value, Lethality, and SAL value are already discussed in the F0 value and its Application.

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.

Sir plz tell me the Z value for 220 degrees. @ 90 min In DHS

Hi Naresh!

Thanks for your query. Actually, it differs for different micro-organisms. But, when we don’t know exact details, we can consider the z-value as 20°C since you mentioned DHS even at 220°C. If you’d have said moist-heat sterilization (steam sterilization), we then should consider the z-value as 10°C when we don’t know exact microbe details to deal with.

Or you can determine the z-value as

1. Determine the D-value of an organism at min. 3 to 4 different temperatures.

2. Construct a death curve by plotting the log D vs. temperature.

I hope this clarifies. Please do not hesitate to ask for any additional information and I would be more than happy to respond.

When calculating with a different program, two values were obtained: Fh=13.78(min) and Fh=0.07(min).

0.07(min) could be obtained in the same way as your writing, but I have no idea how 13.78 is calculated. Do you happen to be able to seek advice?

Hi Jeon!

Glad to see you. It’d be great if you share more details on this. What are the parameters you are dealing with? This will help me to understand and elaborate on what might be the cause.

Parameters:

Z = 10

Tref.℃ = 121℃.

The duration is 25 minutes and the average temperature is 119.41℃.

The resulting values were Fh=13.37 and Fh=0.07(min). Please let me know if you need any more information.

Hi Jeon!

Thanks for getting back. I see your parameters resonate with steam sterilization as Z=10 and Avg. Temperature is 119.41℃ @ 25 mins.

This particular page discusses dry heat sterilization where the Z-value is assumed as 20℃. So, first of all, you should use the F0 value.

Now coming back to your values & considering this as steam sterilization, the F0 value for this scenario would be around 17 mins. Use this link instead I would suggest!

https://pharmagxp.com/process-engineering/online-calculator-for-f0-value/

Let me know if this helps.

Oh, I understand. Thank you.

But when you experiment with steam sterilization at 121℃,

Can’t I get the Value of Fh?

‘Fh’= Is it a Dry Heat Sterilization?

The F0 value also called Equivalent Exposure Time is used for Steam Sterilization. The Fh value also called Heat Penetration Factor is used for Dry Heat Sterilization. You can’t mix them because their purpose is different. You can read above the tabulated differences.

Hope this clarifies!