Autoclave F0 calculations

Hello,

Can anybody help with this dilemma.

During PQ of the autoclave cycle one of the requirements is that the Fo specification must be met.

We are using a Kaye 2000 which calculates the lethality. However, there is some confusion at what point the Fo is taken.

1. Some suggest at the end of the exposure phase (end of 20 minute hold time)
2. Some suggest at the end of the autoclave cycle, as the Fo is still accumulating. (The Kaye recording is stopped 25 minutes after the end of the exposure phase)

Any suggestions

F0 = D121 x (log N0 - log Nt)

where, F0 equals the number of minutes exposure at 121 degrees Celsius which would have the same lethal effect as an alternative designated autoclave cycle. N0 equals the initial contamination level (bioburden) and Nt equals the final or required contamination level (SAL) after t minutes exposure.

[b][COLOR=“blue”]F0 = t x 10 T-121/Z.

t= time in minutes at which product is at exposure temprature

T= sterilisation temprature

Z= A constant considered as 10 for steam sterilisation.[/color][/b]

Thanks Durga,

Useful information. However, its the actual time that is of concern. Our exposure is >121oC for 20 minutes. But as you are aware the some of the thermocouples even after 20 minutes exposure will still be above 121oC. So, for the Fo calculation do you only take into account the exposure phase (20 minutes) or (20 minutes exposure + the additional minutes) that the thermocouples are above 121oC.

Exposure time is noted as time when Thermocouple reaches 121C.Once this temperature is reached, you have to expose the material of concern for 20 minits.

It depends on what you are trying to correlate to the Fo value. Are you trying to demonstrate that the entire cycle provided adequate lethality to destroy the BI or are you trying to demonstrate that the exposure phase provided adequate lethatlity to destroy the BI?

For a PQ, I would start the calculation at the start of exposure and end at the end of exposure. I would then claim that the exposure phase provides an Fo of >20 minutes. That way I would have some wiggle room if an issue arrises during operations. For example, the exposure stops one minute short or dips during exposure. I would calculate Fo start to finish in operations.

[quote=DURGA PRASAD][b][COLOR=“blue”]F0 = t x 10 T-121/Z.

t= time in minutes at which product is at exposure temprature

T= sterilisation temprature

Z= A constant considered as 10 for steam sterilisation.[/color][/b][/quote]

Hi there, i think the right equation is as follows:
“F0 = t x 10(T-121.1/z)” … In which 10 is to the power (T-121.1/z)

Concept of F0 is very vast accoring to me if your autoclave cycles is based on F0 then you should consider exposure end F0 value as the final value which can be surely accumulated because after exposure you can not gurantee the temperature of each probe to be maintained up to end of cycle.
while in case of time based autoclave cycle you should consider end F0 value as the final value which is achived during whole cycle.

Hi Mike. I’m not certain your question was answered. You could continue to calculate F0 until the cycle stopped, however, the amount of lethality added below 100 C is negligible. We use Kaye Valprobes and they support this type of collection, I bet the Kaye 2000 does also. Mike

[quote=mikey70]Thanks Durga,

Useful information. However, its the actual time that is of concern. Our exposure is >121oC for 20 minutes. But as you are aware the some of the thermocouples even after 20 minutes exposure will still be above 121oC. So, for the Fo calculation do you only take into account the exposure phase (20 minutes) or (20 minutes exposure + the additional minutes) that the thermocouples are above 121oC.[/quote]

Hi Mikey70,

According to PDA Technical Report No. 1 - Validation of Moist Heat Sterilization Processes the PQ includes certain acceptance criteria. These are examples:

• Minimum and maximum time above a specified minimum temperature measured with heat penetration probes.
• Minimum and maximum total accumulated F0.
• Minimum F0 at the end of the exposure phase.
• Minimum and maximum pressure during exposure.
• Correlation of temperature and pressure for saturated steam.
• Minimum and maximum chamber temperature during exposure.
• Maximum temperature or F0 variation between heat penetration probes.
• Maximum temperature variation in temperature distribution probes.
• Maximum equilibration time.
• Minimum number of properly functioning probes.

In other words, the PDA suggests taking into consideration the total process F0 (min. and max.), F0 at the end of the exposure phase, and F0 during the exposure phase only (max. variation).

I hope this is useful.

Regards,

Enrique Riis

Fo is Fo, whether generated during exposure or after exposure. As noted in previous posts, it may be of value to understand / know the amount of Fo generated post-exposure (e.g. “wiggle room”). I typically build in “wiggle room” by requiring an additional amount of Fo in the acceptance criteria, and use the total Fo value.

So, it depends on what one is trying to demonstrate…as long as the meaning of that value is stated in the summary report.

It depends on what you are trying to correlate to the Fo value. Are you trying to demonstrate that the entire cycle provided adequate lethality to destroy the BI or are you trying to demonstrate that the exposure phase provided adequate lethatlity to destroy the BI? Autoklavai

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[quote=mikey70]Hello,

Can anybody help with this dilemma.

During PQ of the autoclave cycle one of the requirements is that the Fo specification must be met.

We are using a Kaye 2000 which calculates the lethality. However, there is some confusion at what point the Fo is taken.

1. Some suggest at the end of the exposure phase (end of 20 minute hold time)
2. Some suggest at the end of the autoclave cycle, as the Fo is still accumulating. (The Kaye recording is stopped 25 minutes after the end of the exposure phase)

Any suggestions[/quote]

[quote=mikey70]Hello,

Can anybody help with this dilemma.

During PQ of the autoclave cycle one of the requirements is that the Fo specification must be met.

We are using a Kaye 2000 which calculates the lethality. However, there is some confusion at what point the Fo is taken.

1. Some suggest at the end of the exposure phase (end of 20 minute hold time)
2. Some suggest at the end of the autoclave cycle, as the Fo is still accumulating. (The Kaye recording is stopped 25 minutes after the end of the exposure phase)

Any suggestions[/quote]

My suggestion is when you calculate Fo for equipment which is not termal labile to calculate Fo only for exposure time and Fo collected in heating and cooling phase will be some kind of safety margine. But for termal labile product like some nutrient media it is better to calculate Fo for entire cycle to be sure that your product is not affected by long temperature exposing.
But, as PPG-Validation-Guru said, for porous load according to EN:285 you start to calculate Fo when all temperatures are above 121oC and this is another approach because autoclave exposure time is not important for you, just your termocouples readings.
US audits are more focused on PDA Technical Report and Fo values but EU audits on EN:285.

Hallo Everyone,
I want to ask about "how to calculate the lethality when oven or autoclave qualification.
Is calculating lethality ranging from 0 minutes or 1 minute?
Why? Where i can see the article?

I want to ask about "how to calculate the lethality when oven or autoclave qualification.
Is calculating lethality ranging from 0 minutes or 1 minute?
Why? Where i can see the article?

All about calculation of Fo you can find:
http://www.fedegari.com/servizi_documenti_EN.aspx

Dear all,

Please answer what is the lag and log phase in Autoclave validation?

[quote=ynreddy83]Dear all,

Please answer what is the lag and log phase in Autoclave validation?[/quote]

Lag time is the time in minute between your first sensor reached 121.1 or ur set temperature and last sensor reached 121.1 or set temperature.

I would look up various regulatory agency requirements on this. EN285 is the most stringent (for Europe) and has quite a few requirements other than just Fo that you might want to be aware of.

To answer your question though. The most conservative approach is to use only the exposure time (when it is at 121.1 C or above). Anytime the temperature is below 121.1 there will be some accumulation (but it shouldn’t be much if you are properly ramping up, and then ramping down at the end).

The reason I wouldn’t rely on additional exposure/lethality accumulated during the ramp-up and ramp-down phase, is because often, those phases aren’t reliable or repeatable as much as the exposure phase.

The purpose of validation is to ensure repeatability. The logic of the autoclave during ramp up and ramp down is pretty “dumb” and doesn’t control that tightly, while the control during the exposure phase is very tight and consistent.

Another lack of control is the manual process after the autoclave cycle ends. Do your people open the autoclave and take the parts out immediately or in 1-2 hours? This will affect the overall lethality too. Again, making the results unrepeatable (bad).

@JaredCroft, I agree with you but just to make some points clearly - EN285 do not ask for Fo values. This is most often approach in Great Britain - they ask for time above 121 or 134 and equilibration time. This standard is mostly for porous load and original standard was used for hospital autoclaves but now is used for sterilization validation in several areas (med devices, pharmaceuticals…). In this standard request is that holding time is longer than 15 minutes and that time is not connected with sterilization phase of autoclaves…

Technical Report NO.1 - Validation of sterilization cycles is better for undestanding of Fo values…

Most common approach is that for porousl load calculate Fo values for exposure time (autoclave sterilization phase) and for liquid load for whole cycle (because of thermal lability, specialy for nutrient media, product…)