Autoclave cycle optimization

we had several validation tests done on our autoclave. The empty chamber temperature distribution test and hard load test showed that at the beginning of sterilization holding period(121.1C), there are over shootings of temperature above 121.1C (can reach 123C), then going down to or even below 121.1C, and then stabilized at 121.1C or more. This happens within the first minute, maximum 2 minute at the beginning. If we don’t want to touch the PID control valve or program, how can we justify our validation, the whole sterilization time is 30 minutes, the F0 acceptance is 18 minutes ( actual F0 is more than 30 minutes).

We also validated the sterilization on tubings, the lag time is from 20 seconds to 2 minutes for several load items, is this acceptable or we have to optimize the pre-vacuum cycle? do you meet same problems?


[COLOR="#000000"]Why do you need to run your sterilizer for 30 minutes?

You need to prove :
F0 at 121 is greater than equal to 12 minutes-USP

F0 at 121 is greater than equal to 15 minutes-EP

Your Biological indicator kill or your SAL should be motre than 10 to the power of 6. This is the value regulators look.

By killing any thing beyond this you can only put in your calculations and record and technically you cannot prove.

In such casses you need to prove that all your parts in the load and your reference point that is your drain should show 121C for required period of time that is called dwell time for the prescribed time. Your 18 minutes or even 20 minutes is good. By exposing 30 minutes more than 121.1C would destroy your materials if they are polymers. You need to understand your materials well and their temperature stability.

In this dwell time the temperature fluctuation should not be more than 1C across the autoclave chamber.

You need to achieve this temperature by adjusting your vacuum and pressure pulses to with in 15 seconds if you have up to 800 L autoclave. If you have more than this size you can go upto 30 seconds.

Keep it simple. Overkill cycles are for terminally sterilized products or metal products or needles or tubes where penetrability may be a question.

You need not show Kill, kill , kill and a kill.

All you need to show is a good kill as per stated SAL.


As Mr Durga said, there is no need for 30 minutes cycle duration. And Fo greater than 18 is overmuch.

There is a problem with regulation in your case. It is hard to say without more information but you can check where control probes are (in the chamber or in the drain or load), why main valve delay to close when sterilization phase start, are probes in condensate, do you have one or two steam supply line valves. And at the least why not change PID regulation or set some delay time for strilization start.

On the another question - if you calculate lag (equilibration time) properly, 2 minutes delay is something that is really problem. Try to rearrange the load, change prevacuum conditions (number and pressure), position TCs and BIs not to close steam penetration or position the load in a manner not to collect condensate where TCs are

Thanks for both of your reply. The 30 minutes cycle is pre-programmed, it can be adjusted. Actually it is an “Over kill” approach, maybe too much, but it is carried over from previous company. My feeling is that, the F0 value is more important, as long as it is over 12 minutes, or 15 minutes or 18 minutes, do we still need to concern about the physical parameters of the autoclave, i.e. the lag time and equilibration time should be less than 20 seconds, and the difference between load should be less than 2C, et al et al? It may be hard to achieve this for some type of autoclave.

Please correct me!

In this case, we make a important difference between porous and liquid load. For porous load, physical parameters are the most important and for Liquid load Fo value. For porus load, equilibration time is critical. It shows that air is pulled out and replaced with steam. If you do not pull out air from chamber for porous load, then autoclave heat air and air heat surface we want to sterilize. And then we have high Fo values but not effective sterilization. It is more important to have eq time than high Fo values. You can have high Fo values with eq time longer than 30 seconds but remember that if you dont have steam with contact with surface, you have some kind of dry heat sterilization and this sterilization at 121oC in not effective (170oC for 1h).
Overkill approach do not need 30 minutes sterilization at all. According to PDA overkil approach is Fo and Fbio greater than 12. EU regulatives need 121/15 minutes. So from my opinion, your porous load cycle validation should have eq time bellow 30/15 seconds and temperature above 121oC for 15 minutes. Reduce next cycle to have Fbio gretaer than 12 (for US market) and thats it!