Autoclave qualification - Probe positions

Hello forum readers

I realise that there is a fairly large amount of autoclave qualification/validation information in this extremely helpful forum, but i dont think my question has yet been answered.
I am looking to carry out an annual qualification on an a number of autoclaves, which have already had the IQ/OQ and PQ testing carried out. Im looking for ‘guidance’ on a few points.

Firstly, do i need to carry out empty, min load and max load testing?

Secondly, is Bacterial Indicator testing necessary (or can i argue that the USP has stated that 121degC is sufficient, so if i reach that for the set time, then that is enough). If i do need to BI test, do i just need to run the test with my full load, or each time?

Thirdly, i am looking to run with between 10-15 wireless temperature probes, one in each corner, one in the middle and one as close to the drain as product would be. Is this enough (discounting probes insde bottles etc.)?

And finally, is one pressure probe in the centre of the autoclave sufficient - the laws of pressure in a loaded/heated chamber are a bit beyond me.

Thank you so much for taking the time to read this and i hope someone can offer some advice. :slight_smile:

Kind regards


The validation procedure for an autoclave is dependent on the process being performed in it. Autoclaves are used for a multitude of processes beyond sterilization. Thus there are many “rules” for validation. Many of the differences have to do with the material being processed or sterilized, and where the materials or mass end up after the autoclave. Keep in mind that these are used for curing or processing aerospace composites, glass lamination, electronics, building materials, and sterilization.

When you place the mass into the autoclave it will absorb the heat energy until the mass is fully saturated. As the temperature delta diminishes, the saturation rate slows accordingly. Thus one technique is to heat the internal working area to a temperature that is higher than the required saturation temperature for the material being processed.

Unless the autoclave has a method of circulation, uniformity cannot be assured. Steam heated systems are dependent upon saturation of energy. Dry processes utilize the circulation of the internal working fluid to pass the heat energy over the components being processed or cured.

Long story above, but the point is that validation is dependent on the size and process. Typically you would want to sample in a 5 point pattern with on T/C in the center, and a T/C at 12:00, 3:00, 6:00, and 9:00, or some variation of this pattern. The T/C’s should be placed at a distance of 10% of the internal working diameter away from the interior wall. You would repeat this pattern in a spacing based upon the length. The T/C’s are then connected to a chart recorder or data recorder for validation. The same sort of test is then done with T/C probes / wires connected to the “typical” loaded mass. If this is for sterilization, then a probe should be safely placed into the center of the material to record the ore temperature.

Lastly, I would recommend using hard wired T/C’s and not the wireless type. They are far more dependable. Be sure you use T/C wire with certifications.

Mr. Autoclave at