Temperature mapping a steam steriliser

The situation

A steam autoclave used to sterilise equipment and materials for controlled work. Its own controller reports one temperature, from one sensor, and a sterility claim cannot rest on that single reading.

What had to be shown

Sterilisation fails at the coldest point, not the average one. The client needed evidence that the slowest part of the load reaches the sterilising band as quickly as the chamber does, stays inside it for the full hold time, and that the result repeats from one cycle to the next.

How I did it

1. Calibrated the temperature probes at the sterilising temperature before the study and checked them again after it, so any drift during the work would show.
2. Placed probes in the empty chamber first, including the drain, which is usually the coldest point, then repeated the study with a representative load, with probes inside the items hardest for steam to reach.
3. Ran repeat cycles for each configuration, so a single good cycle could not pass for a reliable one.
4. Analysed each cycle for equilibration time, the temperature band through the hold, the spread between probes and agreement with the autoclave’s own sensor, and reported the slowest position.

What the client got

A mapping report showing where the chamber and the load are slowest to heat and that every position meets the acceptance criteria, which gives the client the evidence for the sterility claim and a reference point for routine checks and requalification.

Written from the work, with no client named and no client figures quoted.