When does the sterilization phase start in a autoclave cycle?

I am hoping that I can get a feel for the industry standard here. We would consider the start of an autoclave cycle the time the controlling probe (usually the drain) crosses the minmum temperature (122C). When we map the autoclave load we would have numerous thermocouples with one placed beside the drain probe. Again for the mapping we would look at the time this probe crosses the minimum temperature and mark it as the start of the cycle. The end of the cycle would be the point at which this probes crossed back over the minmum temperature. So the actual sterilisation phase would have +/- 1 minute window. A colleague of mine had a different approach where they would find the end of cycle point (usually a more dramatic change in temperature) and count back say 50 minutes and mark that point as the start of the cycle (therefore , all cycles would be 50 minutes exactly). One of our acceptance criteria is that all other temperature probes would be up to the minimum temperature with 30 seconds after the start of sterilization. Therefore , the two approaches above could potentially deliver different outcomes. i.e. equilibration time could pass or fail depending on the approach taken. I am hoping someone out there has come across this situation before?

Your Validation would determine worse case for cycle length, from start button to automatic end of duration for exposure. Use TC’s, Data Loggers (wireless) in your cycle, look at the consecutive runs for worse case come-up ‘in product’ and then add your needed exposure time to that for parameter. Come-up times were (in product) 7 min., 10 min and 8 minutes. If you wanted exposure at 121C of 50 minutes, overall cycle would be set at 60 minutes minimum. Loads, chamber conditions (warm, cold), etc. make some variance in come-up… so validate 3 consecutive runs and keep conditions and factors such as loading the same. Russ