Paul Daniel

Mar 27, 2019
I'm glad to hear you find our blog helpful!

You are asking a question that does not have a clear answer from the available guidance and regulations. The best you can do is make a choice that is logical, and document that rationale.

The identification of hot spots and colds spots is a by-product of our statistical analysis of mapping data. If we simply figure the overall max and the overall min, and verify it is within our acceptance criteria or specification, we have just found the simplest path of data analysis. And along the way, we identified the hot and cold spots. But does this really mean that the hot spots and cold spots are important? Or are they just a by-product of how we analyze the data?

Personally, I think hot/cold spots do not matter if the overall max and min are within specification. In this case we have just proven by qualification study that the particular chamber can operate as intended - end of story. I think monitoring probes are there to detect catastrophes and disasters, things like doors left open, failed compressors, power outages, etc. If not what are they there for? To tell us what is going on with the product? Impossible. There is no way one or two probes can accurately predict what is going on inside the dynamic environment of a chamber, so we can't rely on them for data about what the product has experienced. we only know that there has been a problem. I think this position is supported by actual industry practice, where there is historically only one probe in small chambers, and that probe is almost always located in the same place (side wall, same side as the door handle, middle height, about 20 to 30 cm from the front)

I just said "I think..." a lot. Does it matter what I think? Does it matter when some guidance says to pick a monitoring location based on (not "at") the location of the not and cold spots? Does it matter when a guidance says to actually place a probe at the hot spot and one at the cold spot? This you will have to decide for yourself. Just because something is in a guidance doesn't mean it is the best idea for your situation.

This is what we know:
*We should definitely re-qualify and re-map periodically based on risk.
*We will determine hot and cold spots (as an analysis by-product) each time we do this.
*We may see hot and cold spot locations changing from year to year. (If all measurements are otherwise in spec, I don't see why it matters.)
If you think it matters, you may need to explain it. But if it is in spec, I would simply explain use the spec as the acceptable limit of variation and say "It doesn't matter".
*If you base your SOP for monitoring probe location on the hot spot or cold spot location, then you may have created a problem for yourself. This seems like a good reason to change that policy.

Another pathway in this is to talk to the chamber manufacturer. These guys are required by law in some countries to map their units extensively, with the expectation that all units of the same model number will behave the same. And it is in their best interests to map as a good mapping tells them the best place to put their control probes and monitoring probes. They will likely share their data with you privately to help you answer this question.

I hope this helps!