Worst-case point in equipment calibration

[SeanN]

Dear All,
Recently, we received an NC from a 2nd party-audit that "the calibration of laboratory instruments is deficient. (Worst-case point) the temperature probe for routine monitoring (such as freezer, fridge etc.) is currently located (e.g. left-top, right-middle etc.) without any supportive rational." IMHO, distribution of temp. could be a concern/risk, but worst-case point method is not a must/practice in ISO 17025. Please correct me if I am wrong here. Are you taking this approach in your lab?
Anyhow, could you advise on How, if we want to adequately address this type of risk?
Thanks a million!

 

[Jen Kirley]

Hello SeanN,

This coming from a customer audit suggests the subject is of interest to them. What is stored in this refrigerator/freezer? What is its criticality - what are the specifications, if any, for the cooling controls of XYZ (customer product)?

There are multiple references to placement of thermometers in a temperature-controlled vessel. Here is an example. I do not think it is unreasonable to ask about controls, but customers really do need to clearly specify requirements before they audit to them. You did not mention which industry you work in. What has your customer used to define this requirement?

I am not affiliated with Coris Monitoring.

 

[SeanN]

Hello SeanN,

This coming from a customer audit suggests the subject is of interest to them. What is stored in this refrigerator/freezer? What is its criticality - what are the specifications, if any, for the cooling controls of XYZ (customer product)?

There are multiple references to placement of thermometers in a temperature-controlled vessel. Here is an example. I do not think it is unreasonable to ask about controls, but customers really do need to clearly specify requirements before they audit to them. You did not mention which industry you work in. What has your customer used to define this requirement?

I am not affiliated with Coris Monitoring.

Thanks Jen, we store different materials (reagents, chemicals, kits, media ...) in different storage conditions/ temp.-monitored equipment (<20C, <0C, 2-8C, 37C, 45C, 65C, etc...). This specific audit took place in one of our molecular microbiology testing labs (doing food testing/environmental monitoring). The customer gave this NC about the way we monitor temperatures on daily basis. Their concern was that materials and specimens might be at risk of not being stored in a specified range. Thanks for sharing Coris Monitoring page. It's helpful.

 

[chris1price]

I don't think this has to do with calibration, but I would expect fridges and freezers containing temperature sensitive materials to be mapped. Have a look at 7.4.4 "When items need to be stored or conditioned under specified environmental conditions, these conditions shall be maintained, monitored and recorded." If the freezer of fridge is not mapped, then you can't be sure the items are stored under the specified environmental conditions.

 

[SeanN]

If the freezer of fridge is not mapped, then you can't be sure the items are stored under the specified environmental conditions.

Our freezers, fridges... are all mapped. But the point here is that the probe (to monitor temp. on daily basis), according to the auditor, must be placed in the "riskiest" location, with supporting document(s). Your thoughts?

 

[chris1price]

As part of the mapping, you should determine the worst case position, i.e. the coldest or warmest locations and place your monitoring probes here. The same would apply to ovens and incubators.

 

[Tidge]

I wouldn't get hung-up on the auditor's specific statement about "must be placed in the riskiest location". It is (more-or-less) a technological constraint that freezers/ovens will have cold/hot spots. The variation among internal temperatures can be mitigated of course, and mapping (with and without loading the temperature-controlled enclosure) needs to be done in order to understand the variation. Ideally, temperature variation is understood and so no single position is "riskier" than any other.

If the "worst" corner of the enclosure varies more than the place where temperature is actually monitored... I think the auditor may be correct to exercise skepticism about how well the temperature is being controlled/monitored. Data should be available to see if there is a reason to be concerned.

 

[SeanN]

If the "worst" corner of the enclosure varies more than the place where temperature is actually monitored.

Do you know any guideline on how to define the worst corner? fluctuations in temperature or variance from mean value? or else?

 

[Tidge]

Do you know any guideline on how to define the worst corner? fluctuations in temperature or variance from mean value? or else?

I think "worst" depends on the actual requirement. Apply some critical thinking, possibly based on personal experiences with home thermostats, overloaded freezers, and/or baking cookies.

Personally I would look for each:

• Any spots which have an obvious temperature offset relative to where the measurements are made, and
• The variation in temperature at all the spots for any specific measurement/set point

Either could be areas of trouble. Ideally there wouldn't be radical offsets in temperatures such that measurements at each spot that is checked vary around a common temperature. In that case, all spots could be considered equal.

The last time I designed an elevated-temperature box, the safety requirement was to not exceed a specific temperature. I mapped out the box and put the safety monitor probe at the point where the temperature was highest, and then incorporated a safety factor based on the inherent accuracy of the temperature probe and the observed variation within the box.

As a practical matter, that device was not concerned with temperatures being "too low", but had there been a specific range the location for the lower limit alarm/control probe would have been chosen by the same approach.

 

[chris1price]

I don't have specific guidance for laboratory freezers, but these documents are intended for cold-stores and warehouses, they should give you some ideas.

How to temperature map cold chain equipment and storage areas

This document provides guidance for undertaking the process. The first temperature mapping should take place at the time of the storage unit’s commissioning, and then should be performed when the cold and freezer rooms, as well as associated storage units (refrigerators and freezers), undergo...

www.who.int

Better Warehouse Mapping

Temperature mapping is vital for preserving GxP product quality during manufacturing, storage, and distribution, especially for frozen products. Warehouses pose unique challenges for temperature mapping due to their size, study duration, and seasonal variations. However, the principles for...

ispe.org