Questions & Answers from our Webinar: Sensor Placement for GMP Temperature Mapping

Questions and answers
Paul Daniel, Vaisala
Senior GxP Regulatory Compliance Expert
Life Science

Today's blog is a Q&A based on yesterday's live webinar on sensor placement in temperature mapping studies. If you were able to join us for that webinar, thank you for being so interactive and engaged!


Did you miss the webinar?

Modern Rules for an Old Practice: Sensor Placement for GxP Environments

Q & A from The Webinar: Modern Rules for an Old Practice

Are there any requirements to place (2) monitoring probes in upright freezers or walk-in freezers/chillers to monitor the warmest and coldest spots as identified in the mapping validation?

There are definitely requirements to monitor these types of spaces.  Depending on the publication, guidance, or regulation you are reading, the particular publication may not specify whether two probes are needed. 

Often the guidance is intended for locations that may not be temperature controlled.  In my experience, only one monitoring probe is used for uprights and smaller, and the logistics of the use of the small space often makes it unreasonable to place a probe in the actual hot or cold spot. Instead a monitoring probe is placed in a sensible reference location, or the user simply standardizes their probe locations to a single type of location, such as just inside the door. 

If your space is large enough to walk into the use of multiple probes becomes possible, but isn't necessary unless there is a significant temperature differential across the unit.  For larger spaces, such as warehouses, multiple probes will be expected just given the size of the space, and you may find it useful to place probes in the actual hot and cold spots.


Criteria for location of sensors in areas greater than 100 m2

There are no published guidances with specific criteria for placement of sensors in large spaces, especially once the volume of the space is over 20 cubic meters.  However, I will give you some basic rules in the webinar to help you in this sort of situation. In a room temperature warehouse, if you use three layers of sensors, with no more than 20 meters of lateral distance between each sensor, you will do fine.  This is conservative, but it makes auditors happy.

Does Vaisala vLog satisfy USP 1079 standards for validation and mapping

vLog can be used to do mapping and validation that would satisfy the requirements of USP 36 Chapter <1079>.  However, I am not aware that <1079> includes any requirements for software that might apply to vLog.  In my experience, <1079> speaks more to the types of environments that should be mapped, how sensors should be placed, and the duration of the mapping study.

How do you define a worst-case location for temperature mapping for 2-8C rooms?

Before the study I would expect every spot to be a potential worst case location.  However, having some experience with similar units might lead you to expect that is directly in front of the cooling units might be a cold area, near the doors might be a warm area, there is probably a warm "dead spot: that gets little air circulation (probably in the back, depending on the cooling unit location). 

Doing the mapping study with a sufficient density of sensors will quickly identify the locations of concern.

How do you determine the frequency of environmental monitoring, validation and revalidation?

 I determine it based on the risk and sensitivity of the process being monitored.  If the items being stored don't cost much, are easily replaced, and aren't sensitive to temperature changes, I would remap infrequently, maybe every 5 years.  I could imagine that this might include standard reagents for a QC lab.  If the items being stored were expensive, hard to replace, or extremely sensitive, I might revalidate yearly.  I could imagine that this might be stability chambers for an expensive and sensitive drug study.

Paul Daniel, Vaisala

Senior GxP Regulatory Compliance Expert

Paul Daniel has worked in the GMP-regulated industries for over 25 years helping manufacturers apply good manufacturing practices in a wide range of qualification projects.  His specialties include mapping, monitoring, and computerized systems.  At Vaisala, Paul oversees and guides the validation program for the Vaisala viewLinc environmental monitoring system.  He serves as a customer advocate to ensure the viewLinc environmental monitoring system matches the demanding requirements of life science and regulated applications.  Paul is a graduate of University of California, Berkeley, with a bachelor’s degree in biology.



Mar 2, 2019
Hi dear
I'm an university student and I am working on smart greenhouses, I will appreciate it if you can help me about the number of temperature and humidity sensors we choose for each square meter in different greenhouses? Is there any references to calculate the exact number of sensors?

Janice Bennett-Livingston

Mar 4, 2019
HI Eli,

We have a white paper that lays out in detail how to calculate sensor density according to the cubic meters you are measuring. Please find the PDF here:
If you have questions, please feel free to email our Senior Regulatory Expert Paul Daniel:
[email protected]

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