Yet More On Sensor Placement: The Whole Warehouse and Nothing but the Warehouse

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Paul Daniel
Sr. Regulatory Compliance Expert
Aug 24th 2013
Industrial Measurements
Life Science
Science & Sensing Technologies

Recently, a colleague wrote in asking for an expert opinion regarding a temperature mapping validation for a warehouse application. In this case, the data loggers were placed at the top locations of the warehouse, positioned below the maximum product storage height (data loggers at 17 ft., and stored products up to 23 ft.).

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Dear Paul,
The subcontractor who performed a validation in our warehouse provided the following rationale for high sensor placement: "The purpose of the placement of the data loggers is to approximate the geometric corners plus middle locations of the warehouse areas. The top location heights were to be in the general area of the top plane, they were not meant to be the extreme top plane. This is standard practice of placement of the data loggers. The temperature variation will not be much in a space of 5-10 feet, considering the whole of the warehouse area was mapped and shown to be within limits."
However, in the Vaisala Validation seminar, Paul recommended that sensors be placed above the maximum storage height. My assumption is that placing sensors above the maximum storage height is the best way to confirm that the temperature of the product storage location is within temperature requirements. Is the rationale provided by the subcontractor appropriate?
Thanks – S


Dear S,
You are correct that the best practice in any mapping exercise is to capture the entire storage area by placing your sensors at the limit of the usable space. This is an easy concept to apply in small units such as refrigerators and incubators. But even then, a similar discussion comes up: If I map a 1 cubic meter refrigerator, with my corner sensors 10 cm from the adjacent sides, am I obligated to never place my sensors out of these bounds? In practice, it’s hard to prevent the users from placing items outside the mapped space of a refrigerator. And we can all probably agree that the 10 cm doesn’t make a difference.
In a large space, such as a warehouse, the challenge is the opposite. We will usually need to store things on top of the top racks, but there is no easy way to get our sensors above the top rack safely, especially in a warehouse that's in use.
You are again correct that the only way to confirm 100% that the product storage locations on the top racks are within the temperature specifications is to get sensors up there.
I will offer these three ideas on how to resolve the issues posed here:
1) Anytime I have ever mapped a warehouse, we have put the sensors up as high as we could on the racks. And in most instances, this meant there was product storage above the sensors. This is one of the real-world facts that don’t always fit with the perfect world we’d like to see in our studies. So, your contractor is more or less correct.
a. (There have been a few instances where we did place sensors above the actual storage area by placing the sensors on the ends of poles. But the data was not convincingly different, except a few cases where the sensors were placed near HVAC vents.)
2) You have data from the top plane. If it is well within temperature limits, then you have nothing to worry about. If it is very near the temperature limits, then perhaps you have something worth investigating. But then the issue is not with the sensor placement, it is with the warehouse controls.
3) If you were to be audited and there was a problem found with the sensor placement, it wouldn’t be a big issue. You are ahead of the game by even mapping your warehouse. Despite it being a GMP requirement, many companies fail to comply with this. At worst, I expect the auditor would ask you to merely place the sensors higher on your next scheduled revalidation. It would be extremely surprising if an immediate revalidation were demanded.
I hope this information is useful in your decision-making process.
Best regards,
Paul Daniel