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'Just Right' Warehouse Mapping

With warehouse mapping as with Goldilocks’ soup, there is definitely a ‘just right’ to shoot for…

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While most quality managers in pharmaceutical companies understand the need for temperature and humidity warehouse mapping in order to safeguard efficacy of both raw materials and final product, the possibility for warehouse mapping overkill is not always recognized. Finding that ‘just right’ sampling rate will spare your operation both the problems of insufficient data to inform on needed plant facility remediation on the one hand, or cumbersome and difficult data analysis on the other.

The first step in determining ‘just right’ warehouse mapping is to determine the critical mapping points for your facility. Studies have shown that spacing temperature/humidity loggers every 3,000 to 5,000 feet in an open warehouse lacking walls to block airflow is adequate to create meaningful data. Even in an open warehouse design temperature and humidity is not usually constant from one spot to another because:

  1. areas near the ceiling or exterior walls may stay warmer or cooler in response to outside temperatures
  2. as warm air rises, temperatures stratify
  3. temperatures are higher near heaters, and especially so if fans are undersized or placed in such a way that they cannot completely mix the air
  4. hot spots are created by racking, shelving and pallet storage areas that obstruct air circulation
  5. frequently opened doors affect temperatures

Moreover, one must usually add enough data loggers to anticipate temperature and humidity variations near HVAC outputs, exits to unconditioned spaces such as


loading docks and staging areas, variations between different height locations in storage areas, and outside temperatures used for comparison purposes.

In most warehouses, temperature/humidity samples spaced in 15-minute intervals provide enough data to evaluate temperature trends. The overkill factor can be seen by contrasting the data load of two pharmaceutical processing plants that are doing warehouse mapping with ten identical data loggers. Plant A is sampling data every 15 minutes for one week and generates 6,720 sample points. Plant B is sampling data every minute for one week, and generates 100,800 sample points.

Plant B clearly has a lot more data to process. One can get an inkling that this is too much data by considering that in typical spaces of 50,000 square feet or greater, temperature and humidity changes typically happen very slowly, and most data loggers take at least one minute to respond to these changes.

Whether one has collected hundreds of thousands of data points or a more manageable and functionally meaningful smaller sample size such as Plant A, the next step is to calculate the mean kinetic temperature, a calculated fixed temperature that simulates the effects of temperature variations over a period of time. Mean kinetic temperature is used to express the cumulative thermal stress experienced by a product at varying temperatures during storage and/or distribution. Application of this formula is more straightforward than it appears:

Mapping Formulas

Once you’ve calculated the mean kinetic temperature, you can determine if conditions are in a zone that is out of acceptable temperature and humidity ranges for your production processes. After you take steps to correct problems, you would then need to repeat the data warehousing exercise to determine that your remediation steps have been adequate.

How many times do you need to do warehouse mapping? Indeed, finding that ‘just right’ balance for warehouse mapping also involves knowing how many data loggers to employ to generate this data and how frequently to repeat the exercise. Moreover, there are numerous ways in which the types of data loggers you employ affects the number of times warehouse mapping will need to be repeated.

Initially, warehouse mapping needs to be repeated until you determine that the facility remediation steps taken have been successful in brining mean kinetic temperatures into the acceptable range. Remediation might involve several steps such as putting in larger fans near hot spots created by shelving or simply rearranging shelves in ways that promote airflow. Or, placing plastic curtains over open hallways or dock entrances can sometimes be sufficient to block the wide temperature variations that often occur when inside and outside temperatures mix. Sometimes, expert HVAC consultations are needed. The point is that you will not know whether remediation steps have been effective until you repeat the warehouse mapping exercise.

Mapping also needs to be re-checked in different seasonal conditions. Also, normal business developments might necessitate repeats of warehouse mapping. For example, new product lines often involve warehouse expansion or redeployment of shelving and other storage areas that might impact airflow.

Consistency in warehouse mapping protocols is highly important. Be sure to document the location of each data logger and label each data logger to ensure that it is repeatedly placed in the same location. Be advised to create labels that are identical on the physical data logger and in the logger’s software, and that reference the placement spot in the logger’s ‘name’. Keep a map on file of named data loggers showing their physical location in the warehouse.

Trying to cut costs by buying fewer data loggers usually backfires because the costs of data loggers per se are only one cost associated with warehouse mapping. Actually, your time and the time of all company staff members involved in the warehouse mapping procedures is a significant part of the cost equation. Since the mapping points are the same whether you use one data logger or 20 data loggers, the primary cost difference will derive from labor costs. If you prolong the process by using too few data loggers, you drive up labor costs. Often, purchasing data loggers with Ethernet connectivity to let you view and download logged data and modify logger settings from your PC on any logger connected to you LAN will also help save time and money.

The completion of warehouse mapping RARELY, if ever, marks the end of product life for a data logger. Rather, data loggers used in warehouse mapping should be used for ongoing critical storage monitoring. There is an ample variety of data loggers that are FDA 21 CFR Part 11-compliant and in other ways customized for pharmaceutical applications. As long as you keep data loggers originally purchased for warehouse mapping calibrated, you can expect an average service life of 5 years, and will be able to re-deploy your data loggers for repeat warehouse mapping exercises when and if they are needed.


by Chris Sorensen, VP, Dickson Company

About the Author: Chris Sorensen is VP of Dickson Company (, which offers the widest range of data loggers and chart recorders available in the world for pharmaceutical and other applications.

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As published in Pharmaceutical Processing magazine (1/2006).