So you have to temperature map a warehouse…couldn’t be easier! Off you go to find the relevant regulations that cover the details for a formal Validation mapping. After rummaging through regulatory archives, three hours on Google and finally asking anybody on LinkedIn, you realize that this isn’t quite as easy as it first sounded. 

Google has left you with more questions than answers, such as “How many sensors per square foot?”; “Do I need to map areas that have no shelving?”; “Should I perform the test over two hours or two weeks?”; ”Empty or full….?”  The reason that nothing specific is found in any of the guidelines you have been reading is that there is no single method for mapping a warehouse; rather it depends on many factors. This blog highlights the considerations needed for the justification or rationale you will need to show in a quality audit or inspection. 

How many sensors are appropriate for a particular warehouse? No standards or set formulas exist for the number or placement of sensors used to map a space. However, your study must demonstrate 3-dimensional uniformity/compliance with product requirements. These multiple data points account for gradients or temperature extremes in critical areas where product will be stored. Good practice is to use a sufficient number to understand the environment, but not more than needed. Too few sensors cannot justify the results; too many means handling more data than needed. 

Here are some important points to remember when determining sensor locations:

• Temperature gradients between the cooler floor and warmer air at the ceiling;

An HVAC system’s capacity to move air, as well as the sizing of blowers or fans to adequately circulate air;

Layout of racks, shelves and pallets – surfaces where product will potentially be stored. Are there obstructions to air flow?

Location of control sensors;

Location of doors and windows and potential effects of stored product nearby including outside walls that may respond to external temperatures;

Effect of incidences like power failures and vulnerable areas where there may be wide variations in temperature such as near shipping doors;

Finally, one that’s often over looked… areas that are non-shelved, but deemed to be used as interim storage areas before placing in racking.

Using a 3-dimensional temperature profile means measurement points or sensors in at least three planes – top to bottom, left to right, front to back. Additional points are added where known cool or warm areas may exist. In any case, use a consistent rationale for sensor distribution. For a larger warehouse, a justification for a 30-60m distance between sensors could be used with additional sensors in vulnerable areas. These areas include loading docks, outside temperature extremes, solar heating from windows, heat generated from artificial lights, air circulation and uneven building insulation.

The question of where to place sensors is just as, if not more, critical than the decision of how many. Measuring the temperature of a space is really an attempt to forecast the temperature experienced by the product.  For example, products stored on a double rack system facing the isles will experience more air circulation and a different temperature than products set back from the isles. Changes in the control system will take longer to reach the products in the interior of the racks.

Now that the first test has shown temperature variability of the warehouse, modifications made and critical storage areas identified, it is time to run a series of validation tests. Ideally, several tests should be repeated consecutively and demonstrate an outcome that meets acceptable temperature variations. Document each step so that each test can be repeated in the same manner.

Once the validation project is completed there can be many variables that can change storage temperatures. Some are under your control but others may not be. For example, there may have been a consistent history of weather conditions for temperature and humidity in the region. With extremes in weather occurring all over the globe, however, weather history is not a forecast for future conditions.

Your validation plan should take into account seasonal changes and even extreme variations within a season by mapping the warehouse with greater frequency and even over a longer period. Some protocols call for mapping every three months over a two-day period. How long before the next set of tests – one year, two years, three years? The rationale should be justified in your validation plan. Frequency will depend on other factors such as warehouse construction, major HVAC repairs or upgrade, or other modifications to the warehouse environment, in addition to weather extremes. Also, use data loggers that can run for long periods without maintenance; if battery powered, there is no need to worry about power failure in the middle of a test.

Regulations or rules that require documentation are very general. They use terms such as adequate, appropriate, reasonable, and proper. Agencies say what regulations you need to meet with some guidance, but not how to meet them. Each company determines how they meet cGMPs with a science-based rationale. What and when to map is determined by the level of risk to quality should a critical environment deviate from recommended conditions.

But most importantly, each process must be validated with thorough records and those records must be gap-free and provide an audit trail. They must be trustworthy, taking into account equipment failures (loss of control), facility failures (power outage) and human intervention (errors, tampering). The FDA interpretation of cGMPs is not static, it evolves as new regulations, guidance and industry documents are published.

In 2011, the FDA’s Center for Drug Evaluation and Research (CDER) had many cGMPs and Industry Guidance under development and revision. Make sure you follow the FDA website ( for all applicable guides and regulations. Become familiar with the regulations, guidance and standards pertinent to your area of business. The cost of compliance is high. The cost of noncompliance is much greater.

About the author: Jon Aldous is the Product Manager for Vaisala’s Life Science Division. His background is in Electronics and Electrical science and he holds a Bachelor of Engineering.  He lectured at the University of the West of England, teaching Digital and Mechanical Engineering and was involved with the development of poly-silicon micro structures for the use within thermopiles and intelligent data acquisition sensors.  After immigrating to the US, he worked for 12 years with Kaye Instruments as Product Manager developing that company’s thermal validation systems. He later joined Veriteq Instruments, which was acquired by Vaisala in 2010. The acquisition has enabled Aldous to expand his role into both software and hardware product management for life science applications

About the company: Vaisala provides comprehensive reliable, high-quality measurement and monitoring solutions in controlled environments within the life science industries. The company offers knowledge and education resources to customers so they are best prepared for an inspection, meeting FDA regulations and maintaining high quality specifically around the measurement and monitoring aspects of production and storage.