Sensor/Thermal Mapping
Study Report FAQ

Thermal mapping is a time-limited qualification study using multiple temperature sensors distributed throughout a space to characterise its full temperature profile and identify hot and cold spots, while routine monitoring uses one or a small number of fixed sensors, placed based on the mapping results, to continuously confirm the space stays within its validated range during ongoing operation.

Routine monitoring is only meaningful if its sensor locations were actually chosen based on mapping results — monitoring at an arbitrary or convenient location that was never confirmed representative during mapping doesn't reliably detect an excursion happening elsewhere in the space.

The rigor and sensor count for a mapping study should be risk-based, scaled to the space's size, the GxP criticality of what's stored there, and how tightly controlled the temperature range needs to be — a small, simple refrigerator storing non-critical items warrants a lighter approach than a large warehouse or a narrow-range stability chamber.

The number of sensors should be determined by the space's volume, geometry, and complexity — larger or more complex spaces, those with multiple air handling zones, or irregular shapes need proportionally more sensors to genuinely characterise the full space, and the sensor count and placement rationale should be documented in the mapping protocol before the study begins, not decided informally during execution.

Yes — every sensor or data logger used in a mapping study must have a current, traceable calibration certificate, since the entire mapping study's validity depends on the accuracy of the instruments recording the data; using uncalibrated or expired-calibration loggers invalidates the mapping results even if the recorded temperatures look reasonable.

Mobile units need mapping under conditions representative of their actual use, including realistic external ambient temperature extremes, typical loading configuration, and the duration of a typical transit, rather than being mapped only under static, stationary conditions that don't reflect the vibration, door-opening frequency, and ambient exposure the unit experiences during real shipments.

Sensor placement should be based on an engineering assessment of the space's airflow pattern, proximity to doors, vents, and heat sources, and known problem areas from prior experience or facility design, with an initial mapping study using a higher sensor density across the full space to actually discover where hot and cold spots occur — placing sensors purely at convenient, accessible heights and locations risks missing the areas most likely to drift out of range.

An empty-chamber mapping study characterises the space's inherent thermal profile but doesn't represent real-world use, since stored product itself affects airflow and temperature distribution — a loaded mapping study, using a representative maximum load configuration, is generally also required to demonstrate the space performs within range under actual operating conditions.

The mapping study should run long enough to capture at least one full operating cycle of the space's temperature control system, including any periodic defrost cycles, door-opening patterns typical of normal use, and, where practical, a full 24-hour period covering any day and night ambient variation that could affect the space — a study too short to capture a full cycle may miss a periodic excursion that only occurs at a specific point in that cycle.

Normal operating condition mapping confirms the space stays within range during typical, expected use; worst-case mapping, such as an extended door-open event or a power failure, characterises how the space behaves under an abnormal but foreseeable stress and how long product remains protected before a corrective action is needed — both are typically part of a complete mapping study, since routine monitoring alone won't tell you how much time you have to respond to a real failure.

The mapping study should include a representative pattern of door openings matching actual normal use — not a study conducted with the door kept closed throughout — since door-opening frequency is often the dominant factor affecting temperature stability near the entrance, and a study that ignores this doesn't represent how the space will actually perform once it's in routine operation.

For spaces significantly affected by external ambient conditions — such as warehouses without full environmental independence from the outside climate — mapping should be performed across both summer and winter extremes, since a single mapping study conducted in one season doesn't demonstrate performance under the opposite seasonal condition; fully environmentally controlled, internally isolated spaces may be able to justify a single mapping study with appropriate risk-based rationale.

Remapping is typically triggered by a significant change to the space, such as HVAC system modification, a change in racking or storage layout, a relocation of the space's air handling equipment, a pattern of temperature excursions suggesting the original mapping no longer reflects reality, or simply reaching a periodic remapping interval defined in the site's requalification schedule.

If a hot or cold spot can't be physically eliminated through HVAC adjustment or layout changes, the area should be excluded from use for GxP-critical storage, clearly marked and controlled to prevent product being placed there, or, if the area must be used, monitored with its own dedicated sensor and defined, tighter operational limits reflecting its actual performance.

Routine monitoring points should be selected from the locations identified during mapping as the worst-case positions — typically the warmest and coolest points found — because if temperature stays within range at the worst-case locations, the rest of the space, which performed better during mapping, can reasonably be assumed to also be within range.

Where humidity is a controlled, GxP-critical parameter for the space, humidity mapping is typically performed concurrently with temperature mapping using combined temperature and humidity data loggers, rather than as an entirely separate study, since both parameters are affected by the same airflow patterns and door-opening events being characterised.

Sensor placement should be documented with a labelled floor plan or diagram showing each sensor's exact location, height, and reference identifier, along with a written description sufficient for someone unfamiliar with the original study to physically reproduce the same placement in a future remapping exercise — a vague description like "near the door" isn't reproducible and undermines the comparability of future mapping results against the original baseline.

An inspection-ready mapping report should let a reviewer confirm exactly how the study was designed, executed, and what it found — including the acceptance criteria, results at every sensor location, and how the routine monitoring point selection was justified by those results.

• Study objective, acceptance criteria, and space description.
• Sensor and data logger identification, with current calibration references.
• Sensor placement diagram with locations, heights, and identifiers.
• Loading configuration and duration of the study.
• Results at each sensor location, including any excursions.
• Conclusion, identification of worst-case locations, and routine monitoring point rationale.

A thermal mapping study report should be retained for at least as long as the space remains in use for GxP-critical storage, since it's the evidence justifying the current routine monitoring point locations — commonly the operational lifetime of the space plus the site's standard retention period after it's decommissioned or repurposed.

Inspectors typically check that the mapping study used calibrated sensors, covered a representative duration and loading condition, actually found and addressed any hot or cold spots rather than reporting a uniformly perfect result, and that the routine monitoring points currently in use trace back to the worst-case locations identified during mapping.

A suspiciously uniform mapping result with no variation across sensor locations is itself a common flag — real spaces almost always show some temperature gradient, and a report showing none may suggest the sensors weren't actually placed in genuinely different locations.

The most common mistake is selecting routine monitoring point locations based on convenience or accessibility rather than the actual worst-case locations identified during mapping — a monitoring sensor placed somewhere easy to reach instead of the space's genuine hot or cold spot can miss a real excursion entirely while still reporting the space as within range.