Temperature mapping - also called thermal mapping - is the process of using calibrated temperature sensors to measure and document temperature distribution throughout a controlled storage or processing environment over time. For pharmaceutical manufacturers, distributors, and storage facilities, thermal mapping is a regulatory requirement for any environment where temperature-sensitive products or starting materials are stored or processed.
This guide covers when thermal mapping is required, how to design a mapping study that will satisfy regulatory expectations, how to place sensors correctly, and how to handle excursions that occur during the mapping exercise.
When Is Thermal Mapping Required?
Thermal mapping is required by EU GMP Annex 15 and is referenced in WHO Technical Report Series guidelines. FDA guidance references temperature distribution studies in the context of process validation and storage condition verification. The environments requiring thermal mapping include:
- Cold rooms and refrigerators - storage at 2–8°C for refrigerated products, vaccines, and biological materials
- Freezers - storage at -15°C to -25°C or ultra-low temperature (-60°C to -80°C) for frozen biologics
- Ambient warehouses - controlled ambient storage at 15–25°C or 25°C/60% RH per ICH Q1A stability conditions
- Stability chambers - ICH-conditioned stability testing chambers must be mapped to confirm uniform conditions throughout the chamber
- Processing areas - where temperature is a critical process parameter (lyophilisation, autoclaving, granulation)
- Cold chain transport vehicles - refrigerated transport vehicles require periodic temperature mapping
Designing a Thermal Mapping Study
Before placing a single sensor, the mapping study must be designed and documented in an approved protocol. The protocol must specify:
- Scope - which environments are being mapped and why
- Sensor specifications - accuracy, resolution, and calibration requirements (typically ±0.5°C accuracy)
- Number and placement of sensors - the mapping grid design with rationale
- Study duration - must cover representative operating conditions including worst-case scenarios
- Loading conditions - whether the study is conducted empty, full, or both (EU GMP expects both conditions to be evaluated)
- Seasonal conditions - for ambient warehouses, studies should cover both winter and summer conditions, or a minimum of the worst-case season with scientific justification
- Acceptance criteria - the temperature ranges that must be maintained throughout the study
- Handling of excursions - what constitutes a study failure and what must happen when an excursion occurs
Sensor Placement: How Many and Where?
The number and placement of temperature sensors is one of the most technically demanding aspects of thermal mapping. There is no universal rule specifying exact numbers - the placement must be justified based on the volume, geometry, and risk profile of the space.
General industry guidance and WHO recommendations suggest:
- A minimum of 12–15 sensors for typical cold rooms (approximately 10–50 m³)
- Sensors at all four upper corners and four lower corners of the space
- Sensors at the geometric centre of the space
- Additional sensors near identified risk areas - air supply vents (where temperature may be extreme), doors (ingress of ambient air), near floor level (for cold rooms, the floor is often warmest due to conduction)
- For stability chambers, sensors at each shelf level
- Reference sensor at the monitoring probe location (to validate that the routine monitoring sensor is positioned in a representative location)
Key finding in thermal mapping: The monitoring probe - the single sensor used for routine continuous temperature monitoring - must be positioned at the worst-case location identified during mapping, or at a location shown by mapping to be representative of the worst-case. Placing the monitoring probe at the coolest, most stable location (which may be near the air supply) gives a false sense of compliance.
Study Duration Requirements
The minimum mapping study duration is driven by regulatory expectation and the variability of the environment:
- For cold rooms and freezers: a minimum of 24–72 hours under each loading condition (empty and full)
- For ambient warehouses: 72–168 hours (3–7 days) per season to capture diurnal temperature variation and business operating cycles (door openings, forklift traffic)
- For stability chambers: 24–48 hours after the chamber has reached equilibrium
- For autoclaves and sterilisers: cycle-based mapping covering the full sterilisation cycle including the coolest and hottest zones identified during heat penetration studies
Handling Excursions During the Mapping Study
An excursion occurs when temperature falls outside the acceptance criteria specified in the mapping protocol. How an excursion is handled determines whether the study data is still usable:
- Minor excursions - brief excursions due to documented external events (door left open, power interruption) may be excluded from the data analysis with appropriate scientific justification documented in the deviation report
- Systematic excursions - excursions that recur, affect multiple sensors, or are not attributable to an identified external cause indicate a facility or equipment deficiency. These require investigation and corrective action before the study can be considered complete
- All excursions must be documented - even excluded excursions must be documented in the mapping report with the exclusion rationale. Inspectors specifically look for evidence of selective data exclusion
Free Temperature Mapping Protocol Template
Download our pharmaceutical temperature mapping protocol template - including sensor placement guidance, acceptance criteria tables, and excursion handling procedures.
Download Free Checklist →