Temperature mapping: method, obligation and report

When mapping is required, and when it is simply useful

For the distribution of medicinal products the text is precise: an initial mapping of the storage area before use, under representative conditions; monitoring devices positioned according to its results, where fluctuations are greatest; and a repeat according to the risk assessment or whenever the facility or the equipment is significantly modified. For small premises at room temperature, a risk assessment (heaters, windows) and a reasoned placement of probes are enough.

For food, no text requires a mapping. It remains the surest way to answer a question the HACCP plan asks anyway: at which point of the cold room should the critical limit be monitored? A probe in the centre measures the most comfortable point; the mapping finds the hot spot, and that is where the measurement is worth something.

The method, in six steps

1. 1

   Define the space and its load state

   Which volume exactly, which range it must hold, and under what conditions it is measured: empty on delivery of the equipment, then under the usual load, doors and defrost cycles included. The guidelines ask for conditions representative of operation.

2. 2

   Place the sensors in three dimensions

   At the corners, in the centre, top and bottom, near the door, near the evaporator or any heat source, and where the products are actually stored. How many depends on the volume and its geometry; what matters is that no plausible hot or cold spot is left unmeasured.

3. 3

   Record continuously, all at once

   All sensors on the same clock, at the same interval, long enough to cover the equipment's cycles, day and night, and a working day of door openings. For an ambient room, the season is part of the representative conditions.

4. 4

   Analyse: minimum, maximum, mean, per point

   For each point, the extremes and the mean over the period, compared with the range to hold; then the map that comes out of it: the warmest point, the coldest, the recovery time after a door opening, the effect of a defrost. That map is what says whether the space is qualified, and where.

5. 5

   Put the permanent monitoring at the worst-case point

   This is the practical reason for mapping: the guidelines require monitoring devices to be positioned according to its results, where fluctuations are greatest. A probe in the middle of a cold room measures the most comfortable point; the useful probe is at the hot spot.

6. 6

   Write the report, and repeat when it is due

   The report keeps the placement plan, the period, the curves, the extremes per point and the decision: space qualified or not, location chosen for monitoring. The mapping is repeated according to the risk assessment and whenever the facility or the equipment is significantly modified.