How do you run a temperature mapping study, and how many data loggers does it need?

1How many data loggers a mapping study needs.

No regulation fixes a number. WHO’s mapping supplement sets spacing and heights and leaves the count to arithmetic and risk:¹

• Length and width. A logger every 5 to 10 metres, or 20 to 30 metres in very large facilities, adjusted for alcoves, airflow and where product is stored; none may be needed where product never goes.
• Ceiling of 3.6 m or less. Three per grid point, high, medium and low, such as floor level, 1.2 m and 3.0 m.
• Ceiling above 3.6 m. Bottom, several in the middle, and top. WHO’s example for a 6 m store is 0.3, 1.8, 3.6 and 5.4 m. High-bay racking is “particularly susceptible to temperature stratification”.
• Extra positions. Centre pallets in a cold room; heating and cooling units, air outlets and existing sensors;¹ heaters, lighting, windows, doors, loading bays and mezzanines.²
• No active temperature control. WHO says such spaces “may also need” mapping;¹ EU GDP asks small room-temperature premises for a risk assessment of hazards such as heaters, with monitors placed to match.³

The MHRA puts the top logger at “the highest point of storage not the highest shelf or pallet location”.² This page counts points along a side as length ÷ spacing, rounded up, plus one, so the grid reaches both walls. Then:

Loggers = points along the length × points across the width × heights + extra positions.

2Example: counting loggers for a warehouse, a cold room and a chamber.

All three are invented.

2.1Warehouse W2: 57 loggers.

An ambient store for products labelled 15 to 25 °C, 30 m by 20 m, open plan, with racking that runs with the airflow and top loads at 5.4 m: WHO’s 10 m spacing, and four heights because racking this tall stratifies.

1. Grid: 30 ÷ 10 = 3, plus one, is 4 points along the length; 20 ÷ 10 = 2, plus one, is 3 across. 4 × 3 = 12 positions.
2. Heights: 0.3, 1.8, 3.6 and 5.4 m. 12 × 4 = 48 loggers.
3. Extras: 2 dock doors and 2 heater outlets, problem areas the MHRA names;² one beside each of the 4 fixed monitoring probes, to compare readings; and one outside in the shade, since external temperature is one of three factors WHO says drive a store’s stability.¹ 2 + 2 + 4 + 1 = 9.
4. Total: 48 + 9 = 57. At 5 m spacing the grid alone would need 7 × 5 × 4 = 140; at 10 m with three heights, 36.

2.2Cold room CR-1: 22 loggers.

A 2 to 8 °C room, 6 m by 4 m, 3.0 m high, shelved to 2.4 m, two pallets in the centre. At 5 m: 6 ÷ 5 rounds up to 2, plus one, is 3; 4 ÷ 5 rounds up to 1, plus one, is 2; 6 positions. Three heights, the top at 2.4 m, the highest stock: 18. Extras: 2 on the centre pallets, 1 in the evaporator’s air stream and 1 inside the door: 22. A full cold room qualification is worked in IQ, OQ and PQ.

2.3Stability chamber SC-3: 10 loggers.

A reach-in chamber held at 25 °C and 60% RH, with five shelves. WHO’s mapping supplement leaves out small equipment such as refrigerators and freezers, which are generally prequalified; its qualification supplement wants loggers “at the top and bottom of the cabinet as well as at the rear and front”, and no product on door shelves.¹⁴ Asked how many monitoring sensors a walk-in stability chamber needs, the MHRA replied that “There is no specific guidance on this”, and that the number “should be defined based on mapping studies, equipment capabilities and the capacity of the chamber”.²

1. Layout. An illustrative choice, not a rule: the front and rear, left and right corners of the top and bottom shelves, 8; the centre of the middle shelf, 1; beside the chamber’s own sensor, 1. Each logs temperature and humidity, because WHO puts humidity monitors at the worst case in the qualified volume and the MHRA says mapping is how probe positions are found.⁶²
2. Pass criteria. Every logger within 25 °C ± 2 °C and 60% RH ± 5% RH, ICH Q1A(R2)’s tolerances for this condition; door-opening spikes are “accepted as unavoidable”.⁷
3. Tests. Health Canada’s list for refrigerators and freezers: empty and full loads, door-open, power-loss and alarm challenges, “sufficient duration in studies to capture compressor and defrost cycles”, and cool-down after a warm load.⁵ For small refrigerators and freezers the MHRA says the simulated load should represent what will be stored, and empty boxes are not appropriate.²

WHO’s qualification supplement covers ultra-low freezers too, and the MHRA sets the same mapping requirements for freezers as for refrigerators, so the same layout and tests serve them.⁴⁸

3Temperature mapping protocol template.

Copy these sections. WHO’s steps 1 to 5, from choosing loggers to marking their locations, must be done before the protocol is approved.¹

3.1Who does what, and how long it takes.

1. Protocol. Written from the site survey and approved, by QA or whoever your procedures name, before the study starts; a wholesaler’s Responsible Person should be “party to the whole mapping process”.¹²
2. Set-up. One interval and start time; loggers fastened so they “cannot be damaged or displaced”.¹
3. Runs. Seven consecutive days in each extreme season for an ambient store, so a first qualification spans about half a year; 24 to 72 hours for a cold room, each duplicate cooling unit running alone.¹ The MHRA expects the length justified “by way of a risk assessment of the storage area concerned”.²
4. Report. Peer reviewed and approved;¹ probe moves and no-storage zones then go through change control.

4Tests, durations and acceptance criteria.

4.1Judgement calls the sources settle.

• No product to load yet. The MHRA suggests dummy product in a small empty area, and mapping again once it is fully stocked.²
• A logger lost or dead mid-study. WHO checks collected loggers’ serial numbers and locations against the installation notes, and puts deviation reports in the report’s annexes, which “may include a recommendation for partial or total re-mapping”.¹ The deviation should show that neighbouring loggers still cover the gap; if it was a likely extreme, such as a rack top, door or heater, re-map that zone.
• Peaks or means. WHO confirms true hot and cold spots from trends and averages, without disregarding readings outside the range.¹
• Humidity. EU GMP asks for special storage conditions such as humidity to be “provided, checked and monitored”, and WHO places humidity sensors “to monitor worst-case humidity levels within the qualified storage volume”, positions that mapping finds.⁹⁶

5Example: the mapping report and where the probes go.

Warehouse W2, fully stocked, was mapped from Monday 12 to Monday 19 January 2026 and from Monday 6 to Monday 13 July 2026: 57 loggers at a 5-minute interval, so 7 × 288 = 2,016 readings per logger per study, against 15.0 to 25.0 °C. The summer results decided the outcome:

The recommendations follow WHO’s list of outcomes:¹

1. Deviation DEV-26-118 for the 9 hours at P12; the stock there assessed as a temperature excursion.
2. The top beam level at P12 closed to stock until its roof vent is rebalanced, then follow-up mapping in July 2027 to show the fix worked.
3. Probes moved to the persistent extremes: M4 up to 3.6 m at P12, the hottest level still holding stock, and M3 down to 0.3 m at P09, the coldest by mean. WHO puts monitoring sensors at the greatest variability “within the qualified and/or tested storage volume”, so M4 rises to 5.4 m only if the 2027 mapping reopens that level, and keeps them “minimally affected by transient events such as door opening”, so none goes at D1 or D2.⁶

6When to re-map.

WHO gives three years as an example, and where fixed monitors record continuously, says “a periodic re-evaluation which assesses all aspects of system performance since the initial mapping may be more appropriate”.¹ Nephron had one study, in January 2020, plus a three-year review of fixed-monitor data; the investigators still found it wanting, because “these monitor locations are not based on a scientific justification”.¹¹ Map both seasons first and put the monitors at the extremes found; then their data can carry the periodic review.

7What each regulator requires.

Part 211 does not use the word mapping, but FDA cites 211.142(b) when a warehouse runs hot, as in its warning letter to kdc/one Chatsworth of 8 September 2026.¹²¹³ USP’s 2023 chapter <1079.4>, Temperature Mapping for the Qualification of Storage Areas, covers the method, and FDA’s procedures say chapters numbered above 1000 are typically “considered informational and not requirements”.¹⁴¹⁵

8What inspectors cite.

“Temperature mapping exercises had not been adequately conducted, to establish the suitability of the storage areas or to determine the placement of the thermometers in the areas that experience the extremes of temperature fluctuations. No conclusion had been drawn as to the suitability of the storage areas.” MHRA GDP inspection deficiency data 2016, November 2017¹⁶

“Your firm did not establish worst case monitoring locations for the temperature monitoring done in your warehouse. The warehouse temperature mapping study is inadequate for the storage conditions listed on your finished drug product label.” Nephron Pharmaceuticals, Murray, Kentucky, warehouse, Form FDA 483, observation 4, 2 December 2022¹¹

A 483 records an investigator’s observations, not a final FDA decision. This one also faults missing data “to support the temperature sensor locations and heights chosen to demonstrate control throughout the warehouse during seasonal temperature fluctuations”: heights and seasons, not only a floor grid.¹¹

9How it runs in Seal.

In Seal, a mapping study can run as a commissioning and qualification test. The protocol is generated from an approved test design, executors scan each instrument with its calibration status at the time of use, and a failed acceptance becomes an exception tied to the exact requirement and evidence. The released baseline is then the reference for change control and periodic review, so requalification follows risk and evidence. If a logger later fails calibration, the mapping run it measured appears among its recorded uses for impact assessment.

Warehouse sensor data keeps its source identity, and an excursion opens a governed assessment with the exposed population already assembled, as in cold chain and temperature excursions.