What is temperature mapping of a refrigerated vehicle?
Temperature mapping measures the temperature at many points inside a space over a set period, to find the warmest and coldest spots. SFDA's guideline defines it as a three-dimensional study of temperature distribution. In a refrigerated vehicle, the study shows how the temperature near the unit differs from the temperature by the rear door, on the floor and inside a full pallet, in hot and cold weather and with different loads.
Qualification uses the mapping to show that a vehicle keeps products within their range on real routes. The result also tells you where to put the probes you use every day: at the warmest and coldest positions the study found.
What does SFDA require for temperature monitoring in vehicles?
SFDA's Guideline of Good Storage and Distribution Practices (OPS-G-112, version 2.1, 4 February 2024) covers medicines for human and veterinary use, active substances, excipients and cosmetics. Its Vehicle and Transport section says:
- Item 14: electronic monitoring devices that can be linked to the authority's systems, activated from dispatch until the shipment arrives, distributed at different locations and heights according to the approved temperature mapping, regularly calibrated, and linked to the receiving and issuing records of each shipment.
- Items 15 and 22: temperature and humidity records kept for the shelf life of the product plus one year, and made available for inspection by SFDA.
- Item 4: modern technology such as GPS should be used where possible to protect products in the vehicle.
The guideline does not set the number of loggers, the logging interval, the calibration interval or how often to repeat the mapping. Those come from your quality procedures and the product owner. For food, the guideline does not apply, so check your authority's current requirement.
How to qualify a refrigerated vehicle, step by step
The method in this template follows the World Health Organization technical supplement Qualification of refrigerated road vehicles (Supplement 11 to Technical Report Series 961, Annex 9, May 2015).
- Check the vehicle first: body and unit details, insulation and cooling performance, and that maintenance is up to date.
- Calibrate the loggers and record each one with its certificate.
- Run a static mapping before road tests to find the likely warmest and coldest positions.
- Run four field tests on a typical worst-case route with drops and door openings: maximum and minimum load in the warmest season, and maximum and minimum load in the coldest season.
- Run a hold-over test: settle the temperature at the mid-range set point, switch the unit off, and record how long until a product position leaves the range.
- Approve the result: qualified when all four field tests pass. WHO treats the vehicle as provisionally qualified after the first two tests, so full qualification can take up to six months.
Where should data loggers go in a reefer truck?
WHO lists the minimum recording points: outside ambient, refrigeration air delivery and return, product near the delivery air, product in areas of restricted airflow, product near the walls and product near the doors. The example layout in the template covers these with 14 positions and leaves two spare. Fix loggers inside the product packaging where you can, and keep the warmest and coldest positions attached to the load until the last drop. Mark supply and return air as not counting for acceptance, because they measure air, not product.
How does the record calculate the result?
The allowed minutes out of range is 0 by default, which matches the WHO acceptance criterion that product temperatures stay in range for the whole route. The 2 to 8 °C range, the 5-minute logging interval, the 12-month calibration and re-mapping intervals are examples on the Settings sheet; replace them with your own.
Worked example: one summer test fails at the rear door
A 7-meter refrigerated truck carries medicines at 2 to 8 °C with a set point of 5 °C. Fourteen loggers record every 5 minutes over 24 hours in July, with outside temperatures up to 46 °C.
- Test 1, maximum load: the warmest position is the rear door (P10) at 7.5 °C during drops, and the coldest is near the delivery air (P03) at 3.3 °C. No product position leaves the range: Pass.
- Test 2, minimum load: with one pallet, a long door opening at the third drop takes P10 to 9.3 °C. Two readings are above 8 °C, so 2 × 5 = 10 minutes out of range: Fail.
- Test 5, hold-over: after the unit is switched off, the first product position passes 8 °C after 30 minutes. That is the time the driver has to restart the unit or move the load.
- Status: Not qualified until the failed test is repeated. The quality team fits a strip curtain at the rear door, marks the first 30 cm behind the door as a zone not to load, and repeats Test 2.
Common mistakes in reefer temperature mapping
- Testing an empty truck only. Load changes airflow; WHO asks for maximum and minimum payload.
- Testing in one season. A truck that holds 5 °C in winter can fail on a summer afternoon.
- Loggers out of calibration. A study with an expired logger cannot support the result.
- Measuring air instead of product. Supply air is far colder than the pallet next to the door.
- Skipping door openings. Drops are where most excursions start, so the test route needs them.
- Never repeating the study. A new unit, body repairs or unexplained readings mean the old map no longer applies.
What the template does not cover
The record calculates the study you run; it does not read loggers or connect to SFDA systems. It assumes all loggers start together and use the same interval. Ranges, allowances, calibration and re-mapping intervals come from the product owner and your quality system, and requirements change, so check your authority's current requirement. The record supports your qualification report; it does not replace your quality procedures. For daily excursions on each shipment, use the Cold Chain Temperature Excursion Log.