When the unit stops, the answer has to rest on a measurement made before the breakdown; without one, everybody offers a guess. WHO TRS 992 Annex 5 Supplement 11 makes this measurement a mandatory part of qualifying refrigerated vehicles (clause 2.4). The test runs like this:
- The set point goes to the middle of the range: +5.0 °C for +2 to +8 °C.
- The load is stabilised for roughly 12 hours.
- The unit is switched off; the test ends when a single product temperature leaves the limit.
- The elapsed time goes into the vehicle's OQ report, and the emergency procedure and response time rest on that figure (clauses 2.4.4 and 2.4.5).
Real product is not used, because it is spoiled irreversibly; a substitute load with similar thermal properties, expired product that has been through a risk assessment, or empty boxes take its place, and the probes sit inside the packaging (clauses 2.4.2 and 2.4.3).
The figure in the report depends on the test conditions: ambient temperature, how full the body is and door openings change it. On the road the time a service van needs to reach the driver is subtracted from it, and if the remaining margin approaches zero, the transfer points for the load are agreed beforehand.
For a passive container WHO Supplement 12 looks for a predefined transport life and requires delivery to finish within it (clause 2.2.3); that is how the two arrangements are compared in hours.
Once both figures are written in hours, the refrigerated vehicle or insulated container debate turns into a plain technical comparison.
