The call arrives at an hour when you still picture the truck rolling: the driver has pulled onto the hard shoulder, the refrigeration unit has gone quiet, and he wants one thing from you, how much time he has. An honest answer at that moment rests on a measurement made long before the breakdown; without one, everybody offers a guess and the load warms up somewhere between those guesses.
In a refrigerated vehicle carrying vaccines or medicines that span of time is measured rather than estimated. Supplement 11 of Annex 5 in WHO TRS 992, "Qualification of refrigerated road vehicles", makes a temperature control failure test a mandatory part of qualification (clause 2.4), so the vehicle's report is expected to state how long the load stays inside its limits once the unit stops.
What the test actually measures
The annex spells the sequence out: the set point goes to the middle of the required range, which for a vehicle running at +2 to +8 °C means +5.0 °C; the load is stabilised for roughly 12 hours; the unit is then switched off and the time until the first point of the load leaves the limit is read off the logger data (clauses 2.4.2, 2.4.4 and 2.4.5). The figure that lands in the report is exactly that elapsed time, and it underpins both your emergency procedure and your response-time rule.
The same clause carries a short note that decides how the trial is arranged: real product cannot be used, because the test spoils it irreversibly (clause 2.4, Note). Your own number therefore comes out of a planned run with a dummy load that behaves thermally like the goods, performed while nothing of value is at stake.
What makes the logged figure valid
| What the logger must offer | WHO Supplement 13, clause 2.4 |
|---|---|
| Resolution | 0.1 °C or better |
| Accuracy | ±0.5 °C over roughly -20 to +50 °C |
| Logging interval | 30 minutes at most, 5-10 minutes preferred |
| Calibration | valid NIST-traceable certificate attached to the report |
The same clause puts at least one logger inside the load and one outside it (steps f, g, i and j). Acceptance is written in numbers as well: for a consignment specified at +2.0 to +8.0 °C the lowest recorded product temperature must not fall below +2.0 °C (tolerance -0.5 °C), the highest must not exceed +8.0 °C (tolerance +0.5 °C), and at least two probes covering the warmest and the coldest spot have to stay with the load until the final delivery point (Supplement 11, clauses 2.3.3 and 2.3.5).
Once the measured time is in your hands you still cannot repeat it verbatim over the phone, because the report describes the conditions of the test: ambient temperature, how full the body is, how often the doors were opened and the product temperature at the moment the unit stopped will all pull the figure one way or the other. The arithmetic that helps on the road stays plain, since you subtract the time a service van or a replacement vehicle needs to reach the driver from the measured time, and what remains is your intervention margin; on routes where that margin comes close to zero, the transfer points have to be agreed beforehand. Running the same trial once in high summer and once in winter also gives a more realistic picture than trusting a single figure.
Where the same number comes from in a passive box
In a refrigerated vehicle the figure has to be dug out with a dedicated failure test, whereas an insulated passive container already carries it as an ordinary operating parameter: Supplement 12 of the same annex states that a passive system has a predefined transport life, that delivery must be completed within it, and that the system may only be used once both the route and the container have been qualified (clause 2.2.3). Hours are the common unit in which the two arrangements can be compared on the record.
Once both figures are written in hours, the refrigerated vehicle or insulated container debate turns into a plain technical comparison.
The order of work follows from all this. You begin where section 10.2 of the TİTCK GDP guideline points, with a risk assessment of your delivery routes that records where temperature control is genuinely needed, and because the same section requires monitoring equipment in vehicles and containers to be calibrated at least once a year, you refresh those certificate dates in the same round. Then you prepare the vehicle with a dummy load, put the set point in the middle of the range, let the load stabilise for about 12 hours, switch the unit off and read the time out of the logger. That number goes into the OQ report and the emergency procedure, and from there into a single line the driver can find on his phone. The last step belongs to route planning, where passive shipments get a delivery window that stays inside the transport life, while active vehicles get a response plan that stays inside the measured time. Take both figures with you when you sit down to discuss containers and loggers; with Aris Makina they are the first thing on the table anyway.
