There is a duration on the side of the box, on most boxes somewhere near the lid, written so that it cannot be rubbed off: hours on some, days on others. The person taking delivery from a pharmaceutical warehouse reads that line to see how much time the load still has. Where the figure came from is not written anywhere on the box.
The marking is not there out of courtesy. The inspection form attached to TİTCK's guide on Good Distribution Practice inspections asks, in item 7.14.9, whether the maximum period for which the product can be held inside the cold chain device is written on the device itself, in days or hours, in indelible form. It is one of the first lines an inspector looks for once the box is in hand.
What the form checks is that the number exists; how it was arrived at falls outside the form. Since you are the party who has to defend the file, finding out which test lies behind the figure falls to you, and your supplier is the one to ask.
Which test produces the printed figure
The scale used most often for passive containers is defined in WHO's own glossary. The glossary of Supplement 14 to Annex 5 of TRS 992 sets the cool life test up like this: the empty container is stabilised at +43.0 °C, then loaded with water packs that have been conditioned at +5.0 °C for at least 24 hours, and the lid is closed.
The clock starts the moment the lid closes and stops when the warmest point in the load compartment first reaches +20.0 °C, and what lies in between is the cool life of the container. Two conclusions follow. The figure was measured with one particular coolant load and one particular end temperature, so if the upper limit of your own product sits below +20.0 °C, the time you can genuinely use is shorter than the time printed on the wall.
One container, two separate scales
The second scale comes out of the vaccine chain. The WHO/PQS/E004/CB04.1 performance specification defines cold life with the clock stopping once the warmest point reaches +10 °C, a definition set out in section 3 of the specification, under terms and definitions. Clause 4.2.3 of the same document asks for at least 10 days in a hot zone cycle of +43 °C by day and +25 °C by night, while clause 4.2.2 requires the compartment to stay above 0 °C for the whole test.
The same box gives two different numbers under these two methods, and both of them are honest. If one supplier quotes cool life and another quotes PQS cold life, putting the two offers side by side and taking the bigger figure only compares sheets of paper; as long as the method goes unasked, the numbers never settle onto one scale.
| Scale | End temperature | Ambient condition |
|---|---|---|
| Cool life (Supplement 14) | +20.0 °C | steady +43.0 °C |
| PQS cold life (CB04.1) | +10 °C | +43 °C day / +25 °C night |
The gap between the two rows comes from where the clock was stopped, while the container stays the same in both. Which row means something in your operation depends on the upper limit of your product: the closer the end temperature sits to that limit, the more realistic the printed duration is for you.
The measuring chain behind the number
A duration is produced by the instrument as much as by the test setup. Clause 2.4 of Supplement 13, in the same annex, asks for 0.1 °C resolution, ±0.5 °C accuracy, a logging interval no longer than 30 minutes and calibration traceable to NIST. A curve recorded without those four conditions cannot carry the duration written on top of it.
In the field the logging interval is what slips past most often: a logger sampling once every 30 minutes never sees a lid opening that fits between two samples, so the curve comes out flatter than the day was. The ±0.5 °C accuracy pulls the same way, because near the end temperature the instrument's own uncertainty moves the duration within a half-degree band. That is why the recorder, the interval and the calibration are asked for alongside the duration itself.
These questions earn their keep on inspection day. Items 7.14.6 and 7.14.7 of the same TİTCK form require a cold cabin, a refrigerated cabinet, a specially insulated container or a similar suitable system in the vehicle according to the duration and the volume of the transport, and require it to be guaranteed that this system holds the product within the intended range. What an inspector is after is proven performance around the product, and a figure with a known test behind it is easier to defend than a description of the bodywork.
Tying the figure on the box to the journey the product actually makes is where last-mile cold chain planning begins.
What to ask your supplier
Your turn. Put four questions first to whoever supplies the box. Which test is this duration based on, cool life or PQS cold life? At what temperature was the clock stopped? What ambient profile was used, a steady temperature or a day-night cycle? What was the container loaded with during the test, water packs or a load that imitates the product, and at what mass?
Four more questions close off the measurement side. Which logger was used, and what are its resolution and accuracy? How many minutes lay between readings? Is the calibration traceable, and what date is on the certificate? Does the test report sit in the same file as the number printed on the box? For Isotec containers we obtain these documents from GEBHARDT and pass them on to you; if you run another brand, hand the same list to your own supplier and ask for the answers in writing.
