Temperature-controlled containers are usually discussed in the context of keeping cargo cold. On northern winter routings the more common failure is the opposite: cargo that must not freeze, sitting in an unpowered box on a quay in temperatures well below the set point, with the unit switched off between plug-out and plug-in.
Chilled pharmaceutical and beverage consignments are the ones most often affected, and the damage is frequently invisible until the consignee tests the product.
The unpowered gaps
A reefer is unplugged for the terminal move at origin, potentially again at transhipment, and once more from discharge until it is connected at the destination depot or delivered. Each gap is normally short. In winter, short is enough. An insulated box loses less than an uninsulated one, but a container standing overnight at minus ten will approach ambient at the corners well before morning.
What actually helps
- Set a realistic set point rather than the lowest safe one. Cargo that must stay between two and eight degrees should not be set at two.
- Ask for pre-trip inspection records and check them, particularly on older units.
- Use a data logger inside the cargo, not only the unit trace. The unit records the return air temperature, which is not the same as the temperature of a pallet in the corner.
- Specify plug-in priority at destination in the booking and confirm the depot can honour it before the vessel arrives.
If something goes wrong
Download the unit trace before the container is returned, because retrieving it afterwards is slow and sometimes impossible. Keep the logger. Photograph the set point display before the unit is switched off. Those three items decide most temperature claims.