Below −60 °C the problem stops being refrigeration and becomes consumable management. Nothing is actively cooled in transit: the shipper holds because of what was loaded into it, and the clock starts the moment it is sealed.
Two carriers, two disciplines
Dry ice shippers
Sublimation is predictable, so the routing is built around it. We schedule top-ups at hub touchpoints rather than hoping the original charge lasts, and every shipper is weighed at each touch to confirm the remaining charge against the profile.
Vapour-phase nitrogen dewars
Dry vapour shippers hold below −150 °C with no free liquid, which keeps them out of the dangerous goods regime for air movement. They are charged, held and re-charged on a fixed cycle, and every unit carries a hold-time certificate from its last charge.
- Dangerous goods documentation filed before booking confirmation.
- Two independent loggers per shipment, sampling at one-minute intervals.
- Top-up points scheduled into the route rather than triggered by alarm.
The trace shown is a consignment where a connecting movement slipped and the dry ice charge ran thin before top-up. It peaked at −58.4 °C, outside the band, and the material was assessed against its stability data before release.
