A dry shipper uses liquid nitrogen absorbed into a porous material inside the vessel wall, holding samples at approximately -190 degrees C during transport with no free liquid present. Because there is no free liquid nitrogen, the unit is not subject to the dangerous goods regulations under IATA Special Provision A152, making it acceptable for passenger and cargo aircraft without the restrictions that apply to open LN2 containers, provided the packaging cannot build pressure or release nitrogen in any orientation and the air waybill carries the words not restricted and the number A152. Packing Instruction 650 is a separate requirement covering the biological samples inside where those are classified as UN 3373 Category B, not the nitrogen holding them cold.
Why does absorbed liquid nitrogen behave differently to free liquid?
When liquid nitrogen is absorbed into a porous sorbent material, it cannot spill even if the vessel is tipped, inverted, or dropped. This is the critical safety property that makes dry shippers viable for air freight. The nitrogen vapour that maintains the cold temperature is released slowly and continuously from the sorbent, keeping the interior at cryogenic temperature for the duration of the shipment.
How long does a dry shipper stay cold?
Hold time varies by model and how well the vessel was charged before shipment. A properly charged dry shipper of 3 to 10 litres capacity will typically maintain cryogenic temperatures for 7 to 14 days. The charging process – filling with liquid nitrogen, allowing the sorbent to fully absorb it, then draining any free liquid before use – is critical. Insufficient charging time is the most common cause of shorter-than-expected hold times.
Can a dry shipper be recharged and reused?
Yes. A well-maintained dry shipper can be recharged and reused hundreds of times. The sorbent material does not degrade with normal use, though it can be damaged by contamination from spilled biological material or from allowing the vessel to warm completely too many times without proper cycling. Regular inspection of the vacuum integrity is good practice.
A dry shipper charged in a rush is one of the most common causes of sample loss in transit. The sorbent needs adequate time – typically two to four hours – to fully absorb the liquid nitrogen before the excess is drained and the vessel is sealed for shipment.
Cryolab’s CryoStork dry shipper range covers 2 to 10 litre capacities for IVF sample transport. Contact Cryolab for guidance on which model suits your route and sample type.
