How to Properly Charge a Dry Shipper — and What Happens If You Get It Wrong

Charging a dry shipper correctly is one of those tasks that looks simple but has a failure mode with serious consequences. In a busy fertility clinic or sperm bank where dry shippers are being prepared for transfers, the temptation to rush the process is understandable. The consequences of doing so are not.

What Charging Actually Does

A dry shipper contains an absorbent inner material – typically a porous matrix – that holds liquid nitrogen within its structure rather than as a free liquid. When you charge the vessel, you are saturating this material with liquid nitrogen. Once saturated and drained of any free liquid, the shipper maintains cryogenic temperature by slowly releasing nitrogen vapour without any liquid being present. This is what makes dry shippers safe for air transport as not restricted under IATA Special Provision A152, because the nitrogen is fully absorbed and cannot escape in any orientation. 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.

The Correct Charging Process

Fill the vessel slowly with liquid nitrogen, allowing the absorbent material to become fully saturated. The vessel will initially boil vigorously – this boiling will gradually subside as the material approaches liquid nitrogen temperature. Do not rush this stage. Once boiling subsides, continue filling until the vessel holds a stable level above the absorbent material. Leave the vessel to fully equilibrate – typically a minimum of two hours, longer for larger vessels. Finally, invert the vessel to confirm no free liquid nitrogen remains.

The inversion test is non-negotiable. A vessel shipped with free liquid nitrogen is a safety incident waiting to happen and a regulatory violation for air transport.

What Happens If You Get It Wrong

An under-charged vessel will not hold cryogenic temperature for its rated duration. Temperature may exceed the critical threshold partway through a transfer, compromising every sample the vessel contains. In a multi-patient shipment from a sperm bank, this is a serious clinical incident with potentially irreversible consequences.

The CryoStork range includes handling guidance with every vessel. If there is any uncertainty about your team’s current charging procedure, the Cryolab team can walk through the correct process. You can also ask CryoGPT for immediate guidance.