The liquid in a nitrogen storage tank sits at about minus 196°C. The vapour above it does not have a single temperature. It is a gradient, coldest at the liquid surface and warmest at the neck, and where any given sample sits in that column depends on liquid level, neck design and how recently the lid was open.
Why minus 150°C is the number that matters
ASRM’s 2020 cryostorage committee opinion describes vapour phase storage as typically minus 150°C and lower. ESHRE’s 2026 laboratory recommendations use the same threshold when validating dry shippers. Treat it as the ceiling, not a target.
What happens as the level drops
The whole column rises. Samples in the highest positions move towards that ceiling first, which is why ASRM recommends level probes suspended in the liquid over temperature probes suspended in the vapour: level falls before temperature climbs, so it warns you earlier.
What to do about it
Map the temperature at your highest and lowest sample positions with the vessel at its minimum working level, not full. That is the condition that matters, and it belongs in the commissioning record. Vessels built for vapour storage keep samples close to the liquid on a platform rather than relying on the column alone.
The other storage vessels range includes vapour shippers and storage options where phase choice is part of the specification.
