Cryolab Guidance Explains Why Vapour Phase Cryogenic Storage Is Not at Minus 196

CHICHESTER, U.K. - EntSun -- Cryolab, a specialist supplier of cryogenic equipment, consumables and servicing to the healthcare, fertility and research sectors, has published guidance on cryogenic storage temperature for laboratories.

The guidance addresses a specification error the company encounters frequently: the treatment of minus 196 degrees Celsius as a single storage temperature applicable to all cryogenic storage.

Liquid nitrogen boils at minus 195.8 degrees Celsius at atmospheric pressure, and samples immersed in the liquid sit at that temperature uniformly, because the boiling liquid holds the whole canister at its boiling point. Minus 196 is the rounded figure used in most documentation.

Vapour phase storage, where samples sit above the liquid in cold nitrogen gas, is not at that temperature. The guidance notes that vapour phase storage removes direct contact with the liquid, and with it the cross contamination route associated with the liquid. The ASRM and SART Practice Committees, writing on cryostorage in Fertility and Sterility (2020;114:486-491), note that liquid nitrogen is not sterile.

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The trade off is a vertical temperature gradient within the vessel. The bottom of a canister sits close to the liquid temperature while the top sits warmer, by an amount that depends on vessel design, liquid level and how frequently the lid is opened. Laboratories are advised to specify against the warmest position a sample can occupy rather than the temperature at the bottom of the vessel.

The guidance further notes that the gradient worsens as the liquid level falls, and that in vapour phase storage there is no margin of liquid covering the samples. The ESHRE recommendations on good practice in the IVF laboratory, published in Human Reproduction 41(8), 1245, expect cryostorage tanks to be continuously monitored with alarms that detect and log out of range temperature or liquid nitrogen level.

On vessel construction, the guidance explains that a cryogenic storage vessel contains no conventional insulation. It comprises an inner vessel, an outer jacket and an evacuated space between them, containing multilayer insulation to interrupt radiant heat, internal materials selected for low outgassing, and a getter that absorbs stray gas molecules over the vessel's service life. Degradation of that vacuum, whether gradual or following mechanical shock, is identified first through a rising nitrogen consumption trend at unchanged workload.

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Cryolab was established in 2000 and supplies cryogenic equipment, consumables, accessories and servicing to IVF clinics, hospitals, blood banks, tissue banks and research facilities in the United Kingdom and internationally. The company holds ISO 9001:2015 certification.

The full article is available at https://cryolab.co.uk/liquid-nitrogen-storage-temperature/