A liquid nitrogen storage dewar is a vacuum-jacketed vessel that holds LN2 at -195.8 degrees C for the long-term preservation of biological samples including embryos, sperm, oocytes, and tissue. The dewar – named after Scottish scientist Sir James Dewar – uses the same principle as a vacuum flask, but built to a precision that consumer products cannot match.
What is the difference between a storage dewar and a transport dewar?
A storage dewar holds free liquid nitrogen and is designed to sit in one location. A transport dewar – or dry shipper – uses an absorbent material to retain LN2 as vapour with no free liquid, making it legal for air transport under IATA dangerous goods regulations. You cannot use a standard storage dewar as a shipping container.
How often does a storage dewar need topping up?
That depends entirely on the vessel’s static evaporation rate and the volume of liquid nitrogen it holds. A 35-litre dewar with a static evaporation rate of 0.15 litres per day will need topping up roughly every 200 days under ideal conditions. In practice, frequent lid openings and ambient temperature fluctuations reduce that figure. Most labs top up every four to eight weeks as a routine.
What happens if liquid nitrogen runs out in a storage dewar?
If LN2 levels drop to zero, samples move out of the vapour phase and begin warming. Depending on how quickly the temperature rises, irreversible damage to biological material can occur within hours. Continuous monitoring with an LN2 level alarm is standard practice in any HFEA-licensed clinic and is strongly recommended in all other settings.
The HFEA expects clinics to have robust liquid nitrogen monitoring in place. An undetected low LN2 event is one of the most preventable causes of sample loss in fertility storage.
Cryolab supplies storage dewars for IVF clinics and research labs across the UK. Browse the CryoNest Series or contact the team.
