How are cryogenic storage tanks maintained and monitored?
Cryogenic storage tanks are usually stored in a secure access room. All tanks are connected to an alarm system that is capable of remotely alerting laboratory staff members in event of a significant temperature variation or LN2level deviation. In the event of an alarm, standard protocol calls for laboratory staff to immediately report to the laboratory at any time to investigate the cause of the alarm. The alarm system is tested monthly and should undergo preventative maintenance at least once a year. Standard protocols for following these regimens is essential to reduce the contribution of human error to catastrophic failure.
Because redundancy is an essential feature of all critical monitoring system, nitrogen levels are measured in all tanks at least three times per week, if not daily to ensure temperature uniformity. A yardstick-like instrument is used to measure the level of LN2and these data are graphically charted to detect increased consumption of LN2, which may be a signal that a tank is failing. If the cryogenic storage tank does not have an autofill mechanism, it is manually filled with LN2to a pre-determined level.
All cryogenic storage tanks are checked daily for signs of frost or condensation that may indicate impending tank failure. If there are any signs of malfunction, a tank must be replaced. At least one empty back-up tank should be readily available and filled with LN2, in the event of a tank failure emergency.
When a natural disaster is anticipated or another event that would potentially preclude access to the tanks or delivery of additional LN2, undamaged cryogenic storage tanks should be capable of maintaining appropriate temperatures for at least six weeks to ensure safety of the reproductive tissues.
What is a failure of a cryogenic storage tank?
A catastrophic failure occurs when a cryogenic storage tank’s vacuum is abruptly lost without warning. Unless a backup tank is available and the contained cryopreserved reproductive tissues are immediately transferred, loss of the cryopreserved specimens is imminent. Other tank failures occur when there is slow deterioration of the tank’s vacuum due to mechanical insult, overfill with LN2, inertial stress, and metal or weld fatigue. Signs of frost or condensation are the most common signs of impending cryogenic storage tank failure and increased LN2 consumption. Most manufacturers guarantee the tank’s vacuum for five years and cite a lifespan of ten years.
How often does a cryogenic storage tank failure happen?
There are no national or international agencies that track incidence of cryogenic storage tank failures and most available information is anecdotal. However, a generalized industry opinion is that catastrophic tank failures are rare. Known cryogenic storage tank failures with complete loss of productive tissues occur once or twice a decade. A survey of cryostorage centers in UK and Ireland cited three failures from 17 respondents using nitrogen vapor systems.4
The authors report no potential conflicts of interest with regard to this article.
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- Dowling-Lacey D, Mayer JF, Jones E, Bocca S, Stadtmauer L, Oehninger S. Live birth from a frozen-thawed pronuclear stage embryo almost 20 years after its cryopreservation. Fertil Steril. 2011;95:1120.e1-1120.e3.
- Tomlinson M, Morroll D.. Risks associated with cryopreservation: a survey of assisted conception units in the UK and Ireland. Hum Fertil. (Camb) 2008;11:33-42.
- Standards and technical manual reproductive cells and tissues. American Association of Tissue Banks, 2002.