Our hearts go out to each person impacted by this tragic event. We are heartened by the reality that this is an extremely rare event, and want to reassure our patients why an event like this would be extremely unlikely to happen at USC Fertility.
Firstly, it is important to understand how cryotanks function. These are NOT freezers like we have in our homes, which depend on electricity to keep them cold. When power is lost at home, the kitchen freezer gradually warms up to room temperature. That is NOT how a cryotank functions. A cryotank doesn’t actually need any electrical power in order to maintain its low temperature.
Cryotanks are best thought of as giant thermos bottles. They are made of stainless steel, cylindrical, with thick insulation in the walls and the bottom, and a thick insulated lid. They are filled with liquid nitrogen, which boils at -196° Celsius, or -321° Fahrenheit. All of the eggs, sperm and embryos are kept submerged in the liquid nitrogen. If the temperature at the surface of the liquid were to increase, the liquid nitrogen would start to boil, while the temperature of the remaining liquid would stay at the very low temperature of the boiling point, until it was gone. There is no such thing as lukewarm liquid nitrogen!
Since the liquid nitrogen is always slowly evaporating, it has to be replenished. The normal rate of evaporation in our large tank with the lid closed is just under 1 inch of depth of liquid per day. That means that if no nitrogen were added, it would take more than 2 weeks for all of it to evaporate. If somehow the lid were to be left off, it would still take 2-3 days for all of it to evaporate.
Of course, we have no intention of letting the nitrogen disappear! Our tanks have an automatic refill function. They are continuously monitored. The alarm system not only sounds in the lab, it also sends a text, email, and phone call to our lab director, so he is always informed about the status of the cryotanks. Additionally, levels of liquid nitrogen are visually checked daily. Even if the automatic filling equipment and all the monitoring were to malfunction at the same time, nothing bad would happen to the stored eggs and embryos for at least 2 weeks, and, of course, we are monitoring them continuously.
A most unusual set of circumstances must have taken place in Cleveland, and we will be waiting for the final report of that incident in order to make sure we learn from that experience. However, we feel confident that the safeguards that we have in place will minimize the risk of such a tragedy happening at USC Fertility.