If a dewar runs completely dry and samples are exposed to temperatures above minus 130 degrees Celsius for more than a few minutes, irreversible ice recrystallisation occurs. Cell membranes rupture, DNA is fragmented, and motility is destroyed. Samples that have experienced a depletion event cannot be rescued. Prevention is the only strategy: liquid nitrogen level should never fall below the top of the uppermost canister, and continuous monitoring systems with alarm triggers are strongly recommended for any facility storing irreplaceable material. Cryolab supplies level monitoring systems compatible with its full vessel range.