Memory for coldness
Nitrogen is cold
The cold energy is reduced to half in the heat of evaporation, which is released in the conversion from the liquid phase to the gas phase. The remaining energy is stored as sensitive coldness in the nitrogen gas. With a boiling temperature of -196 °C the danger of frost-bite during transference and handling of the stored samples is clear for anybody.
Sometimes the risk is underestimated, as the skin is protected by a vapour layer for a short time. If the temperature of the skin's surface falls below 0 °C, it is possible the skin freezes solid to any cold object and can only be thawed with warm water. Tissue damage, similar to the violation of burning, is the result. The eyes are particularly endangered. Please always wear hand and face protection when transferring liquid nitrogen.