Liquid nitrogen has special physical and chemical properties because it is compressed and cooled by nitrogen. The main features are as follows:

Ultra-low temperature: the boiling point of liquid nitrogen is -195.8, when liquid nitrogen gasification can absorb 48 calories per kilogram.

Liquid nitrogen is colorless, odorless, non-toxic liquid.

The permeability of liquid nitrogen is very weak, but when human skin contact liquid nitrogen will be severely frostbite.

Expansibility: liquid nitrogen is made by air compression cooling, its gasification can be restored to nitrogen. It was measured that for every liter of liquid nitrogen gasification, the temperature rose 15℃ and the volume expanded about 180 times.

Asphyxiation: Nitrogen itself cannot cause asphyxiation, but in a certain space, if too much nitrogen isolates oxygen, the operator will also cause asphyxiation. According to the determination, 10 kg liquid nitrogen in 10 cubic meters of indoor instant evaporation, can make the space oxygen suddenly dropped to 13%, causing space oxygen deprivation. Under these conditions, it can cause suffocation and even death.