Hazards and properties
Liquid nitrogen is a colourless, odourless liquid with a boiling point of -196°C. At low temperatures the gas / vapour is heavier than air. Small amounts of liquid vaporise rapidly to produce large volumes of gas (1 litre of liquid nitrogen will produce 0.7m3 of gas). Nitrogen gas is invisible - the cloudy vapour which appears when liquid nitrogen is exposed to air is condensed moisture, not the gas itself.
One of the main dangers associated with liquid nitrogen is the risk of asphyxiation when used or stored in poorly ventilated areas. Liquid nitrogen evolves nitrogen gas which is inert and non-toxic but there is a risk of asphyxiation in situations where high concentrations may accumulate and subsequently displace air from the room. Short exposures to cold gas vapour leads to discomfort in breathing whilst prolonged inhalation can produce serious affects on the lungs and could possibly provoke an asthma attack. Methods for calculating the potential for oxygen depletion are given in the Assessment of ventilation requirements
- Cryogenic burns
Liquid nitrogen can cause cryogenic burns if the substance itself, or surfaces which are or have been in contact with the substance (e.g. metal transfer hoses), come into contact with the skin. Local pain may be felt as the skin cools, though intense pain can occur when cold burns thaw and, if the area affected is large enough, the person may go into shock.
Continued exposure of unprotected flesh to cold atmospheres can result in frostbite. There is usually sufficient warning by local pain whilst the freezing action is taking place.
Low air temperatures arising from the proximity of liquefied gases can cause hypothermia. Susceptibility is dependent upon temperature, exposure time and the individual concerned (older people are more likely to succumb).