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SAFETY
Introduction
In all cryogen handling the following appropriate safety guidelines are essential if damage to equipment and
personal injury are to be avoided. The following guidelines provide a basic level of instruction in the precautions
necessary but are by no means exhaustive, a comprehensive approach involving staff training on a recognised
course is strongly recommended.
Liquid Nitrogen
The boiling point of liquid nitrogen is -196°c (77K).
The molecular weight of nitrogen is 28.
Nitrogen gas is inert, odourless, tasteless and colourless.
Nitrogen gas is an asphyxiant.
Liquid nitrogen is odourless, colourless, slightly lighter than water and does not produce toxic or irritating
vapours.
Hazards and Precautions
Cryogenic Burns
Appropriate protective clothing should always be worn when handling cryogenic equipment.
The extreme cold can cause cryogenic burns which have a similar effect on the skin to frostbite.
Similar methods should be used in the treatment of both.
Re-warm the affected area as quickly as possible in WARM water at about 40°c or by warm air.
Maintain general body warmth.
Do not rub or massage the affected area as this may cause more serious damage than already exists.
Seek medical advice as soon as possible.
Oxygen Depletion
Liquid nitrogen should always be stored and used in well ventilated areas and the use of oxygen deficiency
monitors is strongly recommended.
Liquid nitrogen expands when vaporised into a gaseous state by a factor of 842 times, causing a significant
danger from asphyxiation in confined or poorly ventilated spaces. Suffocation can occur rapidly as the oxygen is
displaced. (A drop of only 2% in the oxygen content is enough to pose a significant risk.)
Loss of consciousness or dizziness while working with liquid nitrogen are obvious signs of asphyxiation due to
an oxygen deprived atmosphere. At the first signs of this the subject should be moved as quickly as possible
from the affected area. If breathing has stopped apply artificial respiration and summon medical assistance
immediately.
Condensed Air
Due to extreme cold, air on the outside of transfer hoses and dewars can condense and form liquid air.
Adequate ventilation should ensure that any risk from this occurring is minimised. However, as with liquid
oxygen a strict no smoking or naked flame rule must be observed.
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