Activities Involving Liquid Nitrogen
Hazards:
Liquid nitrogen is used within the laboratory environment, for traps on pumps, cooling, to liquefy gases, and in preparation and cryogenic storage of biological specimens. The hazards associated with its use include: a. Cold burns. Liquid nitrogen can cause severe frostbite and cold burns. b. The low temperature of the vapour produced during a spill can cause damage to the soft tissue e.g. eyes and lungs. c. Soft materials such as plastics and rubber may become brittle and break, causing spills due to mechanical failure. d. Trauma wounds caused from touching a metal surface that has been in contact with liquid nitrogen, touching the surface will cause the skin to stick fast and tear the flesh when you attempt to withdraw away from it. e. Asphyxiation. Liquid nitrogen can rapidly be converted into a gas and in an enclosed space can displace the oxygen present causing varying degrees of asphyxiation and even death. f. Gradual asphyxia. Degrees of asphyxia will occur when the atmosphere contains less than 20.9% oxygen by volume.
Oxygen content
(vol. %)
20
– 14
Effects and symptoms (at atmospheric pressure)
Diminution of physical and intellectual performance without person’s knowledge
14
– 10
Judgement becomes faulty. Severe injury may cause no pain.
Ill temper easily aroused. Rapid fatigue on exertion.
10
– 6
Nausea and vomiting may appear. Loss of ability to move vigorously or at all. Inability to walk, stand or crawl is often first warning and it comes too late. Person may really believe
0 – 6 that they are dying but does not care. Resuscitation possible if carried out immediately.
Fainting almost immediate, painless death ensues, brain damage even if rescued.
Risk Factors

Using liquid nitrogen in laboratories, rooms which do not have adequate ventilation;

Liquid nitrogen that has been used to store biological/human samples may be contaminated with pathogenic micro-organisms;

Transportation of liquid nitrogen in lifts;

Transportation of liquid nitrogen;

Splashing of liquid nitrogen whilst filling dewars;

Not wearing adequate personal protective equipment;

Wearing open shoes such as sandals;

Overfilling of the receiving vessel from a pressurised container will result in a spill;
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
Pouring from a large vessel into another vessel (particularly if the receiving vessel is small) can result in a spill;

Tubing must not be placed directly into the liquid nitrogen as this will cause the liquid to fountain;

Vessels which are not designed for liquid nitrogen may break and cause a spill;

Damage to a vessel due to an impact blow will result in the rapid release of gas and/or liquid;

Damage to flooring caused by liquid nitrogen spills;
 Boiling or splashing due to the receiving vessel being ‘hot’ in comparison to the liquid will release gas or liquid;

Liquid nitrogen left in an open container for long periods of time, significant amounts of liquid oxygen may condense into it, which may cause a serous explosion if organic material is allowed to come into contact with it;
Risk Control Measures:

All staff should be trained in the use of liquid nitrogen, storage, handling and associated risks;

Areas where liquid nitrogen is stored should have adequate ventilation and oxygen level monitoring equipment installed;

Areas where liquid nitrogen is being used must have adequate ventilation, if large quantities are being used, oxygen monitoring equipment must be installed;

If lift transportation is unavoidable, the lift must have a security control system to enable staff to maintain independent control of the lift during the transport operation. Members of staff must not travel in the lift with the container. A second person should be at the destination floor to take charge of the container;

If human or other biological material has been stored the sample should be allowed to reach room temperature in a suitable category cabinet;

Concentrate on the task in hand to reduce the risk of spills and splashes due to carelessness or lack of concentration;

The minimum personal protective equipment, is gloves (suitable for cryogenic work, these must be checked regularly for damage as contact with liquid nitrogen may cause deterioration. Cryogenic gloves should never be immersed in liquid nitrogen), safety glasses and lab-coat;

Open shoes should never be worn when handling liquid nitrogen;

Only use equipment suitable for use with liquid nitrogen;

Check all dewars and equipment for signs of damage that may impair the efficiency of the equipment;

Flooring may be damaged by contact with liquid nitrogen, this can cause a trip hazard or provide areas where biological or radioactive material may accumulate;

Try to ensure that the temperature difference between the vessels being used is as close as possible.
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
Ensure that all containers where practically possible are left open for a short a time as possible. If this is not practicable the liquid nitrogen should be changed regularly;
Persons at Special Risk:
Untrained staff such as cleaners, porters and security that may come into contact with equipment and storage Dewars. Such contact should be kept to a minimum and all area should be adequately signed to give warning of the hazard.
Health Surveillance:
None
Exclusions:
This model assessment may not be suitable if liquid nitrogen is being used to condense oxygen or other dangerous gases.
Relevant Statutory Provisions and Other Guidance:
Safety Bulletin SB-2-1992: Oxygen-deficient atmospheres, Compressed Gas
Association. http://www.cganet.com/pubs/free/SB-2_3.pdf
Handling LN
2
Safely, Cryosafe. . http://www.cryodafe.com/index.html
“HSE issues warning about use of liquid nitrogen”, HSE Press Release
E229:99 18 th November 1999
BOC gases – Liquid Nitrogen Data sheet
BOC
– Prevention of oxygen enrichment or deficiency accidents
British Cryogenics Council, Cryogenics Safety Manual, Oxford, 1991
National Physics Laboratory, Safety Measures in Chemical Laboratories,
London, 1964
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