Estates, Facilities and Capital Services
Estates Services Manager (VHK)Pharmacy Technician Team Leader, Health & Social Care Partnership
NHS Fife Medical Gas Committee
Director of Estates, Facilities & Capital Services - Director of Pharmacy
01 May 2013
01 November 2019
01 November 2022





This procedure supports the safe storage, use and transport of liquid nitrogen.  It is essential that all persons, storing or handling Liquid Nitrogen are fully aware of the risks posed in its use, and are not exposed to unnecessary danger.

Further and more comprehensive information can be found in the British Compressed Gases Association's Code of Practice CP30 - "The Safe Use of Liquid Nitrogen Dewars up To 50 Litres", Rev 1, 2008




Within all NHS Fife properties and all non-NHS Fife settings where NHS Fife staff store, dispense and/or use Liquid Nitrogen.




Any member of NHS Fife staff storing transporting or handling liquid nitrogen must ensure that it is done in accordance with this procedure.

 NHS Fife Health and Safety Team are available for advice and assistance.


Any member of NHS Fife staff storing, transporting or handling liquid nitrogen must have undertaken appropriate training and this must be refreshed every 3 years.






Liquid Nitrogen is a colourless, odourless liquid boiling at -196°C. It is not toxic and does not support life or combustion. The density changes with temperature and, critically below 5.5°C, the gas is heavier than air.

As a liquid the gas will expand to 683 times its volume.



Exposure of skin to very low temperatures can produce effects similar to a burn. Prolonged exposure to cold can result in frostbite. If unprotected skin should come into contact with a very cold surface it may stick fast as the natural moisture on the skin is frozen. Flesh can be torn whilst trying to break free therefore appropriate Personal Protective Equipment (PPE) should always be worn (see Section 4.2). 

All cold burns must be reported to a first-aider for treatment. Treatment will include:

  • For a severe burn calling an ambulance or transfer casualty to A&E
  • Flush the area with tepid water continuously- in order to avoid tissue damage, a forceful flow of water should NOT be used
  • Do not apply direct heat to affected area
  • Move the casualty to a warm place (approximately 22OC), keeping the patient warm and at rest
  • Loosen the casualty’s clothing
  • Do not allow the casualty  to smoke and avoid hot beverages


OXYGEN DEFICIENCY (spillages & venting/leaking Dewars)

Upon evaporation Liquid Nitrogen will expand to 683 times its volume. It will cause asphyxiation if it is at a concentration sufficient to displace the Oxygen in a room. Especially at risk are areas with little or no air movement, particularly enclosed spaces with little or no ventilation. There is little or no warning to the individual that s/he is in an oxygen deficient atmosphere. Asphyxiation will take one of two forms:

  • Sudden Asphyxia (inhalation of a gas containing practically no oxygen), unconsciousness is immediate. Death can follow in a few minutes unless immediate remedial action is taken.
  • Gradual Asphyxia - can occur as oxygen levels in the atmosphere decrease.

 Signs and symptoms of person at rest of gradual asphyxiation due to reduction of oxygen in air:

  • 21% to 14% - depth of breathing increases, pulse rate accelerates. There is reduced ability to maintain attention and think clearly. Muscular co-ordination is disturbed.
  • 14% to 10% - still conscious but judgement faulty, may feel less pain from serious injury. Muscular effort leads to rapid fatigue. Emotions are disturbed – irritation and anger can appear
  • 10% to 6% - rate of breathing is doubled, may have nausea and vomiting. There is a loss of ability to perform vigorous muscle movements or even to move at all. There is a lack of awareness that anything is wrong. Legs may give way. Even if resuscitated may result in permanent brain damage.
  •  Less than 6% - respiration is in gasps with increasing gaps. Convulsions may occur. Respiratory arrest then cardiac arrest within a few minutes



Inhalation of cold vapour or gas can damage the lungs. Short exposures produce discomfort in breathing whilst prolonged exposure can cause more serious effects.



The low temperature of Liquid Nitrogen can cause oxygen to condense out of atmospheric air. This can occur around cold pipe work, valves and in open dewars. This oxygen enrichment may result in increased flammability and explosion risk.

Oxygen enriched liquid must not be allowed to come into contact with oil, grease or flammable materials as spontaneous combustion can occur.



Ice plugs may form in the neck of open dewar flasks and cause a build-up of pressure. As the pressure rises within the dewar, the ice plug may be expelled at high velocity or in extreme cases the pressure may build up sufficiently to rupture the vessel. Serious injury can result.

If an ice plug is found extreme caution should be exercised and the local vicinity must be evacuated immediately.

Advice on how to deal with an ice blockage should be sought from the gas supplier or dewar manufacturer.

Ensure that the manufacturer examines the dewar before returning it to service.

Ice plugs can be prevented by diligent use of the correct dewar stopper.




A risk assessment of the dangers posed must be undertaken in each area where Liquid Nitrogen is used, transported or stored.


Equipment and systems of work should be designed, operated and maintained to reduce the risk of an accidental spillage.

In the event of a spillage the quantity of Liquid Nitrogen that might be spilt should be minimised by storing, transporting and using only those quantities immediately required.



The following PPE must provided and used when handling Liquid Nitrogen:

  • Eyes: face visor (to protect both the eyes and face)
  • Hands: loose fitting, non-absorbent, insulated gloves (leather or similar). Gauntlets are not recommended as liquid could collect in them.
  • Body: overalls, lab coat or similar are recommended. In order to avoid collection of liquid, such clothing should preferably not have pockets, and trousers should not be tucked into boots or have turn-ups.
  • Feet: Open footwear must not be worn, and legs should be covered.




Ventilation requirements of a Liquid Nitrogen storage area depends on several factors e.g. volume of room, amount of Liquid Nitrogen stored and evaporation rates.

  • For rooms above ground level with no special ventilation openings, natural ventilation will provide typically one air change per hour. With well-sealed windows e.g. double-glazing, this will be less. Basement rooms may only average 0.4 changes per hour.
  • For general handling of Liquid Nitrogen, vessels in locations at or above ground level, natural ventilation is generally sufficient provided the room is large enough.
  • An indoor location should have ventilation openings provided which are at least 1% of the floor area and positioned diagonally opposite with the main opening at ground level. Cold Nitrogen gas is heavier than air and will accumulate at low level.
  • Liquid Nitrogen must not be handled in basement rooms, rooms with ventilation at high level only, and rooms where the gas can be trapped in gullies, ducts or pits.
  • Rooms should be adequately ventilated to allow normal evaporation of vessels and evaporation during filling without the Oxygen concentration falling below 19.5%.
  • In addition, the complete spillage of the contents of the largest vessel should not allow the oxygen concentration to fall below 18%.

NHS Fife Health & Safety Team can assist with risk assessment.



A written Emergency Procedures must be prepared by Departmental Head, taking into account possible spillages and venting/leaking dewars/ flasks. The following must be considered:

  • Raising the alarm
  • Summoning help and emergency services
  • Isolating the source of leakage if appropriate and where it is safe to do so
  • Evacuating persons from the danger area and preventing access. Remember persons in pits, basements, cellars, stairwells, lower floors etc
  • Ventilation of the area by opening exterior doors and windows, where safe to do so. This will allow Liquid Nitrogen to evaporate naturally. Do not try to clean it up.
  • Alerting neighbours to possible dangers from vapour clouds and evacuate where necessary
  • Preventing reoccupation of the area until all gas has dispersed. If necessary Oxygen monitors should be used to check the atmosphere before occupation.


After the Liquid Nitrogen spillage has been isolated oxygen deficiency checks should be carried out in any enclosed areas where the vapour cloud may have entered. This includes basements, pits and confined spaces. Staff likely to be involved must be clear about the actions required to minimise any adverse effects.



Liquid Nitrogen should never be poured down a sink as waste pipes will crack offering the potential for gas leaks into occupied areas. Unwanted Liquid Nitrogen should be allowed to evaporate in well ventilated areas, preferably outside.





All personnel handling Liquid Nitrogen and those directly involved in the commissioning, operation and maintenance of Liquid Nitrogen storage systems must be fully informed regarding the hazards.

 Training should cover, but not necessarily be confined to, the following subjects for all personnel:

  • Potential hazards of Liquid Nitrogen
  • Site safety rules
  • Handling procedures e.g. method of dispensing, sample retrieval, transportation
  • Use of protective clothing/apparatus including breathing sets where applicable
  • Emergency procedures
  • First aid treatment for cryogenic burns


NHS Fife provides face to face training three times a year. It can be booked by contacting Pharmacy Services (01383 565351).

Staff handling liquid nitrogen are required to undertake refresher training every 3 years.

All training must be recorded on appropriate staff records.




Precautions during use:

It is the responsibility of the ward/department staff using the dewar to ensure that it is safe for use. The following precautions must be observed:

  • Only proprietary insulated liquid nitrogen containers  must be used for holding Liquid Nitrogen. They should be clearly labelled. Never fill a dewar labelled for another product.
  • For stability the dewar should hold a minimum of 25 Litres and be placed on a movable trolley.
  • Check first that the dewar /insulted flask is in good condition and do not fill if the dewar / flask is damaged, including damage to seals.  It is the responsibility of the flask owner to ensure that it is maintained appropriately.
  • Ensure that there is no excessive frosting around the neck
  • Filling / decanting must be undertaken by two members of staff whenever possible and  in a well ventilated area to prevent oxygen depletion
  • In order to prevent unnecessary wastage through evaporation, the dewar should be fitted with a liquid withdrawal device. This will have the added benefit of ensuring that transfer of Liquid Nitrogen is easier and safer than pouring and ensuring that the dewar is unlikely to be knocked over causing spillage
  • Never overfill dewars or insulted flasks.
  • Pouring Liquid Nitrogen or immersing items should be done slowly to minimise boil off and splashing. Use tongs or similar tool when placing objects into or removing from Liquid Nitrogen.
  • Treat dewars and insulated flasks with care. Even minor impacts may lead to slow or catastrophic loss of vacuum.
  •  Trolleys and tipping trolleys should be used for vessels of 25 litres and above.
  • After the removal of samples from Liquid Nitrogen storage, be aware of the danger of sudden overpressure of the sample vial. This can occur when Liquid Nitrogen has entered the vial during storage and its rapid vaporisation when exposed to ambient temperature. Do not remove your face visor until the samples have thawed and you are sure that all the Nitrogen has evaporated.
  • Leaving dewars and insulated flasks of Liquid Nitrogen open can allow oxygen to condense and give rise to the risk of explosion/fire if allowed to contact flammable solvents, oil or grease
  • After decanting, two members of staff should ensure that the valves on the liquid withdrawal device are properly closed



The precautions for the safe storage of dewars should apply whether they are full, part full or empty.

The storage area should preferably be external to a building, be dry, have adequate ventilation and be capable of being viewed from the outside i.e. through a window.

If a dewar is being stored internally the storage rooms must be fitted with mechanical ventilation, must have an alarm fitted outside the room to indicate failure and must have a window to view inside the room before entering.

Unauthorised access to any storage area should be prevented.



  • When transporting containers of Liquid Nitrogen care must be taken to ensure they are not left, even temporarily, in an enclosed space due to the risk of oxygen depletion.
  • Do not drag dewars along the floor.
  • Trolleys should be used for vessels of 25 litres and above.



 In Passenger Lifts

Procedures must be in place to ensure that no-one travels in a lift with Liquid Nitrogen; the unexpected evaporation of relatively small quantities of Liquid Nitrogen can reduce the available oxygen to a dangerous level in a standard size passenger lift. Where lifts have to be used the following procedure must be followed:

  • one person places the dewar in the lift whilst another meets the lift at the designated floor ( a suitable qualified person must be at every floor if lift travels through multiple floors to ensure no person can enter lift whilst Liquid Nitrogen is being transported).  The Dewar travels unaccompanied. This activity should be supervised by competent persons who are aware of the potential hazards and the appropriate emergency action.


Transporting in a Vehicle

Liquid Nitrogen should never be transported by car for the following reasons

  • Spillage of Liquid Nitrogen in a car (or other unsuitable vehicle) could result in asphyxiation through oxygen depletion.
  • Spillage can cause serious damage to the car's interior. For example contact with the spare wheel will make the tyre lethally dangerous if subsequently fitted to the car.
  • The driver will not be covered by their own or NHS Fife's insurance policy.

For carriage by suitable vehicle the following precautions must always be adhered to:

  • Vehicles used for the transport of Liquid Nitrogen must be designed to prevent a build up of Nitrogen gas in the event of a leak or spill. This can be achieved by provision of adequate high and low level vents to encourage a free-flow of air through the load compartment and a bulkhead to prevent escaped gas reaching the passenger compartment.
  • Vehicles must be equipped with means of securing the Dewar.
  • Dewar caps / flask lids may come loose during transportation. A retaining device should be fitted which keeps the cap in place but does not seal the dewar e.g. a short piece of chain or wire.
  • If the case of a road accident the emergency services must be advised that Liquid Nitrogen is being carried. However, Dewars /flasks should be labelled adequately in case the driver is unable to communicate with them following the accident.
  • Drivers must be adequately trained regarding the hazards of Liquid Nitrogen.



A Maintenance regime for Dewars must be in place by the department using the dewar.

The following checks to be carried out regularly (generally each time before the Dewar is filled); for Dewars used infrequently this should be at least 6 monthly:

  • Condition of the cap
  • Damage to seals
  • Twisting or other damage to the neck
  • Damage to the dewar body, trolley and wheels
  • Interior is free of dirt or other contaminants; including insulating bungs which may have detached from the cap and fallen in
  • liquid withdrawal devices free from damage




The quantities of Liquid Nitrogen used in clinics and health centres and hospital departments are generally small e.g. 1 or 2 litres flasks. However, appropriate delivery, storage and use of the Liquid Nitrogen is essential to safeguard staff and patients.

Insulated flasks are usually refilled every 1-2 weeks.


Staff involved in the storage, use and transport of Liquid Nitrogen in insulated flasks must be aware of the hazards and the appropriate method of decanting , including the wearing of appropriate face protection, gloves and clothing as a minimum level of PPE.

  • The storage/ in-use area must be display appropriate warning labels
  • The storage/in-use  area must be capable of being viewed from the outside
  • A risk assessment must be carried out to ensure that the ventilation of the area where the flask is stored /used is suitable for safe use (see 4.2)



NHS Fife currently does not have any bulk storage of liquid nitrogen above 50Litres.

Should it be considered the following factors have to be taken into consideration. NHS Fife Estates Department and NHS Fife Health and Safety advisors must be included at the planning stage of any such facility.


Where bulk storage of Liquid Nitrogen takes place, the installation must conform to the British Compressed Gases Association's Code of Practice CP21. For further information consult an NHS Fife Health and Safety Advisor.


Siting of Liquid Nitrogen Bulk Storage Facilities Bulk tanks over 500 litre capacity must be situated outside in a location that is acceptable to the gas supplier. The location must be exclusively for the storage of Liquid Nitrogen, at above ground level and away from ducts, drains and other ground depressions. It should also be designated a ‘No Parking’ area



The following must be observed:

  • only authorised personnel should have access to the storage facility and be allowed to operate the installation
  • personal Oxygen level alarms should be worn at all times
  • Standard Operating Procedures must be written and risk assessments of all activities recorded. Operatives must be formally trained in their use
  • All hand wheels of valves should be colour coded or identified easily and quickly by other means. This will aid the operator in an emergency. These valves would include the user line feed isolation valve and the withdrawal valve
  • Formal training must be given to all operatives and records kept. Refresher training should be given on a periodic basis.
  • Any modifications made to the installation must be agreed with the Nitrogen supplier prior to implementation. warning signs must be displayed e.g.


Permit to Work

Any works required must be undertaken by a person who is certified as competent to do so.

Before maintenance or pressure testing is carried out on the installation, a written Permit to Work for the particular type of work (i.e. cold work, hot work, entry of vessel, pressure test, electrical work etc.) should be issued by the appointed authorised person to the individual(s) carrying out the work.


Periodic Inspection and Maintenance

The Pressure Systems and Transportable Gas Containers Regulations introduced specific requirements covering design, manufacture, installation, maintenance and examination of pressure systems. Full guidance on the implementation of these regulations may be found in the British Compressed Gases Association's document CP23.

 The facility should be inspected regularly to ensure that it is maintained in a proper condition. Periodic and planned maintenance of the installed equipment must be carried out by a competent person. This work should include:

  • External vessels and pipe work
  • Inner vessel
  • Vaporisers
  • Pressure relief devices
  • Ancillary equipment
  • Isolation Valves

All inspection and maintenance work should be recorded.



NHS Fife Pharmacy

Pharmacy Governance Team, Queen Margaret  Hospital


Tel: 01383 565345 / 565347

Ext 27093

NHS Fife Health & Safety Team

Willow Drive,  Kirkcaldy

Tel: 01592 643355


 20400, 20413, 20415, 20416, 20412

Fire Officer:



 20417, 20418, 20419

BOC Healthcare


Current medical gas contractor

Contact Tel: 0800 111 333

Customer Services Tel: 0161 930 6157 Scottish Rep  - David Millar,

Tel: 07879 435749

Air Products PLC

2 Millennium Gate, Westmere Drive, Crewe, CW1 6AP

Tel: 0345 604 7696



Ext: 23151


Ext: 29292 Option 1


Risk Management


Equipment and systems of work must be designed, operated and maintained to reduce the risk of an accidental spillage. In the event of a spillage the quantity of Nitrogen that might be spilt should be minimised. To this end a risk assessment of the dangers posed must be undertaken in each area where Liquid Nitrogen is either used, transported or stored.


A DATIX must be completed in the event of any incident or near miss in relation to the transport storage or use of liquid nitrogen    




NHS Fife Policy GP/M3 : Medical Gases Policy




Code of Practice CP30 - "The Safe Use of Liquid Nitrogen Dewars up To Litres", rev 1, 2008, published by the British Compressed Gases Association (BCGA).


1992 No 2793 The Manual Handling Operations Regulations, 1992.


SI 1999 No 3242 The Management of Health and Safety at Work Regulations 1999.


SI 1999 No 3242 The Management of Health and Safety at Work Regulations 1999.