- A specific risk assessment must be completed for areas storing quantities of liquid nitrogen that present a significant risk of asphyxiation, for example, use of pressurised cylinders which could release contents in the event of a valve failure. A Liquid nitrogen example: Risk assessment (PDF , 62kb) can be used for information and guidance. Contact Department Safety Advisor (David Nelson, e: dn6) for assistance if required.
- The risks associated with:
are generic to all laboratory areas. The application of the working practices outlined in the tabs on this page will ensure risks are reduced to a low and acceptable level:
- the storage of biological materials in non-pressurised liquid nitrogen dewars
- use of small quantities of liquid nitrogen for laboratory activities
- The process for completing a risk assessment for the handling and use of liquid nitrogen follows the same general rules for all risk assessments:
- Identify hazards (see the Hazards tab)
- Decide who might be harmed and how
- Evaluate the risks and decide whether existing precautions are adequate or whether more needs to be done
- Record your findings
- Review and revise your assessment as appropriate.
Information provided in other sections of these web pages will help you to identify the hazards and determine the relevant control measures needed.
Personal Protective Equipment (PPE)
This should be appropriate to the task in hand and readily available.
Hands: non-absorbent insulated gloves must always be worn when handling anything that is or has been in recent contact with liquid nitrogen. Cryogenic gloves are designed to be used in the vapour phase only and should not be immersed into liquid nitrogen under any circumstances. They should be a loose fit to facilitate easy removal. Gauntlet style gloves are not recommended for some liquid handling uses as liquid can drip into them and become trapped against the skin; sleeves should cover the ends of gloves or alternatively, a ribbed cuff style may be used.
There are a range of commercially available gloves suitable for use at cold temperatures, some of which meet the requirements of BS EN 420: 1994 'General requirements for gloves'.
Face: a full face visor should be used to protect the eyes and face where splashing or spraying may occur and, in particular, where operations are carried out at eye level e.g. when topping up reservoirs on electron microscopes.
Body: a laboratory coat or overalls should be worn at all times. Non-absorbent cryogenic aprons are also commercially available. Open pockets and turn-ups where liquid could collect should be avoided. Trouser bottoms should overlap boots or shoes for the same reason.
Feet: sturdy shoes, providing full protection of the foot, must be worn when handling liquid nitrogen vessels. Open toed shoes should not be worn under any circumstances.
When not in use, all PPE should be stored in an appropriate manner (e.g. visors on wall mounted hooks) to ensure that it does not become damaged or contaminated.
In the event of a large spillage or accidental release, the following procedures should be followed:
- Evacuate the area. Deploy warning signs if necessary.
- Ventilate the area. Open doors and windows or activate forced ventilation to allow any spilt liquid to evaporate and the resultant gas to disperse.
- Try to stop the release if at all possible e.g. turn off valves, but only if it is safe to do so - always wear protective clothing.
- Do not re-enter area unless it is proved safe to do so. The presence of oxygen deficiency monitors will indicate the oxygen levels in the vicinity.
- Prevent liquid nitrogen from entering drains, basements, pits or any confined space where accumulation may be dangerous.
Storage & use
Ventilation is the key issue. Large scale vacuum insulated tanks are normally stored outside buildings because of the quantities of stored liquid. Where smaller pressurised containers and non-pressurised dewars are stored within buildings, the following points should be considered:
- store below 50°C in well ventilated place
- ensure appropriate hazard warning signs are displayed (yellow triangle with exclamation symbol and text: 'Liquid nitrogen')
- use only properly specified equipment for storing liquid nitrogen
- do not leave vessels unattended when filling
- use only proper transfer equipment
- do not overfill vessels
- with non -pressurised containers, do not plug the entrance with any device that would interfere with the venting of gas; use only the loose fitting necktube core or an approved accessory
- do not use brittle plastics which may shatter on contact with the cold liquid
- do not use hollow dipsticks - use solid metal or wood; if a warm hollow tube is inserted into liquid nitrogen, liquid will spout from the tube due to rapid expansion of liquid inside the tube and gasification
- any instructions given to staff should detail not only what they are required to do but also what they should not do.
- See Local rules tab for procedures that apply for filling vessels from the storage dewars in room B/E/012
Working with liquid nitrogen in cold rooms
This is permissible providing that risk assessment determines that it is acceptable. The following points should be considered:
- Ventilation: is it adequate? Most cold rooms do not have any air supply or extract system and so there is little or no air change. Can the door be left open to allow gas to dissipate when vessels are being filled?
- Do people spend significant periods working in the cold room (on unrelated tasks)?
- Is the room fitted with an oxygen deficiency monitor / alarm?
- Is the door fitted with a viewing panel?
- Is there a ‘panic button’ within the room?
Maintenance of Storage Vessels
All static and transportable pressurised vessels must be maintained and tested in accordance with the Pressure Systems Safety Regulations 2000. Completion of a written scheme of examination and the periodic examination itself is usually carried out by trained engineers appointed by the insurance company responsible for insuring the vessel. The maintenance of transportable vessels is a Departmental responsibility and all records of inspections should be filed and readily accessible to present to the enforcing authorities if requested.
Any obvious damage sustained by vessels (either static or transportable) must be reported immediately to the Laboratory Supervisor and if necessary, the vessel should be taken out of use until inspected by a competent person.
Forced ventilation systems and oxygen deficiency alarms should be maintained in good working order. (Details see Appendix 2)
All liquid nitrogen users must be made aware of the properties and hazards and be fully trained in the local departmental procedures for usage, storage and transportation before they engage in handling the substance.
All users of the departmental storage dewars in room B/E/012 must be authorised. Please contact Lucy Hudson or Colin Bingham to arrange training before use.
Local rules for decanting liquid nitrogen in main departmental storage area
- All users must be trained and authorised to dispense liquid nitrogen from these storage vessels
- Liquid nitrogen may only be dispensed into containers designed for liquid nitrogen use of the narrow neck style.
- Liquid must not be dispensed into small volume wide necked vessels even where designed for liquid nitrogen use.
- Wear PPE provided (Gloves and eye/face protection) at all times during the dispensing process
- Both doors must be fully open at all times during filling of vessels
- If oxygen deficiency monitor alarm sounds immediately shut off delivery valve (if safe to do so) and evacuate the room. Report the incident. The monitor will reset once the level of oxygen has returned to normal. (Oxygen deficiency monitor in Room B/E/012 supplied and serviced by GDS Technologies, Leeds (T 0113 2860 166). Service carried out twice per year. Service records kept by Lucy Hudson Operational Manager Tel 8745).
- If liquid leaking from delivery hose or joints. Stop filling and report the problem.
- Decanting activities should normally be restricted to normal working hours (Weekdays 08:00 to 18:00hrs).
Reports to Lucy Hudson or Colin Bingham
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).