Liquid Nitrogen Handling Risk Assessment

Liquid Nitrogen Handling Risk Assessment

Description: This is the reference risk assessment for general liquid nitrogen handling.

See liquid Nitrogen Handling belowSee liquid Nitrogen Handling below

Hazard information

Cold burns, frostbite and hypothermia from the intense cold

Liquid nitrogen poses special problems due to its extreme low temperature (-196 oC). Contact with the liquid, or even cold vapour or gas, can produce damage to the skin similar to heat burns. Wear the eye protection and cryogloves provided (see Handling / Preparation, below)

    • Asphyxiation in oxygen deficient atmospheres

Liquid nitrogen is an asphyxiant. When the liquid vaporises, a large volume of gas is generated. This presents an asphyxiation hazard the magnitude of which is dependent on the volume of the liquid nitrogen flask in relation to that of the room.

    • Over-pressurisation from the large volume expansion of the liquid

The ratio of the volume of gas to liquid, measured at 15°C and one atmosphere, is 682. Confinement of the gas can result in a potentially explosive situation (see flask venting and type below).

    • Fire in oxygen enriched atmospheres

Be aware that oxygen enrichment and a fire hazard can result from the condensation of oxygen (boiling point -183C) from the air onto piping cooled by liquid nitrogen (boiling point -196°C). This risk can be limited by restricting the volume of liquid nitrogen used.

PROCEDURES

Storage/transportation

    • Liquid nitrogen should be stored in a flask that has been designed specifically for containing cryogenic liquids (6 litre stainless steel Dewar or 25 litre egg) in a well ventilated room.
    • Never attempt to prevent vapours from escaping from storage containers. Since they are not at thermal equilibrium, vapour is produced as the liquid boils and, if not vented to the atmosphere, could produce excessive pressures resulting in the container rupturing - possibly explosively.
    • The practice of using domestic, or outdoor activity, type flasks is dangerous because the stoppers on these flasks can form a seal at the neck.
    • Transport only in the 25 litre egg in a van that has front and rear compartments for personnel and 'goods', each vented separately to the outside air. The egg should be securely fixed to prevent movement. It is a statutory requirement that the driver is aware of what he or she is transporting and the flask cannot become overpressurized.
    • The 25 litre egg of liquid nitrogen should never be carried in a lift (elevator) alongside people, because of the remote possibility that the Dewar containing the liquid will go "soft" (i.e. lose the vacuum in the Dewar flask) and lead to sudden and rapid generation of vapour.
    • The 25 litre egg must be carried on the special trolley provided or carried by two people. The route into the demonstration site must be reconnoitred for specific risks in manual handling (see below). Ensure there is no potential for an accident with pupils in the corridors or playground. Where 'team' handling has to be used, do not involve school staff or pupils. Only specifically trained personnel are to handle the liquid nitrogen container. It is acceptable, if necessary, to prop open smoke stop doors temporarily since the avoidance of manual handling difficulties will outweigh the short term fire risks. Ensure any props are removed immediately.
    • Handling / Preparation
    • Work in a well ventilated area of adequate volume and ensure that emergency exits are always clear.
    • Eye protection and thermal gloves must be worn whenever handling liquid nitrogen.
    • Care should be taken when using liquid nitrogen not to spill the liquid on clothing, since this can easily become saturated with the liquid and then hold the liquid next to the skin for a significant period of time, leading to serious burns. Wear loose-fitting thermal gloves, eye protection (goggles or face-shield), and trousers over closed shoes (slip-ons being preferable to lace-ups). Be extremely cautious carrying the liquid nitrogen into the school. Plan the route in to the demonstration area and the time of entry (see also "Storage/Transportation" and "Setting-up").
    • Never leave the Dewar unattended and always keep the audience at least 2-3 m away. Ensure that the Dewar is placed on a stable, steady table. When the audience are entering and leaving, stand between them and the table so that there is no danger of the Dewar being knocked over.

Disposal

    • Do not attempt to dispose of residual waste or unused quantities. Return in the container to an authorised distributor for proper disposal.

Spillage

    • Evacuate all personnel from the affected area.

Remedial Measures

Cold Burns - BOC advise that the aim of treatment is to raise the temperature of the affected part slowly back to normal.

For minor exposures:

    1. Move the victim to a comfortable room if possible.
    2. Ensure that clothing is loose to provide unrestricted circulation. Do not remove clothing that is stuck to the body until thawed thoroughly.
    3. Place affected part in TEPID WATER or run TEPID WATER over for half an hour until the skin changes from pale yellow through blue to pink or red. Do not use hot water or any other form of direct heat.
    4. Cover the affected part with a bulky, dry, sterile dressing.
    5. Send the victim to a hospital casualty department.

Asphyxiation – In case of severe drowsiness or asphyxiation open windows and then remove patient to an area with uncomtaminated air. Keep warm and place in the recovery position. A trained First Aider may be needed to apply CPR as necessary.

Setting-up

    • Again, remember the need to plan your route into the demonstration area and the timing of your entry (see above). Ensure that it is safe to carry in the equipment. If you enter during breaktime, is there potential that pupils at play or moving in corridors could be a hazard?
    • Set up your demonstration table so that it doesn’t obstruct any fire exits or thoroughfares and is in a position in the room that the audience can easily enter and exit without coming into contact with your equipment.
    • Take control of the audience as they come into the room, standing where you want the first row to sit (approx. 3 m from the demonstration table).
    • Eye protection and cryogenic gloves must be worn at all times when handling and demonstrating with liquid nitrogen. Ensure eye protection is cleaned before use.
    • All volunteers must wear eye protection.
    • If performing the demonstration in a classroom or similar sized room only put 3 l of liquid nitrogen in the Dewar. The risk being minimised by reducing the volume of liquid nitrogen which could be subject to catastrophic spillage.