Cryogenic materials explained
A cryogenic material is a material at a very low (or 'cryogenic') temperature. This includes liquids and solids such as cardice. Cryogenic liquids are gases at normal temperature and pressure that are liquefied at very low temperatures. Examples include nitrogen, argon and helium. Different cryogens become liquids under different conditions of temperature and pressure, but all have two properties in common: they are extremely cold, and small amounts of liquid can expand into very large volumes of gas.
Direct contact with cryogenic materials can lead to severe cold burns, frostbite and retinal damage if the eye is affected. A leak of cryogenic liquids into a room can lead to a displacement of oxygen − resulting in a potential risk of asphyxiation to occupants.
How to use cryogenic materials safely
1) Ensure risk assessments include an assessment of risk associated with tasks using cryogenic materials.
2) The storage of bulk quantities of cryogenic materials within buildings should be avoided where possible. If considered necessary, this must be justified in the risk assessment and the volumes used minimised.
3) Cryogenic liquids should only be used in well ventilated areas. Decanting of liquid nitrogen shall not take place in small enclosed side rooms off labs.
4) Filling of smaller containers, such as Dewars, from bulk storage vessels to be carried out by trained users only, wearing appropriate PPE: dry thermally insulated gloves and face shield.
5) Users of cryogenic materials should be provided with suitable information, instruction and training in hazards, safe use and movement of Dewars and what to do in an emergency. The training should be recorded and should cover:
signs of oxygen deficiency symptoms and how to treat a casualty
what to do if an oxygen depletion alarm sounds
treating frostbite or cold burns
Please refer to BCGA CP30 Safe Use of Liquid Nitrogen Dewars for more information.
6) Cryogenic materials should only be stored and used in containers specifically designed for their use. Thermos flasks are not suitable for liquids as they are not designed for the extreme differences in temperature and can fail, leading to a release of the cryogenic liquid.
7) Where the potential for an asphyxiation hazard is identified in the risk assessment, a calculation of the potential oxygen depletion in the area should be made. The outcome of this calculation will determine if further action is required.
If there is the potential for oxygen levels to fall below 21% vol, the following needs to be considered in accordance with the hierarchy of control:
eliminate hazard − remove cryogenic material from area
minimise hazard − reduce quantity being used
engineered control − improve ventilation in area
administrative control − place oxygen monitor in area with instructions (for levels >19.5% vol only)
Oxygen monitors should only be used as a control measure if there is still a residual risk that levels could fall to 19.5% vol. If there is the potential for lower levels than this, the controls identified on this page need to be revisited. Refer to BCGA guidance note 11.
The University's Safe use of cryogenic materials safety standard describes the arrangements for managing and undertaking works with cryogenic materials safely. This standard is due for review March 2025.