Cryogenic substances

A variety of gases may become liquid under particular conditions of low temperature and high pressure. Several of these are commonly used across the University.  Storage and use of these creates risks associated with;

  • the extremely low temperatures involved
  • the pressures that can be generated by the change of state back to gas
  • the risk of asphxiation through release of liquid, or gas, and displacemnt of oxygen

The very low temperatures create a risk of cold burns and may also change the properties of other materials that the cryogenic liquid comes into contact with.  High rates of expansion as the liquid changes state back to a gas can cause potential for pressure build up and subsequent explosion.  The fundamental properties of the material (e.g. flammability, oxidiser) must also be borne in mind. 

Accidental release combined with a high expansion rate can also create a very serious risk of asphyxiation due to displacement of air from a work room.   (1 litre of liquid nitrogen = 750 litres of nitrogen gas!) Manual handling of storage vessels can also create risks to workers.

The most commonly used cryogenic material within the University is liquid nitrogen. However, helium is also used and a range of other cryogenic gases, including liquid oxygen, may also be found.   All units who handle these materials must ensure that risk assessments have been carried out to identify and manage all of the foreseeable risks that may arise from the storage and handling of these materials.

Installation of oxygen monitoring equipment is likely to be required in many situations where these substances are stored and used.  Advice on this is available from SEPS. 

It is important that anyone who uses cryogenic materials has received suitable safety training and is provided with appropriate personal protective equipment. 

Correct emergency action is critically important in any situation where potential asphyxiation risks might arise. Particular attention must be paid to minimising this risk and ensuring that correct action will be taken by staff should it occur. All users should be trained to fully understand the risks of the materials being used and, in particular, the risk of asphyxiation and that they MUST NOT enter are area in which a low oxygen alarm is sounding unless they have first verified by a suitable procedure and measurements that the area is safe to enter.

Click link to access SEPS guidance on Liquid Nitrogen

The British Compressed Gases Association(BCGA) publish a number of Codes of Practice on installation and use of croygenic facilities. these provide 'industry standard'  guidance and can be accessed via BCGA link in the 'Useful Links' section.