What are cryogens?
Several cryogens are commonly used within the University:
- Liquid nitrogen and argon are colourless, odourless liquids used in many laboratory processes e.g. freezing samples for storage. Because of their extremely low temperature they are stored in specialized dewar (vacuum) flasks, which are vented to the atmosphere to release gas
- Dry ice (solid carbon dioxide) is an opaque, white solid with an extremely low temperature (-78.4ºC). The solid sublimes to form colourless, slightly acidic asphyxiant gas, which is heavier than air. Dry ice is used for short-term cryopreservation of biological samples prior to long-term cryogenic storage or during transit.
- Liquid helium, because of its low boiling point, is used in many cryogenic systems when temperatures below the boiling point of nitrogen are needed. A convenient way to cool many kinds of apparatus is to submerge them in liquid helium. Due to its extremely low temperature, it is stored in specialized dewar (vacuum) flasks, which are vented to the atmosphere to release gas.
Assessing the risks of cryogens
- Ventilation: Cryogens can cause asphyxiation by displacing oxygen (O2) from the air. They are stored are handled in well ventilated areas containing O2 depletion monitors because relatively small amounts of solid will sublimate to form large volumes of gas.
- Temperature: Dry ice pellets should be stored at -80ºC. The extreme temperatures of the cryogens will cause severe burns when in contact with the skin or eyes.
- Storage vessels: Dry ice pellets must not be stored in a sealed vessel such as a screwtop tube. The tube may explode due to gas build up or pop open violently during thawing after being stored at cryogenic temperatures.
- Disposal: Dry ice pellets must never be poured down sinks as they will damage pipework and may result in trap explosion due to gas build up.
If an alarm sounds
What to do if an oxygen-depletion alarm sounds:
- Evacuate and secure the area
- Find a member of staff and tell them there is an alarm sounding
- Wait for the all clear before re-entering the area
Any work involving a cryogen must be covered by a current risk assessment that considers the physical risks such as burns, asphyxiation, manual handling, transport, air distillation and explosive atmospheres around cold pipework.
Cryogens must only be purchased by authorised persons via the University's purchasing system.
You must not travel in the lift at the same time as a cryogen. If there is a spill, it could result in asphyxiation of the lift occupants.
Cryogens must not be transported in vehicles unless suitably modified. Any vehicle used for transportation must have been assessed for suitability with a comprehensive risk assessment produced to cover transportation, including maximum permitted volumes.
PPE, including loose-fitting, insulated gloves and a face visor with a chin guard must be worn whilst handling any cryogens.
Due to their cold temperature, direct contact with the skin or eyes can result in severe burns.
Cryogens must never be poured down the sink or on the floor. This could result in severe damage to floor coverings and pipework.
Excess liquid or solid should be left in the appropriate container to evaporate off in a well ventilated area.