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Nigel's surgery 86: Storing liquid nitrogen
Liquid nitrogen is widely used for cryotherapy.
Cryotherapy is treatment using low temperature and is used to treat some skin lesions by freezing them. The most common product used is liquid nitrogen.
Providers must carry out a risk assessment to ensure that both staff and members of the public are protected from potential hazards associated with using liquid nitrogen. In our inspections we would consider this under key line of enquiry S1.10 – Do the maintenance and use of equipment keep people safe?
Risks from liquid nitrogen
In any quantity, the extremely low temperature of liquid nitrogen presents a risk – it must be handled carefully. If it touches the skin it can cause cryogenic burns (cold burns).
If it turns to gas, liquid nitrogen can displace the oxygen in a room.
In a small space this can be highly dangerous and lead to suffocation even though an individual still feels that they are breathing.
Small vacuum flask containers of liquid nitrogen – to carry out one day’s worth of cryotherapy – are unlikely to contain enough to displace a significant amount of oxygen in the environment.
Safe storage of liquid nitrogen
Some practices store liquid nitrogen in large vessels and decant it into a treatment flask. These need to be handled with great care:
- Store below 50°C in a well ventilated place.
- Display hazard warning signs (yellow triangle with exclamation symbol and text: ‘Liquid nitrogen’).
- Use properly specified and undamaged storage equipment.
- Keep storage vessels padlocked with the key kept separately.
- Store in a large-enough room (see risk assessments below) or in a cupboard where a person could not also fit inside.
- Protect staff by providing non-absorbent thermal gloves and a suitable face mask or goggles.
The volume of the storage area in relation to the quantity of gas released will determine the extent to which oxygen is depleted. Generally there is a low risk of liquid nitrogen displacing air in the environment while filling a treatment flask.
Risk assessment tools
Assessing ventilation requirements
Appendix 1 of the standard operating procedure – liquid nitrogen (University of Edinburgh) describes:
- The effects of reduced oxygen content in the atmosphere.
- How to assess the likely effect on the percentage of oxygen in a given space.
Safety audit and training
Commercial suppliers can carry-out risk assessments and offer training, for example Liquid Nitrogen from BOC Healthcare, product and service guide.
- Last updated:
- 29 June 2018