GP mythbuster 86: Storing liquid nitrogen

Liquid nitrogen is widely used for cryotherapy. Cryotherapy is treatment using low temperature. It 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. This is to protect staff and the public from potential hazards of using liquid nitrogen. In our inspections we consider this under key line of enquiry key line of enquiry S1.10 – Do the maintenance and use of equipment keep people safe?

Control of Substances Hazardous to Health (COSHH) regulations 2002 were amended in 2004. They now include nitrogen as a substance hazardous to health.

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. It can lead to suffocation even though an individual still feels that they are breathing

Small vacuum flask containers/vessels (dewars) of liquid nitrogen are used to carry out one day’s worth of cryotherapy. They 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 to decant it into a treatment flask, and 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 or in a cupboard where a person could not also fit inside
• protect staff with 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 determines 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

COSHH Regulation 2 defines Liquid Nitrogen as a substance hazardous to health.

COSHH Regulation 6(1)(a) requires that employers should not carry out work liable to expose employees to substances hazardous to health until all risks have been evaluated and minimised.

You can read more detail about COSHH risk assessments in the general enforcement guidance and advice on the Health and Safety Executive (HSE) website. HSE have also published an approved code of practice to COSHH regulations.

You can find a code of practice for the safe use of liquid nitrogen dewars on the British Compressed Gasses Association website.

Safety audit and training

Commercial suppliers can sometimes carry-out risk assessments and offer training. Please check with your liquid nitrogen provider.