Liquid nitrogen

Liquid nitrogen is a colourless, odourless liquid with a temperature of minus 196 °C. Due to its low temperature, skin contact with liquid nitrogen or cooling equipment can cause severe frostbite. Eyes are especially sensitive and must always be protected from splashes.

Nitrogen is an inert gas that is non-toxic and non-combustible. At room temperature, nitrogen gas takes up about 700 times more volume than nitrogen in its liquid state. Spilt liquid nitrogen evaporates rapidly and transitions into gas that is cold and heavier than air, which causes it to spread at floor level. This means that even a relatively small amount of leaked nitrogen in small rooms or poorly ventilated premises can displace oxygen in the air and potentially cause unconsciousness and asphyxiation.

Liquid nitrogen is neither oxidising nor flammable in itself. However, air can condense under certain circumstances if it comes into contact with uninsulated cooled equipment. The air around this equipment will condense and have an elevated oxygen content. Since oxygen has a higher boiling point than nitrogen, this increases the risk for fire if in contact with flammable material.

Handling

When handling and transporting liquid nitrogen, all materials must be specially intended for the purpose – thermos flasks, receptacles, pipes, etc. All materials must be fully functional. The risk assessment should determine what personal protective equipment is required for internal transportation, filling, and handling of liquid nitrogen. Generally, complete protective clothing is required – a protective coat, full-coverage footwear, thermal gloves, and face shields. Closed cryogenic cylinders should be insulated to prevent frost build-up. Closed cryogenic cylinders must be equipped with at least one pressure relief valve.

Storage

Nitrogen cylinders shall be secured to trolleys recommended by the manufacturer or supplier. Only the number of pressurised gas cylinders needed to perform work on-premises or other spaces where work is carried out is allowed.

Transport

Transport of liquid nitrogen cylinders indoors must be done by cart or special trolley that prevents the containers from tipping over.

Signage

All premises where liquid nitrogen is handled must have the following signs:

• warning for liquid nitrogen
• warning for extremely cold
• warning for pressurised cylinders with safety pressure valves and if pressure is more than 2 bar – “Gas cylinders should be moved in the case of fire”