Liquid nitrogen is inert, colourless, odourless, noncorrosive, nonflammable, and extremely cold.
Why this substance is hazardous
- Asphyxiation from the release of nitrogen either as a liquid or a gas reducing the oxygen content in the air.
- Freeze burns from spilled liquid nitrogen that leaves the dewar or the equipment, for example when retrieving samples.
- Pressure explosion of cryopreservation (cryo) vials caused by trapped liquid nitrogen rapidly heating inside the vial and changing state from liquid to gas.
- It has the potential to condense oxygen from the atmosphere to form liquid oxygen so increasing the risk of fire and explosion
Liquid nitrogen’s volume expands by 1: 700 from liquid to gas at room temperature. This results in the explosive qualities that nitrogen demonstrates in vials and other containers, that is not immediately recognisable from reading the Safety Data Sheets (SDS). Explosions are caused when liquid nitrogen is trapped in the sample vials at any part of the cryopreservation process. The explosion causes shrapnel and contents to be sprayed from the vial, which can cause injury and contamination.
- Liquid nitrogen is the commonest material to preserve biological samples at a temperature that stops biological processes.
- As part of the system to maintain superconducting magnets nuclear magnetic resonance spectroscopy (NMR) and magnetic resonance imaging (MRI).
Recommended Control Measures
- Store in well-ventilated areas, if indoors have oxygen alarms to warn of low oxygen levels.
- Have procedures in place to minimise the risks from lone working.
- When decanting liquid nitrogen from a pressurised dewar, always use a transfer dewar, which will reduce spills by controlling the rate of supply to a small transportable dewar.
- Never travel in lifts or use nitrogen in a small space. A small volume of liquid can evaporate to a 700 fold volume of gas that can displace oxygen to cause asphyxiation and death. Many scientists have died from nitrogen asphyxiation.
- Properly induct and train new users - use the Local Induction for liquid nitrogen checklist.
- For cryostores, keep cryogenically preserved samples at low temperature and only handle as necessary. If handling a number of samples or raising samples to room temperature, do this as slowly as possible and place samples in a secondary container to contain the contents if an explosion occurs. Remember that even heat through gloves when holding samples in your hand will increase the rate of expansion within the vial.
- Elimination of cryo-storage is sometimes possible with the use of freezers, however there are costs associated with other methods (such as power) and the risk associated if there is a power failure
Personal Protective Equiment (PPE)
- As much skin as possible should be covered (lab coats with elastic cuffs and shoes that cover the top of the foot). Gloves should be worn due to the risk of samples being splashed on the skin, and to prevent cold burns. The type of glove needs to be assessed for the task being carried out.
- Eye protection needs to worn and the type of protection will depend on the task being done.
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Last updated: Tuesday, June 23, 2020