This information sheet provides advice for developing, maintaining and implementing local safe work practices for staff, students, contractors and visitors working or studying at the university who are required to use liquid nitrogen. Liquid nitrogen is commonly used across Monash University for the purposes of snap-freezing and long-term storage of biological samples and in cold traps on vacuum lines/equipment
1. What is liquid nitrogen?
LN2 (liquid nitrogen) is a cryogenic liquid and is the liquefied form of nitrogen gas at atmospheric pressure and subzero temperature. Its properties are listed in the following table.
Dangerous goods class
Boiling point (°C)
Colour of gas
Odour of gas
Taste of gas
Gas density (27°C air = 1·18g/L)
2. Hazards associated with Liquid Nitrogen
When LN2 boils it produces gaseous nitrogen, which displaces oxygen from the air. This results in an oxygen-deficient atmosphere, particularly if vented into a closed space, and asphyxia can result.
The health effects of diminished oxygen in the environment can be acute and the impact severe as detailed below.
O2 > 19·5%
14% < O2 ≤ 19·5%
Diminution of physical and intellectual performance without person's knowledge
O2 ≤ 14%
Fainting, unconsciousness, death depending on level and duration without adequate oxygen
Due to its extremely low temperature, the cold vapour and gas that are produced when LN2 boils can give rise to cold burns or frostbite upon contact with unprotected skin. Exposure may also produce discomfort in breathing and can provoke an asthma attack in susceptible individuals.
Fire in oxygen-enriched atmosphere
LN2 can condense oxygen from the atmosphere. Liquid oxygen creates potentially flammable or explosive conditions by greatly increasing the combustibility of many materials (e.g. solvents, hydrocarbons).
Pressure build-up/Ice plug formation
Due to the large expansion ratio (liquid to gas), if LN2 is evaporating within a closed system, the pressure can build up with a high risk of explosion. Ice plugs can form on the neck of narrow storage vessels if there is no relief vent, as water is readily condensed by LN2 to form ice. This will lead to pressure build up in the storage vessel.
3. First aid
In no circumstances is it considered safe to enter an oxygen-deprived environment for the purposes of patient rescue.
4. Risk management & safe work practices
Risk assessments must be completed by each department/school/centre where LN2 is handled and stored using the Risk management program (pdf 385kb), the information detailed in the Material Safety Data Sheet (MSDS) and that which is detailed below. It is important to consider the task being performed and the quantities of LN2 used in order to select the most appropriate control measures. Safe work instructions must then be developed and control measures implemented and followed.
The control measures required in facilities used for using and/or storing LN2 differ depending on the lowest likely oxygen level.
likely oxygen level
O2 > 19·5%
14% < O2 ≤ 19·5%
In addition to the basic requirements:
O2 ≤ 14%
All of the above controls required, plus:
Dewars and storage vessels
- Storage vessels are classed as pressure vessels and must meet the requirements of AS2030.4 They have an internal volume capacity of ≥ 50L and are used for bulk storage. In most cases, these are leased from the supplier and it is their responsibility to maintain the storage vessels in accordance with the standard.
- Dewars are portable, double walled containers that are open-necked, free-venting and non-pressurised. Only dewars that meet AS 1894 should be used and a regular physical inspection should be carried out to check the external surface integrity.
Transport and filling operations
- Containers that meet the requirements of AS 1894 must be used when handling small volumes of LN2 for use in the laboratory, e.g. for snap freezing of samples. Domestic thermo flasks are not appropriate for this purpose, as they are not designed to be free-venting and can result in pressure build-up and a subsequent explosion.
- Only appropriately trained personnel should perform LN2 filling and transferring tasks. Controls to minimise the likelihood of splashes as well as exposure to escaping liquid/gases must be in place, e.g. using LN2 pumps and ensuring there is adequate ventilation.
- Appropriate trolleys must be used for transporting dewars between buildings to ensure that the dewar is secure at all times.
- Dewars must never be accompanied in lifts due to the risk of asphyxiation. In areas where dewars need to be transported between floors via lift, a clear procedure must be in place and available to all staff. Where possible, access to intervening floors should be locked out or the lift must be clearly sign-posted whilst LN2 dewars are in transit with a trained member of staff receiving the dewar at the final destination.
- For transport between different locations, dewars must be firmly secured in an open truck, utility or trailer. Alternatively, a cryoporter or dry shipper can be used and these are also suitable when samples need to be mailed.
In addition to the engineering and administrative controls outlined above, appropriate Personal Protective Equipment (PPE) must be selected and used, based on the principle that it should prevent LN2 from touching the skin and eyes.
- Thermo-insulated gloves (elbow length and loose fitting).
- Safety glasses/full face shield.
- Long sleeve lab coat.
- Apron/Long pants.
- Fully enclosed footwear.
- Australian Dangerous Goods Code for the transport of Dangerous Goods, version 7.
- AS 1894 (1997): The storage and handling of non-flammable cryogenic & refrigerated liquids.
- AS 2030.4 (1985): The verification, filling, inspection, testing and maintenance of cylinders for the storage & transport of compressed gases.
- Using chemicals at Monash (pdf 95kb).
6. Further information
For further information, contact your local OHS Consultant or Occupational Health and Safety:
- telephone: 990 51016
- e-mail: email@example.com