This page provides guidance when working with cryogenic substances, such as liquid nitrogen, at UCL.
On this page
- What are cryogenic substances?
- Handling cryogenic substances
- Storage of cryogenic substances
- Personal Protective Equipment (PPE)
- Transporting cryogenic substances
What are cryogenic substances?
Some of the hazards of working with cryogenic substances are:
- Extreme cold
- Oxygen depletion (nitrogen, carbon dioxide, helium and argon)
- Aids combustion (liquid oxygen only)
The potential for harm from these hazards can lead to:
- Skin burns
- Embrittlement of materials
- Asphyxiation (small amounts of liquid can expand into very large volumes of gas).
The Laboratory Manager or relevant Department Safety Officer (DSO) shall ensure that cryogenic liquids are properly managed and disposed of in their area of responsibility.
Training for applicable personnel shall occur before working with cryogenic liquids and when any significant changes are made. Records of training are to be retained by the DSO or Laboratory Manager.
Handling cryogenic substances
The following are some of the risks associated with the handling of cryogenic materials that can lead to oxygen depletion:
- Over-filling of the receiving vessel from a pressurised container will result in a spill. This can occur due to lack of concentration, distraction or leaving unattended.
- Pouring from a large vessel into another vessel (particularly if the receiving vessel is small) can result in a spill.
- Vessels which are not designed for liquid nitrogen may break and cause a spill.
- Damage to a vessel due to an impact or blow will result in a rapid release of gas and/or liquid.
- Boiling or splashing due to the receiving vessel being "hot" in comparison to the liquid will release gas and or liquid.
These risks must be controlled by the development of a safe system of work, which can be defined as the set of controls necessary to minimise the risks associated with the work.
Storage of cryogenic substances
Areas where cryogenic substances are used and stored, must have adequate ventilation. Adequate means that oxygen levels are maintained at 20.8% concentration during normal storage and handling.
Gas release can occur during storage of liquid nitrogen:
- From open non-pressurised vessels during routine operations.
- Due to the warming of liquid nitrogen vessels. In the case of non-pressurised vessels this occurs naturally through the insulation. In pressurised vessels when the pressure increases the valve opens to relieve the build up and then resets;
- Due to the failure of the pressure relief valve which will rupture the burst disc on pressurised vessels. This will cause a rapid release of gas in a short space of time.
The volume of the storage area in relation to the quantity of gas released will determine the extent to which oxygen will be depleted. You should calculate the oxygen concentration that would result should the full contents of the largest vessel be accidentally released in a short space of time (i.e. worst-case scenario).
If the resultant O2 concentration is greater than 18% then it may not be necessary to install an O2 depletion monitor, however, if it is less than this a monitor is essential.
- Guidance when storing and handling cryogenic substances
- Store dewars/cryogens in a well-ventilated area equipped with an oxygen depletion monitor and alarm to alert of oxygen deficiency.
- Use only storage vessels that have been approved by UCL or the Department.
- Never adjust, block or plug a pressure relief valve. The pressure relief valve shall be inspected before filling the dewar.
- Avoid contact of moisture with storage containers to prevent ice plugs in relief devices.
- Periodically check the dewar/container neck for ice plugs.
- Heat sources must shall be kept away from cryogenic liquids.
- Do not use cryogens of dry ice in walk-in cold rooms, because they may not have sufficient air exchange and could become oxygen deficient.
- Always push dewars if they need to be moved. Never pull on dewars. They are heavy and can tip and injure you. Large dewars can lead to ergonomic injuries (i.e. crushing of hands/feet, back/neck injuries).
N.B. An alarm is not an alternative to the provision of a safe system of work but is an additional control measure, which gives an early warning that something has gone wrong, i.e. a spill or rapid release of liquid nitrogen.
> Further information at Gases - monitors and detectors
Personal Protective Equipment (PPE)
PPE is intended to protect the wearer from accidental contact with cryogenic substances and must never be immersed. For this reason, it should ALWAYS be inspected for damage before it's worn.
Protection should be provided as follows:
- Face shield should be worn to protect the face
- Eye protection
- Gloves with cuffs (EN511 standard)
Transporting cryogenic substances
There is a risk of oxygen depletion in a lift when transporting cryogenic substances. The following steps should be followed to mitigate that risk:
- Avoid transporting by lift wherever possible.
- If lift transportation is the only option, the lift must have a security control system to enable staff to maintain independent control of the lift during the transport operation.
- The container should be placed in the lift by a member of staff at the outset of the operation. By means of the security control system, the lift must be sent directly to its destination floor with no intermediary stops.
- No persons must not travel in the lift with the container.
- A second person should meet the lift at the destination floor and remove the container.
- The lift can then be released from the security control system and returned to normal use.
The following must be considered when preparing procedures to deal with cryogenic substance emergencies.
Ensure that staff are aware of the action to take if:
- The oxygen depletion alarm is heard (i.e. not to enter the area).
- The oxygen depletion alarm sounds while working in the area (i.e. evacuate).
- The fire alarm sounds while working with cryogenic substances (i.e. a procedure to make safe). If it has not been possible to make safe before evacuating the building then the fire brigade must be informed of the risk of oxygen depletion.
- Spills and accidental release of cryogenic substances
In the event of a large spillage or accidental release or whenever the detection monitor sounds, the following procedures should be followed:
- Evacuate the area. Deploy warning signs where necessary.
- Do not enter any area when a monitor is sounding.
- Do not re-enter area unless it is safe to do so. The presence of oxygen deficiency monitors will indicate the oxygen levels in the vicinity.
- Ventilate the area. Open doors and windows or activate forced ventilation to allow any spilt liquid to evaporate and the resultant gas to disperse.
- Try to stop the release if at all possible e.g. turn off valves, but only if it is safe to do so.
Last updated: Tuesday, July 21, 2020
> Gases - compressed
> Gases - monitors and detectors
> BCGA Guidance Note 11: The Management of risk when using gases in enclosed workplaces (pdf)
> BCGA Code Of Practice 30: The Safe use of Liquid Nitrogen Dewars Revision 3: 2019 (pdf)
> BCGA Code Of Practice 36: Cryogenic liquid storage at users premises Revision 2: 2013 (pdf)
> BCGA Code Of Practice CP 27 Transportable vacuum insulated containers of not more than 1,000 Litres Volume (pdf)
> BGCA Code Of Practice 34: The application of the pressure equipment regulations to customers sites Revision 1: 2014 (pdf)
> Care with Cryogenics (BOC pdf)