M6/11: Liquid Nitrogen - Bulk Storage
Following two recent incidents involving the bulk storage and use of liquid nitrogen, those departments who have such storage are asked to review their risk assessments and procedures.
The first incident involved the release of up to 1200 litres of liquid nitrogen into a laboratory from an external bulk tank. The cause of the incident is still to be determined, but the initial investigation highlighted the following issues:
- There was no clear understanding of how to isolate the supply from outside the room, or a clear appreciation of danger, as someone entered the laboratory during the incident to isolate the system.
- The external solenoid valve did not close as designed after activation of the oxygen alarm, hence the bulk tank continued to supply liquid nitrogen into the room.
The second incident involved the loss of a small amount of liquid nitrogen into a room from an external supply vessel. The supply vessel had been emptied, but the manual valve had been left open inside the building. The supply vessel itself was connected to a bulk storage tank that automatically filled at a set time. Once the supply vessel refilled, it started pumping liquid nitrogen into the building.
The use of liquid nitrogen is outlined within University policy statement S4/03:
In light of these incidents, departments must:
- Review their risk assessments to identify all foreseeable circumstances that could lead to a loss of liquid nitrogen.
- Calculate the affect that this loss would have on the oxygen concentration inside rooms. The policy explains how to conduct these calculations or departments may wish to utilise the many web-based programs that exist e.g.: http://www.nottingham.ac.uk/safety/calc_cryo.htm
- Ensure all relevant control measures are in place e.g. oxygen alarms, extraction systems, and isolation of bulk contents. The Safety Office should be consulted if there is any doubt as to their adequacy.
- Clarify the emergency procedures to be used following a potential oxygen concentration drop of below 18%, including the means of isolating the liquid nitrogen supply from outside the room. The procedure for dealing with emergencies must be documented, and communicated clearly and explicitly to all concerned.
- Make sure that all relevant safety controls are routinely tested and suitable records maintained (e.g. for oxygen sensors, audible/visual alarms, extraction systems, external solenoid isolation, and relief valves). If service agreements are in place, they should be checked to ensure all safety components are covered.
- The bulk tank and supply lines may also come under the Pressure Systems Safety Regulations 2000 (UPS S7/00). Departments should check with their suppliers to what extent examination schemes and inspections are required, and ensure that any requirements are met.
If you have any questions or require further information, please contact the University Safety Office.