Storage of Liquid Nitrogen
The following information is provided to assist Departments in the identification of suitable
liquid nitrogen storage areas and the subsequent management of those areas.
Liquid Nitrogen Storage Areas
Areas where liquid nitrogen is 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. An oxygen depletion calculator is provided. To use it
you will need to know the width, height (exclude space over 2.4m) and length of the liquid
nitrogen storage area and the volume of liquid nitrogen contained in the vessel. 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.
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.
Oxygen Depletion Monitoring
Where an O2 depletion monitor is in use it must be re-calibrated, serviced and a replacement
battery fitted according to the manufacturers instructions. The monitor should be fitted near
to the liquid nitrogen vessel(s) approximately eighteen inches from the floor. The monitor
alarm should be audible in adjacent areas. A remote sounder can be mounted outside the
door to warn of the danger inside. Remote sounders can be purchased with digital readouts
indicating actual oxygen concentrations.
A log should be kept of all occasions when the alarm sounds. If the monitor alarm sounds
frequently during routine operations DO NOT SWITCH IT OFF. Review the system of work
and the siting of the monitor.
Signs
All vessels containing liquid nitrogen and rooms used for the storage of liquid nitrogen must
be signed to indicate the hazard. If an oxygen depletion monitor is installed then a sign on
the door to the storage area must state “Do not enter while alarm is sounding” and a contact
name provided if it sounds out of hours.
Authorised Users
Only authorised personnel should have access to areas where liquid nitrogen is stored.
Access by maintenance and cleaning staff must be controlled.
UCL Safety Services
Emergency Procedures
Emergency procedures must be prepared and suitable training given for all those involved
who might have a part to play in an emergency.
The following must be considered when preparing your procedures.
Ensure that staff are aware of the action to take if:
• the oxygen depletion alarm is heard;
• the fire alarm sounds while working with liquid nitrogen i.e. a procedure to make it 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;
Handling Liquid Nitrogen
The following are some of the risks associated with the handling of liquid nitrogen 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.
Personal Protective Equipment (PPE)
The minimum PPE required is non-absorbent leather gloves (EN511) and eye protection, but
consideration must also be given to other areas of the body which may be exposed to
splashes. PPE must be inspected regularly for damage and replaced periodically. Gloves are
especially prone to deterioration when subjected to repeated splashing from liquid nitrogen.
N.B. Gloves supplied for cryogenic liquid use must not be immersed.
Transporting Liquid Nitrogen in Lifts
If lift transportation is unavoidable, 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. Then, by
means of the security control system, the lift must be sent directly to its destination floor with
no intermediary stops. Members of staff must not travel in the lift with the container and no
other person must be allowed to 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.
Safety Services Reference(s):
Storage of Liquid Nitrogen
First Published
Reviewed
UCL Safety Services
September 2001
August 2004