On 28th August 1992, there was a catastrophic failure of a storage tank
containing liquefied nitrogen. The failure resulted in the collapse of
almost half of the manufacturing site and damage to houses and vehicles
within a 400 metre radius. Fragments of the vessel were projected up to 350
metres, the largest of which, a section of the outer shell head was 1.5
metres wide and 8mm thick.
The tank was a double-walled vacuum-insulated ultra-low temperature
storage vessel designed to operate at -196°C and 9.3 bar (maximum normal
operating pressure).
The inner vessel broke into seven fragments and the outer vessel broke
into eleven main fragments and numerous smaller pieces. It was discovered
during the course of the investigation that most of the valves on the system
were closed including the top liquid inlet, liquid outlet and the isolation
valves for the relief valve and bursting disc. The vessel was therefore
under completely closed conditions at the time of the accident. The bursting
disc was found to be ruptured despite the closed inlet valve, however it was
believed that the valve might have been closed after the disc ruptured on a
previous occasion. The inner and outer shells ruptured as a result of
excessive pressure under closed conditions. It was estimated that the inner
shell ruptured at a pressure of 68.7 bar. The pressure reached this level as
a result of heat inflow over the sixty days between its final filling and
the time of the explosion.
Failures in technical measures
- Isolation valves were fitted below both relief devices without any
interlocking system to ensure that one device was always protecting the
vessel.
- Relief Systems / Vent Systems:
relief valves, bursting discs
- There were no manuals for the operation of the nitrogen vessel. The
daily inspections required on the vessel were largely neglected and no
safety instructions were given to employees.
- Training: operator training
- Operating Procedures: provision of
comprehensive operating procedures
Source: https://www.hse.gov.uk/comah/sragtech/caseliqnitro92.htm