Fire from a flange with a wrong seal at a solvent manufacturing plant

The hydrogen fire occurred at a solvent manufacturing plant. Hydrogen leaked from a flange of a hydrogen supply pipe and ignited inside the thermal insulation around the pipe. This first fire was relatively small, but it damaged the gasket of another flange with which the first flange shared the thermal insulation, causing a much larger hydrogen release which contributed spreading the fire.

The reason for the first leak was a gasket with the wrong size. The gasket was regularly replaced, during the periodic maintenances exchanging catalyst. The last time, a smaller than the standard one was installed. It could not withstand the hydrogen pressure during the operation.

Damage was limited only to the initiating area of the fire, thanks to the a timely intervention which replaced hydrogen with nitrogen in the pipe.

The INITIATING/direct cause was a mistake during maintenance, which brought to install the wrong flange gasket.
This could be attributed to human error or shortcoming in the management of the periodic turnaround shutdowns, specifically the material- and parts-handling management.

gaskets, thermal insulation, fhanges

The operation was ongoing as expected, the leakage was the effect of a mistake occurred at the previous turnaround shutdown.

Damage was limited only to the immediate area of the fire

15:00 - A loud abnormal noise coming from the isomerisation unit was heard by the personnel working near that unit. Having identified the in the compressor the cause of the noise, they tried to stop it via the emergency shut-off switch.
In the control room the emergency shut-down procedure was activated, triggering the a rapid depressurisation by blowing down the system.
Immediately afterwards a violent release of a hydrogen rich gas mixture occurred from the compressor bottom, the jet ignited almost instantly and hit the adjoining part of the benzene saturation unit.
The refinery personnel closed the manual valves installed on the pipe mains and started to extinguish the fire, activating the fixed cooling systems and the foaming system of the units involved and nearby units.
15:03 - the onsite Emergency Control Centre team gathered and established communication with the Advanced Control Centre.
15:12 - Off-site fire brigade alerted. Meanwhile the on-site emergency response team fought the fire with a fixed and mobile extinguishing units from all sides.
15:16 - Emergency shut-down procedure started for the entire establishment.
15:30 - First off-site fire brigade team on-site, supporting response operations.
15:50 The size of the fire greatly reduced by because the compression section of the plant no longer fed the fire; fire continued in the benzene unit engulfing it with flames.
16:25 the fire almost extinguished; cooling operations continued.
16:50 the emergency called off.

The accident could have caused more severe damage without the adoption of effective response measures and the joint effort of the on-site personnel and the off-site fire brigades; even if the on-site emergency response organisation could be improved.

(i) In case of fires fed by a considerable amount of hydrogen, it is crucial for a successful fire-fighting to be able to stop the leak. Otherwise, mitigating measures from outside risk to have limited effect.
(ii) As in the case of event 038, the affected flange passed the leak test. This test is too short and not executed under the same conditions experienced by the flange during operation.
(iii) Thermal insulations around pipes hinders the early discovery of damages or leaks.

(1) To prevent the use of the wrong gaskets, the management of the maintenance and turnaround shutdown procedures was improved.
(2) To detect a gas leak inside thermal insulation, inspection windows were installed on thermal insulation and the gas leak checks were strengthened.
(3) The flange construction itself was improved.