Fire in a process reactor of a metallurgical plant

The event occurred in a classified-Seveso metallurgical plant. A fire initiated in a acid treatment reactor of a workshop handling cementation of indium .
Under normal conditions, the reaction of the process in the tank releases hydrogen.
The fire propagated to the plastic components above the tank, causing black smoke released inside the workshop.

The origin of the fire were sparks produced by the grinding of metal gratings overhanging the tank. According to the ARIA report (see references), they must have come into contact with the gaseous atmosphere of the tank through the throughput of the stirring shaft.
The grinding work had been allowed by an intervention permit and was equipped with protections designed to limit the dispersion of sparks.

INITIATING CAUSE were the sparks generated by grinding, supposed to enter the tank containing hydrogen as reaction product.

The ROOT CAUSE is not reported. Nevertheless, considering that the grinding works were designed to preventing hydrogen ignition, the root cause could be attributed to shortcoming i design of the reactor and of risk-preventing measures.

acid metallurgical treatment reactor

Maintenance works were executed on top of the reactor tank

The inspection of Seveso-classified installations required a detailed inspection of the tank in question and the systematic implementation of thermal camera control of hot spots following a fire

The second responders extinguished the fire after 15 minutes using foamers and cooled the installations. The fire resumed after a few minutes, as some undetected hot spots had remained. The further use of foamers allowed its final extinguishment.

The fact that the inspection required for the future the systematic implementation of thermal camera during firefighting is due to the fact that during the emergency actions, the fire regained strength due to undetected hot spots.

The ARIA report (see references) does not report any lesson learnt. Nevertheless, it may be reasonably assumed that the event would profit from improved maintenance procedure, such as purging of the tank and monitoring hydrogen concentrations in the gaseous phase of tank.