Lightning striking the stake of a chemical plant

A lightning strike ignited the hydrogen exiting a stack in a chemical factory. The hydrogen, produced by the chlorine electrolysis cells, was conveyed to the stack when the manufacturing unit using it was shut down.
The internal emergency plan was activated. The electrolysis production chain was put into minimal operation mode. Nitrogen and steam were injected into the stack, which was kept cooled by in-house first responders. The situation was brought under control at 40 minutes later. The emergency plan was lifted and chlorine production resumed at its usual pace.

Following a previous similar accident (ARIA database number 44133), the plant had set up a preventive procedure in the event of a thunderstorm hazard, including a storm alert subscription and preventive injection of steam into the stack to dilute the hydrogen and increase the energy needed to ignite it. However, the system was not active at this time of year (storms were traditionally rarer during the winter).

As the accident had already occurred once before (ARIA database number 44133), a preventive procedure in the event of a thunderstorm hazard had been set up (including a Storm Alert subscription and preventive injection of steam into the stack to dilute the hydrogen and increase the energy needed to ignite it), but the system was not active at this time of year (storms were traditionally rarer during the winter).

hydrogen stack, chlorine electrolyser

Abnormal conditions due to lightning. Similar events had laready taken place 6 and 1 year before this one.

THE ROLE OF HYDROGEN
The hydrogen is a byproduct of the chlorine electrolyser cells. Apparently, i ntis plant, it was usedina non-further specified manufacturing workshop. when the workshop was not in function, the hydrogen was conveyed to the stack as waste product.

The electrolysis chain was put into minimal operation mode.

The internal emergency plan was activated. The electrolysis chain was put into minimal operation mode. Nitrogen and steam were injected into the stack, which was cooled by in-house first responders. The situation was brought under control at 10:30 a.m. The emergency plan was lifted and chlorine production resumed at its usual pace

The accident had already occurred twice before. After the first occurrence, various corrective measures had been adopted, among which:
(1) a storm alert subscription, to be informed of increased hazard from lightnings.
(2) preventive injection of steam into the stack to dilute the hydrogen and increase the energy needed to ignite it).
Second occurrence (HIAD_931) made clear that dilution does not bring (always) the hydrogen concentration below the flammability threshold.

In this more recent incident, the “alarm & dilution” system was not active at the time of year when this second incident occurred, because storms were traditionally rarer during the winter.