A lightning strike caused a voltage drop on the power supply of a chlorine-alkali plant using the mercury process.The emergency electrical system was activated, though restoring the external supply voltage in less than 200 ms rendered the entire system inconsistent; some units were operating normally, but all units connected to the emergency devices (including the mercury pump) remained idle. An explosive mix of 500 kg of chlorine and an unknown amount of hydrogen accumulated inside the low-pressure chlorine treatment circuit.

The sodium chlorate production unit had restarted after a maintenance shutdown phase. The mercury cells had been under nitrogen flushing since the beginning of the shutdown to avoid the presence of oxygen (prevention of the risk of explosion of the oxygen/hydrogen mixture). Although the ARIA report (see references) does not mention it, the shutdown probably had been caused by a hydrogen leak signal. Around mid-day a new hydrogen leak was detected on the nozzle of a cell collector which had just been repaired.

Hydrogen leaked and ignited on a cell in the sodium chlorate (NaClO3) workshop of a chlorinated products plant.There were no victims and no damage to the environment. On-site firefighters controlled the start of the fire in 10 minutes.

Hydrogen fire at a chlorine chemical production plant (Seveso-classified)Hydrogen ignited in a chlorine electrolyzer unit. The facility was shutdown. The staff of the unit, present on site, triggered the fire alarm and put the installations in a safe state. The fire was extinguished after the start of the intervention of the internal fire brigade.According to the ARIA report (see reference), a variation in electrolyzer pressure was caused by the shutdown of a tank due to the malfunction of its level detection gauge.

Hydrogen explosion at a chlorine chemical production plant (Seveso-classified) The plant had been shut down for two weeks, and maintenance works were ongoing. Two subcontractor employees were cutting a purge pipe on a hydrogen manifold in the chlorine electrolysis room while a manufacturing operator was purging the brine circuit (brine is used as a raw material in chlorine production).

Fire in chemical plant (Seveso-classified)The fire developed at the top of the flare stack of a during a violent thunderstorm.The flare stack is used to discharge hydrogen produced by the restarting of chlorine electrolysis cells. The fire was ignited despite steam and nitrogen had specifically were injected to prevent it from occurring. The sites firefighters cooled the flare stack while the technicians turned off the electrolysis cells to cut off the hydrogen feeding the flames.

The fire started in a electrolysis cell. The fire originated from a hydrogen leak in the hydrogen over pressure control system of the cell and an unidentified ignition source. The ARIA report (sew references) calls this control system a "hydrogen guard". The hydrogen leak comes from a lack of water in the guard due to the lack of filling of the guards by the operators and their flushing.The flushing of the hydrogen through the guard was caused by the rise in pressure of the hydrogen line due to the activation of the chlorine burner.

First an explosion and then a fire occurred on the condensate piping of an chlorine electrolysis plant (SEVESO upper tiers). Flames escape from the end of the pipe and spill into a 75 m open sky tank, containing the electrolysis products (water, HCL, NaOH, Na). According to the ARIA report, (see source) a maintenance operation was ongoing on the HCl furnace located nearby. Investigations conducted by the operator identified a design defect as the cause of the incident. The overflow of the guard hydrogen hydraulic system was wrongly connected to the condensate piping.

The pressure vessel in a chlorine separation system exploded after the corrosion of the steel process equipment allowed chlorine and hydrogen to mix and form a volatile mixture. The chlorine receiving tank ruptured violently into five pieces (three large ones and two smaller) causing considerable damage to nearby equipment. The appearance of the pieces confirmed that a the tank had failed by a rapid brittle fracture. The large size of the pieces and the degree of external damage implied a vapour-phase explosion rather than a more energetic liquid-explosion.

The fire occurred around 13:20 on three cells of the chlorine manufacturing unit. A leak of hydrogen in the electrolysis room was at the origin of the fire; the ignition of the H2 cloud caused a noticeable noise outside the site.The emergency plan was initiated; the gas alert resulted in the confinement of personnel located in the area of the site concerned.