Explosion ina chlor-alkali electrolyser

An internal explosion occurred when restating a chlor-alkali electrolyser.
A power outage caused a lack of power to the electrolytic cells and to the pump supplying the electrolyte to the cells.
In absence of electrolyte flow, a high-temperature gas space formed above the electrolytic cell.
Upon restarting the power supply to the cells, a delay occurred in the re-start of the electrolyte supply pump. Without electrolyte, the ion exchange membranes in the electrolytic cell dried out and shrunk, producing cracks in some of them. This allowed hydrogen gas to mix with the chlorine gas system and to form gas within the explosive range, ignited by a spark.

The INITIATING CAUSE was a loss of power which triggered a series of degradations in the electrolytic cells and eventually the cross-over of hydrogen into the chlorine space.
The power loss had been caused by maintenance to the electrical equipment.
The H2-Cl2 explosive mixture was ignited by sparks generated when an operator increased the electric current.
For unexplained reasons, no gas analysis had been performed before re-starting the normal electrolyser operation. It is unclear if this was a consequence of a human error or a lack of adequate safety instruction. In general, it could be concluded that the risk management of the plant was inadequate and unable to manage unplanned shutdowns.

cylinder, blow-off pipe

One of source reported "Ten nearby residents who suffered coughing from inhaling the chlorine gas were taken to hospital for treatment. ". This is not confirmed by another souce, which mentioned only 1 light injury.