Pollution
Humain
Environnement
Economique

A chlorine gas release occurred at 3:00 p.m. at the water treatment unit of a thermal power station while a sodium hypochlorite tank and its bund wall were being pumped of their contents prior to maintenance work. The driver of the vacuum tanker and an employee were affected by the gas. At the driver’s request, a laboratory technician wearing a respirator stopped the pumping system by turning off the ignition. The firefighters secured the unit and ventilated it until 9:00 p.m.

The chlorine gas was generated when the sodium hypochlorite pumped from the tank mixed with the liquid pumped from the bund wall. The liquid in question came from a mixer located at the sodium hydroxide unloading station; a leak had been repaired on the mixer the previous month. The acid flowed onto the sodium hydroxide unloading station and into the gutter connecting it to the bund wall.

Following the accident, the operator looked into replacing the plastic strip curtains between the acid mixer and the sodium hydroxide unloading station with a solid type of separation. He changed its procedures by recommending separate pumping of the tanks and basins and required that products be analysed (pH test) each time before pumping is started. The intervals between bund-wall inspections were shortened and gas detectors were fitted.