500 kg de Cl2 leaked from a scrubber of a chemical plant producing chlorine and its derivatives for 1 hour. The plant has three interconnected substations lowering the voltage from 63 to 5 KV; 2 of them are supplied by a substation based in the town, one of them by an electric line (L1), the second by 2 electric lines (L2 & L3). The third substation is connected to the thermal station of the site. At 2.55 pm, a serious fault on substation P1 caused several circuit-breakers to trip in the other substations of the site as well as on substation P1 itself. Since it was not possible to determine the origin of the fault from the control room of the thermal station, the technicians performed opening and closing operations on the lines which in turn caused the gas turbines supplying power to the plant to stop. At 3.12 pm, line L3 was re-commissioned and the power supply restored on substations 2 and 3 but not on substation P1 supplied by line L1 that was open before the incident. Since the fault was still not identified, a test was carried out to close line L4 supplying substation P1 from the substation P2. A new fault between the phases of the bus of substation P1 shuts down line L3 again. The technicians, once informed, went to substation P1 where they found out that one of the voltage transformers that measured the voltage change on the line 63 KV was destroyed with the transformer oil still burning. The substation P1 was totally isolated. The power supply was restored in the site at 3.47 pm.
During a general power failure, the equipment was secured and the eight diesel generator sets were automatically started to supply only the equipment required to stop the units. Even if seven of them started normally including one manually, the eighth supplying the Cl2 production unit and three other units stopped two seconds at the latest since the fuse had blown. Overpressure in the upstream circuits containing liquefied Cl2 lifted the frangible roof of the scourer and also damaged a joint on an ammonia pipeline in a desalting unit. The released NH3 and Cl2 formed ammonium chloride that helped see the toxic cloud rise 1,000 m high and drift 10 km away before being dispersed by the favourable weather conditions. Two technicians involved were slightly poisoned by the fumes.