Réflexion de passé

Around 1 a.m. on Monday, the 3rd of December, 1984, in a densely populated region in the city of Bhopal, Central India, a poisonous vapor burst from the tall stacks of the Union Carbide pesticide plant. This vapor was a highly toxic cloud of methyl isocyanate. Of the 800,000 people living in Bhopal at the time, 2,000 died immediately, and as many as 300,000 were injured. In addition, about 7,000 animals were injured, of which about one thousand were killed.

Possible Causes: The post-accident analysis of the process showed that the accident started when a tank containing methyl isocyanate (MIC) leaked. MIC is an extremely reactive chemical and is used in production of the insecticide carbaryl. It is presumed that the scientific reason for the accident at Bhopal is that water entered the tank where about 40 cubic meters of MIC was stored. When water and MIC mixed, an exothermic chemical reaction started, producing a lot of heat. As a result, the safety valve of the tank burst because of the increase in pressure. This burst was so violent that the coating of concrete around the tank also broke. It is presumed that between 20 and 30 tonnes of MIC were released during the hour that the leak took place. The gas leaked from a 30 m high chimney and this height was not enough to reduce the effects of the discharge. The reason was that the high moisture content (aerosol) in the discharge when evaporating, gave rise to a heavy gas which rapidly sank to the ground. The weather egged on this process. The conditions on the fateful day were typical for a clear night in the region, with a weak wind which frequently changed direction, which in turn helped the gas to cover more area in a shorter period of time (about one hour). The weak wind and the weak vertical turbulence caused a slow dilution of gas and thus allowed the poisonous gas to spread over considerable distances.