On the night of December 2, 1984, at about 9:30 p.m., a large quantity of water entered a storage tank containing over 40 tons of MIC during routine maintenance work at the plant.
This triggered off a reaction, resulting in tremendous increase in temperature and pressure inside the tank. 40 tons of MIC along with Hydrogen Cyanide and other reaction products burst past the ruptured disc into the night air of Bhopal at around 12:30 a.m. Safety systems were grossly under-designed and inoperative. Senior factory officials knew about the lethal build up in the tank at least one hour before the leakage
