Sometime after midnight on December 2, 1984, water got into a tank full of methyl isocyanate (MIC) at the Union Carbide India plant in Bhopal and started what’s called a runaway reaction. By evening of the next day 3,000 people were dead from the toxic gas cloud that came from the plant. In the weeks that followed nearly 10,000 died as a result of injuries. Somewhere between 40,000 and a half million people were ultimately affected.
The UCI plant was half-owned by Union Carbide U.S. and half by the Indian government. It manufactured the pesticide Sevin. It had no safety procedures like those of its U.S. counterparts, the MIC tank alarms weren’t working, the gas scrubber – which would have removed some contaminants that were being released – hadn’t worked for five months.
The gas cloud that escaped might have contained, besides MIC, hydrogen cyanide, hydrogen chloride, carbon monoxide and phosgene. Scientists can only theorize because UC has never identified the composition of the cloud.
All the available details are here, including this:
The gas cloud was composed mainly of materials denser than the surrounding air, stayed close to the ground and spread outwards through the surrounding community. The initial effects of exposure were coughing, vomiting, severe eye irritation and a feeling of suffocation. People awakened by these symptoms fled away from the plant. Those who ran inhaled more than those who had a vehicle to ride. Owing to their height, children and other people of shorter stature inhaled higher concentrations. Many people were trampled trying to escape…
Doctors and hospitals were not informed of proper treatment methods for MIC gas inhalation. They were told to simply give cough medicine and eye drops to their patients.
It also turned out that the area around the plant had been used to dump chemical waste. In 2004, in connection with an anniversary special on Bhopal, the BBC took a water sample from a public well north of the plant. Tests showed it contained 1000 times the level of carbon tetrachloride that the World Health Organization considers acceptable.
Union Carbide sold its share of the plant to Eveready Industries of India in 1994. Eveready relinquished the site to the government in 1998.
In 2001, Union Carbide was bought by Dow Chemical for $10 billion. UC has always claimed that the incident was caused by employee sabotage.