Bhopal disaster

On December 3, 1984, at least 27 tons of methyl isocyanate gas leaked from a pesticide plant in Bhopal (23°17’ North, 77°28’ East), in the state of Madhya Pradesh, India, immediately killing at least 3,800 people and causing significant morbidity and premature death for many thousands more.

The Bhopal plant was owned and operated by Union Carbide India, Limited (UCIL), an Indian company in which Union Carbide Corporation (UCC) held just over half the stock. The company involved in what became the worst industrial accident in history immediately tried to dissociate itself from legal responsibility. Eventually it reached a settlement with the Indian Government through mediation of that country's Supreme Court and accepted moral responsibility. It paid $470 million in compensation, a relatively small amount based on significant underestimations of the long-term health consequences of exposure and the number of people exposed.

The Bhopal disaster indicated a need for enforceable international standards for environmental safety, preventative strategies to avoid similar accidents and industrial disaster preparedness.

The Accident

During the early morning hours of December 3, 1984, methyl isocyanate (MIC), a reactive and toxic gas, leaked from a storage tank in the Union Carbide plant when water was introduced into the storage tank creating a chemical reaction. This reaction generated a substantial increase in the temperature of liquid inside the tank, building pressure and venting off a large volume of toxic gas. Safety systems, such as a flare stack (for the burning of excess gas), a caustic soda scrubber (for neutralization) and a refrigeration unit for cooling, did not contain the reaction. More than 27 tons of the gas had escaped into the air, spreading approximately eight kilometers downwind, over the city of nearly 900,000.

Prevailing atmospheric conditions such as an inversion aloft and a low wind speed prevented dispersion of the gas. Eyewitnesses reported that a cloud of gas enveloped the area and moved slowly through the residential neighborhood of Bhopal. The MIC concentration was estimated to be about 27 parts per million (ppm), or about 1,350 times that of the 0.02 ppm set by the U.S. Occupational Safety and Health Administration (OSHA) as their Permissible Exposure Limit (PEL) as well as by the National Institute for Occupational Safety and Health (NIOSH) as their Recommended Exposure Limit (REL).

The acute irritant effects of MIC created panic, anxiety, and disorientation, and it caused people to run out of their homes into the gas cloud, the result of which was an increased dose of the chemical. Variability in human exposure, therefore, was likely to have resulted related to the distance of the residence from the plant, duration of exposure, and activity during exposure.

Health Effects

Of the more than 200,000 persons exposed to the gas, the death toll one week following the accident exceeded 2,500. In November 1989, the Department of Relief and Rehabilitation, Government of Madhya Pradesh, placed the death toll at 3,598, and by 1994 the toll was estimated at 6,000+. Some uncertainty exists regarding the number of deaths because a portion of the population left the city after the accident and never returned. Independent agencies estimate that the number of disaster-related deaths is currently between 15,000 and 20,000. Pulmonary edema was the probable cause of death in most cases, with many deaths resulting from secondary respiratory infections. Chronic inflammatory damage to the eyes and lungs appears to be the main cause of morbidity.