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Bhopal disaster
Bhopal-Union Carbide 1 crop memorial.jpg
Memorial by Dutch artist Ruth Kupferschmidt for those killed and disabled by the 1984 toxic gas release
Date2 December 1984 – 3 December 1984
LocationBhopal, Madhya Pradesh, India
Coordinates23°16′51″N 77°24′38″ECoordinates: 23°16′51″N 77°24′38″E
Also known asBhopal gas tragedy
CauseMethyl isocyanate leak from Union Carbide India Limited plant
DeathsAt least 3,787; over 16,000 claimed
Non-fatal injuriesAt least 558,125

The Bhopal disaster, also referred to as the Bhopal gas tragedy, was a gas leak incident on the night of 2–3 December 1984 at the Union Carbide India Limited (UCIL) pesticide plant in Bhopal, Madhya Pradesh, India. It is considered among the world's worst industrial disasters. Over 500,000 people were exposed to methyl isocyanate (MIC) gas. The highly toxic substance made its way into and around the small towns located near the plant.

Estimates vary on the death toll. The official immediate death toll was 2,259. In 2008, the Government of Madhya Pradesh had paid compensation to the family members of 3,787 victims killed in the gas release, and to 574,366 injured victims. A government affidavit in 2006 stated that the leak caused 558,125 injuries, including 38,478 temporary partial injuries and approximately 3,900 severely and permanently disabling injuries. Others estimate that 8,000 died within two weeks, and another 8,000 or more have since died from gas-related diseases. The cause of the disaster remains under debate. The Indian government and local activists argue that slack management and deferred maintenance created a situation where routine pipe maintenance caused a backflow of water into a MIC tank, triggering the disaster. Union Carbide Corporation (UCC) argues that water entered the tank through an act of sabotage.

The owner of the factory, UCIL, was majority owned by UCC, with Indian Government-controlled banks and the Indian public holding a 49.1 percent stake. In 1989, UCC paid $470 million (equivalent to $860 million in 2019) to settle litigation stemming from the disaster. In 1994, UCC sold its stake in UCIL to Eveready Industries India Limited (EIIL), which subsequently merged with McLeod Russel (India) Ltd. Eveready ended clean-up on the site in 1998, when it terminated its 99-year lease and turned over control of the site to the state government of Madhya Pradesh. Dow Chemical Company purchased UCC in 2001, seventeen years after the disaster.

Civil and criminal cases filed in the United States against UCC and Warren Anderson, UCC CEO at the time of the disaster, were dismissed and redirected to Indian courts on multiple occasions between 1986 and 2012, as the US courts focused on UCIL being a standalone entity of India. Civil and criminal cases were also filed in the District Court of Bhopal, India, involving UCC, UCIL and UCC CEO Anderson. In June 2010, seven Indian nationals who were UCIL employees in 1984, including the former UCIL chairman, were convicted in Bhopal of causing death by negligence and sentenced to two years imprisonment and a fine of about $2,000 each, the maximum punishment allowed by Indian law. All were released on bail shortly after the verdict. An eighth former employee was also convicted, but died before the judgement was passed.

Background

The UCIL factory was built in 1969 to produce the pesticide Sevin (UCC's brand name for carbaryl) using methyl isocyanate (MIC) as an intermediate. An MIC production plant was added to the UCIL site in 1979. The chemical process employed in the Bhopal plant had methylamine reacting with phosgene to form MIC, which was then reacted with 1-naphthol to form the final product, carbaryl. Another manufacturer, Bayer, also used this MIC-intermediate process at the chemical plant once owned by UCC at Institute, West Virginia, in the United States.

After the Bhopal plant was built, other manufacturers (including Bayer) produced carbaryl without MIC, though at a greater manufacturing cost. This "route" differed from the MIC-free routes used elsewhere, in which the same raw materials were combined in a different manufacturing order, with phosgene first reacting with naphthol to form a chloroformate ester, which was, in turn, reacted with methylamine. In the early 1980s, the demand for pesticides had fallen, but production continued regardless, leading to an accumulation of stores of unused MIC where that method was used.

Earlier leaks

In 1976, two local trade unions complained of pollution within the plant. In 1981, a worker was accidentally splashed with phosgene as he was carrying out a maintenance job of the plant's pipes. In a panic, he removed his gas mask and inhaled a large amount of toxic phosgene gas, leading to his death 72 hours later. Following these events, journalist Rajkumar Keswani began investigating and published his findings in Bhopal's local paper Rapat, in which he urged "Wake up, people of Bhopal, you are on the edge of a volcano."

In January 1982, a phosgene leak exposed 24 workers, all of whom were admitted to a hospital. None of the workers had been ordered to wear protective equipment. One month later, in February 1982, a MIC leak affected 18 workers. In August 1982, a chemical engineer came into contact with liquid MIC, resulting in burns over 30% of his body. In October 1982, there was another MIC leak. In attempting to stop the leak, the MIC supervisor suffered severe chemical burns and two other workers were severely exposed to the gases. During 1983 and 1984, there were leaks of MIC, chlorine, monomethylamine, phosgene, and carbon tetrachloride, sometimes in combination.

Leakage and its effects

Liquid MIC storage

The Bhopal UCIL facility housed three underground 68,000-litre (~18,000 gals) liquid MIC storage tanks: E610, E611, and E619. In the months leading up to the December leak, liquid MIC production was in progress and being used to fill these tanks. UCC safety regulations specified that no one tank should be filled more than 50% (here, 30 tons) with liquid MIC. Each tank was pressurized with inert nitrogen gas. This pressurization allowed liquid MIC to be pumped out of each tank as needed, and also kept impurities out of the tanks.

In late October 1984, tank E610 lost the ability to effectively contain most of its nitrogen gas pressure, which meant that the liquid MIC contained within could not be pumped out. At the time of this failure, tank E610 contained 42 tons of liquid MIC. Shortly after this failure, MIC production was halted at the Bhopal facility, and parts of the plant were shut down for maintenance. Maintenance included the shutdown of the plant's flare tower so that a corroded pipe could be repaired. With the flare tower still out of service, production of carbaryl was resumed in late November, using MIC stored in the two tanks still in service. An attempt to re-establish pressure in tank E610 on 1 December failed, so the 42 tons of liquid MIC contained within still could not be pumped out of it.

The release