Toxic Gas Leaks from a Union Carbide Plant in Bhopal, India Summary

  • Last updated on November 10, 2022

A leak of toxic gas from a pesticide plant in Bhopal, India, caused one of the worst industrial disasters in history.

Summary of Event

In the early morning hours of December 3, 1984, toxic gas leaked from a pesticide plant owned by a subsidiary of Union Carbide Corporation Union Carbide Corporation in Bhopal, India, causing one of the worst industrial disasters in history. As a direct result of the leaking gas, within a few hours thousands of Bhopal residents were dead and tens of thousands were injured or permanently disabled. The escaping gas, methyl isocyanate, spread south from the chemical plant and eventually covered forty square kilometers (about fifteen square miles) of the Bhopal residential area. From the estimated time when the leak began, 12:30 a.m., December 3, until 3:00 a.m., one to two thousand immediate deaths were attributed to the spreading asphyxiating gas. Estimates of the total death toll range from a conservative twenty-five hundred up to ten thousand victims. Determining responsibility for such a tragic industrial accident was a complex, perplexing, and agonizing topic subject to speculation, litigation, and international jurisdiction. Disasters;industrial Bhopal disaster (1984) [kw]Toxic Gas Leaks from a Union Carbide Plant in Bhopal, India (Dec. 3, 1984) [kw]Gas Leaks from a Union Carbide Plant in Bhopal, India, Toxic (Dec. 3, 1984) [kw]Union Carbide Plant in Bhopal, India, Toxic Gas Leaks from a (Dec. 3, 1984) [kw]Bhopal, India, Toxic Gas Leaks from a Union Carbide Plant in (Dec. 3, 1984) [kw]India, Toxic Gas Leaks from a Union Carbide Plant in Bhopal, (Dec. 3, 1984) Disasters;industrial Bhopal disaster (1984) [g]South Asia;Dec. 3, 1984: Toxic Gas Leaks from a Union Carbide Plant in Bhopal, India[05600] [g]India;Dec. 3, 1984: Toxic Gas Leaks from a Union Carbide Plant in Bhopal, India[05600] [c]Disasters;Dec. 3, 1984: Toxic Gas Leaks from a Union Carbide Plant in Bhopal, India[05600] [c]Manufacturing and industry;Dec. 3, 1984: Toxic Gas Leaks from a Union Carbide Plant in Bhopal, India[05600] Anderson, Warren Gandhi, Rajiv

In 1984, Union Carbide Corporation (UCC) had fourteen plants in India, manufacturing chemicals, pesticides, batteries, and other products. Union Carbide’s operations in India were conducted through a subsidiary, Union Carbide India, Ltd. (UCIL). The parent U.S. company (UCC) held 50.9 percent of UCIL stock, with the balance of 49.1 percent owned by various Indian investors. Managerial control of UCIL was exercised by Union Carbide through its Eastern Division, headquartered in Hong Kong.

In 1969, Union Carbide set up a small plant in Bhopal, the capital of the Indian state of Madhya Pradesh, to manufacture a range of pesticides and herbicides derived from a carbaryl base. The process of carbaryl manufacture begins with the reaction of carbon monoxide with chlorine to yield the intermediate phosgene. Phosgene is in turn reacted with monomethylamine to produce methyl isocyanate Methyl isocyanate (MIC), the principal gas involved in the Bhopal tragedy. In the final stage, MIC is reacted with alpha napthol to produce carbaryl, which is used in different concentrations to make various pesticides and herbicides. Until 1989, UCIL imported both MIC and alpha napthol from its parent firm. In 1979, however, the company commissioned its own facility in Bhopal to manufacture MIC. During the planning for production of MIC, UCC decided to build large-scale storage facilities for MIC at Bhopal. As a result, the company built three tanks, each forty feet long and eight feet in diameter, code numbered E610, E611, and E619. Each had a storage capacity of fifteen thousand gallons.

In November, 1984, the Bhopal plant was shut down for a complete maintenance overhaul and a reduction of inventories. On November 26, plant operators were instructed by management to pressurize tank E610, which contained approximately forty-two tons of MIC, in order to transfer some of the chemical for processing. Workers found, however, that despite feeding nitrogen into the tank they could not generate the required pressure to vent MIC. The problem appeared to be a defective valve within the nitrogen system. Instead of correcting the defective valve, management decided to switch over to tank E611, which contained about forty tons of MIC.

One well-documented theory of the disaster was that at 9:30 p.m. on December 2, 1984, workers began washing out four lines downstream of the MIC storage area, all of which were connected to the relief valve vent header (RVVH). The RVVH provided a relief line for toxic gases to be vented to the vent gas scrubber (VGS) in the event that a pressure buildup in any one of the tanks caused a large volume of gas to escape. The system was designed so that if the pressure within the tanks exceeded forty pounds per square inch above atmospheric pressure, it would cause a rupture disk fitted to the end of the RVVH line to give. The gas thus released would force the relief valve to open, allowing the gas to flow down the RVVH directly to the VGS. The VGS was a large, bottle-shaped steel vessel designed to neutralize toxic gas emissions. When gas entered the scrubber, it reacted with caustic soda and was rendered harmless.





A second safety device, the flare tower, was a tall steel structure with a flame constantly burning on top. The line of the VGS to the flare tower allowed gasses that were not completely neutralized to be burned. A second line, called the process vent header (PVH), led from the tanks to the VGS. Connected to this line was the nitrogen pressurization system. MIC, a highly volatile compound, reacts violently with water. To ensure that MIC does not come in contact with moisture in the air, the chemical is stored under pressure and protected by a blanket of dry nitrogen. If the pressure in the tanks falls, nitrogen is fed into the tank. Conversely, if the tank pressure is too high, some of the pressure can be reduced through venting of the nitrogen.

During the second work shift of December 2, 1984, workers continued washing four downstream branches of the RVVH line. The operator started pumping water under high pressure into the line. Bleeders on the lines were not releasing water at the same rate at which it was being pumped in. Apparently two valves were clogged, and the other two were only partly clear. As water was continually pumped, it soon reached the RVVH isolation valve. As the isolation valve could not provide a complete seal on the line, water soon passed the valve and entered the RVVH. Although unable to gain direct access through the RVVH, apparently the water found an alternative route to the tank, through the “jumper” or shunt line connecting the RVVH and the PVH. It has been speculated that approximately 120-240 gallons of water traveled down the jumper into the PVH past the nitrogen outflow valve and into Tank E610, setting off a rapid reaction.

The reaction of MIC with water produced 1,3-dimethyl urea and liberated large quantities of carbon dioxide and heat. Under the extremely high temperatures created, MIC began to react with itself, causing polymerization. Of the forty-two tons of MIC in E610, approximately five tons had been polymerized when the rapid pressure buildup caused the rupture disk to give, releasing a torrent of heated gas down the RVVH and into the VGS. Unfortunately, the VGS was not operational, nor was the flare tower. The gas flowed straight through the scrubber and out into the night. By 3:00 a.m., most of the deadly contents of storage tank E610 had escaped.


Within three hours, the escaping MIC gas covered some forty square kilometers of the metropolitan Bhopal area. The vapor passed first over the shantytowns of Jaiprakash and Chhola, leaving hundreds dead as they slept. Those who awoke did so with a sensation of choking, their eyes and throats stinging. Soon thousands of people were on the roads, gasping for breath and unable to see because of the terrible stinging in their eyes. By the week’s end, an estimated 2,500 people were dead. Others were overcome by nausea and fatigue. It is estimated that 200,000 individuals were directly or indirectly afflicted by the poisonous gas. General symptoms of the affected population included severe chest congestion, vomiting, paralysis, sore throat, chills, coma, fever, swelling of legs, damage to vision, and palpitations.

Demonstrators shout slogans and burn effigies of Indian leaders and former Union Carbide chairman Warren Anderson in Bhopal, India, on the eighteenth anniversary of the 1984 industrial disaster that killed thousands and contaminated the area when methyl isocyanate leaked from a Union Carbide pesticide plant.

(AP/Wide World Photos)

Within hours of the accident, police in Bhopal closed the Union Carbide plant and arrested its manager, J. Mukund, and four of his assistants, charging them with “culpable homicide through negligence.” When a team of five technical experts from Union Carbide’s headquarters in Danbury, Connecticut, arrived to inspect the plant, they were turned away by local authorities. The Indian Central Bureau of Investigation also seized records and logbooks at the plant and ordered a judicial inquiry into the accident. When Warren Anderson, Union Carbide’s chief executive officer, flew into Bhopal later in the week, he and two officials of the company’s Indian subsidiary were immediately arrested. They were charged with seven offenses, including criminal conspiracy, culpable homicide not amounting to murder, making the atmosphere noxious to health, and causing death by negligence. Authorities took the corporate executives to the company’s guesthouse and held them there for more than six hours. Anderson was then released on bond. Under orders from the government to leave the country, he was flown to New Delhi. He was never allowed to visit the Bhopal chemical plant.

World reaction to the disaster was immediate. President Ronald Reagan Reagan, Ronald sent a message of compassion expressing the grief shared by him and the American people. The Soviet news agency, TASS, called the disaster “the logical consequence of the general policy pursued by multinational corporations, which market low-quality products and outdated technology to developing countries.” Rajiv Gandhi, India’s prime minister, visited the disaster site and announced the immediate creation of a relief fund for victims and their families. During his visit, he accused Union Carbide Corporation of maintaining “double standards” for plant operational practices and safety compliance. He also vowed to prevent any other multinational corporations from setting up “dangerous factories” in India.

The legal implications of this particular disaster were overwhelming. Determining fault, responsibility, and ultimate financial obligation was a tedious and time-consuming process. Within weeks of the accident, three American attorneys, including Melvin Belli, a renowned criminal lawyer, filed a lawsuit in Charleston, West Virginia, on behalf of Bhopal victims, asking damages from Union Carbide in the amount of $15 billion. Two California lawyers, Jay Gould and Federico Sayre, sued Union Carbide in New York State for $20 billion to compensate Bhopal victims and their families.

The financial implications of the Bhopal tragedy were immediate for Union Carbide Corporation. From the date of the accident, December 3, to December 11, 1984, the corporation’s stock dropped more than twelve points, wiping out 27 percent, or almost $1 billion, of its market value. Warren Anderson announced an immediate donation of $2.3 million by UCC to a special relief fund for disabled survivors of the tragedy; the firm also offered to set up a home for orphaned children. Estimates indicate, however, that insurance coverage liability would have been in the range of $250 to $350 million for the type of disaster that had occurred at Bhopal.

The implications of the Bhopal disaster for world chemical manufacturing were sobering. In the United States alone, about six thousand chemical plants were operating, and the worldwide total was at least twice that. Adding in nuclear power plants and related facilities, equipment for handling liquefied natural gas and other explosive fuels, and laboratories for studying new biological organisms raised the number of potential sites for disaster to the tens of thousands. It became clear that, even if the chance of a major accident at any one of these places in a given year is only 1 in 100,000, it is likely that some deadly accident will occur somewhere in the world perhaps every decade or so. Disasters;industrial Bhopal disaster (1984)

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Austen, Ian. “Aftermath of a Poison Cloud.” Maclean’s, December 24, 1984, 34-36. Addresses the aftermath of the accident in Bhopal. Discusses the consequences of the plant’s poison gas disaster, the potential liabilities for Union Carbide, and the immediate financial implications for the multinational corporation.
  • citation-type="booksimple"

    xlink:type="simple">Clark, Matt, and Mariana Gosnell. “It Was Like Breathing Fire . . . .” Newsweek, December 17, 1984, 26-32. Discusses the gas leak in Bhopal and gives statistics on the tragedy. Describes the characteristics of the leaked gas, methyl isocyanate, and its devastating effects on Bhopal’s population.
  • citation-type="booksimple"

    xlink:type="simple">Fortun, Kim. Advocacy After Bhopal: Environmentalism, Disaster, New Global Orders. Chicago: University of Chicago Press, 2001. Examines the litigation that followed the disaster and discusses the case’s impact on environmental legislation in a global system. Includes bibliography and index.
  • citation-type="booksimple"

    xlink:type="simple">Iyer, Pico. “All the World Gasped.” Time, December 17, 1984, 20-26. Discusses the events in Bhopal and presents the responses of leaders from the United States, the Soviet Union, and India.
  • citation-type="booksimple"

    xlink:type="simple">Kalelkar, Ashok S. Investigation of Large-Magnitude Incidents: Bhopal as a Case Study. Cambridge, Mass.: A. D. Little, 1988. Discusses the probable causes of the leak at Bhopal and demonstrates that one suggested cause of the disaster, water washing of a certain header, could not have been to blame. Presents evidence that direct water entry into the MIC storage tank was the likely initiating cause of the disaster.
  • citation-type="booksimple"

    xlink:type="simple">Lang, John S. “India’s Tragedy: A Warning Heard Around the World.” U.S. News & World Report, December 17, 1984, 25-26. Discusses the grim aftermath of the accident as well as the potential hazards brought by industrial growth and the huge number of problems for Union Carbide Corporation in terms of potential liability and financial losses.
  • citation-type="booksimple"

    xlink:type="simple">Morehouse, Ward, and M. Arun Subramaniam. The Bhopal Tragedy. New York: Council on International and Public Affairs, 1986. Excellent background report on the Bhopal tragedy, produced for the Citizens Commission on Bhopal, is well researched, detailed, and scientifically convincing. Provides a comprehensive, if somewhat biased, summary of the events leading to the gas leak as well as the aftermath of a tragic event.
  • citation-type="booksimple"

    xlink:type="simple">Ohlendorf, Pat. “Lingering Terror in Bhopal.” Maclean’s, December 17, 1984, 26-30. Discusses the reactions of the citizens of Bhopal, India, to the industrial accident as well as the anger expressed by Indian officials.
  • citation-type="booksimple"

    xlink:type="simple">Pearson, John, “Union Carbide Fights for Its Life.” BusinessWeek, December 24, 1984, 52-61. Describes the financial impacts on Union Carbide Corporation in the aftermath of the accident. Discusses the potential for corporate bankruptcy, such as that faced by the Manville Corporation because of its liability for asbestos dangers.

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