Cause of the Bhopal Tragedy

Union Carbide's Investigation
A Union Carbide Corporation (UCC) investigation team arrived in Bhopal within days of the incident, but could not begin its investigation because the Indian Central Bureau of Investigation (CBI) had taken control of and sealed the plant; seized control of the plant’s records; and prohibited interviews of plant employees on duty the night of the incident. What was known was that the methylisocyanate (MIC) unit had been shut down six weeks before the incident, and the MIC storage Tank 610 -- from which the gas was released -- had been isolated at that time.

The UCC team was only permitted to take samples of the residue in Tank 610 and, after several months of extensive analyses, issued a report in March 1985. UCC’s initial investigation showed that a large volume of water had been introduced into the MIC tank and caused a chemical reaction that forced the pressure release valve to open and allowed the gas to leak. A committee of experts, working on behalf of the Indian government, conducted its own investigation and reached the same conclusion. The incident occurred despite the fact that the system had been designed and operated to keep out even trace amounts of water and that no water had ever entered any of the tanks during the five years the plant had been in operation.

Cause Finally Determined
For more than a year, the CBI prohibited interviews with plant employees and denied meaningful access to plant records. However, in December 1985, a U.S. magistrate ordered the Government of India (GOI) to provide UCC with copies of plant records that had been seized. Moreover, the GOI could no longer restrict access to plant employees while it was before a U.S. court seeking discovery from UCC.

Shortly after the gas release, UCC launched an aggressive effort to identify the cause. With access to employees and plant records, UCC investigators conducted more than 70 interviews in India and examined some 70,000 pages of plant records and documentation that the Indian government had reluctantly released. UCC's follow-up investigation confirmed its initial conclusion: a large volume of water had been introduced into the MIC tank. This caused a chemical reaction that forced the pressure release valve to open and allowed the gas to leak.

Some two and a half years after the tragedy, UCC filed a lengthy court document in India detailing the findings of its scientific and legal investigations: the cause of the disaster was sabotage. Click here to view the Jackson Browning Report. UCC’s investigation proved with virtual certainty that the disaster was caused by the direct entry of water into Tank 610 through a hose connected to the tank.

All of this was supported by hard evidence set forth in the presentation made by Ashok S. Kalelkar of Arthur D. Little, Inc. at The Institution of Chemical Engineers Conference on Preventing Major Chemical Accidents in London, U.K., in 1988. Click here to view the Arthur D. Little Report. Early accounts of the disaster that focused on the GOI’s theory that water-washing caused the accident subsequently were disproved.

Frequently Asked Questions About the Cause of the Bhopal Gas Tragedy

1. What caused the gas leak?
A. Shortly after the gas release, UCC launched an aggressive effort to identify the cause. An initial investigation by UCC showed that a large volume of water had been introduced into the MIC tank. This caused a chemical reaction that forced the pressure release valve to open and allowed the gas to leak. A committee of experts working on behalf of the Indian government conducted its own investigation and reached the same conclusion.

Some two and a half years after the tragedy, and only after the Indian government's reluctant release of some 70,000 pages of documentation, UCC filed a lengthy court document in India detailing the findings of its scientific and legal investigations: the cause of the disaster was undeniably sabotage. Click here to view the Jackson Browning Report. UCC’s investigation proved with virtual certainty that the disaster was caused by the direct entry of water into Tank 610 through a hose connected to the tank.

All of this was supported by hard evidence set forth in the presentation made by Ashok S. Kalelkar of Arthur D. Little, Inc. at The Institution of Chemical Engineers Conference in London in 1988.

2. Who could have sabotaged plant operations and caused the gas leak?
A. Investigations suggest that only an employee with the appropriate skills and knowledge of the site could have tampered with the tank. An independent investigation by the engineering consulting firm Arthur D. Little, Inc., determined that the water could only have been introduced into the tank deliberately, since process safety systems -- in place and operational -- would have prevented water from entering the tank by accident.

3. Were the valves faulty on the MIC tanks at the plant?
A. No. In fact, documented evidence gathered after the incident showed that the valve near to the plant's water-washing operation was closed and leak-tight. Furthermore, process safety systems -- in place and operational -- would have prevented water from entering the tank by accident.

4. Why didn’t the plant’s safety systems contain the leak?
A. Based on several investigations, the safety systems in place could not have prevented a chemical reaction of this magnitude from causing a leak. In designing the plant's safety systems, a chemical reaction of this magnitude was not factored in for two reasons:

  1. The tank's gas storage system was designed to prevent such a large amount of water from being inadvertently introduced into the system; and
  2. Process safety systems -- in place and operational -- would have prevented water from entering the tank by accident.

5. How do you respond to concerns expressed about the technologies used at the plant prior to the incident?
A. Contrary to allegations made by certain parties in various lawsuits, UCC did not design, construct or operate the Bhopal plant. And, most importantly, all of the decisions with respect to the plant and its design, construction, and operation were either made by UCIL or mandated by GOI policies and directives.

In 1987, the U.S. Court of Appeals upheld a lower court's ruling that "UCC’s participation was limited and its involvement in plant operations terminated long before the accident....the UOI [Union of India] controlled the terms of the agreements and precluded UCC from exercising any authority to 'detail design, erect and commission the plant,' which was done independently over the period from 1972 to 1980 by UCIL process design engineers....The preliminary process design information furnished by UCC could not have been used to construct the plant. Construction required the detailed process design and engineering data prepared by hundreds of Indian engineers, process designers and sub-contractors..." Please click here to read the U.S. Court of Appeals complete 1987 decision.