2 December 1984, Bhopal incident

The Disaster at Bhopal

On the night of December 2, 1984, a leak developed in a storage tank at a Union Carbide chemical plant in Bhopal, India. The tank contained 10,000 gallons of methyl isocyanate (MIC), a highly toxic chemical used in the manufacture of pesticides, such as Sevin. The leak sent a toxic cloud of gas over the surrounding slums of Bhopal, resulting in the death of over 2,000 people, and injuries to over 200,000 more.

The leak happened because of the accidental pouring of water into the tank. Water reacts very vigorously with MIC causing heating of the liquid due to which the temperature increased to 400°F.

The high temperature caused the MIC to vaporize, leading to a buildup of high pressure within the tank. When the internal pressure became high enough, a pressure -relief valve popped open, leaking MIC vapors into the air.

A utility section on the site contained two pipes side by side. One pipe carried nitrogen, which was used to pressurize the tank to allow the liquid MIC to be removed. The other pipe contained water. It appears that instead of connecting the nitrogen pipe, someone accidentally connected the water pipe to the MIC tank. The accident was precipitated when an estimated 240 gallons of water were injected into the MIC storage tank.

The MIC storage tank had a refrigerator unit on it, which should have helped to keep the tank temperatures closer to normal, even with the water added, and might have prevented the vaporization of liquid. However, this refrigeration unit had stopped working five months before the accident and had not yet been repaired.

The tank also was equipped with an alarm that should have alerted  plant workers to the dangerous temperatures; this alarm was improperly set, so no warning was given. 

The plant was equipped with a flare tower.  This is a device designed to burn vapors before they enter the atmosphere, and it would have been able to reduce, if not eliminate, the amount of MIC reaching the surrounding neighborhood. The flare tower was not functioning at the time of the accident. 

Finally, a scrubber that was used to neutralize toxic vapors was not activated until the vapor release was already in progress. Some investigators pointed out that the scrubber and flare systems were probably inadequate, even had they been functioning. 

However, had any of these systems been functioning at the time of the accident, the disaster could have at least been mitigated, if not completely averted. 

It is unclear to whom the ultimate blame for this accident should be laid. The plant designers clearly did their job by anticipating problems that would occur and installing safety systems to prevent or mitigate potential accidents. The management of the plant seems obviously negligent. It is sometimes necessary for some safety features to be taken off-line for repair or maintenance. But to have all of the safety systems inoperative simultaneously is inexensable. Union Carbide also seems negligent in not preparing a plan for notifying and evacuating the surrounding population in the event of an accident such plans are standard in the United States and are often required by local ordinance.