By Peterson, Ivars
Science News , Vol. 127
Shortly after midnight on Dec. 3 last year, a cloud of deadly methyl isocyanate vapor escaped from a storage tank at a Union Carbide chemical plant in Bhopal, India. Within hours, more than 2,000 people died and tens of thousands were injured. Since then, two questions have dominated investigations of the Bhopal tragedy: Why did it happen, and could such as disaster occur in the United States?
The answer to the first question is slowly emerging, although findings so far are incomplete and controversial. Last week, Union Carbide Corp., based in Danbury, Conn., reported the results of its investigation. A team of seven engineers and scientists did about 500 experiments in trying to match the chemical residues in the leaking storage tank in order to reconstruct the events at Bhopal. They conclude: "This incident was the result of a unique combination of unusual events."
The study suggests that somehow a large volume of water--between 120 and 240 gallons--was "inadvertently or deliberately" pumped ito one of three tanks storing liquid methyl isocyanate. The investigators did not rule out sabotage. The presence of water triggered a heat-generating chemical reaction. The high temperature allowed chloroform, a solvent contaminating the methyl isocyanate, to decompose. The resulting chloride ions corroded the stainless steel tank, releasing iron, which catalyzed another "runaway" reaction. At some point, the tank could no longer withstand the steadily increasing temperature and pressure, and in the end about 50,000 pounds of methyl isocyanate escaped.
The Union Carbide report notes that several "critical" violations of company safety procedures also contributed to the disastrous leak. A refrigeration system that was supposed to keep methyl isocyanate cool and relatively unreactive had been shut down five months before the accident. A flare tower designed to burn off vented gases was not operating. An alarm meant to warn of rapid temperature rises did not sound at the time of the accident.
Responsibility for safety lies chiefly with local plant managers. Says Union Carbide Chairman Warren M. Anderson: "That plant should not have been operating."
Partly because the Indian government denied Union Carbide investigators access to important documents and to plant employees, uncertainty still surrounds the events in Bhopal. A spokesman for the Indian Embassy in Washington, D.C., protested that Union Carbide's implication that jobs properly was "unjustified and unacceptable. …