What is believed to have caused the uncontrolled reaction and toxic vapor release in the Bhopal disaster?

• A. A failure of the temperature sensor on the caustic scrubber
• B. Water was somehow added to a storage tank of MIC
• C. An operator erroneously closed a valve that should have remained open
• D. The refrigeration system experienced a sudden leak

Answer: (B)

Water reacts with methyl isocyanate in an extremely exothermic way. If water gets into a MIC storage tank, it triggers a runaway hydrolysis reaction that releases a lot of heat and rapidly raises the temperature and pressure inside the tank. In the Bhopal incident, this sudden exothermic event overwhelmed cooling and containment systems, causing relief valves to vent large amounts of toxic MIC vapor into the surrounding area. That sequence—water ingress into the MIC storage—is the widely held explanation for the uncontrolled reaction and toxic vapor release.

Other scenarios, like a sensor failure or a valve change, might contribute to the severity, but the fundamental trigger identified in investigations is the unintended introduction of water into the MIC storage tank, which started the runaway reaction.