What is believed to be the primary cause of the Bhopal incident?

• A. A storage tank was insufficiently filled
• B. The water curtain was inoperative
• C. Water was introduced into a MIC storage vessel
• D. The refrigeration system had insufficient coolant

Answer: (C)

Water entering a methyl isocyanate (MIC) storage vessel was the triggering event. MIC reacts violently with water, so when water mixed with the stored MIC, an exothermic hydrolysis occurred, rapidly releasing heat and toxic gases. The heat and gas buildup caused overpressurization and a large release of toxic fumes into the surrounding area. Other safety features matter for preventing or mitigating releases, but they don’t explain the initiating cause; the catastrophe began with water ingress into the MIC storage vessel.