Overview

Accidents rarely have a single cause. Accidents are usually a combination of rare events that people initially assumed were independent and would not happen at the same time. Take as an example the worst chemical accident to date, Bhopal, India, where an estimated 3,000 people died and 200,000 were injured. [Ref. ^[2]]

The material that leaked in Bhopal was MIC (methyl isocyanate). The release occurred from a storage tank which held more material than allowed by company safety requirements. Operating procedures specified using the refrigerant system of the storage tank to keep the temperature of the material below 5 degrees C. A temperature alarm would sound at 11 degrees. The refrigeration unit was turned off due to financial constraints and the material was usually stored at nearly 20 degrees. The temperature alarm threshold was changed from 11 to 20 degrees.

A worker was tasked to wash out some pipes and filters which were clogged. Blind flanges were not installed as required. Water leaked past valves into the tank containing MIC. Temperature and pressure gauges which indicated abnormal conditions were ignored because they were believed to be inaccurate. A vent scrubber, which could have neutralized the release, was not kept operational because it was presumed not to be necessary when production was suspended (as it was at the time). The vent scrubber was inadequate to handle the size of the release anyway. The flare tower, which could have burned off some of the material, was out of service for...