Fatality due to inadvertent reaction

Employee #1, the basement operator at a powerhouse, was purging the liquid residue from the betene entrainment tank to the #16 boiler. Water and steam inadvertently got into the knockout pot, and materials that react to water, such as, but not limited to, acetic anhydride and diketene were in the tank. A reaction occurred, releasing flammable and hazardous materials into the atmosphere through a safety relief valve. The pressure relief device was only sized for an external fire, not a chemical reaction. As a result, the safety relief valves could not withstand the reaction. The overpressurization caused the steel pot to fail and explode. Employee #1 was killed.
Source:OSHA.GOV