On July 17, 2001, an explosion occurred at the Motiva Enterprises refinery in Delaware City, Delaware, killing one contract worker and injuring eight others. A work crew had been performing hot work -- welding and other spark-producing operations -- on a catwalk above a sulfuric acid storage tank farm when sparks ignited flammable vapors inside one of the storage tanks. The tank had holes in its roof and shell due to extensive corrosion, which had allowed flammable vapors from the refinery process environment to accumulate inside.

The CSB investigation found that the corroded spent sulfuric acid tank had not been inspected, repaired, or taken out of service despite documented evidence of corrosion holes. Inspection reports had identified the corrosion, but the facility lacked an effective accountability system for acting on mechanical integrity findings. The hot work permit system did not require testing for flammables inside tanks in the vicinity of hot work -- an omission that allowed workers to perform welding above a tank containing an explosive atmosphere.

The CSB issued 19 recommendations to Motiva Delaware City, Motiva Enterprises LLC, OSHA, API, NACE International, building trades unions, and industry associations. Key recommendations addressed mechanical integrity accountability systems, hot work program requirements for flammable monitoring near tanks, tank inerting, and the need for OSHA to extend PSM coverage to atmospheric storage tanks connected to PSM-covered processes.