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Tesoro Maintenance at Fault in Refinery Blast, U.S. Says

Tesoro Corp. (TSO) didn’t adequately maintain equipment at its Anacortes, Washington, refinery prior to an explosion that killed seven workers last April, the U.S. Chemical Safety and Hazard Investigation Board said.

According to its preliminary findings, hydrogen corrosion caused microscopic cracks in the walls of a heat exchanger in the plant, board Chairman Rafael Moure-Eraso said in a video posted April 1. “This led to a violent rupture of the exchanger, followed by an intense fire as large volumes of naphtha and hydrogen were released,” he said.

The accident, the deadliest at a U.S. refinery in five years, prompted Washington state officials to propose a $2.3 million fine, their largest ever. Tesoro has appealed the fine. An exchanger moves heat around a refinery to help it process crude into fuels.

The company disagrees with Moure-Eraso’s description of operations at Anacortes, Mike Marcy, a spokesman for San Antonio-based Tesoro, said in an e-mailed statement. Marcy said they “look forward to clarifying the facts as the board completes its investigation.”

To contact the reporters on this story: Bradley Olson in Houston at

To contact the editor responsible for this story: Susan Warren at

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