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An April 2010 explosion that killed seven people at an Anacortes refinery occurred in part because Tesoro Refining failed to use safe equipment, had poor inspection procedures and allowed its employees to regularly work in unnecessarily dangerous situations, according to an early draft of a federal investigation released late Wednesday night.

After a four-year investigation, the federal Chemical Safety Board determined that the deaths happened after cracks and fissures in a damaged heat exchanger caused a metal pipe to rupture as it was filling with flammable material.

The process of restarting the refineries heat exchangers had led to so many leaks and fires in the past that workers had come to view that risk as normal. Tesoro didn’t even investigate all the previous incidents, the chemical board found.

But the board’s investigators also determined that refinery industry standards were too lax and largely voluntary and that state regulators had neither the resources nor competence to make sure refineries adequately followed them.

The explosion, said Rafael Moure-Eraso, chair of the Chemical Safety Board, was rooted in “a deficient refinery safety culture, weak industry standards for safeguarding equipment, and a regulatory system that too often emphasizes activities rather than outcomes.”

The investigation should be “a clarion call for refinery safety reform,” he said.

Killed in the April 2, 2010, explosion that rattled Anacortes were Daniel Aldridge, 50, of Anacortes; Matthew Bowen, 31, of Arlington; Darrin Hoines, 43, of Ferndale, Whatcom County; Lew Janz, 41, of Anacortes; Kathryn Powell, 29, of Burlington, Skagit County; Donna Van Dreumel, 36, of Oak Harbor; and Matt Gumbel, 34, of Oak Harbor.

Tesoro and Shell, the refinery’s previous owner, already have settled with families of the victims for about $39 million.

The accident also led to a $2.39 million fine by the Washington Department of Labor and Industries, which also cited Tesoro for 44 workplace violations, ranging from willful disregard of safety regulations to failing to inspect and maintain decaying 40-year-old equipment.

Tesoro appealed the state action, and has waged a 3½ year battle before the state Board of Industrial Insurance Appeals. The company was recently granted a partial summary judgment that could reduce the fine to $858,500.

In a written statement released Thursday morning the company said “We respectfully disagree with several findings in the draft report and, most importantly, take exception to CSB’s (Chemical Safety Board) inaccurate depiction of our process safety culture. However, despite any disagreements regarding the draft report, Tesoro anticipates discussing the CSB’s recommendations with the agency once the report is finalized and will consider them in light of the steps we have taken and are continuing to take to improve the safety of our facilities.”

The board released a video animation of the incident Thursday morning and has scheduled a “listening session” in Anacortes Thursday night. It plans to accept 45 days of public comment before formalizing a list of 40 problems that led to the explosion and a list of recommended fixes.

One reason for the explosion, investigators said, was that the kind of damage that led the pipe to erupt is difficult for inspectors to spot. But neither did Tesoro monitor heat exchangers when they were operating, as the company could have.

Instead it hired corrosion experts to calculate the risk of damage based on the equipment’s design — not on how it actually was being used. That led to incorrect assumptions about the risk of damage and explosions.

“You need to be actually looking at how the equipment operates rather than just design numbers,” said Dan Tillema, investigation team leader for the safety board.

Meanwhile, it was so common for the heat exchangers to leak flammable hydrocarbons that Tesoro kept extra workers around during startup in case there was a fire. That meant when the explosion occurred there were more people around than necessary.

“It’s very significant in terms of how many people were there,” Tillema said.

The board also pointed out that the American Petroleum Institute in 2003 had suggested heat exchangers be made of different material to reduce the risk of accidents.

“They had lots of opportunities to upgrade equipment over the years and didn’t,” Tillema said.

But, Tillema said, no regulations required the company to upgrade.

The safety board is recommending a series of changes, from having the Environmental Protection Agency require refineries to use the safest equipment possible, to urging Washington to hire far more inspectors and increase their training.

Craig Welch: 206-464-2093 or On Twitter @craigawelch