ANACORTES, Wash. -- A Tesoro Corp. oil refinery blast and fire that claimed five lives is now the subject of state and federal investigations. The company has also launched its own probe.
The refinery was recently fined for safety violations amid what federal watchdogs call a troubling trend of serious accidents at refineries.
Three men died at the scene early Friday and two women died later at a Seattle hospital.
Two other men were badly burned. Matt Gumbel, 34, and Lew Janz, 41, were hospitalized in critical condition at Harborview Medical Center in Seattle.
The blast shook houses and woke people miles away at about 12:30 a.m. Friday, shooting flames as high as the refinery's tower before the blaze was extinguished about 90 minutes later.
Anacortes is about 70 miles north of Seattle on Puget Sound.
"We could tell this was horrific, this was huge," said Jan Taylor of La Conner, Wash., who felt the blast rock her motorhome at the RV park across the bay.
It was the largest fatal refinery accident since a 2005 explosion at a BP American refinery in Texas killed 15 people and injured another 170.
Six investigators with the U.S. Chemical Safety and Hazard Investigation Board were dispatched to the scene, and the Washington Department of Labor and Industries launched an investigation.
The company said employees were doing maintenance work on a unit that processes highly flammable liquid derived during the refining process.
Killed were Matthew C. Bowen, 31, of Arlington; Darrin J. Hoines, 43, of Ferndale; and Daniel J. Aldridge, 50, of Anacortes, according to the Skagit County coroner. A 29-year-old woman died of her burns at the hospital; she was identified as Kathryn Powell of Burlington.
Tesoro identified the fifth victim as 36-year-old Donna Van Dreumel, employed at the plant since 2001. The Oak Harbor woman died Friday night at Harborview.
The blast occurred in a unit that was in the dangerous process of returning to operation, turning up heat and pressure, said Tesoro spokesman Greg Wright.
"It's a volatile process," Wright said. "We are diligent about being safe."
Michael Silverstein, an assistant director at the state labor department, described the explosion and fire as occurring in a bank of boilers.
Since the boilers heat fluids to high temperatures under great pressure, they are "inherently vulnerable to events like this unless they are maintained and operated in a safe manner," Silverstein told a Friday afternoon news conference near the state capital of Olympia.
"It's going to take us quite a while to really develop the full chronology and to look at the details," Silverstein said. "We want to do everything possible to help prevent this from ever happening again."
The agency fined the San Antonio-based company $85,700 last April for 17 serious safety and health violations, defined as those with potential to cause death or serious physical injury.
Inspectors found 150 instances of deficiencies and said the company didn't ensure safe work practices and failed to update safety information when changes were made to equipment.
In November, the state reached a settlement with Tesoro, requiring in part that the company correct the hazards and hire a third-party consultant to do a safety audit. The settlement reduced the total penalty to $12,250 and lowered the number of violations to three.
"We don't know if any of those hazards were involved in the incident that happened today," said Hector Castro, a spokesman for the state labor department. The company was also fined $6,000 for two serious violations in 2005, and another $6,000 for two serious violations in 2007, Castro said.
Jeff Haffner, associate general counsel for Tesoro, said the third-party audit was completed in the past few weeks, but the consulting firm hired had not yet issued its report.
Most of the items involved requirements for managing safety, he said.
"There's no way for us to know whether the subject matter of any of those items were related, if at all, to this incident, because we don't know what caused the incident," Haffner said.
The state inspections were part of a national effort to examine all petroleum refineries in the United States after the 2005 explosion in Texas.
Of the 18 major accidents the U.S. chemical safety board is currently examining, at least seven are at refineries, said Daniel Horowitz, spokesman for the board. Yet there are only 150 refineries in the country and tens of thousands of other chemical plants.
"Our board is extremely concerned about safety in this sector," Horowitz told The Associated Press. "There's been a lot of accidents in the refining sector. There's been a lot of safety violations."
Parts of the refinery continue to operate, Wright said, and any loss in production can likely be made up by ramping up production at Tesoro's other West Coast refineries or buying from others.
Tesoro is an independent refiner and marketer of petroleum products. The Anacortes refinery, which Tesoro has owned since 1998, can refine about 130,000 barrels of crude daily, according to the company. It mainly processes Alaska North Slope crude and makes gasoline, diesel and jet fuel, mostly for Washington and Oregon.
There are four large refineries in northwestern Washington. This is the first refinery fire in Anacortes since 2007, when a blaze damaged a storage tank at the Shell Puget Sound Refinery and three people received minor injuries. Tesoro had a previous fire in 2002, with no injuries.
Six refinery workers were killed in an explosion and fire at the Equilon Puget Sound Refinery in Anacortes in 1998.