The fire struck the Tesoro Corp. refinery in Anacortes, about 70 miles north of Seattle on Puget Sound, at about 12:30 a.m., the company said. The blaze occurred while maintenance work was being performed and was extinguished in about 90 minutes.
Three employees are hospitalized with major burns over the majority of their bodies. Susan Gregg-Hanson, a spokeswoman for Harborview Medical Center in Seattle, said one woman, 36, and two men 34 and 41.
The fourth victim was a 29-year-old woman.
All employees have been accounted for and investigators are trying to determine the exact cause of the blaze, said Tesoro spokesman Greg Wright in San Antonio. The extent of the damage is unknown, but parts of the refinery continue to operate, Wright said. The refinery has about 300 employees.
Nearby residents, some five miles from the complex, called Washington TV stations after midnight with reports of an explosion, saying flames were being blown by high winds.
"My house shook, big time," Lisa Wooding told KOMO-TV. "There were flames. First high, then low to the ground and broad."
Tesoro said the Washington Department of Labor and Industries had been notified.
Activity around the complex had calmed down considerably as dawn approached. Guards were turning reporters away from the gate and there was no apparent sign of the fire that had lit up the skies only hours earlier.
The blast occurred in the naphtha unit of the refinery. Naphtha is a volatile, flammable liquid derived during the refining process, and the unit had undergone maintenance and was in the process of returning to operation - a "typically dangerous" step of turning up heat and pressure, Wright said.
"It's a volatile process," Wright said. "We are diligent about being safe."
San Antonio-based Tesoro Corp. is an independent refiner and marketer of petroleum products. The Anacortes refinery can refine about 130,000 barrels of crude daily, according to the company. The U.S. Energy Information Administration Web site ranks it as the 59th largest refinery in the nation.
Tesoro has owned the Anacortes refinery since 1998. It mainly processes Alaska North Slope crude and makes gasoline, diesel and jet fuel, mostly for Washington and Oregon.
Wright said he can't say yet how long production will be affected, but Tesoro likely can make up the loss by ramping up production at its other West Coast refineries or buying from others.
Other than the possibility of a short spike, Wright said he doubted the refinery problem would affect gasoline prices.
Wright said he knew of no other such fires at the Anacortes refinery.
Bruce Smith, Tesoro's chairman, president and CEO, called it a sad time for the company.
"Everyone in the Tesoro family appreciates the impact that this will have on the families involved, and we are responding quickly to ensure the safety for our employees, contractors and the neighboring community," he said.