The water heater at a video store in the shopping plaza rocketed through the building's roof, over a Taco Bell restaurant and into a Pizza Hut parking lot 460 feet away, said Battalion Chief Doug Hudson.
''The whole front of the Mexican restaurant, the video store and the grocery store blew out,'' said J.D. Burtis, who works at a recreational vehicle park across the street. ''They're totally shot. All the windows and glass are gone. There's counters laying on the front door.''
The water heater did not strike anyone in the Friday blast, but glass and bricks rained on parked cars and blanketed the four-lane road next to the building.
''Had there been more people in the business or anyone in the vehicles outside or had that water heater ... hit someone, we'd have a much more serious situation,'' Hudson said.
Fire crews found four people dazed in the parking lot Friday, said Hudson. One, a 50-year-old Burien woman, was treated for second-degree burns to her right arm. She was in satisfactory condition Friday evening at Harborview Medical Center in Seattle, a nursing supervisor said.
The others were taken to Highline Hospital in Burien with minor injuries.
Initial damage estimates were $750,000 to $1 million, said Bill Harm, King County assistant fire marshal.
The explosion was apparently caused by the electric water heater at a video store in the plaza, Puget Sound Energy spokeswoman Dorothy Bracken said.
''The pressure relief valve had been capped, and the tank was partially drained of water,'' Hudson said. ''It built up steam pressure. It was a steam explosion.''
The thermostat on the water heater also may have malfunctioned, Harm said.
The owners of the video store told KIRO-TV that a repairman had been called to look at the water heater on Thursday because it was producing scalding water. They said the repairman told them the heater needed to be replaced, and that he had shut it off in the meantime.
Jose Lopez, of Burien, was just getting out of his car at an insurance firm next door when he heard what he thought was an earthquake.
"'I opened my door and 'boom!' and it exploded," Lopez said. "People started running out full of dust."