Investigators from the Bellevue Fire Department, Puget Sound Energy, the Washington State Utilities and Transportation Commission and a private insurance company said they found the source of the leak in a pipe buried about 18 inches below ground level near the home's foundation.
Investigators found a small hole in the line before its connection with the gas meter. They also said they discovered evidence that the ground directly above the gas line had been used as a drainage area for a sink in the lower level of the home.
A statement from the Bellevue Fire Department said the sink had not been connected properly to the house's plumbing. Instead a pipe was diverted through the foundation wall so that any materials poured down it would drain into the ground over the gas pipe.
"As a result, the potential for unnecessary corrosion increased. Investigators conclude that this situation may have contributed to the failure of the line,'' the fire department said.
The pipe also provided an easy way for the gas leak to reach inside the house, investigators said. They have not discovered what ignited the gas leak.
Frances Schmitz, 68, managed to walk out of her house after the blast Thursday morning but was taken to Harborview Medical Center in Seattle with critical burns.
Schmitz is the sister of Seattle strip club magnate Frank Colacurcio Sr. No one else was in the home at the time of the explosion, and no other injuries were reported.
The blast, which sent debris flying across the street, occurred as a Puget Sound Energy employee was checking the ground to try to find the source of a natural gas odor that had been reported by a neighbor about an hour earlier, fire Lt. Todd Dickerboom said.
"It was like somebody had dropped a bomb,'' said Jane Starkey, who has lived in the Spiritridge neighborhood for 27 years. "The roof went flying. There were sheets of plywood everywhere.''
The 2,100-square-foot house burned to the ground, and firefighters could do little more than prevent the flames from spreading to nearby homes, Dickerboom said.
