While separate regulatory commission and fire department investigations are ongoing, Puget Sound Energy (PSE) determined Tuesday it is probable that a wind-toppled tree in a north Seattle residential neighborhood caused a gas leak at a home blocks away that resulted in an explosion at 6 a.m . Monday. The married couple inside the home were being treated for various burn-related injuries and the home was leveled, a PSE spokesperson told NGI Tuesday.

Given the continuing series of high-profile natural gas pipeline incidents since the devastating transmission pipeline rupture in San Bruno, CA, a year ago, the Seattle incident involving a distribution main and various service lines has received more than usual news media attention, particularly in the Seattle area.

PSE leak survey crews working before the explosion Sunday and after on Monday have identified at least seven leaks. Three in a distribution main were found Sunday afternoon following the tree toppling of a power line that caused arching of an electric current through the nearby underground gas pipeline. PSE determined that the electric charge caused the three leaks in the main.

Subsequent to the blast, PSE crews found a similar small hole in the service pipeline near the meter at the home where the explosion took place. It, too, was probably caused by the arcing, said the PSE spokesperson.

However, three more leaks were found Monday, and those were probably not related to the power incident, the spokesperson said. Crews speculated that corrosion, a poor weld at a joint and others factors were involved.

The incident has caused PSE to undertake more surveys of much broader areas on the north side of Seattle, and the spokesperson said another spate of leak survey work will be started later this week. So far the Seattle Fire Department and state Utilities and Transportation Commission investigators have not said publicly what caused the incident that destroyed a home estimated at $350,000, according to the fire department spokesperson.

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