Washington pipeline safety regulators today released their investigation report into the March 9 natural gas explosion in the Greenwood neighborhood of Seattle.
Utilities and Transportation Commission’s Pipeline Safety staff led the investigation into the cause of the explosion that injured nine firefighters and caused extensive property damage.
The investigation found the immediate cause of the explosion was outside force applied by unauthorized individuals to a gas service line owned by Puget Sound Energy. The damage allowed gas to escape, accumulate in the building occupied by Mr. Gyros restaurant, and ultimately explode.
The broken gas service line was one that PSE records showed as abandoned in 2004. At the time, PSE failed to properly disconnect and seal the line, allowing it to remain in service for nearly 12 years without proper oversight.
As a result of the investigation, the UTC filed a formal complaint against PSE alleging the company committed 17 violations of pipeline safety regulations and recommended a penalty of up to $3.2 million.
The complaint will be scheduled for a hearing before the three-member commission. The commission is not bound by staff’s recommendation.
Pipeline Safety staff allege that PSE violated pipeline safety regulations by failing to:
• Abandon a service line according to federal standards;
• Follow its internal pipeline deactivation plan;
• Perform annual leak surveys of an active service line;
• Perform atmospheric corrosion tests of an active service line at least once every three years; and
• Perform external corrosion tests of an active service line at least once every 10 years.
The gas service line that PSE believed was abandoned in 2004 was located in a space not intended for human occupancy between the Mr. Gyros and Neptune Coffee businesses. Evidence at the scene and witness interviews indicated that the space around the gas line was frequently used by unauthorized individuals to store personal items. Individuals acknowledged to investigators that due to the limited space, they sometimes disturbed the gas line to access the area.
Lab tests confirmed the line failed at the threaded connection due to applied external force.
Staff also recommended the commission require PSE to review all previously abandoned service lines to verify compliance and provide a plan for identifying and mitigating any additional unsuccessful retirements.