UTC: Greenwood explosion caused by unsealed, damaged pipeline

The Utilities and Transportation Commission says the cause of the Greenwood explosion that devastated part of the business core in March was a damaged gas line that was listed as abandoned in Puget Sound Energy records but remained connected for years.

According to UTC, 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, a news release said.

>> Related: Businesses destroyed in Greenwood blast

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The investigation found the immediate cause of the explosion was possibly a homeless person who accessed a space near the pipe without proper authorization. That person "applied force" to the gas line.

The damage allowed gas to escape, accumulate in the building occupied by Mr. Gyros restaurant, and ultimately explode.

>> Before-and-after photos: Greenwood explosion

The gas service line that PSE believed was abandoned in 2004 was located in a space 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, possibly homeless people, to store personal items.

Individuals told investigators that due to the limited space, they sometimes disturbed the gas line to access the area, the UTC said.

Lab tests confirmed the line failed at the threaded connection due to "applied external force."

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.

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.

PSE released the following statement about the UTC report:

"The proposed fine from the state Utilities and Transportation Commission (UTC) staff is disappointing and excessive.

"All parties investigating the March incident, including the UTC and the Seattle Fire Department, agree: the natural gas system at the Greenwood site was damaged by unauthorized individuals in a space not intended for human activity, with the resulting gas leak causing the explosion and fire.

"While we disagree with the UTC staff’s conclusions and recommended fine, we’re committed to the safety of our customers and the community and will continue to review the report as we prepare for final disposition of this investigation by the UTC commissioners."

Cox Media Group