The Washington UTC Pipeline Safety Program found no violations of federal or state safety regulations in regards to a natural gas explosion and fire that occurred in Spokane and injured two people late last year.
On the morning of December 30, 2005, a natural gas explosion occurred inside a building at E. 3818 Joseph Street in Spokane. Katie and Monte Yockey were just opening up their business, Cougar Mechanical, for the day when the explosion occurred. Both were treated for burns. Spokane Fire Department responded to the call and two UTC pipeline safety inspectors were on site the following day.
The natural gas leak that led to the explosion and fire originated at a crack in a two-inch polyethylene natural gas pipe owned by Avista Utilities. The crack was directly adjacent to a coupling that joins two pipe sections. From that leak, the gas migrated approximately 200 feet underground to the foundation of the building and then migrated inside the building wall. Ground frost likely kept the gas from venting to the atmosphere until it reached the side of the building.
As part of this investigation, Avista hired an independent engineering firm, recommended by the UTC pipeline safety program, to analyze the pipe and circumstances involved in the incident.
Engineering Systems, Inc., an Illinois firm, determined that the pipes and fittings involved in this incident were a brand of plastic pipe called DuPont Aldyl A. There was no evidence of material degradation and the method of joining the pipe sections (socket fusion) on both sides of the coupling were properly made according to the DuPont socket fusion procedures. The firm believes the fracture occurred as a result of stress resulting from soil settlement. This soil settlement occurred when underground utilities, located beneath the natural gas pipe sections, were replaced. The new fill dirt underneath the gas pipe had not been sufficiently compacted to avoid future ground settlement. As the ground settled underneath the pipe juncture, the stress on the pipe likely created the fracture.
In its letter to Avista officially closing the incident investigation, Alan Rathbun, UTC pipeline safety program director, encouraged Avista to regularly communicate with excavators in their service territory on the proper care and compaction of soil around all natural gas lines.
The docket number for this investigation is: PG-052049.
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