Thursday’s explosion and fire at the Alderwood Wastewater facility near Edmonds has been ruled accidental by the Snohomish County Fire Marshal’s Office.
The explosion and fire was reported by workers at the site, located at 6315 Picnic Point Road, at about 11 a.m. after a cloud of propane vapors ignited. The incident occurred while a contractor was lifting a 1,000-gallon propane tank onto a truck to remove it from the property.
The tank was estimated to have approximately 300 gallons remaining inside. As the tank was being placed onto the metal deck of the truck, a brass drain valve on the bottom of the tank broke off, releasing propane from under the tank.
It was estimated that it took about 45 seconds for the vapors to be ignited.
Snohomish County Fire District 1 was the first fire agency to arrive at the scene. The fire department triaged about 40 of the 60 employees at the work site and transported five with burn injuries to Harborview Medical Center.
The explosion also damaged two buildings under construction on the property. Estimated loss to the building and contents is $1 million.
According to a news release issued by the Snohomish County Executive’s Office, representatives for the Department of Labor and Industries were on the scene and all evidence has been turned over to them.