Wednesday, July 22, 2015 around 10:00 pm, Central Mason was dispatched to the report of a possible commercial structure fire in downtown Shelton at Simpson’s Mill 3. Central Mason units arrived on scene and found a fire at one of the Mill 3 hoppers. Crews put water on the inside and outside of the hopper to help cool and wet down the materials. Once crews felt confident the material in the hopper was wet enough, the hopper was slowly opened so the leftover materials could be emptied onto the ground without a dust explosion. Sierra Pacific employees used a large loader to spread the material out on the ground so the fire crews could wet down the rest of the content.
The cause of the fire is believed to be spontaneous combustion, a naturally caused fire. When the Simpson Mill closed, the hopper was left 25-30% full of content. This allowed the material the opportunity to expand and heat up until it reached its ignition point. This would be similar to beauty bark or grass stored in a pile. The pile slowly heats up internally until it gets hot enough to reach ignition point. Then it will spontaneously ignite and start a fire.
Assisting agencies were Mason County Fire District 4, 11, and Sierra Pacific.