PORTLAND, Ore. (KOIN) — Fire crews responded to two different fires at the same lumber mill in North Plains Saturday, according to Tualatin Valley Fire & Rescue.

Just before 5 a.m. Saturday, firefighters from TVF&R and Hillsboro Fire & Rescue responded to a fire at a lumber mill located near the corner of Main and Commercial streets in North Plains, officials said.

Crews were able to contain the fire to a small building next to the mill. Firefighters remained on the scene for several hours, mopping up hot spots and using thermal imagers to look for heat signatures in the building. An investigator determined that the cause of the fire was accidental and originated in an electrical room. Workers later demolished the damaged building.

Later at 3:49 p.m., firefighters were called back to the same site because workers spotted smoke coming from a tall hopper containing sawdust, according to TVF&R. Because of the significant amount of combustible material and threatened buildings nearby, the fire commander called a second alarm to bring more firefighters and equipment to the scene.

A semi-truck trailer full of sawdust was found under the hopper and its contents also caught fire. The truck was then moved across the street where firefighters and a City of North Plains public works employee emptied the slow burning contents.

Firefighters have been filling the large hopper with water and will remain on scene for several hours to douse hot spots and decontaminate tools and equipment. The cause of the second fire remains under investigation. No mill workers or firefighters were injured.