Posted at 4:22 pm

Portland Firefighters were dispatched to a call of smoke in a commercial structure located at 10 NW 12 Avenue at 9:41 am. Upon arrival at 9:44 am, responding crews found fire on the fifth floor roof landing within a gas fire heating unit. The initial two responding fire crews called in additional resources to assist with controlling the fire, ensuring it did not spread, and evacuating occupants of the building.  Traffic was shut down on NW Burnside until the fire was brought under control.

PF&R Fire Investigators confirmed that the fire was contained in a gas fire heating unit and the surrounding roof decking. The heating unit was set on five-inch plywood roof decking. A thin piece of sheet metal was the only barrier between the fire box and the wood decking. Deep charring of the wood was present at the time of investigation. A Fire Investigator further confirmed that the fire had been smoldering for some time. 

"The conduction of nails through the sheet metal and into the wood caused decomposition of wood by heat over time.  This is called pyrolysis," said a Portland Fire Investigator.  "Once the wood gets to the right level of pyrolysis and you provide the heat transfer from the heating unit to the sheet metal, a fire can start."

Due to the time of day, an alert building resident who made the 9-1-1 call, and quick actions of firefighters on scene damage from the fire was kept to a minimum and confined to a portion of the building's roof.  The incident was recalled at 10:27 am.