Federal investigators wrap up their probe into the cause of a massive fire at Tulsa Schools for Arts and Sciences.
The building was completely destroyed last Wednesday by the blaze.
Tulsa Fire spokesperson captain Stan May said TFD and federal ATF investigators have ruled the fire and resulting explosions as "accidental".
The fire was a result of "construction related to the installation of an exhaust vent in the lab area," May said.
This investigation also revealed that a back draft was the cause explosions that injured eight Tulsa firefighters.
"The fire had been smoldering in the void between the chemistry lab ceiling and the floor of the room and hallway above. The fire migrated north under the hallway floor into the classroom and the crawl space below where it vented from the classroom window. The resulting smoke explosion or "back draft" occurred when oxygen was introduced into the area by the firefighters entering the room to extinguish the fire," May explained.
The second explosion that followed was the release of a layer of hot gas that had collected in the drop ceiling above.
"Traditionally back drafts occur in a confined space or room, but in this case the fire had been slowly burning in the floor and the crawl space for hours charging both areas with smoke and gases. The fire venting out of the window had not allowed enough oxygen to the back of the room," May elaborated.
May said The Tulsa Fire Department will take this information and try to learn how to prevent it in the future.
At least two firefighters are still in the hospital recovering from their injuries.
