Platoon Chief Eric Garland says smoke and fire could be seen underneath some decking between the first and third floor at the back of the building.
He tells CHSJ News crews later realized the fire was in the wall.
He says crews had to do a lot of ripping and tearing to open up the walls with a chainsaw to make sure they had contained the fire.
10 people living in the building are currently displaced but Garland is hopeful most of them will get back in today. The damage is restricted to one apartment with some in another unit.
A fire investigator is looking into the cause.