The Lancaster City Bureau of fire responded to a reported dwelling fire at 543 E. Chestnut Street around 1451 Hours. Engine 3 on location with a working fire in a 3 story, occupied, duplex and requested a second alarm. Firefighters initiated an aggressive attack on a fire involving the basement. With fire travelling in the void spaces a third was struck bringing county mutual aid to the scene and a recall of off duty firefighters. The fire worked its way in the exposure and walls up the third floor. East Chestnut Street Command requested the general alarm shortly before companies were requested to evacuate the building. The fire was knocked down in about an hour and companies remained on the scene performing extensive overhaul. Two pets and three civilians were displaced in the fire.