Twelve residents of an apartment complex in Shively were displaced after a fire early Monday morning. The fire started around 4:30 Monday morning in an upper level apartment on Stallings Avenue. Firefighters arrived to find flames coming from the second floor of the building. Firefighters believe a mattress caught on fire in that apartment. The man who lives in that apartment told WDRB he thinks the fire could have been sparked by an e-cigarette he was charging. The occupants of the apartment below the man said they were awakened to a loud boom. They saw the fire when they looked out the window. Video shows firefighters going door-to-door checking the building. Several fire alarms could also be heard, but residents told us most smoke detectors didn't begin to sound until firefighters doused the fire with water, causing a lot more smoke.