Cedar Falls investigators now believe a fire at a business Monday started on its own. Investigators are speculating that the fire in the downtown area of Cedar Falls was caused by spontaneous combustion. The fire broke out in the upstairs area of a brick building that was under renovation on Main Street. Workers had left buckets of linseed oil and rags in one of the rooms. There was about 20-thousand dollars in fire and smoke damage to the upper floor and a bar and cell-phone store on the first floor.