Fire investigators are trying to determine the cause of a fire on Sunday afternoon at a metal finishing company on the city's Northwest Side. Chemicals caught fire inside Aero-Tech Metal Finishing on Mainland Drive near Bandera Road at about 2 p.m. Fire crews quickly put out the fire, but hazmat personnel decontaminated some of the firefighters. State environmental officials will test chemical runoff from the water used to extinguish the blaze.