An early Monday morning fire at Buckhorn Rubber Plant in Hannibal was ruled accidental in nature, according to Hannibal fire investigators. Hannibal Fire Department said crews were called to the plant at 3:39 a.m. for a report of a machine on fire. HFD Investigator Mark Kempker said when firefighters arrived workers were outside the building and the fire had set off the building’s sprinkler system. Kempker said it took firefighters about 10 minutes to put the fire out completely. Crews stayed on scene for about an hour. Following an investigation, Kempker said the fire was caused by an electrical malfunction in the control panel of a machine.