A state investigation has found that hundreds of tons of a potentially explosive fertilizer ingredient were improperly stored at a North Carolina plant when it was destroyed by a fire that burned for days earlier this year. The Winston-Salem Journal reports that the North Carolina Department of Labor levied $5,600 in fines on Winston Weaver Co. based on information from interviews with company employees. The agency says 500 tons of ammonium nitrate were exposed to water leaking into the building and wooden storage bins weren’t adequate to keep ammonium nitrate from escaping or other substances from entering. Last week, city officials announced that investigators had been unable to determine the cause or origin of the blaze.