Investigators have determined what they think was the cause of a five-alarm weekend fire in Spencer. The state fire marshall says a fire that destroyed office and warehouse areas at Vander Haag Salvage in north Spencer was likely accidental. Deputy state fire marshall Dave Schipper says the investigation they did together with the Spencer fire department turned up no suspicious circumstances. Schipper says the fire probably was caused by a furnace that burns waste oil; debris in the air ducts apparently caught fire and set fire to other combustible materials. Firefighters were able to save the west shop building and paint-booth areas, though the office and east warehouse buildings are a total loss. Schipper says final damage estimates could reach a million dollars. The five-alarm blaze kept firefighters on the scene for more than sixteen hours Saturday.