The investigation determined that a major explosion occurred when something disturbed the dust, creating a cloud, which ignited. The investigation was unable to determine what disturbed the dust or what ignited it, due to the extensive damage at the plant. However, it is known that the machine had suffered multiple internal fires, including one that was powerful enough to blow off the mixer door. Four other theories were developed regarding possible causes: a batch of rubber that overheated and ignited; an electrical ballast or light fixture that ignited accumulated dust; a spark caused by a possible electrical fault; or ignition of dust in a cooling air duct feeding an electric motor.