The investigation initially focused on two separate possibilities: a failure of a newly installed gas line, and a large dust explosion. From an early stage, the main theory pursued was that of the dust explosion. Within 24 hours of the explosion, the Chemical Safety and Hazard Investigation Board, who conducted the investigation, had determined from eyewitness interviews that the explosion originated in an area known as the "Automated Compounding System". This was a synthetic rubber-processing system. It was the site for mixing, rolling, coating, and drying of a type of rubber called polyisoprene. The process adds oils and fillers to the material, as well as creating significant quantities of dust. Therefore, the working theory from an early point was the rubber dust explosion theory.