Changes to the production process at an asphalt plant and a faulty isolator valve allowed fuel to enter the aggregate bucket elevator via the pneumatic system.
Contact with the hot aggregate resulted in a build up of flammable gases, which ignited when the plant burner started up, causing an explosion; the explosion was sufficient to blow the top of the tower some distance and cause extensive damage to the tower casing. If anyone had been hit by this, it would have caused a serious injury or fatality.
Note: Changes to the original system design, potentially dating back 30 years, did not consider the danger of back pressure in the fuel system. A subsequent change a few months before the incident meant fuel was being delivered at a higher pressure, which allowed it to enter the air system.