Moments before the fatal May 2017 explosions at the Didion milling facility in Cambria, Wisconsin, workers reported seeing dust clouds suspended in the air inside the facility, according to a preliminary report recently released by the United States Chemical Safety and Hazard Investigation Board. The explosions occurred at night, when only 19 workers were present in the facility. Five of the workers died, and the other 14 were injured.

The facility was used for “dry corn milling,” which involves grinding and separating kernels of corn to create corn products. The corn milling process generates corn dust, which is combustible. Based on interviews with 10 of the 14 survivors, CSB’s report identifies two potential sources of corn dust in the facility: an “overpressure event” in milling equipment that caused dust to be thrown in to the air; or the lofting of “fugitive dust” into the air that had accumulated on surfaces inside the mill.

CSB determined that workers believed conditions inside the mill were normal on the night of the explosion. Approximately 15 to 30 minutes prior to the explosions, workers saw a filter blow off the intake line of a piece of equipment called a “gap mill.” Corn dust filled the air, and a flame shot out of the intake line, according to CSB.

The explosions caused four of the facility’s nine buildings to collapse. The other five buildings sustained severe damage.

Source: American Industrial Hygiene Association