Dust is being blamed for a Francesville grain silo explosion that sent two people to the hospital with serious injuries Monday.

A “catastrophic failure” of the north pit in the silo created heat. That sparked an “accidental dust explosion”, Francesville Police Captain Robert Hickman told WNDU.

The nature of the explosion made determining its cause difficult for firefighters in Pulaski County. The force of the blast was one reason. The fact that a firefighter was one of the two seriously hurt was the other.

The cause of the explosion is being ruled accidental. However, investigators from the Indiana Occupational Health and Safety Administration will now conduct their own investigation.