Frequency and Causes of Grain Dust Explosions

Grain dust explosions at elevators are in reality a series of explosions. The first explosion referred to as the "primary explosion" is usually small with pressures less than 2 pounds per square inch, (psi). It propagates a pressure wave and fire front. The pressure wave moves away from the location of the primary explosion at a speed of about 1000 feet per second (fps) while the fire front follows at about 10 fps. The movement of the pressure wave results in secondary concentrations that are subsequently ignited by the relatively slow moving fire front. Secondary explosions can result in rupture pressures in excess of 100 psi.