It’s not just the dust that’s trouble in grain bin explosions. Without an ignition source an explosion or “deflagration” is highly unlikely, says Calvin Parnell, Texas A&M Regents Professor and cotton chair in the biological and agricultural engineering department. He is also director of the Center for Agricultural Air Quality Engineering and Science (CAAQES) at College Station.

“Grain dust is not dangerous until it becomes entrained in the air at high enough concentrations and in the presence of an ignition source, a hot bearing, for instance,” Parnell said.

Grain bin explosions, he told participants in a recent Coastal Bend Grain Storage and Handlers Safety Conference in Sinton, Texas, are different from explosions caused by dynamite or ammonium nitrate. The latter two are detonations; grain bin dust explosions are deflagrations.

With an ignition source and a minimum explosible concentration (MEC) of dust particles in an enclosed space, such as a grain bin, an explosion is possible. More than one explosion usually occurs. “The primary explosion is followed by secondary explosions,” Parnell said. The first typically is relatively small, creating up to two pounds per square inch (psi) of pressure or less. “Secondary explosions are stronger, and pressure may exceed 150 psi. At 2 psi, the explosion can knock down a brick wall,” he said. “At CAAQES, we focus on primary explosions.”

Parnell said incidents such as a sugar plant explosion in Georgia “increased the Occupational Safety and Health Administration (OSHA) interest in testing dust for explosive potential. That led them to cotton gin dust and the finding that gin dust is explosible.

“About two years ago OSHA and the National Institute for Occupational Safety and Health asked CAAQES to study dust explosions in cotton gins,” he noted. “We found that cotton gin dust is not explosible. We were concerned that if cotton gin dust was determined to be explosible but was not they would have all kinds of (needless) expense.