THE MASSIVE LETHAL explosion in a dusty sugar plant in Georgia earlier this month has reopened debates on how to reduce the likelihood of explosions due to combustible dust, hundreds of which have occurred over the past three decades.

Dust explosions unfold in waves, says Daniel A. Crowl, professor of chemical process safety at Michigan Technological University. The rapid-fire explosions can roll through a plant-a moving fireball of flames and violence. The initial blast might not be a dust explosion at all. Even static electricity can set it off.

"But the first explosion can stir up the dust that has settled in the plant over the years, lying on the floor, on beams, above suspended ceilings, in tiles," Crowl explains. "That dust is disturbed by the explosion, is thrown into the air, mixes with oxygen, and is ignited by the first explosion."

And on it goes, Crowl says. More explosions occur as the combustible dust is disturbed and entrained in air and ignition moves through the plant.

Subsequent explosions are often larger than the first, he says, and they can blast through a factory, traveling along conveyor systems, and in pneumatic transfer lines, ducts and vents, and tunnels. The same passages needed to move products, workers, or equipment become chimneys of fire.

Indeed, the first few of nine workers killed at the Feb. 7 Imperial Sugar Co. explosion were found in tunnels that run under the plant floor. Last week, the smoldering fires at the sugar refinery cooled enough to allow accident investigators onto the Port Wentworth site, outside of Savannah. In the weeks ahead, investigators will stir through the rubble and ashes, gather data, and interview survivors. And all of that information will likely lead to a further debate between two federal agencies-the Chemical Safety & Hazard Investigation Board (CSB) and the Occupational Safety & Health Administration (OSHA)-over how the wide range of plants, including chemical companies, that generate combustible dust should be regulated.

"What people often don't understand is that a lot of solid material, when finely divided into a dust form, becomes highly explosive. And I mean really highly explosive," Crowl says.

Full Story: http://pubs.acs.org/cen/government/86/8608gov1.html