Monday, February 11, 2008

Little Particles, Big Problems

Last Thursday night, Feb. 7, a sugar refinery in Savannah, Ga., exploded and burned, killing six people. The blast has been linked to sugar dust in the air.

Not to make light of this tragedy, but exploding sugar?

Duke physicist Robert Behringer says this actually is a well-known phenomenon. If particles of combustible material -- including food grains, coal, wood and chemical products -- become airborne and collect in an enclosed space, a wayward spark can cause them to explode just as gasoline vapors would. A deadly 2003 blast at a pharmaceutical plant in Kinston, N.C., is analyzed here.

Behringer studies the behavior of various types of granular materials that can cause their own set of problems. (In the photo, a storage container collapses as grain particles convert from a "liquid" flow to a "solid" state.) For example, his laboratory studies how coal particles flow. When such flow goes awry -- say, by clogging hoppers in a processing plant -- significant damage may result. Some of their findings have been reported in Duke news releases here and here.

"What we study is part and parcel of the larger spectrum of how granular materials behave and how they can best be handled," Behringer says. "We don't focus on the specific type of event that triggered the sugar refinery explosion. And the problem, as I see it, is that nobody seems to be looking closely at this. In practice, the primary idea simply seems to be, 'if you work with these kinds of materials, you'd better make sure they don't accumulate in the air.' "

For its part, the federal Occupational Safety and Health Administration in October 2007 announced a new National Emphasis Program for inspecting workplaces that create or handle combustible dusts. But while states are encouraged to take part, participation is not (OSHA's emphasis) required.

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