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INFOGRAPHIC: How sawmill dust explosions happen

WATCH ABOVE: A preview for 16×9’s “Deadly Mills.”

According to part five of the Occupational Health and Safety Guidelines, “a layer of dust as thin as a dime dispersed throughout a room can create an explosion hazard.”

How can that possibly happen?

READ MORE: What was behind the deadly B.C. sawmills explosions?

A dust explosion is a perfect storm of events, and the key word is “dispersed.” Dispersal is one of five things needed before a harmless pile of fine wood dust (sometimes called “flour”) can be transformed into the fuel for a devastating explosion. Experts call it the “explosion pentagon.” If even one element is missing, there will be no blast.

Janet Cordahi / Global News

You need the dust (the drier and finer the better) dispersed throughout the air; you need containment—an enclosed space where pressure can build; you need oxygen, which is everywhere; and you need an ignition source—a spark or a flame. The particle size of the dust is critical. As the WorkSafeBC investigation into the Babine explosion explained: “The smaller the particles, and the greater the number of them, the more violent the explosion is likely to be.”

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Put this all together and: BOOM!

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The primary explosion is relatively small. But it begins a chain reaction; the blast dislodges other accumulations of dust from beams, ledges, walls and machinery in the factory. This dust then mixes with the air, providing the fuel for a secondary and much more massive explosion. And that’s what blows the roof off a building, and can kill or injure people.

It’s not a new phenomenon. In 1795 a dust explosion blew up a flour warehouse in Turin, Italy.

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