Last week, firefighters arrived to find smoke billowing from a Vancouver furniture manufacturing plant’s hopper. While trying to access the hopper, dust ignited into what was reported to be an explosion, and engulfed three firefighters in a burst of flames. Amazingly the firefighters escaped injury, due to the protective turnout gear that they were wearing, which has an abrasion-proof layer on the outside of their gear that stops it from being penetrated, ripped, or compromised.
However, the video above is a great reminder of the hazards associated with burning combustible dusts. The “explosion” seen below the hopper that engulfs the firefighters should more accurately be called a flash fire, which is a deflagration (flame propagation through a fuel-air mixture at subsonic speeds) that occurs in open atmosphere without the production of damaging pressure. An explosion occurs when a deflagration is ignited within an enclosure (such as a dust collector or a building), causing a pressure rise sufficient to rupture the enclosure. When the enclosure is equipped with explosion relief vents, the pressure rise ruptures the vent panels, thereby relieving the pressure rise caused by the deflagration within the enclosure. If not equipped with explosion relief vents, the enclosure will eventually rupture when the internal pressure exceeds its strength.
The concussion heard at about 0:37 seconds in the video illustrates how even a relatively small flash fire, if it occurs inside a facility, can create a pressure wave that, in itself, may not be destructive, but could dislodge dust accumulations on the structure or other surfaces, further fueling the deflagration until the pressure rise becomes destructive to the building. This type of event is called a secondary explosion, and it is usually the secondary explosions that end in fatalities. For this reason, we cannot overemphasize the importance of maintaining good housekeeping throughout all powder handling areas of a facility.
Check out our two-part series on Getting a Handle on Your Combustible Dust for more information. If you need a combustible dust assessment for your facility, fill out the form below, and one of our experts will be in touch soon.
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