Page 24 - OHS, September 2020

COMBUSTIBLE DUST
Protecting the Plant from Catastrophic Combustible Dust Explosions
Industrial vacuums are the right tool for preventing secondary explosions.
BY DOAN PENDLETON
The issue of dust explosions has been a hot topic since the early 20th century. In a book published by the NFPA in 1922 titled, “Dust Explosions,” authors David J. Price and Harold H. Brown acknowledge the need for a vacuum that can withstand the rigors of an industrial environment. They stated that despite every precaution to capture dust at the source, small amounts of it “will get out into the atmosphere of the mill and gather on floors, walls and ledges.”
The authors of the book knew then, as it still stands today, “if there is no accumulation of dust and the plant is perfectly clean, the explosion cannot propagate and the plant will not be destroyed.”
Even without a sufficient vacuum cleaner for industrial environments in 1922, the authors still warned against using brooms and compressed air in housekeeping practices because those methods often cause dust to be suspended in the environment during cleaning and could ignite, or settle back onto floors, equipment and beams, lending itself to potential secondary explosions later.
Primary dust explosions occur when combustible dust is present, forms a dust cloud (in sufficient amounts), is in an enclosed environment and there is an ignition source and oxygen present.
“The explosion is caused by the rapid pressure rise as a result of the rapid burning of the dust cloud,”
Bill Stevenson, VP of Engineering at Cv Technology and NFPA 654 committee member, said. “So, it has to be in an enclosure. If it were outside you’d just have a big flash.”
Cv Technology is a Florida-based corporation dedicated to the prevention, protection and mitigation of industrial dust explosions and related fires.
Stevenson further explained that if there was a layer of combustible dust sitting on a desk, “you could get it to burn by putting a flame to it, but it wouldn’t explode. If you took the torch away it would smolder and most would self-extinguish; but, if you take the same dust, throw it in the air and then light it on fire, it would literally blow up in your face.”
Catastrophic secondary explosions occur when the force from the primary explosion dislodges fugitive dust, producing more dust clouds and creating a domino type effect that can cause further explosions. So if you took that same dust smoldering on the desk and waved a piece of paper to make the particles airborne, a dust cloud could form and explode.
According to a NFPA Fact Sheet titled, U.S. Industrial and Manufacturing Property Structure Fires, “U.S. fire departments responded to an estimated average of 10,500 structure fires in industrial and manufacturing properties per year in 2003-2006,” averaging 29 fires per day in the industrial sector. Of those fires, 29 percent involved shop tools or
20 Occupational Health & Safety | SEPTEMBER 2020
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