Sheet Metal & Air Conditioning Contractors’ National Association

Collecting Combustible Dust Can Sweep Open Doors

When the Fike device senses a pressure change, it discharges a suppressant within milliseconds.Combustible dust can be an underestimated hazard in the workplace—but installing dust collection systems for the industries that work with these fine dust particles can also be a smart business opportunity for sheet metal contractors.

Combustible dust is a minute material that—when suspended in the air in the right concentrations and under the right conditions—can become explosive. Combustible materials exist in such industries as agriculture, granaries, food processing, sugar refineries, manufacturing, furniture, fossil fuel plants, recycling, and metal working. This dust includes such diverse materials as sugar, spices, flour, feed,grains, tobacco, plastics, wood, paper, rubber, pharmaceuticals, coal, and metals.

“Good housekeeping is the best way to avoid an explosion caused by combustible dust,” said Scott Vidimos, president of SMACNA member company Vidimos Inc. of East Chicago, Indiana. “We perform dust collection work and have to incorporate safety devices into systems to address the hazard.” A combustible dust collection system is an effective way to provide this housekeeping.

“When a change in pressure is sensed in the duct or equipment, bottles installed on the ductwork discharge a suppressant within milliseconds to suppress an explosion,” Vidimos explained. His company installs dust collection systems as well as devices related to explosion suppression, explosion venting, and preventing an explosion from traveling back through the duct system.

The backflow preventer is installed upstream of the dust collector to protect the process equipment.For dust to combust, five elements, in what’s known as the “explosive pentagon,” must be present: fuel (dust), oxygen, an ignition source, a confined or enclosed space, and dispersion (the mixing of fuel and oxygen).

“You could be in the middle of a huge explosion without warning,” noted Randy Krocka, administrator of the Sheet Metal Occupational Health Institute Trust and a person who is keenly aware of the dangers of combustible dust. “It’s the secondary explosions that can be the worst. When the first explosion happens, it rocks the building, causing all the dust in the rafters and everywhere else to fall. This creates an explosive pentagon for secondary explosions.”

Vidimos notes that while many industries are aware of the dangers of creating potentially explosive conditions when handling their products, others are not. “Some fortunately have not experienced any disasters, but it may be more a matter of luck than of good engineering design,” he said.

“Dust collection systems can also be installed in plants that do not necessarily present the potential for explosion,” Vidimos said. “Dust collection can also be used to reclaim product that escapes the process, as well as for housekeeping and to provide a safe working environment for employees.”

In Vidimos’ experience, dust collection is always “a balance between functionality and practicality.” Though it’s ideal to collect dust at the source, the facility’s operations and maintenance also factor into the installation decision.

Vidimos credits SMACNA’s Technical Resources Department for their technical expertise and guidance. “The systems involve design outside of normal duct design and they helped us assess the various scenarios. The largest difference from normal duct design/fabrication is that explosions introduce a rapid change in duct pressure that isn’t contemplated in normal duct design.”

The Farr collector has a rupture disc that relieves the force of an explosion outdoors.Dust collection can be a worthwhile business for sheet metal contractors. “Knowledge of dust collection design and the ability to fabricate and install these systems can open a lot of doors for business opportunities,” Vidimos said.

“Adding the ability to sell explosion suppressant or venting systems may involve partnering with manufacturers of those products. It puts the sheet metal contractor in the position of being a problem-solver for their customers.”

The National Fire Protection Association developed NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. This standard is a good safety resource for contractors and offers safety measures to prevent and mitigate fires and dust explosions in facilities that handle combustible particulate solids.

Related Links

Vidimos Inc. » 

Read about combustible dust »

See the NFPA 654 Standard »