When designing a dust collection system, the ductwork is like the highways of the system. They allow the dust to move from the area of production to the dust collector. The dust should move fast enough so it doesn’t fall out while not moving too fast to cause undue wear and pressure drop. What this means is when you are designing your dust collector ductwork, pay attention to the ductwork diameters. When picking the ductwork diameters throughout the system, make sure the velocities correlate with the design velocities shown below.

Low Velocity Causes Dust Build-Up

A velocity that is too low will cause major issues in your ductwork. Dust will fall out and begin to pile up in the ductwork. This will do three (3) things:

• The dust builds up, decreasing the area of the ductwork, until the open area is large enough to get the velocity back up within the range to prevent further dust buildup.
• Dust buildup will increase the weight of the ductwork, and could cause issues with the support of the ductwork.
• If the dust is explosive, the dust buildup creates fuel for an incident and could cause serious problems.

The table below is from the Industrial Ventilation Booklet (5-1) and gives the velocity ranges of various applications and dusts.

Nature of Contaminant	Examples	Design Velocity
Vapor, gases, smoke		Any desired velocity (1000-2000 FPM suggested)
Fumes, metal smokes	Welding	2000 – 2500 fpm
Very fine light dust	Cotton lint, wood flour, litho powder	2500 – 3000 fpm
Dry dusts & powders	Fine rubber dust, Bakelite molding, powder dust, jute lint, cotton dust, shavings (light), soap dust, leather shavings	3000 – 3500 fpm
Average industrial dust	Grinding dust, buffing lint (dry), wool jute dust (shaker waste), coffee beans, shoe dust, granite dust, silica flour, general material handling, brick cutting clay dust, foundry (general), limestone dust, packaging and weighing asbestos dust in textile industries	3500 – 4000 fpm
Heavy dusts	Sawdust (heavy and wet), metal turnings, foundry tumbling barrels and shake-out, sand blast dust, wood blocks, hog waste, brass turnings, cast iron boring dust, lead dust	4000 – 4500 fpm
Heavy or moist dusts	Lead dust with small chips, moist cement dust, buffing line (sticky), quick-lime dust	4500 fpm and up

 

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How Tough Dust Can Affect Your Dust Collection System

Watch this video from the Dust Efficiency Clinic and learn how to deal with all these tough dust issues.

As always the Dust Efficiency Clinic offers its ‘outside the box’ thinking and solutions to your tough dust problems.

 

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To learn more about which dust collector, please contact our experts at 440-543-7400 or visit our website: www.dustcollectorhq.com.

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To improve efficiency and safety, there is no substitute for an on-site inspection by an experienced expert. Click below to start with a free 20-minute phone consultation by clicking the button.

 

 

When protecting vessels from explosions, one of the most common ways is to install explosion vents. The explosion vent is an engineered weak spot in the vessel that fails when the internal pressure reaches a certain point. This failure allows the pressure to be released in a controlled way so that the entire vessel doesn’t explode. The explosion vent needs to be installed so that the venting is away from any equipment, walkways, roads, picnic areas, etc.

Explosion vents are primarily used when the vessels are located outdoors, however they can be used indoors, if certain criteria is met. To install an explosion vent indoors, the vessel has to be located by an exterior wall. The vent would then be ducted through the wall, so in case of an explosion it is directed outdoors. An indoor explosion vent will usually need to be larger than an outdoor explosion vent. This is due to additional combustion of material in the duct and the inertia of the air mass in the ductwork.

The following is an explanation taken from FM Global 7- 76 Section 3.1.8

During the early part of the venting process, unburned dust is ejected into the duct ahead of the flame front from the vessel. When the flame front moves into the duct, dust starts to burn within the duct and generate additional combustion products. Those combustion products expand in ALL directions, thus slowing down or even reversing the flow out of the vessel and the pressure builds up within the vessel.

Inertia of the air within the duct also increases explosion pressure within the protected vessel. When the explosion vent opens and combustion gases first start flowing into the duct, those gases must push all the air out of the duct. During the time required to eject the air, the pressure continues to grow within the vessel because the combustion gases are obstructed from reaching the open atmosphere. In a long duct, that mass of air can delay the venting of the combustion gases enough to significantly increase the pressure in the vessel.

So if you’re installing a vessel indoors and you want to vent it outside, keep it as close to the outside wall as possible.

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Are you in compliance with the 2018 version of NFPA 68?

Simply click the button for direct access to the webinar to learn more about how to these recent changes may require modifications to your system.

 

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To learn more about which dust collector, please contact our experts at 440-543-7400 or visit our website: www.dustcollectorhq.com.

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To improve efficiency and safety, there is no substitute for an on-site inspection by an experienced expert. Click below to start with a free 20-minute phone consultation by clicking the button.

 

 

When it is time to add a dust collector to your application, you have to find a place for the dust collector.  This isn’t always easy.  New facilities are usually designed around the equipment that is being installed.  However when a system in an existing facility is modified or installed, you will have limited space to install the dust collector system.  There are four factors that you should take into account when finding a place for your dust collector. (Part 1 of 4)

Explosive dust

One of the most important factors to take into account is the explosibility of the dust.  If the dust is explosive you will have to make sure the location of the dust collector conforms with the appropriate NFPA specification.

The NFPA specifications require dust collectors to be located outdoors if they have explosive dust, unless specific explosion venting or mitigation equipment is being used.  Even if your dust collector is located outdoors, it should still have venting, because you don’t want your collector to create shrapnel during and incident.

Explosive Vent

One of the most common and least expensive explosion protection methods is the installation of explosion vents on the dust collector.  The explosion vent directs the pressure wave out of the vessel through an area, thereby controlling the explosion.  This protects the dust collector from the worst of the damage.

When using explosion vents, it does matter if your dust collector is indoors out outside.  When located indoors, the explosion is required to be vented outside.  The vent is connected to ductwork to an opening in an outside wall or roof.  When this is used, the dust collector should usually be within 5 feet of the wall.

When the dust collector is outdoors it should be orientated so that the explosion vents are directed away from the building and any other equipment.  The vents should also be directed away from any walkways, roadways, and areas where employees would be. (Ex. Rally points, picnic tables, etc.)

Flameless Vent

A flameless vent can be used instead, which allows the dust collector to be installed inside without venting it outdoors.  The flameless vent directs and vents the explosion as a standard vent, but it has metal fins mounted on the vent so the explosive wave travels past the fins.  The metals fins rapidly cool the wave, stopping the flame, so only a hot pressure wave is left.  Enough room must be left around the flameless vent so that adjacent equipment isn’t damaged.  The vent area should not be an area where workers are or a walkway.

Chemical Suppression

Chemical suppression is another technology that is used to protect dust collectors from explosions.  The technology uses non-explosive chemicals to flood the dust collector and prevent an explosion.  Sensors located in the dust collector and the ductwork measure the temperature and pressure to monitor for an explosion.  When they detect an explosion the chemical suppression system is activated.

Chemical suppression systems require yearly maintenance to make sure the system is still protected.  So the sensors and chemical canisters need to be accessible for the maintenance checkups.  This means platforms or open spaces for portable lifts should be located around the equipment.

To learn more about which dust collector, please contact our experts at 440-543-7400 or visit our website: www.dustcollectorhq.com. 

Click below and watch our Webinar that offers a thorough explanation of the changes in NFPA 68 and how they may affect your existing system design.