• ● Maintain air velocity safety above the minimum conveying velocity: One of the most common sources of potential fuel for combustible dusts is found in the dust collector ductwork. Accumulated dust in ductwork often provides the fuel for devastating secondary explosions or fires. Maintaining the air speed inside the duct safety above the minimum conveying velocity will prevent material buildup.
• ● Spark arrestor: A mechanical device designed to extinguish spark and embers. They are installed in the ductwork on the inlet side of the dust collector (the dirty air line coming into the unit) upstream from the last pickup but downstream of the collector.
• A few variations exist, but the device causes the embers to burn out by a combination of the following: Turning vanes that cause the dust-laden air to change direction rapidly and forcing it to take a tortuous path that allows more time for the spark to burn out; screens that break up the ember into smaller pieces that then burn out; a housing larger than the ductwork to reduce the air velocity causing particles large enough to burn to fall out of the airstream; forcing the dust-laden air to impact a flat surface, causing the larger particles to fall out. For proper functioning of the spark trap, the length of duct between the spark source and the spark trap should be at least one duct diameter, and between the spark trap and the dust collector should be at least ten times the duct diameter. A shorter distance will prevent the spark trap from working correctly and is not recommended. Finally, be careful not to confuse a knockout box like device or a cyclone dust collector with a spark arrestor. These devices cannot guarantee 100% spark removal.
• ● Special Filter Media: While there is no such thing as a “Fire proof filter” certain filter medias provide a level of added resistance to sparks and embers such as flame retardant coatings. Others use conductive materials within the fabric and can assist with static dissipation.
• ● Sprinklers: Per local building codes you may be required to install traditional water sprinklers inside certain parts of the process, including inside the dust collector incase of fire.
• ● Choice of filter style: For applications with high dust loading, heavy dusts or “sticky” dusts the use of cartridges may create an additional hazard. With horizontally-mounted cartridges, dust becomes trapped in the pleats in the upper third of the filters This trapped dust can burn even if the filter media is fire retardant.
• ● Hopper discharge devices: Normally the choice of a discharge varies depending on the process needs and budgetary concerns. With combustible dust applications however the choice of a discharge device can have a major impact on safe operation. Rotary airlocks rated for combustible dust applications work best. Rotary valves enable quick and continuous emptying of the hopper, eliminating the potential for material in the hopper to serve as fuel for a potential explosion or fire. Discharge to a seal drum or hopper can also work well if they are rated to withstand potential explosion pressures. But these must be constantly replaced in order to prevent material backing up into the hopper. Finally, double dump valves rated for combustible dust applications can prove useful in applications with combustible dust but also larger pieces that could potentially jam rotary valves.

So, now that we have seen more clearly what are the hazards you might face and the pasive and active approaches to make your facility safer… its time to make an honest review of what needs to be adjusted in order to minimize risks.