In most industrial settings, dust will accumulate over time in nooks and crannies across the site. Many of us may find dust irritating, but we also often assume it's relatively harmless.

That misconception is one of many that, if not addressed, can lead to dangerous situations on site. In many manufacturing environments, the dust can be combustible, meaning the risk of fires and explosions is a reality. 

Thousands of workplaces worldwide have some level of combustible dust on site. That is why misconceptions about combustible dust must be tackled.  This article examines five of the more prevalent combustible dust collection myths. 

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Misconception #1: Flame-retardant media eliminates the risk of an event in a dust collector 

Flame-retardant treatments adjust the properties of a filter media (i.e. cellulose or polyester) so that it will self-extinguish when removed from an external ignition source. However, when air and particulates are actively drawn toward the filter media, a “dust cake” (or a build-up of dust) can occur on the filter. Even if you regularly clean your filters, the dust layer will never fully dislodge from the surface of the filter media. 

If an ignition source, such as a spark or ember, enters the dust collector, it could come in contact with the dust cake. While the flame retardant media will not support a fire by itself and therefore slow down any potential fire, it cannot extinguish the dust cake fire. In metal fabrication processes, such as welding or grinding, flame-retardant media is typically one component of a larger mitigation strategy. 

Misconception #2: Fans start fires 

Most dust collectors operate under negative pressure, meaning the fan is located downstream of the filter media or on the clean side of the collector. Normally, the fan pulls air and particulates from upstream of the filter media into the system. If any external ignition sources are present, they can also get drawn into the dust collector. That could lead to potential combustion events. 

Because the fan inlet pulls in all the air and particulates, it is also the hottest place in the dust collector. That is why fans often suffer the greatest damage when fires occur. But it doesn't make them the cause of the fire. 

A fan that goes out of balance resulting in a spark is more likely to exhaust the spark in the direction of the outlet. In that case, the bigger concern would be determining where the exhaust leads. 

Misconception #3: An explosion vent is all you need 

Explosion vents are an important part of your mitigation strategy, but they aren’t the only thing you need to prevent or control combustible dust events. Furthermore, the NFPA recognizes fires and flash fires as combustible dust risks. The equipment or solutions used to mitigate those events are different from what you typically use to handle explosions.   

There are plenty of dust collection technologies in the industry. Many of them can effectively support various mitigation strategies. You need to find the right mix to mitigate the specific hazards your business is faced with. 

It’s important to understand the hazard you’re trying to mitigate. For example, when collecting pharmaceutical dust from a manufacturing process, you may want a mitigation strategy that contains and suppresses an event rather than one that releases material to the outside environment. 

Misconception #4: Dust collectors smaller than eight cubic feet are risk-free 

According to NFPA 652, a dust collector greater than eight cubic feet must be protected from deflagration. As a result, many people assume that a dust collector smaller than eight cubic feet means they shouldn't be concerned about meeting NFPA requirements. 

While the guideline may seem straightforward, it complicates things. The size of a dust collector does not change the combustible properties of the dust. The risk remains, but applying some mitigation equipment to a vessel of that size becomes more challenging.

An explosion in dust collection equipment of less than eight cubic feet can still cause injury to others or damage to property in the surrounding area. If you use smaller equipment, the area around the equipment enclosure should be a part of your dust hazard assessment, making factors like good housekeeping more important. 

Misconception #5: The only mitigation choices are the prescriptive actions outlined in the NFPA standards 

NFPA standards are recommendations written like codes so they can easily be adopted by a city, state, or municipality. But they aren’t code per se. Within the NFPA standards, there are two acceptable methods of compliance:

• Prescriptive: using methods outlined in the NFPA standards. 
• Performance-based: an undefined alternative option that accomplishes the same objective as the prescriptive strategy. 

When utilising the performance-based method of compliance, you can create your mitigation strategy based on your process, risk assessment and dust hazard analysis. In many cases, you will have to rely on an external expert during the design or evaluation process to identify existing and additional safeguards. Documenting decisions and involving the local Authorities Having Jurisdiction (AHJs) in the process will help you get your mitigation strategy approved. 

Not as straightforward as it seems