The different types of fugitive dust

There are many ways to understand dust. But if you need to reduce your dust emissions, there should only really be one way.

To control dust in an environmentally friendly, efficient and effective manner, one must first understand it. The dividing up of dust into its different types is a crucial part of this. In particular, our dividing up of the different types of fugitive dust will be of the utmost importance. But here we shouldn’t get ahead of ourselves. Let’s proceed with caution. For the distinctions we draw should not be made willy-nilly, but instead be informed by their usefulness to our guiding aim: the halting of the dust’s dispersal into the air.

different types of dust labelled badly
We can divide dust up into types any way we want, really. But some ways will be more effective relative to our goal than others.

For it would not be very sensible if we drew up our types of dust ultra-specifically: if we named each and every one of them, Sally, Dave, Jennifer and so on, according to their own particular unique qualities. For while they would indeed have such particular qualities, these wouldn’t be relevant to our stopping their airborne flight. Likewise it would not be very sensible if we drew up our types ultra-broadly: if we were just to call it all dust, no matter how it became airborne, nor how best to stop it.

But there must be a middle way. Let’s take a look at how the EPA draw up their types of dust, and we’ll see if it suits our purpose.

The EPA’s typology of dust

In the EPA’s (The Environmental Protection Agency of the United States) encyclopaedic guide to the various sources of air pollution, AP-42: Compilation of Air Emissions Factors, dust is divided into two types: fugitive, and non-fugitive. The two are distinguished from one another according to their source, and its relation to the air.

This seems like an advantageous joint at which to split the broader concept apart. As above, we want by the end of this article to end up with a set of dust-distinctions useful relative to our guiding aim: the stopping of airborne dust. How the dust enters the air is, with this aim in mind, intuitively one of the key candidate variables we are going to want to control – preventing dust from becoming airborne in the first place is the ideal method of dust control, if possible. But let’s move on to the EPA’s actual distinctions.

Fugitive dust comes from open sources. ‘Open’ here means exposed to the open air, so that the dust “is not discharged to the atmosphere in a confined flow stream” (EPA, AP-42, 13.2). The EPA here lists common sources as “unpaved roads”, “aggregate storage piles” or “heavy construction operations”.

Non-fugitive dust, on the other hand, comes from closed sources. ‘Closed’ here means closed off from the open air, so that the air is discharged to the atmosphere in a confined flow stream. Common sources here are any industrial process which makes use of a flow-stack, or exhaust chimney: lime and cement kilns, power plants or recycling incinerators.

It should be clear already that the two types of dust are going to require different methods of control. Non-fugitive dust emissions can be processed and filtered until the particulate matter levels, along with other dangerous pollutants, are reduced to safe levels.

This cannot be the case with fugitive dust emissions, however. The dust enters the air not from one isolatable, easily controllable source, but from a source which can be hard to pinpoint. It therefore requires different approaches, and, as it turns out, another pair of distinctions. These will again be based upon the different types of fugitive dust sources, and their different relations to the air.

The different types of fugitive dust sources

There are generally two types of fugitive dust sources in industry in terms of their relation to the air: the industrial processes themselves, and the roads and pathways used to transport the finished goods, workers and any other materials or equipment.

We can call fugitive dust escaping from the industrial processes process-based fugitive dust, and that fugitive dust which escapes from roads and pathways road-based fugitive dust.

The two, under the EPA’s fugitive and non-fugitive categorisation schema, both fall into the fugitive category, as they both emit dust straight into the open air. But, practically speaking, while their relation to the air is of the same type, it is not anywhere near to being of the same degree.

We will need examples to make this point clear. For the industrial process, we can take a stone-crushing operation studied for its PM10 emissions by the EPA in 1992.

gravel pit with different types of fugitive dust sources annotated
Both the road-based and process-based fugitive dust needs to be controlled to ensure a healthy and legally compliant operation.

The operation was composed of a tertiary crusher and a vibrating screen. Dust was emitted from three points: the stone-crusher inlet, the stone-crusher outlet, and the vibrating screen. The researchers constructed ducts around the emission points to facilitate accurate measurement of the emissions. We can take the dimensions of these ducts to be the area from which dust was emitted. This was 4.68 metres squared for the stone-crusher inlet, 5.95 metres squared for the outlet, and 0.74 metres squared for the vibrator screen, all to two significant numbers. This gives a total area of 11.37 metres squared from which dust was being emitted.

For the transit-based fugitive dust, we can take an averagely long access road of 700 metres length and 7 metres width. Assuming that the whole surface of the road to be a potential dust emitting source, this gives an area of 4900 metres squared from which dust is being emitted.

It is clear, then, that the two types of fugitive dust sources are exposed to the open air in very different magnitudes, even if they are still essentially both fugitive sources in the EPA’s sense. This naturally has consequences for the most practical means by which to control their emissions.

For, due to the size of the industrial processes’ dust emittance source, they are in general amenable to control through their confinement, in some way, from the open air. Confining an area of 12 metres squared need not pose great technical problems.

And conversely, due to the size of the roads and pathways’ dust emittance source, they are not amenable to control through confinement. Attempting to control a road of any normal size’s dust emissions by confining it from the open air will be impractical and cost inefficient.

Understanding this division of the types of fugitive-dust sources, processes and roads, therefore serves as the first step towards developing targeted solutions. The most ideal solution for process-based fugitive dust will not be the ideal solution for road-based fugitive dust, and vice versa.

LAMI’s solution

Our dust control systems operate along the above distinctions between the different types of fugitive dust. A short description of each system type will exemplify the utility of their being designed along such lines. The distinctions upon which your dust control plans rests are key to its eventual success or failure.

For process-based fugitive dust, we provide the NBB Fogging System. It confines the dust source through a dust-impenetrable barrier of fog. The heavy fog, unlike the alternative of a solid, physical containment barrier, does not interfere with the proper running of the process.

LAMI NBB dust control system in action
The NBB surrounds the process source, confining its fugitive dust from the open air until it falls once more to the floor.

For road-based fugitive dust, we provide either the DSB or RBB Natural Rain Systems. As confinement is not a practically viable option for road-based fugitive dust, another approach had to be taken. Rather than acting to meet the dust in the air, they act to prevent the dust from becoming airborne in the first place. In this they act along the same principles of rain’s dust controlling effect – they simply wet the road just enough that its dormant surface dust cannot jump up into the air.

LAMI DSB dust control system in action
The DSB system, standing at the roadside, dampens the road’s width just enough so that its dust can’t become airborne.

Each dust type needs its own type of dust control

We remarked at the start that the dividing of dust into types based upon its source, and that source’s relation to the air around it, is key to developing environmentally friendly, efficient and effective dust control methods.

It should now be clear why.

For imagine if one were to treat both process-based and road-based fugitive dust as one type of dust source. Suppose you implemented a system like the NBB. While this would effectively control the dust from both one’s roads and one’s processes, it would only do so efficiently for one’s processes, and not for one’s roads. This inefficiency would in turn mean that the method was not environmentally friendly; it would involve the wasting of a precious resource, and the likely degradation of one’s roads through the over-application of water.

On the other hand, if you were just to use the RBB across both types of fugitive dust sources, only the roads‘ dust would be effectively controlled, if efficiently so. The process-based dust would remain uncontrolled, however, so that in the end one’s aim in implementing the system would not even be fulfilled.

Either way, a failure to attune one’s dust-distinctions properly would be a costly mistake. To effectively control dust, one needs to know the qualities which need to be controlled. To efficiently control dust, one needs to know just how much those qualities need to be controlled, relative to your control measure. And to control the dust in an environmentally friendly way, you need to do both of these things while using only non-toxic materials, and the lowest amount of them at that.

The fulfilling of these three criteria will need a lot of knowledge. Our distinguishing between the different types of fugitive dust is one of the first steps. If you want to find out more, read some of our other articles about dust and its peculiar qualities. But if you’re too busy to become a dust expert, but you still need to control your dust problem, then just contact us here. We’ll be happy to help.

References

https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors

https://www3.epa.gov/ttnchie1/old/ap42/ch11/s1902/reference/ref_12c11s1902_1995.pdf

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