Putting Dust in Its Place

THE AIR QUALITY INDEX (AQI) is a number used by government agencies to characterize the quality of the air at a given location. As the AQI increases, a larger percentage of the population is likely to experience increasingly severe adverse health effects.

To help simplify our lives, and to make it easier for television weather forecasters to have something colorful to show on the television screen, the AQI has a pretty color code guide. This ranges from green, which is very good, to purple which indicates the air quality is so unhealthy that no one should even attempt to breathe it.

Suffice to say that even without the use of a fancy government acronym, or colorful charts, any air you can see is generally unhealthy to breathe. Our “good” air is composed of 78% nitrogen, 20% oxygen and various amounts of carbon dioxide and other gases. What is not naturally found in air are all of those fine particles of soil which are removed from the earth’s surface as a result of either manmade or natural wind erosion. In a word: dust.

Dust can be a simple annoyance when it accumulates on furniture surfaces, or it can become a lifethreatening problem to those who suffer from respiratory ailments such as bronchitis and influenza. Most of us don’t enjoy walking around in a dust cloud, like the Peanuts character Pigpen. Real human beings know that dust needs to be managed and controlled.

Since Congress enacted the Clean Air Act Extension of 1970, tragedies such as the 1930’s Dust Bowl, and the toxic waste “Love Canal” incident of the ’80s have never been duplicated. The increased regulations implemented by the Environmental Protection Agency (EPA) were specifically designed to protect the general public from dust and other toxic airborne chemicals. In 2011, the standards will be reviewed again, so staying on top of the latest legislation is important for anyone involved in dust control.

Water as a dust controller

Water, of course, is the time-tested method of mollifying dust, but water use has gotten complicated. Water shortages abound across the country, particularly in the dry areas of the Southeast and the West. The shortages make water both impractical and, in some areas, impossible to use due to soaring costs.

Water also evaporates quickly, and without any additives blended in to help bind the dust particles together, some contractors find themselves re-treading the same spots several times over to keep the dust compacted.

The good news is that the market is filled with a variety of dust control products. These products attract moisture, bind dust particles together, seal the surface, and promote vegetation or some combination of these effects.

Chemical dust controllers

Chemical suppressants increase water’s ability to hold back dust by allowing it to be deeply absorbed rather than simply run off the surface. They evaporate more slowly than plain water, allowing you more time between applications.

Lignin-based products, for example, are able to bind dirt particles to one another while retaining some plasticity. They will dissolve quickly in rain, but they may not be the best dust control method for areas that receive high levels of rainfall and snow.

Chlorides are a common chemical suppressant. These dust control agents use salt to attract moisture from the air. Chlorides are particularly handy in areas of high humidity. They will also work in areas where the temperature is below freezing. The downside is that chlorides can be very corrosive to equipment, due to the fact that they’re introducing a salt.

For unpaved roads, chloridebased products such as calcium chloride and magnesium chloride are the perennial favorites. They work by creating adhesion among dust particles. The salts are hydroscopic, attracting moisture in the air during periods of high humidity and holding it in the ground. Dust particles are then coated and bound together. This type of dust suppressant can also reduce the evaporation rate of water when the air is hot and dry.

Although time has proven chlorides to be an effective method of dust control, controversy surrounding their use has been fueled by studies which claim that chlorides cause contamination of soil and damage to vegetation.

In a similar fashion to chlorides, acrylic polymers and polymer emulsions are bonding agents that penetrate soil and hold soil particles together. Some polymer products contain dyes that allow the operator to see how much ground has been covered, making it easier to keep track of application.

Like polymer products and chlorides, resins bind the dust particles together as well as protect against wind erosion. Moreover, they fortify soil against wind erosion and the overall environmental impact is low. Resins have most often been used to good effect in drier climates. However, some surfaces have the potential to become brittle and slippery following the application of traditional resins. This creates the need for more frequent follow-up. Also, the cost of resins can run high.

Bitumins are a good choice for larger projects. Bitumens are compounds derived from petroleum that create a film that covers dust particles, making them heavier and less likely to become airborne. A bitumen product can be added to asphalt for roadways.

But while bitumens are known for their effectiveness, they are also often more expensive.

A newer approach to dust control involves material that is formulated from a byproduct of soybean oil extraction. These soy-based commercial products are known as soybean feedstock, or SBFs. They work by infiltrating a road’s surface, affixing to the soil and creating a protective shield. As a benefit, SBFs are noncorrosive and are not toxic to animals or plants (although weeds and grass in the roadbed will be suppressed). Since they are organic-oil based, they are not as easily disturbed by water as salts, either.

Aside from chemicals, other products can police dust as well. Bentonite, for example, is a naturally-occurring mineral best suited for limestone roads. A university study found that bentonite blends with road surface material and sticks to it like “electrochemical glue.” Grading or other maintenance activities will not reduce its long-term effectiveness. Furthermore, the cost of bentonite is about half of the cost of calcium chloride.

Fibers and mulches can also be implemented to stabilize soil and palliate dust. Although dust control is often not the express purpose of such products, they do hasten revegetation by forming a crust. Underneath the crust, soil is nourished to produce growth. It creates an organic cover that will protect seeds, enhance germination and speed up the vegetation process. Increased plants, in turn, will stabilize the soil and prevent loss due to erosion.

Non-chemical methods may include geotextiles, too, which are permeable to increase stability and decrease erosion. Often geotextilerelated materials such as erosioncontrol blankets, grids and mats are used as a temporary solution during construction. Vegetation is, however, the best long-term defense against dust. For that reason, hydroseeding can also be counted among dust’s enemies, as it speeds up plant growth.

With all of those options, how do you know which is right for you? When selecting a dust suppressant, there are certain factors that must be considered. Your first and most basic concern is whether the product will provide adequate dust control. This calls into question your equipment, the climate and traffic volume. Look at the soils onsite and match the seed mixture to the type.

Secondly, ask whether the product will be cost effective. Freight is a major component of the cost. You need to ask yourself if the product will be viable given the freight expense. Storage is also significant. It’s also worth noting how difficult liquid products will be to transport and store.

Once you select a product, develop a prevention and control plan. A plan can make fugitive dust a little less overwhelming. Include documentation of your dust control activities and information such as average wind speed and direction, temperature, rainfall, etc. With this data, you can track and evaluate your efforts.

In addition to having a solid plan in place, it’s a good idea to grade no more area than necessary at any given time and to cover graded areas that aren’t being used. Impose low speed limits around the affected areas. Furthermore, educate your equipment operators on how to control dust.

While it may be true that we are all just “dust in the wind,” we need not put up with it in our homes, on our clothes or in our lungs. The technology is already out there to eliminate most of the controllable problems completely. It only takes a bit of effort to keep dust in its place.

Add New Comment  |  Show Comments (0)