What is Dust?

 Dust consists of tiny solid particles carried by air currents. These articles are formed by a disintegration or fracture process, such as grinding, crushing, or impact. The Mine Safety and Health Administration (MSHA) defines dust as finely divided solids that may become airborne from the original state without any chemical or physical change other than fracture.

How is Dust Generated?

 Dust is generated by a wide range of manufacturing, domestic, and industrial activities. Construction, agriculture, and mining are among the industries that contribute most to atmospheric dust levels.

In minerals processing operations, dust is emitted when ore is broken by impact, abrasion, crushing, grinding, etc. Through release of previously generated dust during operations such as loading, dumping, and transferring through recirculation of previously generated dust by wind or by the movement of workers and machinery. The amount of dust emitted by these activities depends on the physical characteristics of the material and the way in which the material is handled.

Types of Dust

 Fibrogenic dust, such as free crystalline silica (FCS) or asbestos, is biologically toxic and, if retained in the lungs, can form scar tissue and impair the lungs' ability to function properly.

Nuisance dust, or inert dust, can be defined as dust that contains less than 1% quartz. Because of its low content of silicates, nuisance dust has a long history of having little adverse effect on the lungs. Any reaction that may occur from nuisance dust is potentially reversible. However, excessive concentrations of nuisance dust in the workplace may reduce visibility (e.g., iron oxide), may cause unpleasant deposits in eyes, cars, and nasal passages (e.g., portland cement dust), and may cause injury to the skin or mucous membranes by chemical or mechanical action.

From an occupational health point of view, dust is classified by size into three primary categories:

1. Respirable dust
2. Inhalable dust
3. Total dust

Respirable Dust

Refers to those dust particles that are small enough to penetrate the nose and upper respiratory system and deep into the lungs. Particles that penetrate deep into the respiratory system are generally beyond the body's natural clearance mechanisms of cilia and mucous and are more likely to be retained.

Inhalable Dust

The EPA describes inhalable dust as that size fraction of dust which enters the body, but is trapped in the nose, throat, and upper respiratory tract. The median aerodynamic diameter of this dust is about 10 µm.

Total Dust

Total dust includes all airborne particles, regardless of their size or composition.

Benefits of a Dust Control Program

Controlling dust emissions:

• Reduces dust-related human respiratory health problems like asthma, bronchitis, emphysema, hay fever, and allergies.
• Reduces vehicle accidents and human injuries due to poor visibility and road conditions.
• Reduces impacts on fish and other aquatic life, vegetation, agricultural crops, and water quality due to dusting, turbidity, and sedimentation.
• Reduces vehicle and equipment wear and damage due to mechanical abrasion, road impact, and intake of particles in operating equipment.
• Reduces unpaved road maintenance costs by reducing frequency of grading, decreasing loss of fine-grained surface material, and lowering re-graveling costs.
• Reduces liability for damage caused to property or people
• Improves property values and quality of life.
• Reduces complaints from employees and the public.

Dust Emissions and Prevention

Dust emissions can be prevented or reduced in four basic ways:

1. Limiting the creation or presence of dust-sized particles.
2. Reducing wind speed at ground level.
3. Binding dust particles together.
4. Capturing and removing dust from its sources.

 All of the following techniques rely on one or more of these strategies.

 Techniques Applicable to Many Sources:

 Vegetate or mulch areas that won’t receive vehicle traffic.

In areas where planting, mulching or paving is impractical, apply gravel or landscaping rock; clear vegetation only from those areas where you will work right away. Construct natural or artificial wind breaks or wind screens. These may be designed as enclosures for small dust sources.

 Apply water to reduce emissions from temporary sources.

Limited use of water-absorbing (hygroscopic) salts with water will reduce how often you must water trafficked areas.  Apply surface chemical suppressants to untrafficked areas to form a less erodible soil surface.

Techniques for Unpaved, Trafficked Areas:

Lower speed limits.

High vehicle speed increases the amount of dust stirred up from unpaved roads and lots. Lowering the speed of a vehicle from 45 miles per hour to 35 miles per hour can reduce emissions by up to 22 percent.

 Upgrade the road by:

• Increasing surface strength by improving particle size, shape, and mineral types that make up the surface and base materials.
• Adding surface gravel to reduce the source of dust emission. Limit the amount of fine particles (those smaller than .075 mm) to 10 to 20 per cent.
• Improving drainage and crown.
• Using geotextile fabrics to increase the strength of new roads or roads under going reconstruction.
• Encourage use of alternate, paved routes, if available. Dust emissions from paved surfaces are up to 90 percent less than from unpaved surfaces.
• Restricting use by tracked vehicles and heavy trucks to prevent damage to road surface and base.
• Appling chemical dust suppressants using the admix method, blending the product with the top few inches of surface material. Suppressants may also be applied as surface treatments. Chemical treatment can reduce emissions by 30 to 95 percent.
• Paving unpaved permanent roads and other trafficked areas.
• Paving or treat permanent unpaved haul roads, construction sites, and parking or staging areas at commercial, municipal, or industrial facilities.

 Techniques for Paved, Trafficked Areas:

 Vacuum or wet sweep fine dirt and skid control materials from paved roads soon after winter weather ends and at other times, when needed.  Flush roads with high pressure low volume nozzles in areas where sweeping is not effective.

 Minimize vehicle “track-out” material by:

• Filling in muddy areas with gravel or other surface material.
• Chemically stabilize all adjacent unpaved areas.
• Installing “grizzlies.” These rough-surfaced areas, such as lengths of gravel or cattle guards, scrub soil and mud from vehicle tires.
• Building vehicle tire/underbody wash stations near unpaved road junctions at project sites.
• Pave or stabilize shoulders of paved roads with gravel and vegetation.
• Provide for storm water drainage and construct curbing to prevent water erosion onto paved roads.

 Total Cost Accounting for Dust Suppression Projects

 Developing an effective and cost-efficient dust control program means accurately identifying and accounting for the true costs and savings of any new alternative.  Many sites that implement constant watering practices believe that they have no cost associated to their program. For unpaved roads, the costs can be grouped into the categories listed below:

Road Improvement Costs

• Drainage improvements, geometric improvements, repairing of failed areas, excavation and removal of substandard material, and addition of surface material. (Note: These costs are not part of dust suppression program costs if they would be required anyway, without dust suppression.)
• Surface Preparation Costs
• Addition of select material (fines or coarse material), breaking up and loosening the road surface (scarifying), watering, shaping, and compacting.
• Product Supply and Application Costs
• Material cost, transportation cost, application cost, and contract supervisor cost
• Miscellaneous Costs
• Traffic control, detour, inspection, crew supervision, material storage (if inventory is maintained) and liability costs.

 Dust program savings or benefits can be grouped as follows:

• Road Improvement Costs Avoided; these costs are avoided or reduced over time due to greater road stability and durability resulting from chemical treatment.
• Road Maintenance and Repair Savings; these savings are due to less frequent regrading and less frequent need to add supplementary road materials. They accumulate due to reduced loss of gravel and fines, along with greater durability of the road surface.
• Savings from Non-road and Off-site Benefits; these are the savings that accrue from the many dust control program benefits not specifically related to the road itself, i.e., human health, vehicle-related, and environmental.

 Recommendations

Approach your dust control problem systematically, looking first at prevention options.   Evaluate the cost of current practices and the potential cost of ignoring the issue.

 Prepare a Dust Control Plan

• Identify of all fugitive dust sources.
• Identify all state, local, and federal regulations that may be applicable.
• A description of the dust control method(s) to be used for each source.
• A schedule, rate of application, calculation or some other means of identifying how often, how much or when the control method is to be used.
• Provisions for monitoring and record-keeping.
• A backup plan in case the first control plan does not work or is in sufficient.
• The name and phone number of the person responsible for making sure the plan is implemented and who can be contacted in the event of a dust complaint.

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