Health and safety hazards and environmental impacts in mining and construction take many forms. One of the most ubiquitous risks, and among the hardest to prevent or control, is the generation of dust.
At its most basic level, dust consists of tiny solid particles that have become airborne though physical means such as wind or the action of machinery. Dust particles are generally measured in microns (one-millionths of a metre) and can often be too small for the eye to see.

“Dust is not only a health and safety hazard that creates impaired visibility, irritated nasal passages and lung disease,” says Frank Fox, chairman of the health and safety task force at the International Council on Mining and Metals. “It also accelerates wear and tear on pulleys and bearings, increasing the likelihood of costly accidents, repairs and maintenance. Dust increases the risk of corrosion and the cost of maintenance, and can even be explosive. The hazard from dust is often underestimated and may be a real danger.”

Large dust particles are filtered out by the human nose and mouth, but smaller particles can beat these defences and be deposited in the deepest areas of the lungs. Clearing dust from the lungs can be a very slow process, allowing time for physical and biological damage to occur. In minerals processing and construction, dust is emitted when rock is hammered or crushed and during operations such as loading, dumping or transferring. After it settles, dust can be suspended again by wind or by the movement of workers and machinery.

“If controlling dust were a simple matter, dust problems in tunnels and mines would have been eradicated years ago,” writes Fred N. Kissel, editor of the U.S. Centers for Disease Control and Prevention’s Handbook for Dust Control in Mining.

At 132 pages, the handbook demonstrates the large number of challenges posed by dust. The problems and solutions are closely connected to the type of rock being mined, the mining methods used and the location and condition of the site.

Dust can also pose significant environmental problems by polluting waterways or damaging fauna and flora in areas adjacent to mining and construction sites. So it is not surprising to find that most countries have strict legislative requirements to control industrial dust emissions for environmental, health and safety reasons. For contractors and mine operators, knowing how to control dust can help reduce complaints from neighbors and employees and increase goodwill in the local community.

“Reducing the airborne concentrations of inhalable coal and silica dust through better machine design and proper ventilation practices is a high priority in the mining industry,” says Professor Kadri Dagdelen of the mining engineering department at the Colorado School of Mines.

Alan Gissing, general manager aftermarket at Sandvik in South Africa, says that by following correct maintenance procedures on equipment dust can be curtailed.

“Well-designed systems deteriorate with time, but with preventive interventions and replacement strategies, dust can be maintained at acceptable levels.”

Dust control is the science of reducing harmful dust emissions, and the first approach is always to look for better engineering solutions. Properly designed, maintained and operated, dust control systems can reduce emissions, and thus workers’ exposure to harmful dust.

While many of the techniques for dust prevention are quite technically advanced, others are simple and based on common sense. The city of Albuquerque, New Mexico, a dusty desert place to begin with, recommends installing fencing at construction sites and reducing vehicle speed as ways to reduce dust.  In the mining industry, four important groups of technology-based solutions are currently used to control dust – dust collection, wet dust suppression, airborne dust capture through water sprays, and electrostatic dust suppression systems (see sidebar). These are in addition to simple methods like sealed shrouds, covers and enclosures around a dust source. Dust collection systems use ventilation principles (high pressure/low pressure) to capture and channel the dust-filled air stream and carry it away from the source.

Wet dust suppression techniques use water sprays to wet the material being mined so that it generates less dust.  Airborne dust capture systems usually also involve spraying with water. When the dust particles collide with the water droplets, they become too heavy to remain airborne and settle.

“The surface blast hole drills have handled dust quite successfully through better dust collection systems,” Professor Dagdelen says. “The long-wall shearers have also significantly reduced the dust generation through improved orientation of the cutting picks. Yet we still have a lot of work to do in this area.”

Dust collection systems can provide reliable and efficient control over a long period of time, but the capital and operating costs are high. Wet dust suppression and airborne dust capture systems, while somewhat less efficient, are less expensive to install and operate, according to the Handbook for Dust Control in Mining.

“As real-time personal dust monitors come into common use, new opportunities exist for reducing dust to lower levels,” Dagdelen says.

The U.S. Department of Labor’s Occupational Safety and Health Administration notes in its own Dust Control Handbook that justifying a capital investment usually requires a 10 to 15 percent return. For dust control, however, such a return on investment is not always practical.

In the United States, tax relief benefits are available at both the federal and state levels for industries that install pollution control systems such as dust control. As important considerations in justifying dust control, OSHA points to intangible benefits such as reducing health hazards, explosions and wear and tear on machinery, improving relations with neighbours and creating better working conditions in general.