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Engineering Controls Database

Reducing Hazardous Dust Exposure when Rock Drilling During Construction

Construction workers may be exposed to hazardous dust containing crystalline silica during site preparation when drilling systems are used. NIOSH found that drill dust could be decreased by using wet or dry dust reduction engineering controls, enclosed cabs, and implementing a dust control program.
Breathing dust that contains crystalline silica can lead to the development of silicosis, a deadly lung disease. No effective treatment exists for silicosis, but it can be prevented by controlling workers’ exposure to dust containing crystalline silica. Exposure to crystalline silica has also been linked to lung cancer, kidney disease, reduced lung function, and other disorders. Rock drilling before blasting for highway construction may generate a large amount of dust containing crystalline silica. Also, rock drilling for other reasons during construction such as site preparation, pipeline installation, or water well drilling may generate hazardous dust (see Figure 1). Acute and accelerated cases of silicosis have been reported in rock drillers. It has been noted that a drill operator working at a building site where no dust controls were used was exposed to 16 times the NIOSH recommended exposure level (REL).
EPHB and the NIOSH Pittsburgh Research Laboratory have conducted studies in the construction and mining industries where rock drilling is done. Engineering controls and work practices identified in these studies help prevent silicosis by keeping dust containing crystalline silica out of the air workers may breathe (see Figure 2). In addition to the engineering controls described below, A comprehensive site-specific health and safety program should also include recognizing when silica dust may be generated and describe strategies to control or eliminate dust. In addition to the engineering controls noted below, the program should also include personal protective equipment, and work practices.

During rock drilling operations, use wet or dry control systems to control dust. Wet systems are efficient but may freeze in the winter. Caution is advised when using wet systems in the presence of electrical energy sources. When purchasing equipment, look for dust controls. Always use the dust control system and keep it well maintained. Do not use equipment if the dust control system is not working properly. Establish a documented maintenance program for the dust control systems mentioned below. Dry systems require careful maintenance of the drill deck shroud.
When changing filters, the use of respirators by workers may be appropriate. Take safety precautions to minimize the presence of workers near rock drilling. Also, use warning signs and barriers to separate workers, pedestrians, and vehicles from rock drilling equipment. Provide training to rock drillers and assistants in the use of controls and work procedures. During rock drilling, perform air monitoring of respirable crystalline silica exposures to make sure engineering controls are working and to determine whether workers need respiratory protection.

Engineering Controls

• Wet drilling systems pump water through the drill stem to prevent dust from being released into the air. The drill operator controls the flow using a control valve. Some drills are equipped with a flow meter. Raising the water flow will improve dust capture, but too much water will cause operational problems.

• Dry collection systems require an enclosure around the area where the drill stem enters the ground. The enclosure is made by hanging a rubber or cloth shroud from the underside of the drill deck. The enclosure is ducted to a dust collector that has a fan outside of the filter opposite the drill hole. The fan creates negative pressure inside the enclosure capturing dust as it leaves the hole during drilling. The dust is removed in the collector.

• When feasible, use rock drilling equipment with enclosed positive-pressure cabs with air conditioning and filtered air supply to isolate the operator from the dust. Older cabs can be retrofitted with systems that filter, heat, and cool the air.

Figure 1. Rock drilling without appropriate dust control

Figure 1. Rock drilling without appropriate dust control

Figure 2. Dry dust control system working correctly

Figure 2. Dry dust control system working correctly
NIOSH Workplace Solution [2009]. Reducing hazardous dust exposure when rock drilling during construction. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2009-124.
construction workers
highway construction
pipeline installation
rock drillers
rock drilling
water well drillers
It has been reported that the dry dust control system using a “common square shroud” can achieve dust reduction efficiencies that approach the 95% level.