Workers may be exposed to hazardous dust containing crystalline silica during site preparation when drilling systems are used. The National Institute for Occupational Safety and Health (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 silicosis, a deadly lung disease. No effective treatment exists for silicosis, but it can be prevented by controlling workers’ exposures to dust containing crystalline silica. Exposure to crystalline silica also has been linked to lung cancer, kidney disease, reduced lung function and other disorders.
Many tasks in construction may generate dust containing crystalline silica: grinding or cutting concrete, tuckpointing masonry, using a jackhammer to break concrete, or when using drilling systems during construction. 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. Acute and accelerated cases of silicosis have been reported in rock drillers. NIOSH has noted that a drill operator working at a building site where no dust controls are used is exposed to 16 times the NIOSH recommended exposure level (REL).
NIOSH has 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. NIOSH recommends that the same controls and work practices, described below, be used in construction activities where rock drilling may generate silica dust.
Under federal occupational safety and health regulations, employers have the responsibility for implementing engineering controls and administrative controls, providing personal protective equipment, and providing safety and health training for employees.
Things to keep in mind during site setup:
- Develop a site-specific safety and health plan. The plan
should include guidance for recognizing when silica dust may be generated, and
describe strategies to control or eliminate dust. Include engineering controls,
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 dust-control systems.
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.
How to reduce dust problems through 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.
Other important ways to minimize the risk of contamination:
- Wash hands and face before eating, drinking or smoking. Do not eat,
drink or use tobacco products in the work area where construction activities
are being performed.
- Change into disposable or washable work clothes at the worksite. If
possible, shower and change into clean clothes before leaving the worksite to
avoid contaminating cars, homes and other work areas. If it is not possible to
shower or change into clean clothes, use a vacuum with a high-efficiency filter
to remove dust from clothes. An effective method to remove dust from clothing
involves a booth under negative pressure that uses an air spray manifold to
blow dust from clothing. Do not use a compressed air hose to remove dust from
clothing.
- Park cars where they will not be contaminated with silica
dust.
- Remove dust from equipment using a water hose rather than compressed
air.
- Use respiratory protection when needed. The controls cited in this article may greatly reduce worker exposure to dust; however, respirators still may be necessary to reduce exposure to crystalline silica below the NIOSH REL of 50µg/m3.
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