Exposure to Silica
Silica is a mineral that is found in stone, soil and sand. The amount of silica in soil and rock may vary widely depending on the local geology. Breathing in silica dust can cause silicosis, a serious lung disease. Using rock-drilling rigs mounted on trucks, crawlers, or other vehicles to drill into rock, soil, or concrete may expose workers to hazardous levels of airborne silica. The small particles easily become suspended in the air and, when inhaled, penetrate deep into workers’ lungs.
Control Methods for Silica Dust
There are three main methods used to control silica dust during earth and rock drilling. OSHA recommends that drill operators always use a combination of these dust-control techniques.
The three methods are:
Dust Collection Systems: Best practices when using dust-collecting equipment for rock drills include using a movable duct attached to a shroud, a flexible rubber skirt that encloses the drill hole opening and captures cuttings that come through the hole. Equipment without these controls can be retrofitted by the manufacturer or a mechanical shop.
Dusty air is pulled from inside the deck shroud through a flexible duct to primary and secondary filter media. The primary filter or dust separator often includes a self-cleaning back-pulse feature that dumps the collected particles to the ground. Secondary release of particles to the air is minimized by a dump shroud.
Wet Methods: The proper use of wet methods requires a trained and skilled operator. In wet drilling, too much water can create mud slurry at the bottom of the hole that can trap the bit, coupling and steel extensions. Too little water will not effectively control escaping dust.
Operator Isolation: Drill operators using rigs with enclosed cabs can reduce their silica exposure by staying inside the cab as much as possible during drilling. To be effective, the cab must be well-sealed and well-ventilated. Ensure that door jambs, window grooves, powerline entries and other joints are tightly sealed.
Where control methods do not reduce silica exposures to OSHA’s permissible exposure limit, respirators are required, and employers must have a written respiratory protection program in accord with OSHA’s Respiratory Protection standard.
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7-2. Which dust control technique does OSHA recommend for reducing exposure to silica dust?
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