Silica dust can be generated at dangerous levels anytime materials such as ceramics, concrete, masonry, rock and sand are mixed, blasted, chipped, cut, crushed, drilled, dumped, ground, mixed or driven upon.
Employees at construction sites may be exposed to silica dust during general housekeeping activities such as sweeping, emptying vacuum cleaners, and using compressed air for cleaning.
Silica exposures may also occur whenever silica-containing dust is disturbed, such as during material handling. The small particles generated during these activities easily become suspended in the air and, when inhaled, penetrate deep into employees' lungs.
Quartz is the most common form of crystalline silica. In fact, it is the second most common surface material accounting for almost 12% by volume of the earth’s crust. Quartz is present in many materials in the construction industry, such as brick and mortar, concrete, slate, dimensional stone (granite, sandstone), stone aggregate, tile, and sand used for blasting. Other construction materials that contain crystalline silica are asphalt filler, roofing granules, plastic composites, soils, and to a lesser extent, some wallboard joint compounds, paint, plaster, caulking and putty.
Cristobalite and tridymite are natural constituents of some volcanic rock. Man-made forms result from conversion of quartz or amorphous silica that has been subjected to high temperature or pressure. Diatomaceous earth, composed of amorphous silica, crystallizes during heating (calcining), yielding a calcined product that contains as much as 75% cristobalite. Cristobalite is also found in the superficial layers of refractory brick that have repeatedly been subjected to contact with molten metal.
Visible dust contains large particles that are easy to see.
Respirable dust particles pose the greatest risk because they are not visible. They are are so small they can get deep into the lungs.
When exposed to silica dust, it’s important to remember the following:
The first step, and a very important OSHA requirement, in making sure exposure to silica dust is controlled is to design, development, and deploy an effective Exposure Control Plan (ECP).
It is important to conduct regular inspections in general industry workplaces and construction worksites for silica dust exposures, and evaluations of the ECP. To help ensure an effective ECP and positive OSHA enforcement inspections, be sure to check and evaluate the areas in the checklist to the right.
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