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By John A. Mineo - Director of Construction & Engineering
American Insurance Service Group
New York, New York
Crystalline silica is the basic component of sand, quartz and granite rock. Airborne crystalline silica occurs commonly in both work and non-work environments. Activities such as a sandblasting, rock drilling, roof bolting, foundry work, stonecutting, drilling, quarrying, brick/block/concrete cutting, gunite operations, lead-based paint encapsulant applications, asphalt paving, cement products manufacturing, demolition operations, hammering, chipping and sweeping concrete or masonry, and tunneling operations can create an airborne silica exposure hazard.
Occupational exposure and inhalation of airborne crystalline silica can produce silicosis, a disabling, dust-related disease of the lungs. Even materials containing small amounts of crystalline silica may be hazardous if they are used in ways that produce high dust concentrations. Depending on the length of exposure, silicosis is a progressive and many times a fatal disease that accounts for approximately three hundred deaths annually in the construction industry, or 10% of all silicosis-related deaths annually.
Inhaling silica dust has also been associated with other diseases, such as tuberculosis and lung cancer. There is no cure for silicosis, but it is a 100% preventable occupational disease.
What Is Silica?
Silica is the name of a group of minerals containing silicon and oxygen in chemical combination having the general formula SiO2. Silica may be free, in which case only SiO2 is present, or combined, in which the SiO2 is combined chemically to some other atom or molecule. The difference is important to recognize, since the silica problem exists only with free silica. Labels on materials and product analysis sheets (e.g., MSDS sheets) must be read and instructions for use followed carefully.
Types Of Silica
Free silica may occur as amorphous-free silica, of which there are many forms, and crystalline-free silica, of which there are five principal forms. Certain materials contain both amorphous- and crystalline-free silica.
Silica-related diseases are associated only with crystalline-free silica. The most common examples of crystalline-free silica are beach or bank sands. A third form of free silica is fused silica which is produced by heating either the amorphous or crystalline forms. Other forms include cristobalite and tridymite.
Quartz, a principal form of silica, geologically is the second most common mineral in the earth's crust. Quartz is readily found in both sedimentary and igneous rocks. Quartz content can vary among different rock types; for example, granite can contain anywhere from ten to forty percent quartz; shales have been found to average 22 percent quartz; and sandstones can average 70 percent quartz.
Exposure During Construction
The most severe worker exposures to crystalline silica results from sandblasting. In the construction industry, sandblasting may be used to remove paint and rust from stone buildings, metal bridges, tanks, and other surfaces. Other construction activities that may produce crystalline silica dust include jack--hammer operations, rock/well drilling, concrete mixing, concrete tunneling, and brick and concrete block cutting and sawing. Tunneling operations, repair, or replacement of linings of rotary kilns and cupola furnaces, and setting, laying, and repairing railroad tracks are also potential sources of exposure.
Concrete and masonry products contain silica sand and rock containing silica. These products are primary materials for construction, and construction workers may be exposed to respirable crystalline silica during activities such as the following: