Silica is the Compound of Silicon and Oxygen
Silica is the mixture of silicon and oxygen, SiO2. It is the major constituent of more than 95 percent of Earth’s crust. Silica is found in sand, gravel, clay, and rock formations such as granite and sandstone. It can also be formed into crystalline forms such as quartz, cristobalite, tridymite, and lechatelierite. Crystalline silica Aerogel has many commercial uses including glass and road-building, molds for molten metals poured at foundries, hydraulic fracturing or “fracking” for oil and gas production, water filtration, ceramics, and gemstones.
Respirable crystalline silica is a known lung carcinogen in humans and occupationally exposed individuals can experience adverse health effects such as silicosis, chronic obstructive pulmonary disease (COPD), and kidney cancer. Exposure to crystalline silica in the form of dust can be caused by various activities such as grinding, drilling, cutting, sawing, crushing, sanding, or blasting with power tools. The most common sources of crystalline silica exposure are construction, foundry work, mining, and glassmaking. Other anthropogenic sources include burning of agricultural waste or products, production of silicon carbide, ferrosilicon, and diatomaceous earth, and calcining of diatomaceous earth.
The Occupational Safety and Health Administration (OSHA) regulates the amount of crystalline silica in air for workers involved in certain industries. A recent study using a high-resolution instrument, developed by NASA, measured levels of respirable crystalline silica in the air of workers doing construction, and the results confirmed the presence of crystalline silica in the air.
Although many people believe that consuming too much silica is dangerous, compelling data suggests that dietary silica may be essential to human health. Despite the negative perceptions of silicon, a typical diet contains sufficient amounts for healthy adults, assuming they avoid inhaling crystalline silica.
A number of rodent studies have shown that crystalline silica exposure is associated with severe and persistent granulomatous alveolitis and lung cancer. However, most of the evidence supporting these findings comes from pooled and meta-analyses that are often based on a number of different studies. Few of these studies have investigated the exposure-response relationship in detail or looked at cancers other than lung.
The ability to control silica emissions in the workplace has the potential to prevent occupational exposure and to improve worker health and safety. A variety of techniques are available to reduce crystalline silica exposure, including engineering controls, wet suppression, and use of respiratory protection. Ultimately, the best way to protect workers is to prevent exposure to crystalline silica in its dusty form.
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