Danger Dust

Silicosis

Silica is one of the most abundant minerals in the earth's crust and is widely distributed in nature. Silicosis is caused by inhalation of tiny particles of crystalline silica (usually quartz). Workers at greatest risk are those who move or blast rock and sand (miners, quarry workers, stonecutters, construction workers) or who use silica-containing rock or sand abrasives (sand blasters, glass makers, foundry, gemstone, and ceramic workers, potters). Outbreaks of severe silicosis have recently been identified in workers in the engineered stone industry.

Factors that influence the incidence and severity of silicosis include

• Duration and intensity of exposure

• Form and surface characteristics of the silica particles

Amorphous silica, such as glass or diatomaceous earth, does not have a crystalline structure and does not cause silicosis.

When inhaled, silica dust passes into the lungs, and scavenger cells such as macrophages engulf it (see Overview of the Immune System). Enzymes released by the scavenger cells cause the lung tissue to scar and form nodules. In low-intensity or short-term exposures, these nodules remain discrete and do not compromise lung function. With higher-intensity or more prolonged exposures, these nodules coalesce (come together) and cause progressive fibrosis and lung dysfunction, or they sometimes form large masses (called progressive massive fibrosis).