Silica

Crystalline silica is a form of silicon dioxide found in materials such as stone, sand, concrete, and similar mineral-containing products. “Respirable” refers to particles small enough to penetrate deeply into the lungs. Cutting, grinding, drilling, polishing, and other activities that disturb silica-containing materials can generate respirable crystalline silica dust. NIOSH identifies silicosis, lung cancer, COPD, certain autoimmune diseases, and chronic renal failure among the serious health risks associated with excessive occupational exposure.

The significance of an air sample depends on what work occurred during the sampling period. An expert may examine sampling duration, task duration, worker location, equipment, production rate, ventilation or water suppression, respirator use, laboratory methods, and whether the monitored conditions reasonably represent the period being disputed. OSHA's silica standards use exposure assessment and air monitoring as methods for determining employee exposure to respirable crystalline silica.

Controls such as local exhaust ventilation, water delivery, isolation, and work practices can materially reduce airborne dust concentrations. Respiratory protection serves a different function by reducing the amount of airborne silica inhaled by a properly protected worker. The effectiveness of these measures depends on whether they were appropriate for the task and whether they were used or operating as intended. In construction, OSHA's silica standard includes specified engineering and work-practice controls for listed tasks and establishes a permissible exposure limit of 50 μg/m³ as an eight-hour time-weighted average.