This leaflet explains what employers and employees should do to prevent lung disease caused by exposure to silica at work. Silica is a natural substance found in most rocks, sand and clay and in products such as bricks and concrete. In the workplace these materials create dust when they are cut, sanded, carved etc. Some of this dust may be fine enough to breathe deeply into the lungs and cause harm to health. The fine dust is called respirable crystalline silica (RCS) and is too fine to see with normal lighting. The leaflet explains how RCS can damage health and what to do to prevent harm.