Silicosis is a deadly lung disease. Construction workers may get sick with silicosis if they breathe in too much respirable crystalline silica, a fine, sandy dust. Silicosis may take 10 or more years to develop when workers are exposed daily to low concentrations of silica dust. However, when exposures to silica are very high, symptoms can occur after only a few weeks to 4-5 years. To prevent silicosis, researchers from NIOSH (the (National Institute for Occupational Safety and Health) urge construction workers to protect themselves from dust exposure when doing construction work, especially tuck pointing. In tuck pointing, the worker grinds the mortar out from between the bricks the first step to fixing up the outside of an older brick building. Mortar dust contains crystalline silica. During tuck pointing, workers hold power grinders, digging the mortar out to a depth of an inch or less. The grinders often have wheel diameters of 4 to 6 inches and rotate at speeds as high as 12,000 rpm. The grinding process breaks up the mortar and turns it into airborne dust The rotating wheel creates wind that carries this airborne dust throughout the workplace. When workers clean the mortar joints and their clothes, tools, and equipment with compressed air, the strong blast needlessly adds even more dust to the air (see Figures 1 and 2). During a recent study of tuck pointing at a construction site, NIOSH researchers measured very high concentrations of respirable crystalline silica. At This site, the workers' exposures were up to 50 times the REL (recommended exposure limit). At another construction site, investigators from OSHA (Occupational Safety and Health Administration) found high exposures up to 100 times the REL.