Many miners are exposed to respirable crystalline silica (RCS) in respirable dust.  These miners can develop lung diseases such as chronic obstructive pulmonary disease, and various forms of pneumoconiosis, such as silicosis, progressive massive fibrosis, and rapidly progressive pneumoconiosis. These diseases are irreversible and may ultimately be fatal. MSHA’s existing standards limit miners’ exposures to RCS.  MSHA will publish a proposed rule to address the existing permissible exposure limit of RCS for all miners and to update the existing respiratory protection standards under 30 CFR 56, 57, and 72.