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Respirable Crystalline Silica

Final Rule

Occupational exposures to respirable crystalline silica (also known as silica dust or quartz dust) cause adverse health effects, including silicosis (acute silicosis, accelerated silicosis, simple chronic silicosis, progressive massive fibrosis), nonmalignant respiratory diseases (e.g., emphysema and chronic bronchitis), lung cancer, and kidney disease. Each of these effects is chronic, irreversible, and potentially disabling or fatal. 

On April 18, 2024, MSHA issued its final rule, Lowering Miners’ Exposure to Respirable Crystalline Silica and Improving Respiratory Protection, to reduce miner exposures to respirable crystalline silica and improve respiratory protection for all airborne hazards. The final rule: 

  • Lowers the permissible exposure limit (PEL) for respirable crystalline silica to 50 micrograms per cubic meter of air (µg/m3) for a full shift, calculated as an 8-hour time-weighted average (TWA) for all miners; 
  • Establishes an action level for respirable crystalline silica at 25 µg/m3 for a full shift, calculated as an 8-hour TWA for all miners;
  • Includes uniform requirements for controlling and monitoring exposures to respirable crystalline silica at coal and metal and nonmetal (MNM) mines;
  • Includes medical surveillance requirements for MNM mines, modeled on the existing medical surveillance requirements for coal mines; and
  • Updates existing respiratory protection requirements by incorporating by reference a voluntary consensus standard by the American Society of Testing and Materials (ASTM) that reflects the latest advances in respiratory protection technologies and practices – ASTM F3387-19 Standard Practice for Respiratory Protection.

The final rule will take effect on June 17, 2024. Coal mine operators have 12 months to come into compliance with the final rule’s requirements while MNM mine operators have 24 months to come into compliance (including medical surveillance).