MSHA Posts FAQ on New Silica Rule

An FAQ posted to the MSHA website explains the major requirements of the agency’s new silica rule, which went into effect earlier this month. Written for mine operators, the FAQ addresses sampling methods for respirable crystalline silica (RCS), exposure monitoring, corrective actions for overexposures, respiratory protection, and recordkeeping.

MSHA’s rule lowered its permissible exposure limit for RCS to 50 µg/m3 as an eight-hour time-weighted average. As explained in the FAQ, the previous RCS PEL was 100 µg/m3 “reported as an equivalent full-shift TWA concentration as measured by the Mining Research Establishment (MRE) instrument.” This method of determining exposures provided no adjustment for extended work shifts. Under the new rule, mine operators must use respirable particle size-selective samplers that meet the requirements of ISO 7708:1995, Air Quality—Particle Size Fraction Definitions for Health-Related Sampling. “The full-shift, 8-hour TWA calculation provides greater protection for coal miners,” the FAQ states.

Coal mine operators have until April 14, 2025, to comply with the new rule, while metal and nonmetal (MNM) mine operators have until April 8, 2026.

For more information, refer to the FAQ and to the silica rule in the Federal Register.