MSHA Lowers Silica Exposure Limit to 50 µg/m³ for All Mines

**UPDATE — January 30, 2026: Status quo unchanged. The Department of Labor filed a new status report (https://www.courtlistener.com/docket/68506259/00805443376/sorptive-minerals-institute-v-msha/) repeating the exact language from its prior, November 26, 2025 status report. The Department continues to "engage in limited rulemaking to reconsider and seek comments on portions of the Silica Rule impacted by this appeal."

**UPDATE — December 2, 2025: The silica rule, originally published April 18, 2024 (see below) is currently under review by the 8th Circuit. (https://www.courtlistener.com/docket/68506259/sorptive-minerals-institute-v-msha/). The Court has directed the parties to file status reports by February 2, 2026.

**UPDATE — November 26, 2025: The Department of Labor filed a status report (https://www.courtlistener.com/docket/68506259/sorptive-minerals-institute-v-msha/) stating that the Department "will engage in limited rulemaking to reconsider and seek comments on portions of the Silica Rule impacted by this appeal. Accordingly, in order to avoid an unnecessary expenditure of resources by the parties and the Court, the government moves to have this appeal held in abeyance, with status reports due at 60-day intervals."

**UPDATE — Apr 29, 2024: Sorptive Minerals Institute, a trade association, filed with the 8th Circuit a petition for review of the silica rule (https://www.courtlistener.com/docket/68506259/sorptive-minerals-institute-v-msha/)

UPDATE — June 24, 2024: MSHA published a correction to fix typographical and printing errors in the final rule. Most notably, Table VII-4 on page 28299 (Percentage Distribution of Respirable Crystalline Silica Exposures in Coal Industry) was replaced with the correct Table VII-10 (Estimated Annualized Compliance Costs as Percent of Mine Revenues). Other corrections include formatting fixes to mathematical formulas and summary text. No substantive changes to regulatory requirements.

UPDATE — June 14, 2024: MSHA published a correction to clarify amendatory instruction language in the final rule. The correction is non-substantive, changing technical drafting terminology for § 90.100 without altering regulatory requirements.

On April 18, 2024, the Mine Safety and Health Administration published a final rule (Federal Register) establishing a new permissible exposure limit (PEL) for respirable crystalline silica of 50 µg/m³ (8-hour time-weighted average) for all miners. The rule amends 30 CFR Parts 56, 57, 60, 70, 71, 72, 75, and 90, replacing the previous 100 µg/m³ standard that applied to both coal and metal/nonmetal operations.

The new PEL aligns MSHA requirements with OSHA's 2016 general industry standard and the longstanding NIOSH recommendation. The rule also establishes an action level of 25 µg/m³ that triggers corrective actions and enhanced monitoring requirements. This is the first time MSHA has imposed a uniform silica standard across all mine types—previously, coal mines operated under an equivalent concentration framework while metal/nonmetal mines had separate quartz-based standards.

Key provisions include mandatory exposure monitoring using particle size-selective samplers that comply with ISO 7708:1995(E), immediate reporting to MSHA when exposures exceed the PEL, and documented corrective actions. Engineering controls (ventilation, water sprays, dust collection systems) must be the primary means of controlling silica exposure, with administrative controls permitted only as supplementary measures. When engineering and administrative controls cannot reduce exposures below the PEL, respiratory protection is required.

For metal and nonmetal mines, the rule introduces requirements previously applicable only to coal operations: NIOSH-approved respiratory protection programs complying with ASTM F3387-19, and periodic medical surveillance conducted by licensed healthcare professionals at no cost to miners. These medical examinations must be offered to miners whose exposures equal or exceed the action level for 30 or more days per year.

The rule becomes effective June 17, 2024, but compliance deadlines are staggered by sector. Coal mine operators must comply by April 14, 2025 (12 months after publication). Metal and nonmetal mine operators must comply by April 8, 2026 (24 months after publication). These compliance dates apply to the core silica exposure requirements; certain provisions (respiratory protection programs, medical surveillance) may have different phase-in timelines specified in the amendments themselves.

The rule applies to all surface and underground coal, metal, and nonmetal mining operations. There are no exemptions based on mine size, mineral type, or operation scale. Every miner exposed to respirable crystalline silica falls under these requirements.

Several implementation questions remain unaddressed. The rule does not specify the required frequency for ongoing exposure monitoring beyond initial baseline sampling—operators will need to establish monitoring schedules based on their exposure profiles, but MSHA has not issued guidance on acceptable intervals. The rule also does not clarify whether operators who consistently demonstrate exposures below the action level (25 µg/m³) can reduce monitoring frequency or if periodic sampling remains mandatory regardless of exposure levels.

Additionally, the rule does not specify retrofit requirements for existing dust control systems. It is unclear whether legacy ventilation and suppression systems that previously met the 100 µg/m³ standard must be upgraded if they cannot achieve the new 50 µg/m³ limit, or if retrofit obligations apply only when systems are replaced or modified. This distinction matters significantly for capital planning—particularly for older metal/nonmetal operations where existing engineering controls were designed around the higher PEL.

Finally, the interaction between the action level and medical surveillance obligations needs clarification. The rule requires medical exams for miners exposed at or above 25 µg/m³ for "30 or more days per year," but does not define how operators should calculate this threshold when exposure levels fluctuate or when miners rotate between high- and low-exposure tasks. MSHA has not issued guidance on recordkeeping or calculation methods for tracking the 30-day trigger.