Mine safety agency proposes rewriting parts of its 2024 silica rule but keeps the exposure limit

The Mine Safety and Health Administration has proposed changing how its 2024 rule on silica dust in mines is measured and enforced, while keeping the exposure limit that rule set. The proposal, published in the Federal Register on November 12, leaves in place a permissible exposure limit of 50 micrograms of respirable crystalline silica per cubic meter of air and an action level of 25 micrograms, both averaged over an eight-hour shift.

The health review behind the 2024 rule linked silica exposure to silicosis, other non-malignant respiratory disease, lung cancer, kidney disease and autoimmune diseases, the proposal says. MSHA adds that it has found 195 studies published since then and is still reviewing them. The agency says the changes "provide clarity and make improvements" while "maintaining strong protection of miners."

What would change

• Measurement error: a single 21% error factor would be applied to both MSHA's and operators' sample results when judging whether exposure exceeds the limit or reaches the action level. MSHA says a review found inspectors' samples consistent and operators' samples more variable.
• Citations: only samples taken by MSHA inspectors could be the basis for citing an operator for exceeding the limit. Operators would use their own results to decide whether they must act to protect miners.
• Sampling: operators would still have to begin sampling by the compliance date, but follow-up samples due within three months and periodic evaluations would give way to sampling "as frequently as necessary." Miners exposed at or above the action level but not above the limit would be offered approved respirators to wear if they choose.
• Medical exams: mandatory exams for miners new to metal and nonmetal mining would become voluntary, and those mines' operators would have five years instead of one to first offer voluntary exams to all their miners. All operators would have to provide an exam within 60 days to any miner an MSHA sample shows above the limit, unless the miner had one in the past two years.
• Rotation: the rule would spell out when operators may rotate miners through dusty jobs. In MSHA's examples, rotation is allowed only where it is already part of normal work practice, not as a fix for an overexposure.

MSHA estimates the changes would save the mining industry $28.7 million a year in compliance costs, in 2024 dollars at a 7% discount rate, with $24.9 million of that from exposure monitoring. It also asks whether silica exposures from mining and processing sorptive clays should be exempted from the rule.

The court challenge

The 2024 rule took effect on June 17, 2024, with compliance due on April 14, 2025, for coal mines and April 8, 2026, for metal and nonmetal mines. Industry groups, including the National Stone, Sand and Gravel Association and the Sorptive Minerals Institute, challenged it in the U.S. Court of Appeals for the Eighth Circuit over its feasibility, control methods and sampling requirements. On April 11, 2025, the court stayed the compliance deadlines until it completes its review, and MSHA says it continues to temporarily pause enforcement.

In an April 2026 notice, MSHA said the stay was still in effect and delayed indefinitely the 2024 rule's conforming changes for metal and nonmetal mines. As a result, the older silica standards for those mines remain in force, the notice says, and MSHA will announce further action once the court's stay ends.

Where miners and industry stand

The proposal records both sides' earlier positions as MSHA's 2024 final rule described them. The United Mine Workers of America said then that operators should evaluate exposures whenever conditions change, and the union and the AFL-CIO warned that the evaluation schedule proposed at the time could leave miners exposed to dangerous silica levels for up to six months. The stone and gravel association asked MSHA to adopt the Occupational Safety and Health Administration's rule requiring reassessment whenever a change could raise exposures. MSHA now says its "as frequently as necessary" approach resolves those concerns.

The proposal does not record the unions' views on the new changes, such as the error factor or voluntary exams for new miners. The Federal Mine Safety and Health Act bars any new standard that reduces the protection an existing one gives miners, a requirement the proposal cites. MSHA asks for comment on several of its choices, including whether operators' own samples above the limit should also trigger mandatory exams.

What happens next

Written comments are due by midnight Eastern time on January 11, 2027, under docket number MSHA-2026-0200, and MSHA will hold a virtual-only public hearing on December 15, 2026. MSHA says it may change the proposal based on comments. Until a final rule is issued, the 2024 rule remains on the books, with its compliance deadlines on hold under the court's stay.