Understanding MSHA's Respirable Crystalline Silica Rule

Mine operators must understand the new MSHA (Mine Safety & Health Administration) rules for respirable crystalline silica — what’s changed, what’s required, and what is the current enforcement status. As a leader in sample collection, testing, and analysis of respirable and bulk silica, RJ Lee Group has helped organizations across the US remain safe and compliant. We have compiled this high-level overview of the MSHA rule to help understand what you need to do, be sure to check the official rule text or legal guidance for full details. 

Overview & Purpose

• MSHA issued a final rule titled Lowering Miners’ Exposure to Respirable Crystalline Silica and Improving Respiratory Protection on April 18, 2024. 

• The rule is intended to strengthen protections for miners from silica dust exposure, which is linked to silicosis, lung cancer, and other respiratory diseases. 

• It applies to all coal, metal, and nonmetal (MNM) mines (surface and underground) and to contractors in those operations. 

Key Changes & Requirements

Here are the major new requirements in the rule:

1. Lower Exposure Limits (PEL & Action Level)

• • The new Permissible Exposure Limit (PEL) for respirable crystalline silica is 50 micrograms per cubic meter (µg/m³), averaged over an 8-hour time-weighted average (TWA).

  • A new Action Level (AL) is introduced at 25 µg/m³ (8-h TWA). Exposure at or above the AL triggers additional monitoring and medical obligations (though being at the AL alone is not a violation).

2. Exposure Monitoring & Sampling

• • Operators must actively sample miners who are reasonably expected to be exposed to respirable crystalline silica. The rule removes allowance for relying purely on historic or objective data to skip sampling. 

  • Sampling must use respirable, particle size–selective samplers that comply with ISO 7708:1995.

  • Analytical labs must be accredited (ISO/IEC 17025) and use approved analytical methods (e.g. MSHA-specified, OSHA, or NIOSH).

  • Based on sampling results:

• • • If exposure < AL: operators must resample within 3 months (minimum) to confirm low exposure.

    • If exposure ≥ AL but < PEL: sampling must continue at least quarterly. 

    • If exposure > PEL: operator must take immediate corrective action, provide respirators, and resample to verify reductions. 

3. Controls & Corrective Actions

• • The rule places primary responsibility on engineering controls (ventilation, dust suppression, enclosure, water sprays, etc.) to reduce silica exposure. 

  • Administrative controls (e.g. work scheduling) may only be supplementary—not a substitute for control at the source. 

  • Rotation of miners (i.e. moving workers in and out of high-exposure tasks) is not allowed as a compliance strategy.

  • Respiratory protection can be used temporarily while engineering controls are being developed or implemented, but not as a long-term substitute for controls. 

4. Respiratory Protection Program

• • A written respiratory protection program consistent with ASTM F3387-19 must be in place.

  • Miners must be provided with NIOSH-approved respirators: atmosphere-supplying respirators or air-purifying respirators with particulate protection 100-series or “HE” (high efficiency) – N95 is no longer permitted under the rule. 

  • Fit testing, maintenance, selection, use, and training are required as part of the respirator program. 

5. Medical Surveillance

• • For metal/nonmetal mines (MNM), the rule now requires medical surveillance (previously more limited) for miners with exposure at or above the action level. 

  • Current miners exposed at or above AL must be offered exams within 12 months of compliance deadline; new miners within 60 days, and follow-up every 3 years. 

  • The exams include a respiratory health questionnaire, chest X-ray read by NIOSH-certified B-Reader, spirometry (pulmonary function tests), and other evaluations as recommended.

• • Operators receive only a written opinion on whether the miner is medically cleared to use a respirator; detailed results remain confidential. 

  • Medical records must be preserved for the duration of employment plus six months.

6. Recordkeeping & Posting

• • Sampling results, evaluations, and corrective action records must be retained for at least 5 years. 

  • The most recent evaluation (with sample date, occupations sampled, concentrations, etc.) must be posted for 31 days on mine bulletin boards or electronically. 

  • Operators must promptly report overexposures (i.e. any sample exceeding PEL) to MSHA.

7. Qualitative Evaluations & Triggering Re-evaluations

• • Qualitative evaluations (assessments of dust, processes, worker tasks) must be performed at least every 6 months or when changes occur (e.g. new equipment, geological changes, changes in work practices or materials).

  • Any change that could affect silica exposure (ventilation, new process, increased production, different geology) triggers a new evaluation and possibly additional sampling. 

Compliance & Enforcement Timeline / Status

• The rule became effective June 17, 2024.

• For coal mines, the original compliance deadline was April 14, 2025. 

• For metal/nonmetal mines, the compliance deadline is April 8, 2026. 

However, there have been changes and legal developments:

• In April 2025, MSHA temporarily paused enforcement of portions of the rule for coal mine operators, citing implementation challenges and coordination with NIOSH. 

• MSHA stated coal mine compliance enforcement is delayed until August 18, 2025. 

• A federal appeals court (8th Circuit) issued a stay on enforcement of the rule for coal operators pending litigation.

• MSHA’s notice to stakeholders confirms the agency is continuing the enforcement pause for coal until litigation resolves.

• The enforcement pause does not affect the MNM deadline (April 8, 2026) as of current statements.

Because of the ongoing litigation, the final outcomes, interpretations, or timing could still change.

What Mine Operators Should Do Now (Best Practices)

Given the new rule and the shifting enforcement status, here are recommended steps for compliance readiness:

1. Assess current exposures: Begin sampling in job categories at risk for silica exposure under the new limits, even before enforcement begins fully.
   
   
2. Plan engineering controls: Evaluate what dust suppression, ventilation, enclosure, water spray, and other control measures can reduce silica at the source.
   
   
3. Develop respiratory protection program: Draft or update your respirator program to meet ASTM F3387-19, select compliant respirators, plan for fit testing and training, etc.
   
   
4. Set up medical surveillance: Identify providers for chest X-rays, spirometry, etc. Prepare forms, policies, and record systems to offer exams when required.
   
   
5. Create recordkeeping and notification systems: Ensure you can retain required records for 5+ years, post evaluations, and report overexposures properly.
   
   
6. Monitor regulatory developments: Keep track of court rulings, changes in MSHA’s notices, and guidance to adjust your compliance timeline and obligations accordingly.
   
   
7. Train miners and staff: Provide hazard awareness, training on silica risks, safe work practices, respirator use, and how the new rules affect operations.

Understanding and complying with MSHA’s updated silica rule is not just a regulatory obligation—it’s a commitment to protecting the health and safety of your workforce. With enforcement timelines shifting and requirements becoming more stringent, mine operators must act now to assess exposure, implement controls, and prepare documentation.

RJ Lee Group stands ready to support your compliance journey with expert sampling, testing, and analysis services. Don’t wait for enforcement to begin—contact RJ Lee Group today to ensure your operations are safe, compliant, and prepared for what’s ahead.