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MSHA’s Final Silica Rule: Scope, Obligations, and Deadlines

In 2024, MSHA finalized a rule that lowers the allowable silica exposure limit and expands operator obligations around monitoring, controls, and worker health. The rule updates decades-old standards and brings MSHA’s enforcement closer in line with modern occupational health practices. Operators are now responsible for ongoing silica sampling, implementing engineering controls to reduce airborne dust, and providing medical surveillance for affected miners. Enforcement will begin on staggered deadlines, but mine operators need to begin preparing for them well before those dates.

Enforcement Deadlines and Who the Rule Applies To

MSHA’s silica rule is in effect, but compliance deadlines are staggered. Any mine sites where workers are exposed to respirable crystalline silica will be expected to meet the updated standards by applicable dates. While enforcement for coal mines is paused, the rule remains in effect nationwide.

Effective and Compliance Dates

Some key dates included in this rule are:

June 17, 2024 – MSHA’s final silica rule took effect
August 18, 2025 – New enforcement date for coal mine operators (extended from April 14, 2025 following MSHA’s enforcement pause and an administrative stay issued by the 8th Circuit)
April 6, 2026 – Deadline for metal and nonmetal mine operators to become compliant

MSHA originally set April 14, 2025 as the enforcement deadline for coal mines, but issued a temporary stay on April 8, 2025, citing implementation challenges and the need for additional compliance time. The enforcement delay gives coal mine operators until August 18, 2025 to meet all requirements. The court’s administrative stay, issued April 4, 2025, reinforces this pause pending litigation. The metal/nonmetal mine deadline remains unchanged. The rule is also subject to ongoing litigation, and a decision from the 8th Circuit Court of Appeals may affect future enforcement. The court’s stay and MSHA’s enforcement pause currently apply only to coal mine operators.

Which Mining Operations Are Covered

Operations and workers covered under the rule include:

All coal and metal/nonmetal mines, surface and underground
Miners working in extraction, processing, or both
Production-operators and independent contractors working on-site
Operations regulated under both Part 46 and Part 48 training rules
A wide range of roles, including drillers, blasters, haul truck drivers, plant operators, and cleanup crews

Lower Exposure Limits Now Apply Across the Board

The final silica rule establishes a single permissible exposure limit (PEL) for all mining sectors. Prior limits varied by mine type and were based on outdated formulas.

New Permissible Exposure Limit (PEL)

The rule sets a single maximum amount of silica dust a miner can be exposed to during an average workday:

50 µg/m³, averaged over an 8-hour shift
Applies to all forms of crystalline silica, including quartz, cristobalite, and tridymite
Replaces older formula-based limits
Sampling is conducted in the miner’s breathing zone during normal duties
Example: A crusher operator exposed to 58 µg/m³ during one shift exceeds the PEL—even if the exposure occurred over a few hours

Action Level Introduced

The rule also sets a lower threshold called the action level, which adds monitoring and medical obligations even if exposure stays below the PEL:

25 µg/m³, based on an 8-hour average exposure
Does not result in a violation, but triggers monitoring and medical surveillance
Sampling needs to occur every 3 months once the action level is reached
Operators are required to offer medical exams to miners exposed at or above this level
Example: A haul truck driver with 27 µg/m³ exposure requires quarterly sampling and a medical evaluation

What the Rule Requires for Exposure Monitoring

The new rule represents a shift from past practices where MSHA inspectors tended to handle sampling during inspections. Now, operators are responsible for routine monitoring, using approved sampling methods, and maintaining records that show whether miners are above or below the action level or PEL.

Initial Sampling and Representative Sampling

Sample all positions where miners are reasonably expected to be exposed to respirable crystalline silica
Initial sampling should reflect a full work shift under typical conditions
Equipment and methods used need to align with ISO 7708:1995 standards
Representative sampling allowed only for identical tasks, areas, and shifts
Example: One sample may represent two identical crusher operators on the same shift, but not one working nights or doing maintenance

Ongoing Sampling Based on Results

The frequency of follow-up sampling depends on exposure levels, but certain changes at the mine can also trigger new sampling requirements:

Below 25 µg/m³: Reevaluate every 6 months; sample again if conditions change
- Examples of changes in conditions: starting production in a new area, altering materials being mined or processed, changes to ventilation, maintenance that affects dust controls, or a new piece of equipment entering service
Between 25–50 µg/m³: Sample at least every 3 months
Above 50 µg/m³: Take immediate corrective action, provide respirators, and re-sample
Example: A maintenance worker with 34 µg/m³ exposure needs to be sampled every 3 months until levels drop

Recordkeeping and Reporting

Operators are required to maintain documentation of both sampling and compliance actions:

Keep sampling results and related records for at least 5 years
Log all exposure-related changes to equipment or procedures
Post the most recent evaluation for 31 days in a location accessible to miners
Report any result over the PEL to MSHA without delay
Example: A contractor exposed to 65 µg/m³ requires reporting, documentation, and corrective action—even if it occurred on a single shift

How MSHA’s Silica Rule Compares to OSHA’s Standard

Though there are similarities between MSHA’s silica rule and OSHA’s standard, each sets distinct obligations that operators need to evaluate separately. Key differences affect how sampling should be conducted, how long respirators can be used, and how medical surveillance is triggered.

Exposure Limits and Action Levels

Both rules use the same numerical limits, but the context and enforcement vary:

Both use a 50 µg/m³ PEL and 25 µg/m³ action level
MSHA ties the action level to specific monitoring and medical obligations
OSHA treats the action level primarily as a trigger for exposure tracking

Sampling and Monitoring

MSHA places more responsibility on the operator to gather exposure data directly:

MSHA requires operator-led sampling under ISO 7708:1995
OSHA allows more use of historical or objective data
MSHA’s representative sampling rules are more restrictive
Example: OSHA may allow prior data from a similar job; MSHA would not

Use of Respirators

MSHA and OSHA both require operators to protect workers from airborne silica, but they take different positions on when respirators can be used as a compliance method:

MSHA allows respirator use only while engineering controls are being implemented
OSHA permits long-term respirator use if controls are infeasible
Example: A facility under OSHA may rely on respirators for daily dust exposure. MSHA would require changes to reduce the dust itself

Medical Surveillance

Both MSHA and OSHA require employers to offer medical exams when worker exposure reaches the action level, but MSHA’s rule now expands this obligation into mining sectors that previously weren’t covered:

OSHA requires exams for exposed workers in construction and general industry
MSHA now requires exams in MNM mines, which previously had no such requirement
Both standards include chest X-rays, questionnaires, and pulmonary testing
MSHA uses stricter scheduling: exams for current miners within 12 months, new miners within 60 days and again after 3 years
Example: Under MSHA, operators must offer all exposed miners exams—even if they haven’t reported symptoms like cough or shortness of breath

Controls Must Focus on Reducing Dust at the Source

MSHA’s silica rule prioritizes engineering controls over administrative measures or personal protective equipment. Operators are expected to reduce silica at the source—not shift exposure across workers.

Required Use of Engineering Controls

Operators are responsible for reducing silica exposure through physical changes to equipment, systems, or processes:

Controls need to be implemented before considering respirators
Examples include water sprays, enclosed cabs, upgraded ventilation, or dust collection
Equipment that generates excessive dust may need to be replaced or modified
Controls are required when they are technologically and economically feasible
Example: A screening plant producing visible dust may require misting nozzles or chute modifications

Rotation of Miners No Longer Allowed as a Control

Under the new rule, rotating miners through a high-exposure task is not an acceptable method of compliance:

MSHA prohibits rotation to reduce individual exposure
OSHA still allows this practice under certain conditions
Operators are required to fix the source of the exposure, not shift the risk
Example: Splitting a dusty cleanup task between three workers still results in a violation under MSHA if dust levels remain high

What Happens If You Exceed the PEL

If a miner’s exposure exceeds 50 µg/m³, MSHA’s rule requires the operator to take immediate action, regardless of whether MSHA is present or has issued a citation.

Immediate Steps Required

Once an exposure exceeds the PEL, operators are required to take specific corrective actions without delay:

Notify MSHA as soon as an overexposure is confirmed
Provide compliant respirators before the next shift
Investigate and correct the cause of the exposure
Conduct follow-up sampling to verify reduced exposure
Example: A driller with a 68 µg/m³ exposure requires reporting, respirator assignment, dust control improvements, and new sampling

Documentation Requirements

MSHA’s rule requires written records showing how the overexposure was handled:

Create a written record of all corrective actions taken
Retain documentation for 5 years
Provide records to MSHA or miners upon request
Records may help reduce liability or enforcement if an issue reoccurs

Respirator Use Requires a Written Program and Medical Review

If respirators are used to protect miners after an overexposure, the operator is responsible for implementing a full respiratory protection program:

The program has to comply with ASTM F3387-19
A program administrator is required to oversee respirator selection, fit testing, medical evaluations, maintenance, and training
The program needs to be written and specific to the site—generic templates or copied plans from other operations don’t meet the requirement
Only NIOSH-approved respirators with P100 filters or equivalent are acceptable; disposable N95s do not qualify under the rule
Operators also need to plan for miners who cannot wear respirators for medical reasons:
- Affected miners have to be reassigned to a lower-exposure area
- Pay, benefits, and seniority are required to remain the same during the transfer
Example: A miner medically disqualified from wearing a tight-fitting respirator cannot be assigned to a high-exposure role under any condition

Medical Surveillance Now Required for MNM Mines

MSHA’s rule now requires medical surveillance for miners in MNM operations—bringing this sector in line with coal mining and OSHA-regulated workplaces. The exams are designed to catch health problems early and assess respirator fitness.

Who Needs Exams and When

Operators are required to offer medical exams according to the miner’s exposure level and work status:

Current miners with exposure at or above the action level are expected to receive an exam within 12 months of the compliance deadline
New miners need to be examined within 60 days of starting work, with a follow-up scheduled after 3 years
Exams are provided at no cost and cannot be tied to employment conditions

What the Exam Includes

The medical exam includes several components tied to respiratory function and silica exposure:

A respiratory health questionnaire
A chest X-ray reviewed by a NIOSH-certified B Reader
Pulmonary function testing using spirometry
Additional evaluations if recommended by the provider

Records and Confidentiality

Operators are only given limited information from the medical provider:

A written opinion confirming that the exam was completed and stating whether the miner is medically cleared to wear a respirator
No diagnostic results or personal medical history are shared with the operator
Records need to be retained for the duration of employment plus six months
Example: If spirometry reveals early lung restriction, that diagnosis remains confidential—the operator is only informed about the miner’s respirator clearance

How Employers Should Prepare Now

MSHA’s final silica rule is in effect, but coal operators now have until August 18, 2025 to meet the compliance requirements following MSHA’s temporary enforcement pause. For metal and nonmetal mines, the April 6, 2026 deadline remains unchanged. Despite the delay for coal, operators across all sectors should continue preparing now. Exposure controls, monitoring plans, and documentation systems take time to design and implement. Using this period to get ahead of enforcement will reduce risk and help avoid rushed or incomplete compliance later.

Steps that require early planning and coordination:

Evaluate current exposure levels across all job roles where silica dust may be present
Identify tasks that are likely to exceed the action level or PEL under typical conditions
Begin engineering evaluations and vendor consultations to reduce dust at the source
Develop a respirator program that includes equipment acquisition, fit testing, and medical clearance
Create internal tracking systems for sampling results, corrective actions, and ongoing updates to controls and certifications

Use MSHA Resources

Official guidance is available to support planning and implementation:

Review MSHA’s silica rule FAQs, health alerts, and regulatory documents at msha.gov
Contact the local MSHA District Office for answers to site-specific questions about sampling, controls, or recordkeeping
Work with a certified industrial hygienist to build a sampling strategy that meets ISO 7708:1995 and MSHA’s rule language
Review medical surveillance requirements with counsel or HR to confirm that exam offers, records, and reassignment protocols align with the rule

Mine operators now have additional time to prepare for MSHA’s final silica rule—but that time should be used strategically. Whether your operation is preparing for the updated August 18, 2025 deadline for coal mines or the April 6, 2026 deadline for metal and nonmetal, every requirement must be addressed with care. From air monitoring and engineering controls to medical surveillance and enforcement response, the rule demands more than reactive compliance. Conn Maciel Carey LLP's national MSHA Mine Safety & Health Practice Group helps operators build defensible programs, respond to MSHA inquiries, and train personnel to meet the rule’s evolving demands. To discuss how your operation can prepare, call (202) 715-6244 or send us an email.

This article is for informational purposes only and does not constitute legal advice. While we strive to ensure accuracy, laws and regulations may change, and unintended errors may occur. This content may not address every aspect of the relevant legal requirements. For guidance on your specific situation, consult your attorney.