Respirable Silica Fact Sheet

MSHA Offers A Range Of Compliance Assistance Materials For Mine Operators, Informational Materials For Miners and Other Resources.

Respirable crystalline silica, or silica dust, is a common occupational hazard for coal and metal/nonmetal (MNM) miners. Silica dust is released through many mining and milling operations. To avoid any legal issues, producers should stay current on compliance.

Silica dust can be inhaled easily because the dust particles are so small. Once the silica dust particles are inhaled, they may remain in the lung for a long time. Adverse health effects caused by exposure to respirable crystalline silica include silicosis (acute, accelerated, or chronic silicosis and progressive massive fibrosis), lung cancer, nonmalignant respiratory diseases (e.g., emphysema and chronic bronchitis), and kidney disease. Each of these illnesses is chronic, irreversible, and potentially disabling or fatal.

To reduce miner exposures to silica dust and other airborne hazards, MSHA issued a final rule entitled “Lowering Miners’ Exposure to Respirable Crystalline Silica and Improving Respiratory Protection.”

This final rule went into effect on June 17, 2024. Coal mine operators must come into compliance with the final rule by April 8, 2025, and MNM mine operators must come into compliance by April 8, 2026. To assist miners and mine operators in understanding the risks of silica dust and complying with the rule, MSHA offers a range of compliance assistance materials for mine operators, informational materials for miners and other resources.

What Is Respirable Crystalline Silica?
Respirable crystalline silica (also known as RCS, silica dust or quartz dust) is a common occupational hazard for coal and metal/nonmental (MNM) miners. Silica is a common component of rock composed of silicon and oxygen (chemical formula SiO2 ). Due to its small size, this dust may be inhaled and move throughout the lungs. It may be deposited in small airways and air sacs in the lungs and may remain there for long periods of time.

How Are Miners Exposed To Silica Dust?
Silica dust is released through a variety of mining and milling operations. Miners may breathe silica dust while engaging in activities like:

  • Cutting.
  • Scraping.
  • Excavating.
  • Sawing.
  • Sanding.
  • Jackhammering.
  • Grinding.
  • Drilling.
  • Crushing.
  • Hauling materials that contain silica.

What Are Some Important Adverse Health Effects Of Silica Dust Exposure?
Occupational exposure to silica dust results in adverse health effects and increases risk of death. Respirable crystalline silica has been classified by the International Agency for Research on Cancer as carcinogenic to humans. Miners who inhale silica dust may develop:

  • Silicosis (i.e., acute silicosis, accelerated silicosis, and chronic silicosis.)
  • Nonmalignant respiratory diseases (e.g., emphysema, chronic bronchitis.)
  • Lung cancer.
  • Kidney disease.

Miners Exposed To Mixed-Mine Dust Containing Crystalline Silica Can Also Develop:

  • Coal workers’ pneumoconiosis (CWP).
  • Progressive massive fibrosis (PMF) or complicated silicosis.
  • Multi-dust pneumoconiosis.

These diseases are chronic, irreversible and potentially disabling or fatal. But they are also preventable.

What Actions Must Operators Take To Protect Miners From Silica Dust?
MSHA establishes a uniform permissible exposure limit (PEL) for respirable crystalline silica of 50 micrograms per cubic meter (µg/m3) and an action level of 25 µg/m3 over a full shift, calculated as aneight-hour time weighted average (TWA) for all mines.

To Protect Miners From Silica Dust Exposures, Operators Must:

  • Use and maintain engineering controls, such as dust suppression systems or enclosed cabs with filtered breathing air, as the primary means of control.
  • Implement administrative controls, such as housekeeping procedures, cleaning of spills, or prevention methods to minimize contamination of clothing, as a supplemental control. Rotation of miners as a control method for silica dust exposure is prohibited.
  • Monitor silica dust exposures through air dust samplings and evaluations of mining environment.
  • Perform sampling until the exposure levels of miners (or a representative fraction of miners) are shown to be below the action level from two consecutive samplings..
  • Protect affected miners if sampling indicates miner exposures are above the PEL by providing appropriate respirators and ensuring they are worn properly; taking corrective actions and conducting additional sampling; and immediately reporting overexposures to the District Manager or designated office.
  • Perform a periodic evaluation at least every six months, or whenever there are any changes in: production; processes; installation or maintenance of engineering controls; installation or maintenance of equipment; administrative controls; or geological conditions.
  • Implement a respiratory protection program consistent with the requirements of ASTM F3387-19 Standard Practice for Respiratory Protection.
  • Provide medical examinations to MNM miners at no cost to miners.
  • Ensure medical examinations include a review of the miners’ medical and work history, physical exam, chest x-rays, and pulmonary function testing, among other things.

What Are Engineering Controls?
Engineering controls remove or reduce dust at its source. They are the best way to protect miners from breathing silica dust.

Examples are:

  • Air ventilation.
  • Enclosed cabs and control booths.
  • Water sprays.
  • Tool shrouds and vacuums.
  • Skirtboards on conveyor belts.

Do Mine Operators Have To Use Engineering Controls To Protect Miners From Silica Dust?
Yes, mine operators must install engineering controls to protect miners from breathing silica dust above the permissible exposure limit.

What Must Mine Operators Do After Installing Engineering Controls?
Mine operators must inspect, maintain and repair engineering controls to make sure they are working properly to protect miners.

Administrative Controls
What are administrative controls? Administrative controls include changes to work practices or behavior that can help protect miners from breathing silica dust after engineering controls are installed. Examples are:

  • Keeping work areas clean.
  • Working in an area away from a dust source.
  • Walking around the outside of a dusty area.
  • Safely cleaning dust from work clothes.

Can Mine Operators Use Administrative Controls To Protect Miners From Silica Dust?
Yes, mine operators may use administrative controls along with engineering controls to protect miners from breathing silica dust above the permissible exposure limit.

Can Mine Operators Rotate Miners Rather Than Install Engineering Controls To Limit Exposure To Silica Dust?
No, mine operators must use engineering controls and other administrative controls to protect miners from breathing silica dust above the permissible exposure limit. Rotating miners to reduce exposure to silica dust is not permitted since rotation exposes a greater number of miners to silica dust.

For further assistance, check the MSHA website or contact your MSHA District Office.

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