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While most people are familiar with the Occupational Safety and Health Administration (OSHA), few may be familiar with another agency within the U.S. Department of Labor (DOL), the Mine Safety and Health Administration (MSHA). MSHA was originally established in 1978 in accordance with the Federal Mine Safety and Health Act (MINE Act) of 1977. Like OSHA, MSHA focuses on worker health and safety, but its jurisdiction is largely limited to those employed in the mining industry. As such, MSHA’s mission is to work “to prevent death, illness, and injury from mining and promote safe and healthful workplaces for U.S. miners.” In the last decade, one of the most significant issues facing MSHA has been the observed increase of coal workers’ pneumoconiosis (also known as black lung disease), a disease historically associated with exposure to coal dust, but, in more recent cases, may also be a result of exposure to respirable crystalline silica (RCS) (U.S. Department of Labor, 2020).

According to MSHA, coal miners with relatively short employment tenures may be at risk of developing respiratory diseases if their exposures to silica are sufficiently high. Recent studies found progressive massive fibrosis (PMF), the most severe form of black lung disease, in large clusters among miners with fewer than 20 years of mining tenure in Kentucky, West Virginia, and Virginia (MSHA, 2019). Researchers have attributed PMF increase and prevalence in these miners to higher-volume mechanized mining of decreasing deposits of coal, which release more RCS, among other factors (U.S. Department of Labor, 2020).

In November, 2020, the DOL Office of Inspector General (OIG) conducted an audit of MSHA’s efforts to protect coal miners from RCS exposure and issued a report of its findings. The OIG acknowledged that while coal dust exposure can impair miners’ health, silica is significantly more harmful, given that RCS exposure can cause both black lung disease and silicosis. MSHA’s current Permissible Exposure Limit (PEL) for RCS is 100 µg/m³, as an 8-hour Time-Weighted Average (TWA). The MSHA limit is based on an ACGIH Threshold Limit Value (TLV) originally established in the 1960s, and has not been updated since  MSHA first established it in 1978 (NIOSH, 2021). In comparison, in 2016, OSHA established an 8-hour TWA PEL for RCS of 50 µg/m³, and ACGIH currently has a TLV for RCS of 25 µg/m³.

Key findings from the OIG report include:

• “Even though MSHA has known its silica limit did not align with current scientific recommended limits, it continued to maintain essentially the same silica limit established in the 1960s. As a result, workers in coal mines with silica levels above recommended limits continue to be at risk of developing life-threatening health problems.”
• “MSHA has not sufficiently protected coal miners from exposure to respirable silica. MSHA could decrease coal miners’ risk of exposure to silica by updating its regulations to establish a separate, lower limit permitted for silica that is not tied to coal dust.”
• Variances in mine geology and mining activities cannot be captured by samples taken under MSHA’s current sampling requirement of two or four times a year. As such, “the long gaps between MSHA’s required samples allow for possible overexposures to silica that put miners’ safety at risk.”

The 1977 MINE Act requires MSHA to set standards based on the best available evidence to protect miners from exposure to harmful agents. As a result of its audit, the OIG recommended the following actions to the Assistant Secretary for Mine Safety and Health:

1. Adopt a lower legal exposure limit for silica in coal mines based on recent scientific data;
2. Establish a standard for silica, separate from coal dust, that allows MSHA to issue a citation and monetary penalty in response to violations of the silica exposure limit; and
3. Enhance the sampling program to increase the frequency of inspector samples when needed by implementing a risk-based approach.

Cardno ChemRisk is experienced at developing and assisting with exposure and risk assessments, including for silica. To learn more about the ways Cardno ChemRisk can support silica-related matters, please contact Rachel Zisook, or visit our website.