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Respirable Crystalline Silica (30 CFR Part 60) – Frequently Asked Questions

60.1 – Scope; Compliance Dates

1. What is respirable crystalline silica and how can it affect health?

Respirable crystalline silica (also known as silica dust or quartz dust) is a common occupational hazard for coal and metal/nonmetal (MNM) miners. Silica dust is generated by mining activities, including cutting, sanding, drilling, crushing, grinding, sawing, scraping, jackhammering, excavating, and hauling materials that contain silica.

Occupational exposure to respirable crystalline silica results in adverse health effects and increases risk of death. The adverse health effects include silicosis (i.e., acute silicosis, accelerated silicosis, chronic silicosis, and progressive massive fibrosis), nonmalignant respiratory diseases (e.g., emphysema and chronic bronchitis), lung cancer, and kidney disease. Each of these effects is chronic, irreversible, and potentially disabling or fatal. Exposure to mixed coal mine dust containing respirable crystalline silica can lead to the development of coal workers’ pneumoconiosis, progressive massive fibrosis, and multi-dust pneumoconiosis. Occupational exposure to respirable crystalline silica is classified by the International Agency for Research on Cancer (IARC) as a human carcinogen.

2. When do I have to comply with MSHA’s new silica rule?

The final rule took effect on June 17, 2024. Compliance with this final rule is required by April 14, 2025, for coal mine operators and April 8, 2026, for MNM mine operators.

60.10 – Permissible Exposure Limit (PEL)

3. I am an MNM operator. Please explain how the new respirable crystalline silica permissible exposure limit (PEL) differs from the previous PELs.

The final rule establishes a uniform PEL for respirable crystalline silica of 50 μg/m3 and an action level of 25 μg/m3 over a full shift, calculated as an 8-hour time weighted average (TWA) for all mines. The new PEL applies to all three forms of respirable crystalline silica either alone or in any combination (i.e., quartz, cristobalite, and/or tridymite).

The former PELs for the three polymorphs of respirable crystalline silica were based on the TLVs® Threshold Limit Values for Chemical Substances in Workroom Air Adopted by the ACGIH (American Conference of Governmental Industrial Hygienists) for 1973. The TLV® for respirable dust containing greater than 1% quartz was designed to limit exposures to less than 100 μg/m3 for quartz, and to less than 50 μg/m3 for cristobalite and tridymite, calculated as an 8-hour TWA. Read More »


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Original article published by MSHA