April 18, 2024

MSHA Lowers PEL, Establishes Action Level for Silica in Mines

A new final rule published today in the Federal Register by MSHA sets a uniform permissible exposure limit and action level for respirable crystalline silica for all mines. The new PEL is 50 µg/m3 for a full-shift exposure, calculated as an 8-hour time-weighted average, and the action level is 25 µg/m3, also for a full-shift exposure. Other major provisions of the final rule require mine operators to conduct exposure monitoring for respirable crystalline silica, to immediately report overexposures to MSHA and take action to lower the concentration of silica until it is at or below the PEL, and to primarily use engineering controls to control silica. The rule also updates the standards for respirable crystalline silica sampling and respiratory protection by incorporating by reference ISO 7708:1995(E), Air quality—Particle size fraction definitions for health-related sampling, and ASTM F3387-19, Standard Practice for Respiratory Protection, respectively. These provisions require mine operators to conduct sampling using respirable particle size-selective samplers that conform to ISO 7708:1995 and, when respirators are used, to have a written respiratory protection program to protect miners from respirable crystalline silica and other airborne contaminants.

A couple of provisions apply specifically to metal and nonmetal (MNM) mines. Under the new rule, the temporary use of respirators is required at MNM mines when miners must work in concentrations of respirable crystalline silica above the PEL—for example, while engineering controls are being developed or implemented, or for necessary tasks like occasional entry into hazardous atmospheres to perform maintenance. The rule also includes medical surveillance requirements for MNM mines that are modeled after existing requirements for coal mines. MNM mine operators must provide all miners with no-cost, periodic medical examinations performed by a physician or other licensed healthcare professional or specialist. According to MSHA, the medical surveillance requirements are intended to improve early detection of respiratory illnesses, including diseases related to respirable crystalline silica.

The new PEL of 50 µg/m3 for all mines is consistent with the PEL set by OSHA’s 2016 final rule on occupational exposure to respirable crystalline silica, which applies to construction, maritime, and general industry workers. It’s also in line with NIOSH’s criteria for a recommended standard on occupational exposure to crystalline silica that were put forward in 1974: that no worker be exposed to a TWA concentration of respirable crystalline silica greater than 50 µg/m3 as determined by a full-shift sample for up to a 10-hour workday over a 40-hour workweek.

The new final rule will be effective on June 17, 2024. According to MSHA, coal mine operators will have 12 months to come into compliance with the rule’s requirements, whereas MNM mine operators will have 24 months. Agency estimates show that 1,067 lifetime avoided deaths and more than 3,700 lifetime avoided cases of silica-related illnesses will be attributed to the rule.

AIHA provided comments to MSHA in August 2023 during the public comment period on the proposed rulemaking. AIHA’s comments addressed several topic areas, including the proposed PEL, exposure monitoring, medical surveillance for MNM miners, and respiratory protection. The association’s letter to MSHA leadership is available as a PDF.

Read the final rule in the Federal Register. Further details can be found in MSHA’s news release and on its silica rulemaking webpage.

Related: Read “Engineering Controls for Respirable Crystalline Silica Hazards,” the cover article for the April 2022 Synergist, to learn how NIOSH is investigating effective respirable crystalline silica controls. A previous article published in the June/July 2021 issue of the magazine describes the AIHA Mining Working Group’s role in the development of ISO 23875, a standard for mining that specifies performance and design requirements for air quality control systems for operator enclosures and their monitoring devices.