MSHA looks to OSHA’s lead on crystalline silica limits


July 25, 2016

Dust control can be a major concern on industrial worksites and is particularly relevant to the production of aggregate materials. Airborne dust particles present difficulties that are relevant to equipment maintenance, employee comfort, and, most importantly, employee health. Exposure to crystalline silica is of particular importance. In an effort to reduce employee exposure to silicosis, lung cancer, and other diseases, both the Occupational Safety and Health Administration (OSHA) and the Mine Safety and Health Administration (MSHA) have taken steps to limit employee exposure to crystalline silica. On March 24, 2016, OSHA announced a final rule that revises downward the permissible exposure limit (PEL) for exposure to crystalline silica in the workplace. The expectation is that MSHA’s version to lower exposure limits may soon follow.

MSHA is currently in the process of developing a respirable crystalline silica rule of its own that will establish a new PEL for work activities subject to MSHA regulation. At the outset of rulemaking, MSHA intended to publish a final rule by October 2015. The timeline for publishing the new rule has suffered significant delays. At an MSHA Stakeholder Meeting held on May 12, 2016, MSHA was reticent to discuss the specifics of its proposed crystalline silica rule. When asked about the rule, MSHA representatives responded that the process to create the rule was underway, but that they could not comment at this time.


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Although MSHA would not offer specifics, MSHA did mention that it had “looked at the OSHA Rule.” The National Institute for Occupational Safety and Health (NIOSH) recommends exposure limits of 50 µg/m3 averaged over an eight-hour shift, as selected by OSHA. Factors that indicate that MSHA may tack closely to the new OSHA rule include NIOSH’s endorsement of the new OSHA PEL and that the issues faced by MSHA in seeking to limit employee exposure to respirable crystalline silica are very similar to those faced by OSHA.

The newly issued OSHA crystalline silica rule reduces the PEL for respirable crystalline silica to 50 micrograms per cubic meter of air (µg/m3), averaged over an eight-hour shift. Under the rule, the limit of an employee’s exposure to crystalline silica varies according to the duration of exposure. Employees may be exposed to concentrations of respirable crystalline silica of 200 µg/m3 for a maximum two hours, 100 µg/m3 for a maximum of four hours, and 50 µg/m3 for a maximum of eight hours. This represents a significant reduction from the previous PEL for respirable crystalline silica of 100 µg/m3 averaged over an eight-hour shift for general industry and 250 µg/m3 averaged over an eight-hour shift for construction and shipyards.

To implement the reduced PEL for exposure to respirable crystalline silica, OSHA’s rule establishes several requirements that must be met by employers. Employers must employ engineering controls to limit or eliminate employee exposure to respirable crystalline silica. OSHA has identified four categories of engineering controls to limit exposure: substitution, isolation, ventilation, and dust suppression. These controls can take the form of the use of water to reduce dust propagation and increased ventilation to clear areas of airborne dust, amongst others.

Employers are required to provide employees with respirators in situations where engineering controls are not sufficient to adequately limit exposure. Employers must take steps to limit employee access to areas that have, or have the potential to have, high concentrations of respirable crystalline silica. Employers must also develop and implement a written exposure control plan that describes the tasks in the workplace that involve exposure to respirable crystalline silica.

The plan must take steps to ensure that the proper engineering controls are identified and implemented, procedures are developed to restrict employee access to high exposure areas, proper personal protective devices are identified and obtained for use in situations where engineering controls are inadequate, and employee training on work operations that result in high respirable crystalline silica exposure is performed and documented. The plan must also describe the housekeeping measures to be used to limit employee exposure.

OSHA’s new crystalline silica rule implements requirements for employers to provide medical exams and monitoring for employees who are exposed to concentrations of respirable crystalline silica in excess of the PEL for 30 or more days per year. Employers must provide a medical exam to employees within 30 days of initial assignment to a task that exposes them to crystalline silica. The exam must be repeated at least every three years.

The OSHA rule takes effect on June 23, 2016, triggering a five-year window during which employers must achieve compliance with the new standard. Construction employers must comply with the new rule by June 23, 2017, one year from the effective date. General industry and maritime employers must comply by June 23, 2018. Employers involved in the hydraulic fracturing industry must comply with all provisions except those related to engineering controls by June 23, 2018. The hydraulic fracturing engineering controls contemplated by the standard must be implemented by June 23, 2021.

We will continue to monitor MSHA’s regulatory activity and provide updates on any crystalline silica exposure rulemaking from MSHA.

Peter S. Almaas is an associate in the Denver office, practicing in the Occupational Safety and Health Practice Group. He can be reached at 303-390-0178 or

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