The permissible exposure limit (PEL) for respirable crystalline silica is 50 micrograms per cubic meter of air, calculated as an 8-hour time-weighted average. This means that employers must ensure that no employee is exposed to an airborne concentration of respirable crystalline silica in excess of 50 μg/m3. The PEL is the maximum amount of crystalline silica to which workers may be exposed during an 8-hour work shift.

It is important to note that the action level for respirable crystalline silica is 25 micrograms per cubic meter of air, which is the concentration of respirable crystalline silica in air, as an eight-hour time-weighted average, at or above which employers must assess employee exposures and conduct medical surveillance.

Employers are responsible for a range of measures to ensure that workers are protected from silica, including controlling dust levels below the PEL, offering medical exams as required by OSHA, and providing worker training about the hazards of silica exposure. Additionally, mining operators can go to the NIOSH Mining webpage for silica-related requirements and safe mining guidance.