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Workplace Exposure Limits

At least four standards are used to regulate respirable crystalline silica exposure in the workplace:

  • The Occupational Safety and Health Administration (OSHA) and Mine Safety and Health Administration (MSHA) currently set the maximum Permissible Exposure Level (PEL) for an 8-hour exposure, 40 hours per week, as the following:
  • Exposure limit = 10 mg SiO2/m3 ÷ (%SiO2 + 2)
  • For dust that is 100% silica, the standard would be 0.1 mg/m3 (%SiO2 = 100).  For dust that has no silica, the standard would be 5 mg/m3 (%SiO2 = 0).
  • However, OSHA is considering lowering its standard by 50%, to 0.05 mg/m3 (50 ug/m3) (

The American Conference of Governmental Industrial Hygienists (ACGIH) has set a recommended exposure limit of 0.025 mg/m3 (25 ug/m3)  Find out more.

The National Institute for Occupational Safety and Health (NIOSH) has set an occupational standard of 0.05 mg/m3 (50 ug/m3). Find out more.

Public Exposure Limits

Safe levels of exposure to the public (sometimes called "environmental exposure limits") to respirable crystalline silica have been established by five states (table from Myers 2010)

Download table

The standards from the California Air Resources Board of 0.03 mg/m3 (3 ug/m3) to protect against silicosis, and the Texas Commission on Environmental Quality of 0.00027 mg/m3 (0.27 ug/m3) to reduce cancer risk are particularly well-researched and documented.  (Note that the designation of particle sizes as "PM4" is essentially equivalent to "respirable" particle sizes.)

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