Note: Before March 1, 1989 and after March 22, 1993, the OSHA PEL is [(5 mg/m3) / (% cristobalite + 2)], for respirable dust containing at least 1 percent cristobalite. From March 1, 1989 to March 22, 1993, the OSHA PEL was 0.05 mg/m3 for respirable cristobalite. For metal/nonmetal mining, the MSHA PEL is [(5 mg/m3) / (% cristobalite + 2)] for respirable dust containing at least 1 percent cristobalite. The NIOSH REL is 0.05 mg/m3. See appendices for source description and methods. |