The OSHA PEL (8-hour TWA) for coal dust (as the respirable fraction) containing less than 5% SiO2 is 2.4 mg/m3 divided by the value "%SiO2 + 2." The OSHA PEL (8-hour TWA) for coal dust (as the respirable fraction) containing greater than or equal to 5% SiO2 is 10 mg/m3 divided by the value "%SiO2 + 2.