30 CFR § 57.5001
Exposure limits for airborne contaminants.
AIR QUALITY--SURFACE AND UNDERGROUND
Except as permitted by §57.5005--
(b) Asbestos standard--(1) Definitions. Asbestos is a generic term for a number of asbestiform hydrated silicates that, when crushed or processed, separate into flexible fibers made up of fibrils. As used in this part--
Asbestos means chrysotile, cummingtonite-grunerite asbestos (amosite), crocidolite, anthophylite asbestos, tremolite asbestos, and actinolite asbestos.
Asbestos fiber means a fiber of asbestos that meets the criteria of a fiber.
Fiber means a particle longer than 5 micrometers ([mu]m) with a length-to-diameter ratio of at least 3-to-1.
(2) Permissible Exposure Limits (PELs)--(i) Full-shift limit. A miner's personal exposure to asbestos shall not exceed an 8-hour time- weighted average full-shift airborne concentration of 0.1 fiber per cubic centimeter of air (f/cc).
(ii) Excursion limit. No miner shall be exposed at any time to airborne concentrations of asbestos in excess of 1 fiber per cubic centimeter of air (f/cc) as averaged over a sampling period of 30 minutes.
(3) Measurement of airborne asbestos fiber concentration. Potential asbestos fiber concentration shall be determined by phase contrast microscopy (PCM) using the OSHA Reference Method in OSHA's asbestos standard found in 29 CFR 1910.1001, Appendix A, or a method at least equivalent to that method in identifying a potential asbestos exposure exceeding the 0.1 f/cc full-shift limit or the 1 f/cc excursion limit. When PCM results indicate a potential exposure exceeding the 0.1 f/cc full-shift limit or the 1 f/cc excursion limit, samples shall be further analyzed using transmission electron microscopy according to NIOSH Method 7402 or a method at least equivalent to that method.
For further information: See MSHA's Program Policy Manual