OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

MICA

CAS: 12001-26-2; Chemical Formula:

      OSHA formerly had a PEL of 20 mppcf TWA for mica containing less than 1 percent crystalline silica; this limit is equivalent to a 3 mg/m3 limit. The ACGIH recommends a limit of 3 mg/m3 TWA for the respirable dust of mica containing less than 1 percent quartz. OSHA proposed, and the final rule establishes, an 8-hour TWA limit of 3 mg/m3 for the respirable dust of mica containing less than 1 percent quartz. NIOSH (Ex. 8-47, Table N1) agreed with this decision.

       Mica is a colorless, odorless, nonflammable, nonfibrous, water-insoluble silicate occurring in plate form and containing less than 1 percent quartz; it includes nine different species.

       The final rule establishes an 8-hour TWA limit of 3 mg/m3 for respirable mica dust containing less than 1 percent quartz; this limit corresponds to the existing 20-mppcf PEL and is in keeping with the Agency's decision to delete mppcf values in favor of respirable dust values expressed in mg/m3. The Agency has decided to express this and other similar limits as mg/m3 to facilitate employee exposure monitoring.