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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.

CAS: 546-93-0; Chemical Formula: MgCO3

OSHA’s former PEL for magnesite was 15 mg/m3, measured as total particulate; this was the Agency’s generic limit for all dusts and particulates. The ACGIH has a TLV-TWA of 10 mg/m3, also measured as total particulate. The proposed PELs for magnesite were 8-hour TWAs of 10 mg/m3 (total particulate) and 5 mg/m3 (respirable fraction). In the final rule, however, OSHA is retaining its former total particulate limit of 15 mg/m3 for magnesite. Magnesite occurs as a white powder.

Magnesite is considered by both OSHA and the ACGIH to be one of the dusts that “do not produce significant organic disease or toxic effect when exposures are kept under reasonable control” (ACGIH 1986/Ex. 1-3). Exposure to excess levels of magnesite in the workplace causes skin or mucous membrane irritation resulting either from contact with the magnesite itself or from the rigorous cleansing procedures necessary for removing the dust. NIOSH, the only commenter on this substance, has not substantively reviewed the effects of exposure to magnesite (Ex. 8-47, Table N4).

OSHA is retaining its 8-hour TWA PEL of 15 mg/m3 TWA for magnesite, measured as total particulate; the 5-mg/m3 TWA limit for the respirable fraction is also being retained. The Agency concludes that these limits protect workers from the significant risk of skin, mucous membrane, and other physical irritation.