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: 1309-48-4 Chemical Formula: MgO

OSHA’s former limit for magnesium oxide (as fume) was 15 mg/m3 as an 8-hour TWA, the Agency’s generic limit for particulates. The ACGIH has a TLV-TWA limit of 10 mg/m3 for the fume of this white, odorless, very fine powder. OSHA proposed 8-hour TWA PELs of 10 mg/m3 (total particulate) and 5 mg/m3 (respirable particulate) for magnesium oxide fume, and the final rule establishes these limits.

Slight reactions (not further specified) have been reported in human subjects after exposures of less than 10 minutes to freshly generated MgO fume at concentrations of from 400 to 600 mg/m3 (Drinker, Thomson, and Finn 1927/Ex. 1-356). Animal and human studies of magnesium oxide fume exposure have shown toxicities less marked than but similar to those attributable to zinc oxide fume (Drinker and Drinker 1928/Ex. 1-314). The symptoms of exposure include those of metal fume fever (fever, chills, muscular pain, nausea, and vomiting) and leukocytosis, symptoms analogous to those caused by exposure to zinc oxide fume. NIOSH does not concur with the final rule’s limit for this fume. NIOSH notes that exposure to magnesium oxide may also cause chronic respiratory disease (Ex. 8-47, p. 12); no other comments on this substance were received.

In the final rule, OSHA is setting a PEL of 10 mg/m3 TWA (total particulate). OSHA concludes that these limits will substantially reduce the significant risks of metal fume fever, leukocytosis, and, perhaps, chronic respiratory disease associated with exposure to magnesium oxide fume in the workplace. OSHA finds that these health effects constitute material health impairments.

Page last reviewed: September 28, 2011