OSHA formerly had no specific limit for calcium silicate; the Agency regulated this substance under its generic 8-hour TWA limit for particulates of 15 mg/m3 (total particulate). The ACGIH classifies calcium silicate as a nuisance dust and has an 8-hour limit of 10 mg/m3 for this white powder. The proposed total particulate PEL was 10 mg/m3; however, OSHA has determined that it is appropriate to retain the former 15-mg/m3 total particulate limit for calcium silicate. The 5-mg/m3 limit for the respirable fraction is also retained. Calcium silicate is a white powder.
There are no reported health effects in humans or animals as a result of exposure to calcium silicate. Calcium silicate is thus without long-term adverse health effects if exposures are kept under reasonable control. NIOSH (Ex. 8-47, Table N4) has not conducted an in-depth evaluation of calcium silicate, and no other comments on this substance were received.
OSHA is retaining its 8-hour TWA limits of 15 mg/m3, total particulate, and 5 mg/m3, as the respirable fraction, for calcium silicate. The Agency concludes that these limits protect workers from the significant risk of physical irritation in the workplace.