FUSED SILICA

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: 60676-86-0; Chemical Formula: SiO₂

Fused silica is a colorless, odorless solid that is a form of quartz. As such, it was formerly covered by OSHA’s limit for quartz (Table Z-3). Exposure to fused silica has long been known to cause the fibrogenic lung disease, silicosis. OSHA’s former limit for quartz dust was the formula 10 mg/m³/ % SiO(2) + 2, measured as total respirable dust. This limit corresponds to a respirable quartz concentration ranging from 0.08 to 0.1 mg/m³, measured as free silica. The ACGIH recommends an 8-hour TWA limit of 0.1 mg/m³, measured as free silica; the ACGIH adopted this limit in 1985 to simplify the monitoring of quartz dust concentrations. Thus, this revision does not represent a re-evaluation of the toxicity data for fused silica. NIOSH (Ex. 8-47, Table N6B) does not concur with the final rule’s limit and recommends a separate 6(b) rulemaking for fused silica, which NIOSH considers a potential occupational carcinogen.

OSHA is replacing its limit for fused silica, which is expressed as the formula presented above, with a numerically equivalent limit of 0.1 mg/m³ as total respirable silica dust; the Agency is establishing this limit to simplify employee exposure monitoring.