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: 21351-79-1; Chemical Formula: CsOH

OSHA formerly had no limit for cesium hydroxide; however, based on the ACGIH recommendation, OSHA proposed the establishment of a 2-mg/m3 limit as an 8-hour TWA. NIOSH (Ex. 8-47, Table N1) concurred with OSHA’s proposed limit for this substance, and the Agency is establishing this limit for cesium hydroxide in the final rule. Cesium hydroxide is a colorless or yellowish fused crystalline mass; it is the strongest base known and is highly soluble in both water and alcohol.

Animal studies indicate that cesium hydroxide has an acute oral toxicity of about one-third that of potassium hydroxide, which causes lesions of the nasal septum and irritation of the eyes and respiratory tract (Karpov 1971/Ex. 1-1115). The oral LD(50) for cesium hydroxide in rats is 1016 mg/kg. Although a concentration of 5 percent cesium hydroxide did not produce skin irritation, contact with this concentration did result in severe eye irritation. Cesium hydroxide does not cause skin sensitization (Johnson, Lewis, and Perone 1972, as cited in ACGIH 1986/Ex. 1-3, p. 113). No rulemaking participants other than NIOSH commented on the proposed 2-mg/m3 TWA limit for cesium hydroxide.

In the final rule, the Agency is promulgating an 8-hour TWA PEL of 2 mg/m3 for cesium hydroxide and concludes that this limit will protect workers from the significant risk of severe eye irritation associated with exposure to this substance at levels above the new PEL. The Agency considers the severe eye irritation caused by exposure to cesium hydroxide a material impairment of health and functional capacity.

Page last reviewed: September 28, 2011