PENTABORANE

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: 19624-22-7; Chemical Formula: B₅H₉

OSHA’s former limit for pentaborane was 0.005 ppm as an 8-hour TWA. The ACGIH has the same 8-hour TWA but additionally recommends a 15-minute STEL of 0.015 ppm. The Agency proposed, and the final rule establishes, permissible exposure limits of 0.005 ppm as an 8-hour TWA and 0.015 ppm as a 15-minute STEL for pentaborane. NIOSH (Ex. 8-47, Table N1) concurs that these limits are appropriate. Pentaborane is a colorless liquid with a strong and penetrating odor.

In both humans and animals, inhalation of pentaborane vapor causes central nervous system effects (Svirbely 1954a/ Ex. 1-385; Rozendaal 1951/Ex. 1-525; Lowe and Freeman 1957/ Ex. 1-518; Cordasco, Cooper, Murphy, and Anderson 1962/ Ex. 1-545).

The 5-minute LC(50) for rats and mice is 67 and 40 ppm, respectively; for 60 minutes, these values are 10 and 6 ppm for rats and mice, respectively (Weir, Bath, and Weeks 1961, as cited in ACGIH 1986/Ex. 1-3, p. 459). Rats exposed repeatedly to 3 ppm pentaborane by inhalation exhibited tremors, hyper-excitability, belligerence, and weight loss (Svirbely 1954a/ Ex. 1-385). Rats, rabbits, monkeys, and dogs exposed repeatedly to pentaborane vapor at concentrations of 1 ppm for four weeks or 0.2 ppm for six months lost weight (Levinskas, Paslian, and Bleckman 1958/Ex. 1-517). In the same experiments, rats and rabbits exposed at 1 ppm showed reduced activity and impaired locomotor ability, respectively, and monkeys and dogs exhibited apathy, loss of appetite, insensitivity to pain, loss of mobility, tremor, and impaired coordination. The ACGIH (1986/Ex. 1-3, p. 459) notes that the 0.2-ppm concentration reported in the Levinskas, Paslian, and Bleckman (1958/Ex. 1-517) study was a calculated rather than measured value and that the actual exposure level was probably closer to 0.01 ppm.

Humans accidentally overexposed to pentaborane experienced tremors, convulsions, behavioral changes, loss of memory, impaired judgment, and other symptoms of central nervous system intoxication (Svirbely 1954a/Ex. 1-385; Rozendaal 1951/ Ex. 1-525; Lowe and Freeman 1957/Ex. 1-518; Cordasco, Cooper, Murphy, and Anderson 1962/Ex. 1-545). No comments other than those from NIOSH were received on the health effects associated with pentaborane exposure.

OSHA is establishing an 8-hour TWA PEL of 0.005 ppm and a 15-minute STEL of 0.015 ppm for pentaborane. The Agency concludes that these limits will protect workers against the significant risk of central nervous system effects, such as tremors and convulsions, behavioral changes, and loss of judgment, potentially associated with exposure to pentaborane at levels only slightly above those formerly permitted by the 8-hour TWA alone. OSHA finds that these neuropathic effects constitute material health impairments within the meaning of the Act.