OSHA had no former limit for undoped bismuth telluride, although OSHA's generic total particulate limit of 15 mg/m3 formerly applied. The ACGIH has a total-dust TLV-TWA of 10 mg/m 3 for the undoped form of this substance. The proposed PELs for bismuth telluride in the undoped form were 10 mg/m3 (total particulate) and 5 mg/m3 (respirable particulate); however, in the final rule, OSHA is retaining the total particulate limit of 15 mg/m3 for this substance, as well as the 5-mg/m3 respirable-fraction limit. Bismuth telluride appears as gray, hexagonal platelets; it is also available as ingots or single crystals.
An eleven-month inhalation study of dogs, rabbits, and rats exposed to pure undoped bismuth telluride dust at 15 mg/m3 showed the pulmonary responses typical of exposures to inert dusts (Wagner, Madden, Zimber, and Stokinger 1974, as cited in ACGIH 1986/Ex. 1-3, p. 59). NIOSH has not evaluated the evidence for undoped bismuth telluride in depth (Ex. 8-47, Table N4). No other comments on this substance were submitted.
OSHA is retaining its permissible exposure limits of 15 mg/m3 TWA, as total particulate, and 5 mg/m3, as the respirable fraction, for pure undoped bismuth telluride. The Agency concludes that these limits protect workers from the significant risks associated with workplace exposures to bismuth telluride.