OSHA's former exposure limit for zinc oxide fume was 5 mg/m3 as an 8-hour TWA. The ACGIH recommends a 5 mg/m3 TWA and also has a STEL of 10 mg/m3. NIOSH recommends a 5 mg/m3 10-hour TWA limit with a 15-minute ceiling of 15 mg/m3. OSHA proposed to retain the 5 mg/m3 8-hour TWA and to add a STEL of 10 mg/m3, and NIOSH (Ex. 8-47, Table N1) concurs with this proposal. The final rule establishes these limits. When heated, zinc oxide produces a white fume.
The most prevalent toxic effect of zinc oxide fume is a condition known as "metal fume fever," whose symptoms include chills, fever, muscular pain, nausea, and vomiting (Turner and Thompson 1926/Ex. 1-1124). Studies in the workplace have shown that welders exposed to zinc oxide fume at concentrations of 320 to 580 mg/m3 reported nausea, with the development of chills, shortness of breath, and severe chest pains 2 to 12 hours later. Most workers took approximately 4 days to recover, and some eventually developed pneumonia (Hammond 1944/Ex. 1-981). Other studies have reported the frequent occurrence of chills in workers exposed to zinc oxide at levels as low as 5 mg/m3 (Hickish 1963 and Wall 1970, both as cited in ACGIH 1986/Ex. 1-3, p. 645). Hammond (1944/Ex. 1-981) reported that workers exposed to 8 to 12 mg/m3 of zinc oxide fume did not suffer from metal fume fever.
Zinc oxide exposures of guinea pigs that lasted only an hour caused a drop in body temperature, followed 6 to 18 hours later by an increase above normal levels (Turner and Thompson 1926/Ex. 1-1124). The animals in the high-exposure group (2500 mg/m3 for three to four hours) died after exposure.
Early studies (Drinker, Thomson, and Finn 1927/Ex. 1-356) suggested that metal fume fever was unlikely to occur at concentrations below 15 mg/m3, but subsequent experience shows that exposures even at 5 mg/m3 can cause this syndrome (Hickish 1963 and Wall 1970, both as cited in ACGIH 1986/Ex. 1-3, p. 646).
NIOSH's criteria document (1975d, as cited in ACGIH 1986/Ex. 1-3, p. 645) reported that the development of metal fume fever was unlikely at levels as low as 5 mg/m3, but the Institute stated that exposures to the fume at this level could cause chronic respiratory effects. Dr. Lawrence Hecker, representing Abbott Laboratories (Ex. 3-678), objected to a STEL for zinc oxide fume. However, in both its criteria document (1975d) and post-hearing testimony (Ex. 150, Comments on Zinc Oxide Fume), NIOSH indicated that a short-term limit is necessary to "prevent pathological tissue changes in the lung from acute exposure." Therefore, OSHA finds that a STEL for zinc oxide fume is necessary to prevent or minimize these effects.
In the final rule, OSHA is retaining the 5 mg/m3 8-hour TWA and adding a STEL of 10 mg/m3. The Agency concludes that both of these limits will protect workers from the significant risk of metal fume fever, which constitutes a material health impairment that is associated with acute and chronic exposure to zinc oxide fumes.