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: 91-20-3; Chemical Formula: C10H8

OSHA’s former exposure limit for naphthalene was 10 ppm as an 8-hour TWA. The final rule retains this TWA and adds a short-term limit of 15 ppm for this substance, which occurs as a colorless to brown solid and has the odor of mothballs. The ACGIH also has a 10-ppm 8-hour TWA and a 15-ppm STEL for naphthalene. NIOSH (Ex. 8-47, Table N1) concurs with the PELs selected for this substance.

The oral LD(50) for naphthalene in rats is 1760 mg/kg (Flury and Zernik 1931g/Ex. 1-995). In humans, the inhalation of naphthalene vapor causes headache, loss of appetite, and nausea (Flury and Zernik 1931g/Ex. 1-995; Patty 1949b, as cited in ACGIH 1986/Ex. 1-3, p. 420). These authors also report that exposure causes optical neuritis, corneal damage, and kidney injury. Eight of 21 workers exposed for five years to unspecified levels of naphthalene developed opacities of the lens of the eye (Ghetti and Mariani 1956/Ex. 1-739). Ingestion of large amounts of naphthalene causes severe hemolytic anemia and hemoglobinuria (Stokinger and Mountain 1963/Ex. 1-765). The lethal dose in humans has been reported as 50 mg/kg (NIOSH 1977i/Ex. 1-1182). Concentrations somewhat above 15 ppm are reported to cause marked eye irritation (Robbins 1951/ Ex. 1-799).

Only the American Iron and Steel Institute (AISI) and NIOSH commented on naphthalene. The AISI (Exs. 129 and 188) believes that a STEL for naphthalene is not warranted by the evidence. However, the Robbins (1951/Ex. 1-799) study discussed above clearly shows that excursions to 15 ppm cause severe eye irritation, and OSHA thus finds the STEL both necessary and appropriate.

In the final rule, the Agency is retaining the 8-hour TWA of 10 ppm and adding a 15-minute STEL of 15 ppm for naphthalene. This STEL is designed to protect against the eye irritation observed in workers at elevated levels (Robbins 1951/Ex. 1-799). The Agency concludes that these limits will protect workers from the significant risks of eye irritation and serious ocular effects, which constitute material health impairments that are potentially associated with exposure to levels above the 8-hour limit.

Page last reviewed: September 28, 2011