PROPIONIC ACID

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: 79-09-4; Chemical Formula: CH₃CH₂COOH

OSHA previously had no limit for propionic acid. The ACGIH has a TLV-TWA of 10 ppm for this substance; the TLV was set on the basis of analogy with acetic acid (10 ppm 8-hour TLV). The proposed PELs were 10 ppm as an 8-hour TWA and 15 ppm as a 15-minute STEL. NIOSH (Ex. 8-47, Table N1) concurred that these limits are appropriate, and the final rule establishes an 8-hour TWA of 10 ppm but does not include a STEL. Propionic acid is a colorless, oily liquid with a pungent odor.

The primary health effects associated with exposure to propionic acid are skin burns and irritation of the eyes and respiratory system. Smyth, Carpenter, Weil, and co-workers (1962/Ex. 1-441) reported that the oral LD(50) for rats is 4.3 g/kg; NIOSH (1977i/Ex. 1-1182) stated that the intravenous LD(50) for mice is 625 mg/kg and the skin absorption LD(50) for rabbits is 500 mg/kg. Inhalation of the saturated vapor for eight hours caused no fatalities in rats (ACGIH 1986/Ex. 1-3, p. 498).

Acute industrial exposures to propionic acid have been reported to cause mild to moderate skin burns, eye irritation, and, in a single incident, asthmatic cough. No irritation was observed as a consequence of exposures in humans averaging below 0.25 ppm with excursions to 2.1 ppm in an eight-hour period (Dow Chemical Company 1977o, as cited in ACGIH 1986/Ex. 1-3, p. 498).

Two commenters in addition to NIOSH commented on propionic acid. The American Industrial Hygiene Association (AIHA) (Tr. 3-307) urged OSHA to delete the STEL for propionic acid on the ground that the ACGIH has put the STEL for this substance on its List of Intended Changes (ACGIH 1988). Kodak (Ex. 661) agrees with the AIHA on the issue of a STEL, noting that, in Kodak’s opinion, the 15-ppm STEL “cannot be justified on either available toxicological data or…[Kodak’s] own experience.” After a review of the evidence for propionic acid’s short-term effects, OSHA has determined, in accordance with the STEL policy outlined in Section VI.C.17 of this preamble, that no STEL is necessary for propionic acid. Accordingly, the final rule contains no short-term limit for this substance.

In the final rule, OSHA establishes an 8-hour TWA limit of 10 ppm (8-hour TWA) for propionic acid. The Agency concludes that this limit is required to protect workers against the significant risk of eye and respiratory tract irritation, which are material impairments of health that are associated with exposure to levels above the new PEL.