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: 78-93-3; Chemical Formula: CH3COCH2CH3

OSHA’s former exposure limit for 2-butanone was 200 ppm TWA. OSHA proposed to supplement this limit with a STEL of 300 ppm, based on the ACGIH (1986/Ex. 1-3) recommendation. NIOSH (Ex. 8-47, Table N1) concurred with this proposal. The final rule establishes a 200-ppm TWA limit and a 300-ppm STEL for 2-butanone. 2-Butanone is a colorless, flammable liquid with an objectionable odor.

2-Butanone is an ocular and upper respiratory tract irritant. One study (Nelson, Enge, Ross et al. 1943/Ex. 1-66) reported that exposures to 200 ppm for 3 to 5 minutes caused mild eye irritation in some subjects and that others experienced slight nose and throat irritation at concentrations of 100 ppm. Exposure to 350 ppm caused eye and nasal irritation in a majority of subjects tested. Studies conducted in the 1940s noted low-grade intoxication resulting from exposure to 300 to 600 ppm (Smith and Mayers 1944, as cited in ACGIH 1986/Ex. 1-3, p. 395). Later studies have shown that approximately 50 percent of trained panelists experienced eye and nose irritation at 200 ppm (as reported in ACGIH 1986/Ex. 1-3, p. 395).

In the preamble discussion on 2-butanone, OSHA noted that a number of studies indicate that the proposed limits may not be sufficient to fully protect workers from the irritant effects of this substance (ACGIH 1986/Ex. 1-3; Nelson, Enge, Ross et al. 1943/Ex. 1-66). The ACGIH also cited a manufacturer’s publication that stated that 200 ppm was the highest concentration judged by human subjects to be “satisfactory” for eight hours. In addition, another study cited by the ACGIH (1986/Ex. 1-3) reported that exposure to 200 ppm was associated with a 50-percent response rate for eye and nasal irritation (the degree of irritation was not specified).

OSHA specifically requested comment on whether its proposed limits for 2-butanone were sufficiently protective. The New Jersey Department of Public Health (Exs. 144, 144A) urged OSHA to set its limits for 2-butanone based on EPA’s IRIS data. The use of such an approach is discussed in Section VI.A of the preamble. The AFL-CIO (Ex. 194) supported the establishment of a STEL for butanone.

OSHA has determined that its previous 8-hour TWA limit of 200 ppm was not sufficient to protect workers from experiencing the significant irritation and narcotic effects that are associated with short-term exposures to high concentrations of 2-butanone. After reviewing the available reports describing human sensory responses to short-term exposures to 2-butanone, the Agency concludes that a 300-ppm STEL is also necessary to reduce the significant risk of sensory irritation; exposure to 350 ppm for three to five minutes was reported to cause eye, nose, and throat irritation in a majority of subjects (Nelson, Enge, Ross et al. 1943/Ex. 1-66). Accordingly, OSHA is establishing a 200-ppm TWA limit and a 300-ppm 15-minute STEL for 2-butanone to protect employees from the significant risk of sensory irritation; OSHA considers the irritation caused by 2-butanone to be a material impairment of health or functional capacity.

Page last reviewed: September 28, 2011