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: 2698-41-1; Chemical Formula: ClC6H4CH=C(CN)2

OSHA’s previous PEL for o-chlorobenzylidene malononitrile (OCBM) was 0.05 ppm as an 8-hour TWA. The Agency has proposed revising this limit to 0.05 ppm as a ceiling, with a skin notation, based on the ACGIH (1986/Ex. 1-3) recommendation. This revision is incorporated in the final rule. NIOSH (Ex. 8-47, Table N1) concurred with OSHA’s proposed limit for this substance. o-Chlorobenzylidene malononitrile is a white crystalline solid with a pepper-like odor.

OCBM has extremely irritating properties. It causes intense eye and skin irritation, coughing, difficulty in breathing, chest tightness, running nose, dizziness, nausea, and vomiting. These effects are evident on exposure to concentrations between 12 and 20 mg/m3 (1.5 to 2.5 ppm), and they become incapacitating within 20 seconds of exposure; the effects persist for approximately 5 to 10 minutes after the victim has been removed to fresh air (Military Chemistry and Chemical Agents 1963, as cited in ACGIH 1986/Ex. 1-3, p. 124).

OCBM is only slightly toxic to laboratory animals when they are exposed intravenously, subcutaneously, or through inhalation (Punte, Weimer, Ballard, and Wilding 1962/ Ex. 1-354). In animals, it has been demonstrated that OCBM is metabolized by the body into cyanide (Frankenberg and Sorbo 1973/Ex. 1-480). Short-term exposures to high levels of OCBM did not cause carcinogenic, teratogenic, or embryolethal effects in animals (McNamara et al. 1973, as cited in ACGIH 1986/Ex. 1-3, p. 124).

Three of four human volunteers exposed to a 1.5-mg/m3 (0.19-ppm) concentration of OCBM aerosol dispersed from a 10-percent solution of methylene chloride for 90 minutes developed headaches, and one showed mild eye and nose irritation. Headache persisted for 24 hours in two subjects. At 4 to 5 mg/m3 (0.5 to 0.6 ppm), subjects’ problem-solving abilities were affected and they showed eye irritation, conjunctivitis, lacrimation, and skin burning (Punte, Owens, and Gutentag 1963/Ex. 1-353). Other researchers observed no persistent clinical abnormalities in seven subjects exposed to OCBM at concentrations ranging from 1 to 13 mg/m3 (0.13 to 1.6 ppm) over a 15-day period; however, none of these subjects developed a tolerance for the compound. Severe skin sensitization has also been reported in workers handling OCBM (Shmunes and Taylor 1973/Ex. 1-370). No comments, except those submitted by NIOSH, were received on OSHA’s proposed revision of the limit for OCBM.

In the final rule, OSHA is establishing a PEL of 0.05 ppm as a ceiling, with a skin notation, to reduce the risks associated with elevated short-term exposures to OCBM. The Agency concludes that workers are at significant risk of experiencing the severe eye and upper respiratory tract irritation, skin sensitization, dyspnea, nausea, lacrimation, vomiting, and performance decrements that are associated with brief exposures to this substance at the former 8-hour TWA PEL. Furthermore, OSHA considers the effects related to exposure to OCBM to represent material impairments of health.

Page last reviewed: September 28, 2011