DIMETHYLANILINE

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: 121-69-7; Chemical Formula: C₆H₅N(CH₃)₂

OSHA’s former permissible exposure limit for dimethylaniline was 5 ppm as an 8-hour TWA, with a skin notation. The ACGIH has an 8-hour TWA limit of 5 ppm, with a 15-minute STEL of 10 ppm and a skin notation. OSHA proposed to retain its 8-hour TWA PEL of 5 ppm with a skin notation and to add a STEL of 10 ppm, and NIOSH (Ex. 8-47, Table N1) concurred with these limits. The 5-ppm 8-hour TWA and skin notation are retained in the final rule, and the 10-ppm STEL is established. Dimethylaniline is a yellow to brown, oily liquid.

One of the major toxic effects of dimethylaniline exposure is methemoglobinemia, although authorities disagree concerning the level at which humans can tolerate exposure to this substance (ACGIH 1986/Ex. 1-3, p. 207).

Hamblin (1963a/Ex. 1-1084) reported that dimethylaniline is quantitatively less toxic than aniline. Dogs administered a single oral dose of 50 mg/kg exhibited methemoglobinemia, and absorption of dimethylaniline through the skin can increase the overall exposure (Hamblin 1963b/Ex. 1-1085). The dermal LD(50) in rabbits is 1770 mg/kg (Dangerous Properties of Industrial Materials, 7th ed., Sax and Lewis 1989, p. 1360). Mayer (1930/Ex. 1-973) reported that dimethylaniline’s necrotic potential was markedly lower than that of aniline, which has a TLV-TWA of 2 ppm. However, von Oettingen (1941/Ex. 1-874) stated that dimethylaniline has a greater depressant effect on the nervous system than does aniline.

The literature on industrial experience with dimethylaniline is limited. Hamilton (1919/Ex. 1-741) reported collapse, prolonged unconsciousness, visual disturbances, and intense abdominal pain following the severe exposure of two workers. Only NIOSH commented on dimethylaniline.

In the final rule, the Agency is retaining the 8-hour TWA PEL of 5 ppm and a skin notation for dimethylaniline; a STEL of 10 ppm is also being promulgated. OSHA finds that the STEL is necessary to afford protection from the CNS depression that follows acute exposures. OSHA concludes that these limits, taken together, will provide workers with protection from the significant risks of skin absorption, methemoglobinemia, and neuropathic effects associated with exposure to this substance; the Agency finds that these effects clearly constitute material health impairments.