OSHA formerly had no PEL for VM & P (Varnish Makers' and Printers') naphtha. The Agency proposed to establish an 8-hour TWA of 300 ppm and a STEL of 400 ppm for this substance. NIOSH (Ex. 8-47, Table N1) concurred with these limits, which are based on the ACGIH TLVs. These limits are established in the final rule. VM & P naphtha, also known as ligroin, is a colorless, flammable liquid.
A study in which rats and beagles received inhalation doses of 500 ppm VM & P naphtha for 30 hours per week for 13 weeks resulted in no chronic or latent effects (Carpenter, Kinkead, Geary et al. 1975a/Ex. 1-302). These authors also noted that the acute toxicity of VM & P naphtha for rats and other species was four times greater than that of rubber solvent naphtha, which has a limit of 400 ppm. Carpenter and associates (1975a/Ex. 1-302) also reported on an experiment in which rats lost coordination and went into convulsions within 15 minutes during exposures to saturation concentrations at ambient room temperature. The 4-hour inhalation LC(50) was 3400 ppm, and the acclimated rats survived 5800 ppm for six hours.
Seven human volunteers exposed to 880 ppm VM & P naphtha for 15 minutes reported upper respiratory tract, eye, and nose irritation, in addition to olfactory fatigue (ACGIH 1986/ Ex. 1-3, p. 631). Elkins (1959d, as cited in ACGIH 1986/ Ex. 1-3, p. 631) noted one case of a worker, exposed to levels of VM & P naphtha averaging 800 ppm, who developed unspecified chronic effects. Elkins also reported that the VM & P naphtha level producing significant irritation in human volunteers was about half as great for this form of naphtha as for rubber solvent naphtha.
The Agency concludes that the 300-ppm TWA is necessary to protect workers against the risk of possible chronic effects associated with naphtha exposure. In addition, OSHA finds that a STEL is necessary to prevent upper respiratory tract and eye irritation, which are considered by OSHA to be material impairments of health that have been demonstrated to occur on short-term exposure to 880 ppm VM & P naphtha (ACGIH 1986/Ex. 1-3, p. 631); the proposed 300-ppm TWA limit alone would permit such excursions. Therefore, OSHA is establishing both a 300-ppm 8-hour TWA and a 400-ppm STEL for VM & P naphtha in the final rule.