OSHA's former permissible exposure limit for ethyl silicate was 100 ppm as an 8-hour TWA. The proposal included a limit of 10 ppm TWA for this colorless, flammable liquid with a faint odor; NIOSH (Ex. 8-47, Table N1) agreed with the selection of this limit. In the final rule, a PEL of 10 ppm is established for ethyl silicate; this limit is consistent with that of the ACGIH.
Ethyl silicate has been reported to cause both irritation and systemic toxicity. In guinea pigs and rats, a 60-minute exposure of 2000 ppm was reported as the maximal duration/concentration that did not cause serious disturbances; 500 ppm was the maximal no-effect exposure level for an exposure of several hours' duration (Smyth and Seaton 1940b/Ex. 1-376). Thirty-day exposures to 400 ppm ethyl silicate for seven hours/day caused significant mortality in rats and damage to the lungs, liver, and kidney in the surviving animals. Exposures of rats, guinea pigs, and mice to 88, 50, or 23 ppm for 90 days (seven hours/day, five days/week) resulted only in decreased kidney weights in mice exposed at the 88-ppm level (Pozzani and Carpenter 1951/Ex. 1-166). In another study, Kasper, McCord, and Fredrick (1937/Ex. 1-1155) showed that animals exposed to 164 ppm ethyl silicate for 17 eight-hour days showed less weight gain than did controls. Rowe and associates (1948/Ex. 1-359) reported that three 7-hour exposures at 1000 ppm were fatal to 4 of 10 rats; similar exposures to 500 ppm caused pronounced kidney changes and slight lung irritation. Four to 10 similar exposures at 250 ppm caused slow weight loss and some lung and renal changes; at 125 ppm, slight to moderate kidney damage was observed (Rowe, Spencer, and Bass 1948/Ex. 1-359). Smyth and Seaton (1940b/Ex. 1-376) reported that exposure to a concentration of 1200 ppm causes lacrimation in humans and that 250 ppm causes eye and nose irritation. Only NIOSH submitted comments to the rulemaking record on ethyl silicate.
OSHA is establishing a PEL for ethyl silicate of 10 ppm as an 8-hour TWA. The Agency concludes that this limit is required to protect workers from the significant risk of renal damage, which constitutes material health impairment, that is associated with exposures to this substance at concentrations above the revised PEL. OSHA finds that this reduced limit will substantially reduce this risk.