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XYLENES								Related Pages
										*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:** 1330-20-7; **Chemical Formula:** C6H4(CH3)2
The previous OSHA limit for the xylenes was 100 ppm as an 8-hour TWA. Based on the ACGIH recommendation, OSHA proposed to revise this limit to a TWA of 100 ppm and a 15-minute STEL of 150 ppm. NIOSH (Ex. 8-47, Table N1) as well as the AFL-CIO (Ex. 194) concurred with these limits, and they are established in the final rule. The xylene isomers are clear, flammable liquids with an aromatic hydrocarbon odor.
Rats and rabbits exposed to a mixture of xylene isomers at a concentration of 690 ppm for eight hours daily, six days per week showed no blood abnormalities, but rabbits exposed on the same regimen at 1150 ppm for 55 days showed a decrease in red and white blood cell counts and an increase in platelet count (Fabre and Truhaut 1954, as cited in ACGIH 1986/Ex. 1-3, p. 637).
Studies of workers exposed to xylene revealed headache, fatigue, lassitude, irritability, and gastrointestinal disturbances as the most common symptoms (Gerarde 1960d/Ex. 1-738a). At unspecified exposure levels, Browning (1965b/Ex. 1-1016) also noted gastrointestinal disturbances, in addition to kidney, heart, liver, and neurological damage; blood dyscrasias, some of which resulted in death, were also reported in these workers. A study by Nelson, Enge, Ross et al. (1943/Ex. 1-66), in which human volunteers were exposed to 200 ppm xylene, found eye, nose, and throat irritation in the subjects at this level of exposure.
NIOSH developed a criteria document for xylene in 1975 (NIOSH 1975; as cited in ACGIH 1986/Ex. 1-3, p. 637), in which the work of Morley, Eccleston, Douglas, and colleagues (1970/Ex. 1-794) was discussed. These authors observed liver dysfunction and renal impairment in three workers overexposed to xylene (estimated concentration of 10,000 ppm). One of these workers died, but the others recovered slowly. Furniture polishers were reported by Matthaus (1964/Ex. 1-830) to have suffered corneal damage as a result of exposure to xylene at unknown concentrations.
One other commenter, Stanley L. Dryen of Chevron Corporation (Ex. 3-896, p. 15), objected to OSHA’s issuing of a STEL, stating that there was no basis for one. OSHA disagrees and points out that a 100-ppm TWA limit alone would permit short-term exposure to several hundred ppm xylene, well above the 200-ppm level reported to be irritating as a result of short-term exposures. OSHA notes that NIOSH also recommends a short-term limit to supplement the TWA.
After reviewing this evidence, OSHA concludes that both a TWA and a STEL are necessary to prevent the risks of narcosis, blood effects, and irritant effects at the elevated levels possible at the current exposure limit. The Agency considers the effects of narcosis, irritation, and blood effects to constitute material impairments of health and functional capacity. Therefore, to reduce the risk of irritation to workers exposed to the xylenes, OSHA is establishing a 150-ppm STEL and a 100-ppm TWA for xylene isomers in the final rule.
										
							
								Page last reviewed:  September 28, 2011						Content source:  	National Institute for Occupational Safety and Health NIOSH
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