| heal.abstract |
There are three commonly used occupational exposure limits for respirable (quartz) silica: the American Conference of Governmental Industrial Hygienists' (ACGIH's) threshold limit value (TLV®) of 0.1 mg/m 3; the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) of 0.05 mg/m 3; and the U.S. Department of Labor/Occupational Safety and Health Administration (USDOL/OSHA) permissible exposure level (PEL) for silica that uses a formula where 10 mg/m 3 is divided by the sum of the percent SiO 2 and 2. It is commonly stated that there is no significant difference between the TLV and the PEL, and it is assumed that the REL is more stringent than the PEL. In fact, the PEL is always a more conservative value than the TLV and, at silica percentages at or below 2%, the PEL is more stringent than the REL. Although at the higher silica concentrations the ratio of the TLV to the PEL is virtually 1.0, at lower silica concentrations the differences become geometrically larger, reaching greater than 1.2 at 10% SiO 2 and 1.4 at 5% SiO 2. Below 5% SiO 2 the difference is most significant, and the PEL is three times more conservative than the TLV at 1% SiO 2. For these reasons one should not assume that meeting the TLV or REL for silica assures compliance with the PEL for silica. Further, the change proposed in the 1989 Air Contaminants USDOL/OSHA rulemaking would increase the allowable silica exposure level in the workplace. |
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