Question: What are PELs and how are they calculated for silica?

Answer: OSHA sets enforceable permissible exposure limits (PELs) to protect workers against the health effects of exposure to hazardous substances. PELs are regulatory limits on the amount or concentration of a substance in the air. The OSHA general industry PEL for quartz, the common form of crystalline silica found in sand, is an 8-hour time-weighted average exposure to respirable dust calculated from the following formula: PEL = 10 / [(% Silica) + 2] The PEL is approximately equal to 0.1 mg/m3 for pure quartz silica. The PEL is outlined in 29 CFR 1910.1000 Table Z-3. If other forms of crystalline silica are present, the PEL calculation must be modified per Table Z-3.