Exposure to respirable crystalline silica is nothing new for employees on construction sites. However, this exposure can cause serious health issues. In response to these concerns, OSHA issued a new rule on exposure to silica in construction (29 CFR 1926.1153). The PEL is now 50 micrograms per cubic meter of air (μg/m3) for an 8-hour time-weighted average (TWA).  The action level of airborne silica is 25 μg/m3, calculated as an 8-hour TWA. The action level (set at half the PEL) triggers requirements for exposure assessment. 

The standard does not apply where silica exposures will remain low under any foreseeable conditions. This includes tasks like mixing mortar; pouring concrete footers, slab foundation and foundation walls; and removing concrete formwork.