Respirable crystalline silica is quartz, cristobalite and/or tridymite contained in airborne particles that are determined to be respirable by a sampling device designed to meet the size-selective sampler characteristics in ISO 7708:1995. The standard applies to all occupational exposures except construction work (covered by its own silica standard, 29 CFR 1926.1153), agricultural operations, and exposures from processing sorptive clays. It also does not apply where the employer has objective data showing exposure will remain below 25 µg/m³ as an 8-hour TWA under any foreseeable conditions, or where the employer complies with 29 CFR 1926.1153 for a task that is indistinguishable from a construction task listed in that standard's Table 1 and will not be performed regularly in the same environment and conditions.

Health hazards

Your employer's hazard communication training must cover at least these silica hazards:

Cancer

Lung effects

Immune system effects

Kidney effects

Two numbers to know

Limit	Level (8-hour time-weighted average)	What it triggers
Permissible exposure limit (PEL)	50 µg/m³	No employee may be exposed above this
Action level	25 µg/m³	Exposure assessment, and medical exams if you are at or above it 30 or more days a year

"Employee exposure" means the exposure you would have if you were not wearing a respirator. A respirator protects you, but it does not lower your exposure as the rule defines it.