OSHA will measure the level of exposure to respirable silica dust over an 8-hour period to determine if a jobsite is at or below the PEL of 50 μg/m³.
Silica exposure is determined one of two ways:
- By referencing objective data, which means studies or reports by recognized experts who have evaluated dust exposures for certain tasks*
- By directly monitoring actual employee exposure
Actual exposure is measured using an air sampling device that is placed in the work area or worn by an employee. An industrial hygienist (IH)** will generally oversee the sample collection. The samples are collected and sent to a qualified lab for analysis and the IH will review the results and make recommendations.
Note: Only a small fraction (typically less than 5%) of the total dust produced when cutting fiber cement is considered to be respirable silica dust.