Exposure Limits
When employees perform tasks listed in OSHA Standard 1926.1153, Table 1 for more than four hours, they may be required to use respiratory protection. (Click on the link above for more specific information.)
Respirable Dust and/ or Silica Sampling NIOSH
Action Level (AL) and Permissible Exposure Limit (PEL) Requirements
Depending on the degree of exposure, the silica standard for construction requires employers to:
- assess the exposure of each employee who is or may reasonably be expected to be exposed to respirable crystalline silica at or above the action level of 25 μg/m3 (micrograms of silica per cubic meter of air), calculated as an 8-hour TWA (Time-Weighted Average);
- ensure that no employee is exposed to an airborne concentration of respirable crystalline silica in excess the permissible exposure limit (PEL) of 50 μg/m3, calculated as an 8-hour TWA;
- limit worker access to areas where they could be exposed above the PEL; and
- use dust controls to protect workers from silica exposures above the PEL;
Where exposure exceeds the action level, the employer must assess exposure either through a performance option or monitoring. Where the most recent exposure monitoring indicates that employee exposures are at or above the action level but at or below the PEL, the employer must repeat monitoring within six months.
Collecting an Air Sample
A trained specialist, such as a certified industrial hygienist, will use a device called a cyclone assembly and a sampling pump to trap tiny respirable silica particles from the air in the work environment.
- The cyclone assembly and sampling pump will be placed on an employee, who will wear the device throughout the work shift for up to 8 hours.
- All employees may be fitted with the sampling device or just a select few who are closest to the silica source may be fitted. The industrial hygienist can help you determine what will be most appropriate.
- The hygienist will return at the end of the sampling period to de-activate the sampling pump and remove the filters to be sent for analysis.
Knowledge Check Choose the best answer for the question.
9-4. Who should determine if workers are exposed to silica dust in excess of exposure limits?
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