851 Silica Dust Safety in Construction

Exposure Assessment

The employer should 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 micrograms per cubic meter (µg/m3) using one of the following two methods:

• Performance Option: The employer should assess the 8-hour TWA exposure for each employee on the basis of any combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica, or
• Scheduled Monitoring Option: The employer should perform initial monitoring to assess the 8-hour TWA exposure for each employee on the basis of one or more personal breathing zone air samples that reflect the exposures of employees on each shift, for each job classification, in each work area.
• Representative Sampling: Where several employees perform the same tasks on the same shift and in the same work area, sample a representative fraction of the employees.
• Sample the employee(s) who are expected to have the highest exposure to respirable crystalline silica.
• If employee exposures are below the action level, discontinue monitoring for those employees.
• If employee exposures are at or above the action level but at or below the PEL, repeat monitoring within six months of the most recent monitoring.
• If employee exposures are above the PEL, repeat monitoring within three months of the most recent monitoring.
• If the most recent (non-initial) monitoring shows employee exposures are below the action level, the employer should repeat the monitoring within six months until two consecutive measurements, taken seven or more days apart, are below the action level. At this time, the employer may discontinue monitoring for those employees unless reassessment is required.

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