Monitoring

Employers must assess exposure of employees who may be in contact with respirable crystalline silica at or above the action level of 25 μg/m3 over an eight-hour day.

Time-weighted average (TWA) is the employee's average airborne exposure in any eight-hour work shift of a 40-hour work week which cannot be exceeded. The eight-hour TWA PEL is the level of exposure established as the highest level of exposure an employee may be exposed to without incurring the risk of adverse health effects.

TheOSHAregulation provides two avenues to conduct the monitoring, as follows:

• The performance option: The employer must assess the eight-hour TWA for each employee on the basis of air monitoring data or objective data to accurately characterize exposure to silica
• The scheduled monitoring option: The employer completes an initial eight-hour TWA for each employee on the basis of personal breathing zone air samples that reflect exposures for employees on each shift, each job classification, and in each work area.

When more than one employee works a shift, in a job classification or in a work area, employers need to sample a representative fraction of employees to meet the requirement. When conducting this representative sampling, employers are expected to sample those workers with the highest expected exposure to silica.

As of June 23, 2020, employers must provide medical screening to general industry and maritime workers exposed to respirable crystalline silica equal to or above the action level of 25 μg/m3 for 30 or more days per year.

To learn more about Silica Safety visit our General & Maritime Silica Safety Online Training web page.