Protect Employees From Silica Exposure

Mark Stromme, Contributor

Employees in general industry facilities can be exposed to respirable crystalline silica dust. This exposure occurs during the manufacture of brick, concrete blocks, stone countertops or ceramic products. It also happens when cutting or crushing stone. Industrial sand used in certain operations, such as foundry work and hydraulic fracturing, is also a source of crystalline silica exposure.

These crystalline silica particles are typically at least 100 times smaller than ordinary sand found on beaches or playgrounds. Workers who inhale these very small particles are at increased risk of developing serious silica-related diseases.


Exposure assessment involves assessing employee exposure to silica and limiting exposure to the permissible exposure limit (PEL)—using feasible engineering and work-practice control methods, plus respiratory protection when necessary.

Each of the three components of alternative exposure control methods—the PEL, exposure assessment and methods of compliance—is explained below.

Permissible Exposure Limit

Employers must make sure that their employees’ exposures to silica do not exceed the PEL, which is 50 micrograms per cubic meter of air (50 μg/m3) as an 8-hour, time-weighted average (TWA). This means that over the course of any 8-hour work shift, exposures can fluctuate, but the average exposure to silica cannot exceed 50 μg/m3.

Exposure Assessment

Employers must assess the 8-hour TWA exposure for each employee who is, or may reasonably be expected to be, exposed to silica at or above the action level of 25 micrograms per cubic meter of air (25 μg/m3) using an 8-hour TWA. The purposes of assessing employee exposures include:

  • Identifying where exposures are occurring;
  • Helping the employer select control methods and making sure those methods are effective;
  • Preventing employees from being exposed above the PEL;
  • Providing employees with information about their exposure levels; and
  • Allowing the employer to give the physician performing medical examinations information about employee exposures.

Methods of Compliance

Employers can choose between two options for assessing exposures:

  • The performance option; or
  • The scheduled monitoring option.

The performance option gives employers flexibility to determine the 8-hour TWA exposure for each employee, based on any combination of air-monitoring data or objective data that can accurately characterize employee exposures to silica.

Air-monitoring data are any results of air monitoring (analyzed according to the procedures and requirements in Appendix A to 1910.1053) that the employer has done to meet the requirements of the standard.

Objective data is information that demonstrates employee exposure to silica associated with a product or material or a specific process, task or activity. The data must reflect workplace conditions that closely resemble, or could result in, higher exposures than the processes, types of material, control methods, work practices and environmental conditions in the employer’s current operations.

Examples of objective data are information such as:

  • Air-monitoring data from industry-wide surveys;
  • Calculations based on the composition of a substance;
  • Area sampling results and exposure mapping profile approaches; and
  • Historic air-monitoring data.

Employers choosing the performance option must:

  • Conduct the exposure assessment before work begins;
  • Re-assess exposures whenever a change in production, process, control equipment, personnel or work practices may reasonably be expected to result in new or higher exposures at or above the action level; or when the employer has any reason to believe that new or additional exposures at or above the action level have occurred;
  • Be able to demonstrate that employee exposures have been accurately characterized; and
  • Make sure the exposure assessment reflects the exposures of employees on each shift, for each job classification, in each work area.

The scheduled monitoring option lets employers know when and how often they must perform exposure monitoring to measure employee exposures. When following the scheduled monitoring option, make sure:

  • Results represent the employee’s TWA exposure to silica over an 8-hour workday;
  • Samples are collected from the employee’s breathing zone; and
  • Samples are collected outside respirators, so they represent the exposure that would occur without the use of the respirator.

Employers must conduct initial monitoring as soon as work begins so that they are aware of exposure levels and where control measures are needed.

Under the scheduled monitoring option, just as under the performance option, employers must correctly characterize each employee’s exposure to silica.

Exposure monitoring must include, at a minimum, one full-shift sample taken for each job function in each job classification, in each work area, and on each shift. Characterizing each employee’s exposure may involve monitoring all exposed employees or a smaller number of employees whose exposures can then represent those of other employees.

Representative sampling involves monitoring the employee or employees reasonably expected to have the highest exposure to silica (for example, the employee closest to an exposure source). This exposure is then assigned to the other employees in the group who perform the same tasks on the same shift and in the same work area.


Regulated areas are workplace areas where exposures to respirable crystalline silica are, or can reasonably be expected to be, above the PEL. The standard for general industry requires employers to establish, demarcate, and limit access to regulated areas. The employer must also provide respirators and make sure they are used by those who must enter regulated areas.

The purpose of a regulated area is to:

  • Ensure that employees know that silica levels are likely to exceed the PEL within the regulated area,
  • Restrict the number of employees who could be exposed above the PEL by requiring the employer to mark areas where exposures are or are likely to be higher than the PEL, and
  • Make sure that all who enter are properly protected with an appropriate respirator.

Establishing Regulated Areas

Employers must establish regulated areas where exposures to airborne concentrations of respirable crystalline silica are, or can reasonably be expected to be, greater than the PEL. Information used to measure employees’ exposures can be used to determine where regulated areas are required and identify the boundaries of these areas.

For example, employers can use any combination of personal samples (air samples collected near the employee’s breathing zone) or objective data, such as exposure mapping and real-time measurements, to establish regulated areas.

Demarcating Regulated Areas

Employers must demarcate (mark off) regulated areas from the rest of the workplace in a manner that decreases the number of employees exposed to respirable crystalline silica within the regulated area. Cones, stanchions, tape, barricades, lines or textured flooring are some of the ways of marking the boundaries of regulated areas.

Employers must post a sign at each entrance to regulated areas that reads:







Limiting Access/Providing Respirators

Employers must limit access to regulated areas to:

  • Persons authorized by the employer and required by work duties to be present in the regulated area. This includes persons whose work is with or near the respirable crystalline silica-producing materials, but may also include maintenance and repair personnel, management, quality-control engineers or other employees—if their job duties require them to be in the regulated area;
  • Any person entering the area as a designated representative of employees to observe silica exposure monitoring; or
  • Any person authorized by OSHA to be in a regulated area (e.g., OSHA enforcement personnel).

Access restrictions limit the number of persons who may enter, walk or drive vehicles through areas where exposures exceed the PEL. These restrictions protect employees who would otherwise be exposed when needlessly spending time in, or passing through, the regulated area.

Providing Respirators

The employer must:

  • Provide each employee and the employee’s designated representative entering a regulated area with an appropriate respirator that meets the requirements for respiratory protection under OSHA’s respiratory protection standard; and
  • Require the employee and representative to use the respirator while in the regulated area.

Persons must put on respirators before entering and take off respirators after exiting the regulated area. The employer must provide and ensure the use of the appropriate respirator to any employees or representatives who enter these areas, regardless of their work activities or the amount of time they spend inside.


Employers must train and inform employees covered by the silica standard about respirable crystalline silica hazards and the methods the employer uses to limit their exposures to those hazards. Employers must cover the cost of training and pay employees for the time spent in training. IHW

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