Controlling Respirable Crystalline Silica Exposures in a Stone Countertop Fabrication Company

In response to an online request, the New Hampshire On-Site Consultation Program (WorkWISE NH) located at Keene State College, conducted a visit to a stone countertop manufacturer. WorkWISE NH consultants made multiple health hazard visits to the facility from March 2020 to July 2021. These visits came about from the company’s interest in improving workplace safety and health, with particular interest in Respirable Crystalline Silica (RCS). OSHA’s RCS standard for general industry (29 CFR 1910.1053) requires that employers determine the amount of RCS their workers are exposed to when it is or may reasonably be expected that exposures will to be at or above the action level (AL) of 25 μg/m3 or 0.025 mg/m3. It also requires employers to protect workers from RCS exposures above the permissible exposure limit (PEL) of 50 μg/m3 or 0.050 mg/m3.

Prior to the initial visit, the employer and consultant discussed a sampling strategy. They decided to evaluate exposures to several employees completing varied job tasks that were expected to have a higher risk of exposure to RCS. These included polishing, sawing, material handling, and cutting using the CNC machine. The CNC machine uses computer numerical controls to cut materials. It was also determined that an area sample would be appropriate, to determine any possible exposure to passersby (office personnel, management, or the consultant).

The initial RCS monitoring in March 2020 found that one polisher, one saw operator, one CNC operator, and one of the area samples showed overexposures to the PEL. The material handler was found to be above the AL. Concentrations ranged from 0.034mg/m3 to 0.074mg/m3. A water delivery system was used as an engineering control for the saws and polishers. The consultant made further control recommendations to include:

  • A floor scrubber to reduce accumulation of RCS on floors,
  • An air filtration system to be run around the clock during the work week to reduce airborne concentrations of RCS able to settle on surfaces, and
  • The washing down of all horizontal surfaces of the facility to keep as free as practicable from dust formed during the day that might be contributing to the exposure.

Several follow-up visits were performed from July 2020 to January 2021. After introducing the consistent use of a floor scrubber, installing general exhaust fans in the polishing area, and keeping regular housekeeping procedures, exposures to RCS were reduced below the AL for the CNC operator and the material handler. RCS exposures for the saw operator, polishers, and area near the saw remained above the AL but below the PEL.

The final follow-up visit with a WorkWISE NH consultant was performed in July 2021. To further reduce exposures, the company installed an air scrubber and purchased a fully enclosed saw. Exposure to RCS were successfully reduced to well below the AL for all employees and the immediate area outside the saw machine. New concentrations ranged from 0.0065mg/m3 to 0.0075mg/m3.


Older saw, photo taken on March 12, 2020
Older saw, photo taken on March 12, 2020
New saw, photo taken on July 1, 2021
New saw, photo taken on July 1, 2021


The OSHA On-Site Consultation Program offers no-cost and confidential occupational safety and health services to small and medium-sized businesses in all 50 states, the District of Columbia, and several U.S. territories, with priority given to high hazard worksites. Consultants from state agencies or universities work with employers to identify workplace hazards and how to fix them, provide advice for compliance with OSHA standards, train and educate workers, and assist in establishing and improving safety and health programs. On-Site Consultation services are separate from OSHA enforcement efforts and do not result in penalties or citations. To locate the OSHA On-Site Consultation program nearest you, call 800-321-OSHA (6742) or visit