OSHA, NIOSH Urge Countertop Fabrication Shops to Adopt Silica Controls
In a recently updated hazard alert (PDF), OSHA and NIOSH urge employers in the stone countertop industry to protect workers who manufacture, finish, and install natural and engineered stone products from exposure to respirable crystalline silica, or RCS. Workers who inhale RCS are at risk of developing silicosis, described in the alert as “an incurable, progressively disabling, and potentially fatal lung disease,” as well as lung cancer, chronic obstructive pulmonary disease, tuberculosis, and kidney disease. But employers may prevent or significantly reduce RCS exposures by implementing measures like engineering and administrative controls, personal protective equipment, and training, the report explains.
Countertops may contain more than 90 percent silica, depending on the type of stone. Products made of certain engineered stone—a substance fabricated by combining silica powder with resins and pigments—and the naturally occurring mineral quartzite contain the greatest percentages of silica. However, some engineered stone contains less than 50 percent crystalline silica, the alert notes, while products comprising recycled glass, pigments, and a Portland cement matrix contain less than 0.2 percent crystalline silica. In comparison, granite contains up to 50 percent silica. A table summarizing the crystalline silica content of various types of countertop material may be found on page 2 of the alert.
Dust containing RCS is released when workers quarry, cut, grind, or finish materials with high silica content. In the countertop industry, the highest RCS exposures are associated with tasks that involve powered hand tools such as saws, grinders, and high-speed polishers. Workers manufacturing engineered stone may be exposed to RCS when opening bags of silica powder, moving or mixing materials, cleaning and scraping mixers, changing filters on dust collectors, or cleaning dust collector bag houses. Other workers near areas where dust-generating tasks are performed may also be exposed.
The alert instructs employers to first conduct a worker exposure assessment in consultation with a certified industrial hygienist or other qualified occupational safety and health professional. If the assessment indicates RCS exposures above OSHA’s permissible exposure limit of 50 μg/m3 as an eight-hour time-weighted average, the employer must take action to reduce exposures to levels below the PEL, following the hierarchy of controls. For example, choosing products with little or no crystalline silica content eliminates or reduces the hazard. Engineering controls for RCS include the use of local exhaust ventilation or cutting tools that control dust by wetting the stone. Administrative controls include wet sweeping and the completion of as many work tasks as possible in the shop instead of at the site of installation. Finally, if engineering and administrative controls fail to reduce RCS exposures below the PEL, OSHA’s silica standards require employers to provide respirators and train workers in their use. Medical surveillance is also required for all workers exposed to RCS levels above OSHA’s action level, 25 μg/m3 as an eight-hour TWA.
The hazard alert on worker exposure to silica during countertop manufacturing, finishing, and installation includes a list of controls and summaries of relevant scientific studies. Both English and Spanish versions may be downloaded from OSHA’s hazard alert index.
Related: Read “Protecting Stone Workers: Reducing Exposure to Respirable Crystalline Silica during Stone Countertop Fabrication” in the October 2024 Synergist.