A Review of Airborne Silica Concentrations and Evaluation of Engineering Controls Associated with Engineered Stone Countertop Fabrication Workers

1355 

Professional Poster 

A Banducci¹

¹Insight Exposure & Risk Sciences Group, Boulder, CO

Amber Banducci, MPH  
Insight Exposure & Risk Sciences Group

Recent global outbreaks of accelerated silicosis within the stone countertop fabrication industry have drawn the attention of the regulatory, scientific and OEHS communities concerned with the identification and control of exposures to respirable crystalline silica (RCS). The increasing demand and use of engineered stone (ES) countertops since the early 2000s has coincided with the increased incidence of accelerated silicosis among countertop fabricators who process ES. Unlike natural stone, which generally contains 2 to 50% crystalline silica, ES often comprises >90% crystalline silica. While RCS is a recognized hazard among stone workers, prior to the 2010s, no published study had evaluated the exposure potential to RCS among ES fabrication workers. However, RCS exposure concentration data among this worker population have become increasingly available. The present study includes a review of all publicly available measured RCS concentration data associated with stone fabrication work, an evaluation of utilized engineering controls, and trend analysis on the impact of engineering controls on airborne concentrations. This review and analysis aggregate limited but critical data that can assist OEHS professionals with the selection and implementation of the most effective controls for specific fabrication tasks to protect worker health, as well as identify gaps where more data are necessary to better inform worker health and safety in the stone countertop fabrication industry.

The reported incidence of silicosis has rapidly increased among stone fabrication workers in the United States and worldwide since the 2010s. This concerning increase has been attributed to the increased use and processing of engineered stone in the countertop industry. Engineered stone often comprises >90% crystalline silica compared to natural stone which generally contains 2 to 50% crystalline silica. Occupational safety and health professionals have been presented with critical challenges in reducing exposures to silica during common work practices involved in engineered stone fabrication, including the appropriate selection and implementation of engineering controls. The stone countertop fabrication process involves many steps and there is wide variability in the types of tools, equipment, and work practices used. Additionally, the body of evidence suggests that the effectiveness of controls in this process can be highly tool and task dependent. The present study includes a review of all publicly available measured RCS concentration data associated with stone fabrication work, an evaluation of utilized engineering controls, and trend analysis on the impact of engineering controls on airborne concentrations. This review and analysis can serve as resource to assist OEHS professionals with the selection and implementation of the most effective controls for specific fabrication tasks to protect worker health.

A comprehensive literature search was performed using online publication search tools, including PubMed and Google Scholar, to conduct a combination of searches using key search terms, such as stone, countertop, fabrication, silica, and exposure. Target searches using similar terms were also performed in the National Institute for Occupational Safety and Health's (NIOSH) Health Hazard Evaluation and Technical Reports online databases. In total, the search results included over 300 studies. All studies that measured and reported personal airborne concentrations of respirable crystalline silica associated with stone countertop fabrication published through August 2025 and available in the English language were included in the review. All abstracts identified in the search results were screened and approximately 75 studies were identified and fully reviewed. Additionally, reference lists of all relevant studies were examined to identify other potential studies and additional studies were selected for full review. A total of 23 studies met the inclusion criteria and were included in the literature review. Data extracted from each study were compiled in Excel for analysis, and included stone type (and bulk silica content of stone when available), tools and activities used, activities and task descriptions, controls and ventilation used, facility description, and airborne respirable crystalline silica concentrations.

Of the 23 studies included in the review, RCS concentrations associated with processing engineered stone, natural stone, and both stone types were evaluated in 10 studies, 3 studies, and 10 studies, respectively. 13 studies reported full-shift or 8-hour time weighted average (TWA) concentrations while the remaining studies reported short-term task-based concentrations. Regarding full shift measurements, workers performing sanding activities experienced the highest RCS concentrations, followed by workers who performed a combination of activities using handheld tools often associated with the countertop lamination process. Notably, workers who performed the lamination process and sanding activities were more likely to perform some of these tasks dry compared to other tasks such as cutting and polishing, where wetting methods were more routinely used. Handheld and automated cutting, handheld and automated polishing, and automated combination tasks were often performed using wetting methods and generally resulted in full-shift exposures below the OSHA 8-hour TWA PEL for RCS of 50 ug/m3 as well as below the action level of 25 ug/m3. Unsurprisingly, workers who performed dry tasks were more likely to experience full-shift concentrations above the PEL. With respect to short-term measurements, all studies described the use of handheld tools or table tools (non-automated) to perform the tasks evaluated, and all but three measurements were associated with tasks performed using some form of wetting. Some of the highest short-term RCS concentrations reported were among workers who performed cutting; however, a wide range of measurements were reported from as low as non-detect to as high as 44,370 ug/m3. Short-term concentrations associated with grinding were mostly below 500 ug/m3 although one reported peak exposure during dry grinding reached as high as 4,819 ug/m3. Wetting was by far the most effective exposure control method. In many cases, the additional use of local exhaust ventilation (LEV) further reduced RCS concentrations. However, the data also highlight the critical need to select and implement appropriate control methods based on evidence for each specific fabrication tool and task. For example, one study found that the addition of LEV to water-spray wetting was less effective compared to water-spray wetting alone during a specific grinding task. Another study found that the positioning of the worker between the fabrication activity and a water curtain interfered with the effectiveness of the water curtain. These examples illustrate why more data are needed to comprehensively evaluate the many tools and activities involved in the stone countertop fabrication process to inform the selection of effective controls. Moreover, an examination of existing and emerging technologies (i.e. automated equipment), work practices, and training are necessary to make further improvements that protect worker health in this industry.

Engineering Controls and Ventilation

Exposure Assessment