Engineered Stone Linked to a Resurgence in Silicosis Cases

Silicon dioxide, also referred to as silica, is a molecule made up of one silicon atom and two oxygen atoms (SiO₂). It can exist in both crystalline and noncrystalline forms. In the crystalline form, it is most commonly found as quartz, which is estimated to make up approximately 12% of the earth’s crust. Crystalline silica is present in varying amounts in natural materials such as granites, basalt, sandstone, chert, and sand. Quartz is found at jobsites in the form of sand, which is a major component of Portland cement, other masonry materials, and hydraulic fracturing, as well as in slabs used for countertops, molds in foundries, and several other applications.

Risks of Silica Exposure

Occupational exposure to respirable crystalline silica (RCS) can result in adverse health effects, including silicosis and lung cancer. Silicosis, which is a scarring of the lung tissue, is progressive, even when exposure is stopped, and can lead to progressive massive fibrosis (PMF), respiratory failure, and death.

Prior to 2016, when the Occupational Safety and Health Administration (OSHA) standards for RCS exposure were promulgated, OSHA had established a permissible exposure limit for silica but did not have a stand-alone silica standard. At that time, OSHA estimated that 2.3 million workers were exposed to silica above the new action level—25 micrograms per cubic meter (µg/m³)—as a time-weighted average over eight hours. Of these, 2 million were in construction and 300,000 were in general and maritime industries. OSHA estimated that compliance with the standards would prevent 642 silica-related fatalities and 918 moderate to severe silicosis cases annually over the next 60 years. In addition to adding the action level, the 2016 standard also reduced the permissible exposure limit significantly from what it had been.

Unfortunately, recent studies have found a troubling trend in deaths related to silicosis. A study by the Centers for Disease Control and Prevention (CDC) found that while deaths due to RCS exposure have declined over time, there was continuing silicosis mortality in younger workers in both the stone products industry and hydraulic fracturing. While silicosis outbreaks were first reported in several countries among workers who cut and polish stone materials, they were generally in developing countries where exposure controls are not as widely used as in the United States. More recently, the first case of silicosis in the United States associated with engineered stone in the countertop manufacturing industry was in Texas in 2014. Texas was also the location of the first apparent cluster of silicosis cases related to occupational silica dust exposure in this industry in 2019.

One reason for the persistence of silicosis in the stone industry is likely the increased prevalence of engineered or manufactured stone compared to natural stone. Engineered stone is made by mixing crystalline silica, typically quartz, with resins, pigments, and adhesive to form a slab. Silica content in these slabs can be as high as 90% depending on the type of material used in their manufacturing. With calcium-based materials, such as marble, granite, and slate, the silica content can be as high as 60%. This compares to natural stone slabs, which typically contain less than 45% silica.

In addition to greater silica content, additional exposures to RCS in the engineered stone industry can occur during the manufacturing process, which can involve workers opening bags of ground quartz, moving or mixing bulk raw materials, cleaning and scraping mixers, and cleaning dust collector bag houses, among other activities.

According to the United States International Trade Commission, the import of manufactured stone slab to the United States increased approximately 800% from 2010 to 2018. Another source estimates that the demand for engineered stone throughout the world will increase by 340% from 2013 to 2024.

A study conducted by RHP Risk Management found that when using a shrouded angle grinder to cut and polish engineered stone with a silica content of 64% for 30 minutes, the resulting exposure to RCS was 200 µg/m³, while conducting the same activities on a slab of granite with a silica content of 21% resulted in an exposure of 68 µg/m³. The results suggest an almost linear, positive correlation between the silica content of the countertop slab and the resulting exposure to RCS when cutting and polishing the material. The pilot study was performed to determine the relationship between the respirable dust and RCS concentrations produced during the fabrication of natural stone (granite) and engineered stone (quartz) with and without the use of a dust collection device (shroud). The pilot test involved cutting and polishing granite (natural stone) and quartz (manufactured stone) countertops, both with and without the use of a shroud (or engineering control). The engineering control was a shroud with a HEPA vacuum attached, filtering over 99.97% of particles. The study engineering controls aligned with the guidance in the 2015 health hazard alert provided by OSHA and the National Institute for Occupational Safety and Health (NIOSH).

A CDC report found that 18 cases of silicosis were identified among workers in the engineered stone industry from 2017 through 2019 in California, Colorado, Texas, and Washington. Prior to this period, just one case of silicosis was reported among engineered stone fabrication workers throughout the entire United States.

There is evidence that the disease associated with exposure from working with engineered stone may be more aggressive than the disease traditionally associated with exposure to natural silica-containing materials. A study by León-Jiménez et al. of silicosis in workers from the engineered stone industry found that the disease was occurring in younger workers and progressing more rapidly, even when exposure to silica was ceased, than in cases that involved exposure linked to natural stone. The authors suggest that this may be the result of higher levels of exposure linked to the higher concentrations of silica in engineered stone, or that the high content of transition metal ions or the coating of the silica particles with resin in engineered stone causes it to possess greater toxicity than that of natural stone.

Regulating Silica Exposure

The mounting evidence of increased silicosis risk among stone fabrication workers has not gone unnoticed. In February 2022, OSHA’s Region 8 office announced a new regional emphasis program to identify and reduce hazards to workers in the region’s cut stone and stone products industry. According to the agency, this industry has had the highest documented overexposures to RCS in the region in recent years, estimated at 30% of the documented overexposures. In 2018, the government of Queensland, Australia, initiated health screening for all at-risk employees. In February 2023, the Australian Institute of Occupational Hygienists issued a statement calling for a ban on the use of high-quartz-containing engineered stone by July 2024. The Australian government acted on that recommendation and in December 2023 announced that the use, supply, and manufacture of all engineered stone would be prohibited starting July 1, 2024.

Regulatory agencies in the United States have also ramped up their efforts to control employee exposure to silica in the engineered stone fabrication and installation industries. On September 22, 2023, OSHA issued a new initiative that will increase OSHA enforcement and compliance mechanisms on employers in these industries. The initiative applies to Regions 1 through 8 (essentially the entire country east of Idaho, Nevada, and Arizona), where there is the highest concentration of establishments in the targeted industries, according to OSHA. The initiative requires each local office to complete at least five inspections of engineered stone fabrication and installation establishments within 12 months of the date of the memo.

In California, the Occupational Safety and Health Standards Board of the California Division of Occupational Safety and Health (Cal/OSHA) approved an emergency temporary standard to protect workers from silicosis. The emergency temporary standard went into effect on December 29, 2023. The standard requires employers to implement protections for workers engaged in high-exposure “trigger” tasks such as cutting, grinding, polishing, and cleanup of artificial stone containing more than 0.1% crystalline silica and natural stone containing more than 10% crystalline silica.

Managing Silica Risks in Engineered Stone Work

Employers in the engineered stone fabrication and installation industries should know of the increased risk of silica exposure when working with this material as opposed to natural stone products and should be aware of the increased regulatory enforcement activities. It would also be prudent for them to evaluate and put in place administrative and engineering controls to limit the exposure of silica for their employees when manufacturing or working with countertops made of engineered stone.