Silica exposure during granite countertop fabrication

Chest x-ray has low sensitivity to detect silicosis in artificial stone benchtop industry workers

BACKGROUND AND OBJECTIVE

Chest x-ray (CXR) remains a core component of health monitoring guidelines for workers at risk of exposure to crystalline silica. There has however been a lack of evidence regarding the sensitivity of CXR to detect silicosis in artificial stone benchtop industry workers.

METHODS

Paired CXR and high-resolution computed tomography (HRCT) images were acquired from 110 artificial stone benchtop industry workers. Blinded to the clinical diagnosis, each CXR and HRCT was independently read by two thoracic radiologists from a panel of seven, in accordance with International Labour Office (ILO) methodology for CXR and International Classification of HRCT for Occupational and Environmental Respiratory Diseases. Accuracy of screening positive (ILO major category 1, 2 or 3) and negative (ILO major category 0) CXRs were compared with identification of radiological features of silicosis on HRCT.

RESULTS

CXR was positive for silicosis in 27/110 (24.5%) workers and HRCT in 40/110 (36.4%). Of the 83 with a negative CXR (ILO category 0), 15 (18.1%) had silicosis on HRCT. All 11 workers with ILO category 2 or 3 CXRs had silicosis on HRCT. In 99 workers ILO category 0 or 1 CXRs, the sensitivity of screening positive CXR compared to silicosis identified by HRCT was 48% (95%CI 29-68) and specificity 97% (90-100).

CONCLUSION

Compared to HRCT, sensitivity of CXR was low but specificity was high. Reliance on CXR for health monitoring would provide false reassurance for many workers, delay management and underestimate the prevalence of silicosis in the artificial stone benchtop industry.

Silicosis Among Immigrant Engineered Stone (Quartz) Countertop Fabrication Workers in California

Importance

Silicosis associated with inhalation of respirable crystalline silica among engineered stone countertop fabrication workers is an emerging health concern.

Objective

To describe clinical, socioeconomic, and occupational characteristics of patients diagnosed with silicosis associated with engineered stone in California.

Design, Setting, and Participants

This case series included reported cases of silicosis associated with fabrication of engineered stone countertops, as identified by statewide surveillance by the California Department of Public Health (2019-2022). Data analysis was performed from October 2022 to March 2023.

Exposures

Patient interviews and medical record abstractions were used to assess occupational exposure to respirable crystalline silica, including duration of work tenure and preventive measures undertaken.

Main Outcomes and Measures

Demographics, clinical characteristics, health care utilization, and clinical outcomes were obtained, including vital status, hypoxia, and lung transplant.

Results

This case series identified 52 male patients meeting inclusion criteria; median (IQR) age was 45 (40-49) years, and 51 were Latino immigrants. Ten (19%) were uninsured, and 20 (39%) had restricted-scope Medi-Cal; 25 (48%) presented initially to an emergency department. A delay in diagnosis occurred in 30 (58%) patients, most commonly due to alternative initial diagnoses of bacterial pneumonia (9 [30%]) or tuberculosis (8 [27%]). At diagnosis, 20 (38%) patients had advanced disease (progressive massive fibrosis) with severely or very severely reduced forced expiratory volume in 1 second in 8 (18%) and 5 (11%), respectively. Of the cases, 10 (19%) were fatal; median (IQR) age at death was 46 (38-51) years, and 6 patients (12%) were alive with chronic resting hypoxia. Eleven were referred for lung transplant: 3 underwent transplant with 1 fatality; 7 were declined transplant, with 6 fatalities; and 1 died prior to listing. Median (IQR) work tenure was 15 (10-20) years; 23 (45%) reported use of water suppression for dust mitigation, and 25 (48%) continued to fabricate stone after being diagnosed with silicosis.

Conclusions and Relevance

In this case series performed in California, silicosis associated with occupational exposure to dust from engineered stone primarily occurred among young Latino immigrant men. Many patients presented with severe disease, and some cases were fatal.

Experimental Investigation on Part Quality and Dust Emission during Minimum Quantity Lubricated (MQL) Edge Finishing of Granite

Edge-finishing of granites by grinding is a process frequently used in the granite processing industry to generate the final desired shape and edge quality of products. However, this process releases significant amounts of fine and ultrafine particles (FPs and UFPs) containing crystalline silica. When inhaled, this dust can cause silicosis disease and threaten the health and safety of workers. The purpose of this study is to optimize the process by decreasing the concentrations of dust generated while also maintaining the required surface finish. Experimental tests were planned and performed on granite samples using a full factorial design. Two cutting tool edge shapes were studied (chamfer and concave) using G150 and G600 grit size tools, at various spindle speeds (1500, 2500, 3500 rpm), feed rates (500, 1000, 1500 mm/min) and lubrication flow rates (20, 40, 60 mL/min). The findings show that the particle emissions as well as the surface finish depend on the tool shape, its grit size, and the machining and lubrication parameters used. Higher MQL flow rates led to better finished surface quality and lower concentrations of fine dust. Polishing with flood lubrication reduces the maximum number concentration of FPs corresponding to particles smaller than 1 µm diameter by about 85% as compared to dry polishing and produced the best surface finish. Polishing with lubrication in MQL mode at 60 mL/min led to the production of part with Ra-value comparable with that obtained in flood lubrication condition.

Silica Exposure Estimates in Artificial Stone Benchtop Fabrication and Adverse Respiratory Outcomes

Silicosis is being increasingly reported among young stonemasons in the artificial stone (AS) benchtop fabrication and installation industry. Respiratory health screening, which included a job and exposure history, a chest X-ray (CXR), a respiratory health questionnaire, and gas transfer testing, were offered to stonemasons in Victoria, Australia. Workers typically reported a variety of tasks, including cleaning and labouring, which made exposure assessment complex. We estimated the relative respirable crystalline silica exposure intensity of each job from the proportion of time using AS and the proportion of time doing dry work (work without water suppression). The relative average intensity of exposure for up to five jobs was calculated. Cumulative exposure was calculated as the sum of the duration multiplied by intensity for each job. Installers and factory machinists (other than computer numeric control operators) were the most likely to report dry work with AS, and so had a greater average intensity of exposure. Exposure intensity and cumulative exposure were associated with increased odds of an ILO (International Labour Organisation) CXR profusion major category of ≥1 and with dyspnoea. Exposure duration was also associated with ILO profusion category. In multivariate analyses of health outcomes, only job type was associated with the ILO profusion category. For both most recent and longest-duration job types, when compared to the lowest exposure group, factory machinists were more likely to have an ILO category ≥1. This suggests that intensity of exposure estimated from the proportion of time dry cutting and proportion of time working on AS can predict the risk of adverse respiratory outcomes for workers in this industry.

Characterization of Silica Exposure during Manufacturing of Artificial Stone Countertops

Artificial stone is increasing in popularity in construction applications, including commercial and residential countertops. Eco-friendliness, durability, and resistance to staining, make artificial stone attractive to consumers. Health concerns have arisen during manufacturing of artificial stone due to increased incidence of silicosis after relatively short exposure. Three artificial stone samples (A, B, and C) and one natural granite sample were subjected to cutting and grinding in a controlled environment. Gravimetric analysis, X-Ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy were employed to determine crystalline silica concentrations and particle morphology of bulk and respirable particles. Silica content of bulk dust from artificial samples A and B was 91%, sample C was <10%, while granite was 31%. Silica percent in the respirable fraction for samples A and B was 53% and 54%, respectively, while sample C was <5% and granite was 8%. Number concentrations for samples A and B were mainly in the nano-fraction, indicating potential for translocation of silica particles to other organs outside of the lungs. Respirable dust concentrations inside the chamber were well above Occupational Safety and Health Administration standards for all materials, indicating that confined-space exposures require ventilation to lower risks of acute silicosis regardless of the nature of the stone.

Experimental Evaluation of Respirable Dust and Crystalline Silica Controls During Simulated Performance of Stone Countertop Fabrication Tasks With Powered Hand Tools

Objectives

Workers who fabricate stone countertops using hand tools are at risk of silicosis from overexposure to respirable crystalline silica. This study explored the efficacy of simple engineering controls that can be used for dust suppression during use of hand tools by stone countertop fabricators.

Methods

Controlled experiments were conducted to measure whether wet methods and on-tool local exhaust ventilation (LEV) reduced respirable dust (RD) exposures during use of various powered hand tools on quartz-rich engineered stone. RD samples collected during edge grinding with a diamond cup wheel and a silicon carbide abrasive wheel were analyzed gravimetrically as well as by X-ray diffraction to determine silica content. A personal optical aerosol monitor was used simultaneously with the RD samples and also for rapid assessment of controls for polishing, blade cutting, and core drilling.

Results

On-tool LEV and sheet-flow-wetting were effective in reducing exposures, especially when used in combination. Sheet-flow-wetting with LEV reduced geometric mean exposures by as much as 95%. However, typical water-spray-wetting on a grinding cup was less effective when combined with LEV than without LEV. Mean silica content of RD samples from grinding operations was 53%, and respirable mass and silica mass were very highly correlated (r = 0.980). Optical concentration measures were moderately well correlated with gravimetric measures (r = 0.817), but on average the optical measures during a single trial using the factory calibration were only one-fifth the simultaneous gravimetric measures.

Conclusions

Sheet-flow-wetting combined with on-tool LEV is an effective engineering control for reducing RD exposures during engineered stone edge grinding and blade cutting. On the other hand, addition of LEV to some water-spray-wetted tools may reduce the effectiveness of the wet method.

Respirable silica dust suppression during artificial stone countertop cutting

PURPOSE

To assess the relative efficacy of three types of controls in reducing respirable silica exposure during artificial stone countertop cutting with a handheld circular saw.

APPROACH

A handheld worm drive circular saw equipped with a diamond segmented blade was fitted with water supply to wet the blade as is typical. The normal wetted-blade condition was compared to (i) wetted-blade plus 'water curtain' spray and (ii) wetted-blade plus local exhaust ventilation (LEV). Four replicate 30-min trials of 6-mm deep, 3-mm wide cuts in artificial quartz countertop stone were conducted at each condition in a 24-m(3) unventilated tent. One dry cutting trial was also conducted for comparison. Respirable cyclone breathing zone samples were collected on the saw operator and analyzed gravimetrically for respirable mass and by X-ray diffraction for respirable quartz mass.

RESULTS

Mean quartz content of the respirable dust was 58.5%. The ranges of 30-min mass and quartz task concentrations in mg m(-3) were as follows-wet blade alone: 3.54-7.51 and 1.87-4.85; wet blade + curtain: 1.81-5.97 and 0.92-3.41; and wet blade + LEV: 0.20-0.69 and <0.12-0.20. Dry cutting task concentrations were 69.6 mg m(-3) mass and 44.6 mg m(-3) quartz. There was a statistically significant difference (α = 0.05) between the wet blade + LEV and wet blade only conditions, but not between the wet blade + curtain and wet blade only conditions, for both respirable dust and respirable silica.

CONCLUSIONS

Sawing with a wetted blade plus LEV reduced mean respirable dust and quartz task exposures by a factor of 10 compared to the wet blade only condition. We were unable to show a statistically significant benefit of a water curtain in the ejection path, but the data suggested some respirable dust suppression.

An evaluation of on-tool shrouds for controlling respirable crystalline silica in restoration stone work

OBJECTIVES

The task of grinding sandstone with a 5-inch angle grinder is a major source of exposure to respirable crystalline silica (RCS), known to cause diseases such as silicosis and lung cancer among workers who work with these materials. A shroud may be a suitable engineering control for this task. The objectives of this study were to evaluate the effectiveness of four commercially available shrouds at reducing respirable dust and RCS levels during the task of grinding sandstone using tools and accessories typical of restoration stone work.

METHODS

The task of grinding sandstone with a 5-inch angle grinder, equipped with different grinding wheels, was carried out over three trials at a restoration stone masonry site. Photometric and RCS data were collected when a 5-inch grinder, equipped with different grinding wheels, was used to grind sandstone with and without a shroud. A total of 24 short duration samples were collected for each no shroud and with shroud combination. Worker feedback on the practicalities of each shroud evaluated was also collected.

RESULTS

Respirable dust concentrations and RCS were both significantly lower (P < 0.001) when the grinders were equipped with a shroud compared with grinders without a shroud. Total geometric mean (GM) photometric respirable dust levels measured when grinding with a shroud were 0.5 mg m(-3), a reduction of 92% compared to grinding without a shroud (7.1 mg m(-3)). The overall GM RCS concentrations were reduced by the use of a shroud by 99%. GM photometric exposure levels were highest when using the Hilti 5-inch diamond grinding cup and Diamond turbo cup and lowest when using the Corundum grinding point.

CONCLUSIONS

Concentrations of respirable dust and RCS can be significantly reduced by using commercially available shrouds while grinding sandstone with a 5-inch angle grinder in restoration stonework. The short-term photometric respirable dust and RCS measurements collected with and without a shroud indicate that dust and RCS concentrations are reduced by between 90 and 99%. Supplemental exposure controls such as respiratory protective equipment would be required to reduce worker 8-h time-weighted average RCS exposure to below the Scientific Committee on Occupational Exposure Limits recommended occupational exposure limit value of 0.05 mg m(-3) and the American Conference of Governmental Industrial Hygienists threshold limit value of 0.025 mg m(-3).

Radiation dose to workers due to the inhalation of dust during granite fabrication

There has been very little research conducted to determine internal radiation doses resulting from worker exposure to ionising radiation in granite fabrication shops. To address this issue, we estimated the effective radiation dose of granite workers in US fabrication shops who were exposed to the maximum respirable dust and silica concentrations allowed under current US regulations, and also to concentrations reported in the literature. Radiation doses were calculated using standard methods developed by the International Commission on Radiological Protection. The calculated internal doses were very low, and below both US occupational standards (50 mSv yr(-1)) and limits applicable to the general public (1 mSv yr(-1)). Workers exposed to respirable granite dust concentrations at the US Occupational Safety and Health Administration (OSHA) respirable dust permissible exposure limit (PEL) of 5 mg m(-3) over a full year had an estimated radiation dose of 0.062 mSv yr(-1). Workers exposed to respirable granite dust concentrations at the OSHA silica PEL and at the American Conference of Governmental Industrial Hygienists Threshold Limit Value for a full year had expected radiation doses of 0.007 mSv yr(-1) and 0.002 mSv yr(-1), respectively. Using data from studies of respirable granite dust and silica concentrations measured in granite fabrication shops, we calculated median expected radiation doses that ranged from <0.001 to 0.101 mSv yr(-1).

Determinants of respirable silica exposure in stone countertop fabrication: a preliminary study

A preliminary study of personal exposure to respirable quartz was conducted in four shops that used a variety of wet and dry methods to fabricate countertops from granite and quartz-containing synthetic stone-like materials. Full-shift time-weighted average (TWA) exposures exceeded the ACGIH threshold limit value of 0.025 mg/m(3) for all workers who used dry fabrication methods, even for very limited time, during any part of the work shift (n = 15 person-days). The geometric mean of exposures for workers who used dry methods extensively was about 1 mg/m(3) (n = 12 person-days). Workers who operated only automated or remotely controlled stone cutting or shaping equipment had calculated TWA exposures of approximately 0.02 mg/m(3) (n = 3 person-days). Task-specific geometric mean exposures for various wet and dry manual operations were ranked based on estimated concentrations extracted from multi-task partial-shift sample results using a linear algebra procedure. Limited use of dry methods was observed in shops that had previously reported using only wet methods. These results suggest that even shops that report using only wet methods might, in fact, resort to brief use of dry methods for specific operations. Therefore, there may be reason for concern over potential overexposure to respirable quartz in all stone countertop shops.

Comparative emissions of random orbital sanding between conventional and self-generated vacuum systems

Conventional abrasive sanding generates high concentrations of particles. Depending on the substrate being abraded and exposure duration, overexposure to the particles can cause negative health effects ranging from respiratory irritation to cancer. The goal of this study was to understand the differences in particle emissions between a conventional random orbital sanding system and a self-generated vacuum random orbital sanding system with attached particle filtration bag. Particle concentrations were sampled for each system in a controlled test chamber for oak wood, chromate painted (hexavalent chromium) steel panels, and gel-coated (titanium dioxide) fiberglass panels using a Gesamtstaub-Probenahmesystem (GSP) sampler at three different locations adjacent to the sanding. Elevated concentrations were reported for all particles in the samples collected during conventional sanding. The geometric mean concentration ratios for the three substrates ranged from 320 to 4640 times greater for the conventional sanding system than the self-generated vacuum sanding system. The differences in the particle concentration generated by the two sanding systems were statistically significant with the two sample t-test (P < 0.0001) for all three substances. The data suggest that workers using conventional sanding systems could utilize the self-generated vacuum sanding system technology to potentially reduce exposure to particles and mitigate negative health effects.

Prevalence of dry methods in granite countertop fabrication in Oklahoma

Granite countertop fabricators are at risk of exposure to respirable crystalline silica, which may cause silicosis and other lung conditions. The purpose of this study was to estimate the prevalence of exposure control methods, especially wet methods, in granite countertop fabrication in Oklahoma to assess how many workers might be at risk of overexposure to crystalline silica in this industry. Granite fabrication shops in the three largest metropolitan areas in Oklahoma were enumerated, and 47 of the 52 shops participated in a survey on fabrication methods. Countertop shops were small businesses with average work forces of fewer than 10 employees. Ten shops (21%) reported using exclusively wet methods during all fabrication steps. Thirty-five shops (74%) employing a total of about 200 workers reported using dry methods all or most of the time in at least one fabrication step. The tasks most often performed dry were edge profiling (17% of shops), cutting of grooves for reinforcing rods (62% of shops), and cutting of sink openings (45% of shops). All shops reported providing either half-face or full-face respirators for use during fabrication, but none reported doing respirator fit testing. Few shops reported using any kind of dust collection system. These findings suggest that current consumer demand for granite countertops is giving rise to a new wave of workers at risk of silicosis due to potential overexposure to granite dust.

Evaluation of cytotoxic, genotoxic and inflammatory responses of micro- and nano-particles of granite on human lung fibroblast cell IMR-90

Occupational exposure of granite workers is well known to cause lung impairment and silicosis. Toxicological profiles of different size particles of granite dust, however, are not yet understood. Present evaluation of micro- and nano-particles of granite dust as on human lung fibroblast cells IMR-90, revealed that their toxic effects were dose-dependent, and nanoparticles in general were more toxic. In this study we first demonstrated that nanoparticles caused oxidative stress, inflammatory response and genotoxicity, as seen by nearly 2 fold induction of ROS and LPO, mRNA levels of TNF-α and IL-1β, and induction in micronuclei formation. All these were significantly higher when compared with the effect of micro particles. Thus, the study suggests that separate health safety standards would be required for granite particles of different sizes.

Results of inspections in health hazard industries in a region of the state of Washington

Results from state of Washington Occupational Safety and Health Administration (OSHA) health inspections were reviewed to characterize the level of control that existed at the work sites, identify common problems, and assess the success of targeting programs in finding and correcting uncontrolled health hazards. Data were obtained from 170 inspections conducted by industrial hygienists in a four-county area in 12 industries, including 10 that were targeted. Inspection data were accessed through the use of electronic databases and inspection reports then summarized by the following industries: bathtub refinishing, carbide tool and saw sharpening, fibercement siding installation, furniture refinishing, health care clinics, janitorial floor waxing service, landscaping, lawn maintenance, tree service, road construction, stone countertop fabrication, truck bed lining, warehouse and cold storage, and wood floor finishing. Targeted health hazards included worker exposure to airborne contaminants, noise, and bloodborne pathogens typical of the industry. Method and effectiveness of control of health hazards were evaluated by counting work sites with violations associated with engineering control, personal protective equipment, hearing conservation, or training. Results are presented by industry for the number and percentage of work sites that failed to provide required protection. Poor control of health hazards was generally found across all inspected industries. Follow-up inspections and self-reports of abatement found that more than 85% were able to successfully control the hazards and abate the violations. The results are further discussed as they relate to methods of control and risk and identifying existing and emerging high health hazard industries. Based on employment data and the poor hazard control that was found, most if not all the industries can be described as high health hazard, small-employer industries. The results can be used for the planning of interventions in other regions and industries.

Características da exposição ocupacional a poeiras em marmorarias da cidade de São Paulo

O estudo das características da exposição ocupacional a poeiras no beneficiamento de rochas ornamentais em marmorarias teve como base a aplicação das convenções adotadas pela American Conference of Governmental Industrial Hygienists (ACGIH), pela International Organization for Standardization (ISO) e pelo Comité Europeén de Normalisation (CEN) para a classificação de poeiras por faixa de tamanhos de partícula. Foram consideradas as relações entre as concentrações de poeira nos ambientes de trabalho, os tipos de rochas trabalhadas, as operações a úmido e a seco, as máquinas e as ferramentas utilizadas e os tamanhos das partículas suspensas no ar. Os ambientes de trabalho das marmorarias mostraram altas concentrações de poeira nas frações inalável, torácica e respirável, originadas pelas ferramentas utilizadas no setor de acabamento a seco. As concentrações de sílica chegaram a ser 16 vezes superiores ao valor do limite de exposição ocupacional de 0,05 mg/m³. A avaliação de uma marmoraria que adotou acabamento a úmido mostrou que a probabilidade das concentrações ambientais ultrapassarem os valores de referência ocupacionais pôde ser reduzida em até 99%.