OSHA • NIOSH

HAZARDALERT ////////// Worker Exposure to Silica during Countertop Manufacturing, Finishing, and Installation The Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have identified exposure to silica as a health hazard to workers involved in manufacturing, finishing, and installing natural and engineered stone countertop products. This exposure exists in fabrication shops and during on-site finishing/installation, as well as in the production or quarrying of the countertop material. The hazard can be mitigated in most countertop operations with dust control methods following the requirements of the OSHA silica standard.

Introduction Crystalline silica occurs in nature mostly as the minerals

Courtesy David L. Johnson & Margaret Phillips, quartz, cristobalite, and tridymite, and is found in granite, sandstone, quartzite, various other rocks, and sand. Workers who inhale very small dust particles containing respirable crystalline silica (RCS) are at risk for silicosis — an incurable, progressively disabling,

University of Oklahoma Health Sciences Center and potentially fatal lung disease.

RCS is very small particles — typically 100 times smaller than ordinary sand — that can become trapped in lung tissue, causing inflammation and scarring and reducing the lungs’ ability to take in oxygen. Symptoms of silicosis Dry-cutting stone, as pictured, generates dangerous include shortness of breath, cough, and fatigue, and crystalline silica dust that can become trapped in lung the timeline of developing silicosis symptoms depends tissue and cause silicosis. on duration and intensity of RCS exposure. Exposure to RCS also puts workers at increased risk for lung indicate that exposure levels are not adequately cancer, chronic obstructive pulmonary disease (COPD), controlled in some U.S. stone countertop manufacturing tuberculosis, and kidney disease, and is associated and fabrication worksites. 8,13 Employers can utilize the with development of autoimmune disorders and recommendations listed in this document to adequately cardiovascular damage. control exposure levels. OSHA and NIOSH investigated U.S. worker exposure to RCS and the effectiveness of exposure control measures The Stone Countertop Industry in the stone countertop industry following reports of Stone countertop industry workers in shops and on job engineered stone countertop workers in the United sites saw, grind, polish, and drill slabs of natural (marble States and around the world developing silicosis.1-9 In and granite) and engineered (man-made, manufactured, some cases, workers were operating with inadequate artificial, or cultured) stone as part of manufacturing, or no dust suppression; respiratory protection was finishing, and installing countertops. Whether working also inadequate or not being used at all.1,3,10,11 While the with natural or engineered stone, producing finished stone industry has worked to implement dust controls countertops involves similar tasks. Working with natural to protect workers,12 studies and OSHA inspections stone, however, involves different initial steps than working with engineered stone. Granite and other natural stones

are quarried and cut into large stone slabs. These slabs Certain work tasks release crystalline silica are further cut to countertop sizes at the quarries or at dust into the air countertop fabrication shops. Making engineered stone Workers operating powered hand tools, such as saws, slabs often involves mixing silica powder, resins, and grinders, and high-speed polishers, have some of the pigments. Workers who quarry and cut natural stone highest RCS exposures in the countertop manufacturing, and who manufacture engineered stone, as well as finishing, and installation industries. These exposures those involved in finishing and installing both natural and come from cutting, grinding, edging, and contouring engineered stone countertops, are at risk of RCS exposure. stone, and may occur in shop environments as well as In these industries, production operators (such as on job sites where finishing work is completed. sawyers), inspectors (including quality control technicians), and staff who perform maintenance and housekeeping In the engineered stone industry, workers may also be activities may be exposed to hazardous levels of RCS. exposed to RCS when opening bags of silica powder, moving or mixing bulk raw materials, cleaning and Why is RCS exposure a concern scraping mixers, changing filters on dust collectors, or for workers in stone countertop cleaning dust collector bag houses. manufacturing, finishing, and installation? Workers performing other tasks in areas close to where silica dust-generating operations occur may also be Stone countertops contain high amounts of exposed. the natural mineral silica Depending on the type of stone, countertops may contain What can be done at stone countertop over 90% crystalline silica. The highest crystalline silica worksites to protect workers from levels are associated with quartzite and with certain engineered stones. Crystalline silica can comprise up exposure to silica? to 95% of the material in engineered stone, with resins, Employers with employees who manufacture, finish, pigments, and adhesives making up the rest. Some or install countertops containing crystalline silica engineered stones contain less than 50% crystalline must comply with the applicable OSHA standard silica in a polymer resin matrix, and some engineered for respirable crystalline silica (general industry – stones containing recycled glass and pigments in a 29 CFR 1910.1053; construction – 29 CFR 1926.1153). portland cement matrix have less than 0.2% crystalline The silica standards include provisions for assessing silica. Calcium carbonate-based natural stones, including worker exposures to RCS, a Permissible Exposure limestone and marble, contain little or no crystalline silica. Limit (PEL) of 50 µg/‌m3 as an 8-hour time-weighted In contrast, granite can contain up to 50% crystalline average, controlling exposures, personal protective silica. The table below describes typical crystalline silica equipment, establishing a written exposure control content of common natural and engineered stones. plan, housekeeping, medical surveillance, training, and Note that crystalline silica content will vary among stone recordkeeping. The standards require employers to varieties, and the exact content can be determined by implement engineering and work practice controls to petrographic and X-ray diffraction analysis on each stone. reduce exposures to the PEL or below, and to ensure workers use respirators where exposures remain above Typical Crystalline the PEL. Some requirements vary between general Stone Silica Content (%) industry and construction. Additional guidance can be Engineered stone < 0.2 - 95 found on OSHA’s Safety and Health Topics page on Crystalline Silica. Quartzite ≥ 95 Quartzitic sandstone ≥ 90 A combination of protective measures, such as Sandstone ≥ 60 engineering and administrative controls, personal protective equipment, and worker training, is needed to Marble / Limestone <5 ensure workers are not overexposed to RCS during stone Granite 10 - 50 countertop manufacturing, finishing, and installation. Slate 20-40 Soapstone Varies Worker Exposure Assessment Sources: Characterization of Airborne Dust Generated from the Grinding An assessment of worker exposures, required under of Natural and Engineered Stone Products, NIOSH report, October OSHA’s silica standards, will help identify where 2023; ASTM C616, Standard Specification for Quartz-Based Dimension Stone; American Geological Institute, Dictionary of Geological Terms; exposures occur, assess control effectiveness, prevent Worksafe Victoria, Stonemasons: Preventing crystalline silica exposure overexposures, and provide information to employees

performing the work as well as medical providers choose products with little (substitution) or no conducting exams. An exposure assessment can (elimination) crystalline silica.21, 22 Evaluate whether include collecting airborne RCS samples for tasks that the potential alternative stone products can mitigate expose workers to RCS. Employers should consult with employees’ exposure to RCS without posing a greater or a trained occupational safety and health professional, new hazard to employees. such as a certified industrial hygienist, to assess Engineering controls — prevent or reduce workers’ exposures; small businesses may contact OSHA’s free contact with hazards On-site Consultation Program for assistance. „ Use air monitoring to identify and isolate high If the exposure assessment indicates worker exposures exposure tasks associated with countertop are above OSHA’s PEL, the OSHA silica standards fabrication operations. Isolation can be provided by require employers to take action to reduce worker dust control booths19 or enclosures with local exhaust exposures to the PEL or below. If levels are above ventilation (LEV). 22 OSHA’s Action Level (AL) of 25 µg/m3 as an 8-hour „ Avoid dry operations (e.g., dry cutting, grinding, time-weighted average, employers must conduct further sweeping) and use of compressed air. Replace exposure monitoring as well as, in some cases, provide dry grinders with wet-edge milling machines or medical surveillance. stone routers. „ Improve design of the fabrication process to use OSHA Permissible Exposure Limit (PEL) remote-controlled tools with water-spraying systems The OSHA PEL for respirable crystalline silica is (e.g., large bridge or gantry-like saws, waterjet cutting 50 µg/m3 as an 8-hour time-weighted average. machines, computer numerical control machines) as much as possible. OSHA Action Level „ Modify handheld angle grinders and polishers to The OSHA Action Level for respirable crystalline silica deliver water from multiple locations and/or augment is 25 µg/m3 as an 8-hour time-weighted average. them with additional water wetting methods to ensure effective wetting20 at the point of contact with the stone. Control exposures by following the hierarchy „ Install LEV systems at fixed locations to capture of controls and safe work practices dust near its point of origin. System designs should Controlling exposures to occupational hazards is account for the dimensions of the operation area to the fundamental method of protecting workers. The provide sufficient airflow velocity22 to capture dust hierarchy of controls outlines the following methods without interfering with the water used to control to reduce exposures, from most to least effective: dust.18 LEV systems with air filtration and recirculation elimination, substitution, engineering controls, capability can also provide dilutional ventilation to administrative controls, and personal protective reduce RCS concentration in the surrounding area. equipment. Elimination, substitution, and engineering „ Use a combination of both water and LEV controls, controls are the most effective methods because if necessary. they reduce risks without requiring much action from „ Enhance general ventilation of indoor spaces workers. Administrative controls and personal protective by replacing dusty indoor air with clean air from equipment can also help lower exposure to hazards, outdoors or from recirculating air filtration systems. but they work best when combined with the more The effectiveness of this type of ventilation varies effective methods. Below are practical examples of how depending on the size of the indoor space and the to control worker exposure to RCS during countertop available capacity of the general ventilation. manufacturing, finishing, and installation. Administrative controls — establish work practices Elimination and substitution — remove the hazard that reduce exposure to hazards or use a safer alternative „ Train workers to effectively use LEV (e.g., always „ Verify the crystalline silica content in the stone products positioning themselves upstream of the dust source, under consideration for fabrication by consulting the adjusting the operation area to maximize proximity safety data sheets for the products. When possible, inside or near the LEV’s hooded enclosure). 22

„ Develop a system or schedule to evaluate the use mock models and templates to ensure installation effectiveness of engineering controls and equipment processes can be done without the need for onsite to ensure that they are functioning properly; maintain finishing tasks for the stone countertop. and operate water-treatment, housekeeping (e.g., „ Perform work outdoors and use water to suppress wet floor scrubber), and ventilation equipment dust in situations where onsite finishing tasks cannot (including air filter replacement) in accordance with be avoided. manufacturers’ instructions. „ Train workers to raise awareness of the general risk Personal protective equipment — Respirators of RCS exposure and exposure control measures When engineering and administrative controls alone implemented at the workplace. cannot reduce RCS exposures to OSHA’s PEL or below, „ Use wet sweeping or wet floor scrubbers to keep the the OSHA silica standards require respirators to be floor clean, which will help avoid dust getting back used to protect employee health. Whenever respirators into the air after it has settled on the floor. Do not dry are required, the employer must have a respiratory sweep or use compressed air to clean floors and protection program that meets the requirements of work surfaces. OSHA’s Respiratory Protection standard (29 CFR „ Ensure the quality of water used in the fabrication 1910.134). This program must include proper respirator process. Whenever feasible, use tap water for selection, fit testing, medical evaluations, and training. handheld tools and limit recycled water for use in Any respirator used must be stored in a non-dusty remotely operated machines only. When recycled environment and kept clean or washed (if applicable) so water is used, it should first be treated to remove that wearers are not exposed to additional RCS. solid particles and other harmful residuals. If respirators are provided, use at least a NIOSH „ When using wet method dust suppression controls, Approved® N95® respirator. If the RCS level is more adjust water flow as necessary to control dust, than 10 times the OSHA PEL, a half-face respirator following manufacturers’ recommendations for water is not protective enough and a respirator that offers flow rates. a greater level of protection, such as a full-facepiece „ Pre-wash stone slabs prior to cutting or in between cuts. elastomeric respirator that will protect workers at RCS „ Provide HEPA-filtered vacuums for cleaning worker levels up to 50 times the PEL, must be used. Powered clothes, and provide water for hand, face, and hair air-purifying respirators (PAPR) also provide more cleaning in high exposure areas, such as where cutting, protection than half-face air-purifying respirators. In grinding, or polishing work generates silica dust. general, workers find PAPRs to be more comfortable than negative pressure respirators, including tight-fitting Administrative controls — Installation in elastomeric varieties. commercial and residential spaces For more information, visit OSHA’s Safety and Health „ Do as much work as possible under controlled shop Topics page on Respiratory Protection, OSHA’s eTool on conditions instead of at an installation site. Use laser respiratory protection, and NIOSH’s Workplace Safety & measurement to increase dimension accuracy and Health Topics page on Respirators.

The workers shown above are wearing a NIOSH-approved N95 filtering facepiece respirator (left), a full facepiece elastomeric respirator (center), and a loose-fitting powered air-purifying respirator (PAPR) (right).

Medical surveillance for workers who are exposed The Natural Stone Institute technical module, “Silicosis – to silica An Industry Guide to Awareness and Prevention”, offers Under OSHA’s silica standards, employers are required tips on controlling silica exposures in stone cutting to make medical exams available to: (1) all employees operations. It is available to workers and employers on exposed to RCS at or above the OSHA AL for 30 or more the Institute’s Silica Resources web site. days a year in general industry; and (2) all employees required under the RCS construction standard to wear Findings on Worker Exposures to Silica a respirator for 30 or more days a year. The initial exam Data from OSHA and NIOSH provide estimates of must be completed within 30 days of assignment, and countertop industry worker exposure to RCS. When then periodic exams conducted per the applicable engineering and administrative controls as described standard. The medical exam must include: above are used properly, they are generally effective in reducing worker exposures below the OSHA PEL, „ A medical and work history; and in some instances, to levels below the OSHA AL. „ A physical exam with emphasis on the Respiratory protection may still be necessary to protect respiratory system; workers in some cases, however. „ A chest X-ray, evaluated by a qualified professional; „ A pulmonary function test; In many shops, practices may involve dry cutting, „ Testing for latent tuberculosis infection (initial exam grinding, polishing, and other work that releases silica only); and dust into the air. In a study of 47 shops in Oklahoma, 74% reported using dry methods all or most of the time „ Any other tests deemed appropriate by the physician in at least one step of their work, and only 9% reported or other licensed health care professional providing using dust collection systems.10 During inspections of the exam. 106 engineered stone fabrication facilities in 2019-2020 Although not required by OSHA’s silica standards, chest by Cal/OSHA, 26% of employees reported sometimes high-resolution computed tomography without contrast using dry methods.11 Approximately one quarter of is more sensitive than chest X-ray in detecting silicosis breathing zone samples for RCS taken by OSHA and should be considered for follow-up evaluation of exceeded the OSHA PEL during calendar year 2022 in individuals suspected to have silicosis. 25,26 Low-dose workplaces that work with natural and engineered stone chest computed tomography could also be considered slabs. 23 The data summarized below provides additional for screening of workers in settings where a case of information on worker exposures to RCS and illustrates silicosis has been identified. how the implementation of proper controls can help protect workers from overexposures. Silicosis is a reportable condition in many states. Per state requirements, cases should be reported to state or local health departments to assist in identification of Countertop Finishers in Washington State outbreaks and targeting of prevention efforts. Nineteen air samples were taken in granite countertop shops where fabrication and finishing workers were using dry methods without engineering controls Standards and Directives such as LEV.14 These samples showed exposures to Several OSHA standards and directives cover RCS concentrations between <40 and 770 µg/m3. operations that may expose workers to silica, including: Shops using dry methods switched to wet methods, resulting in a dramatic reduction in worker exposure • Hazard Communication (29 CFR 1910.1200) to RCS. Eighteen samples from workers using wet • Respirable Crystalline Silica (29 CFR 1910.1053, methods showed RCS concentrations between <20 29 CFR 1926.1153) and 100 µg/‌m3. In one shop where the workers were • Respiratory Protection (29 CFR 1910.134) sampled using bridge saws and angle grinders, the Directive CPL 03-00-023, National Emphasis mean RCS concentration dropped by 440 µg/m3 after Program – Respirable Crystalline Silica, has detailed switching to new and retrofitted water-fed tools. information on silica hazards, guidelines for air sampling, and other compliance information. Cutting Stone Blocks and Slabs Directive CPL 02-02-080, Inspection Procedures In 2015, OSHA reviewed the results of exposure samples for the Respirable Crystalline Silica Standards, has for sawyers from 10 OSHA Special Emphasis Program inspection procedures and enforcement policies. inspection reports and one NIOSH report. Among 22 instances in which sawyers used wet methods—

often