Investigation of Ventilation Engineering Controls for Stone Countertop Fabrication

Details

• Personal Author:
  Qi, Chaolong
• Corporate Authors:
  National Institute for Occupational Safety and Health. Division of Applied Research and Technology
• Description:
  Background: Workplace exposure to respirable crystalline silica (RCS) can cause silicosis, a progressive lung disease marked by scarring and thickening of the lung tissue. Quartz is the most common form of crystalline silica. Crystalline silica is found in several materials, such as brick, block, mortar and concrete. Construction and manufacturing tasks that cut, break, grind, abrade, or drill those materials have been associated with overexposure to dust containing RCS. Stone countertop products can contain >90% crystalline silica and working with this material during stone countertop fabrication and installation has been shown to cause excessive RCS exposures. NIOSH scientists are conducting a study to develop engineering control recommendations for RCS during stone countertop fabrication and installation tasks. The site visits described in this report are part of that study. Assessment: A NIOSH engineer conducted three site visits to evaluate the effectiveness of ventilation engineering controls in reducing occupational exposure to RCS at a stone countertop fabrication shop. The evaluated engineering control measures included multiple water-wall dust extractors and pedestal fans, in addition to existing wet grinding and wet polishing work practices and a wet floor scrubber for work-area cleanliness. The configuration of evaluated engineering controls was different among the three site visits to evaluate their respective performance and are referred to as Setting 1, Setting 2, and Setting 3 in this report. Under Setting 1 and Setting 3, four dust extractors were deployed in the final grinding/polishing area, and five were deployed in Setting 2. Moreover, a designated dust extractor booth was used for the grinding process in Setting 2 and Setting 3 while the grinding process in Setting 1 took place within an area that was further away from any of the four dust extractors. The three settings were also distinguished by the frequency of wet floor cleaning by floor flushing and the use of a floor scrubber. During the field evaluations, the NIOSH engineer collected breathing zone air samples to assess the time weighted average (TWA) respirable dust and RCS exposures of workers who performed tasks using wet grinding and polishing tools. Additionally, area samples were collected to assess the overall background TWA respirable dust and RCS concentrations in the sample areas. The NIOSH scientist recorded detailed field notes about the work process to understand conditions leading to measured dust and RCS exposures. Results Respirable Dust: For the grinding task, the TWA exposures ranged from 184.7 to 214.3 µg/m3 under Setting 1, from 62.8 to 80.0 µg/m3 under Setting 2, and from 65.7 to 75.9 µg/m3 under Setting 3. For the polishing task, the TWA exposures ranged from 130.1 to 150.5 µg/m3 under Setting 1, from 135.3 to 152.8 µg/m3 under Setting 2, and from 49.8 to 72.8 µg/m3 under Setting 3. For the lamination task, the TWA exposures were only obtained under Setting 1 and ranged from 91.4 to 123.5 µg/m3. For the area samples, the TWA dust concentrations ranged from 94.7 to 112.9 µg/m3 under Setting 1, from 18.2 to 57.9 µg/m3 under Setting 2, and from 47.4 to 84.0 µg/m3 under Setting 3. All of the TWA respirable dust exposures observed under the three research settings were well below the 5 mg/m3 OSHA Permissible Exposure Limit (PEL) for Particulates Not Otherwise Regulated. However, since this dust contained RCS, the observed RCS exposures must be compared with the RCS PEL (50 µg/m3) to determine whether exposures were successfully controlled. RCS Exposures: For the grinding task, the TWA exposures ranged from 51.5 to 96.9 µg/m3 under Setting 1, which were all higher than the OSHA PEL, from 28.0 to 42.4 µg/m3 under Setting 2, which were all below the OSHA PEL, and from 5.9 to 8.5 µg/m3 under Setting 3, which were all below the action level of the OSHA silica rule (25 µg/m3, above which as an 8-hour TWA, OSHA requires employers to assess the exposures per CFR [2016]). For the polishing task, the TWA exposures ranged from 38.7 to 54.0 µg/m3 and from 29.2 to 53.2 µg/m3 under Settings 1 and 2, respectively, which were below or slightly higher than the OSHA PEL. Under Setting 3, the TWA exposures ranged from 3.1 to 3.4 µg/m3, which were all below the action level of the OSHA silica rule. For the lamination task, the full-shift TWA exposures were only obtained for two days under Setting 1, which were 20.0 and 24.5 µg/m3. For the area samples, the TWA RCS concentrations ranged from 37.7 to 51.4 µg/m3 under Setting 1, which were mostly lower or slightly higher than the OSHA PEL
  
  while it ranged from 5.3 to 25.9 µg/m3 under Setting 2 and from 2.9 to 9.7 µg/m3 under Setting 3, which were substantially lower than the OSHA PEL. Comparing the exposure data between the first two settings and a Baseline Setting when NIOSH researchers assessed workers' exposures and background area concentrations before additional ventilation engineering controls were identified and implemented, the engineering control and work practice approaches evaluated under Setting 2 showed significantly reduced respirable dust (P = 0.002) and RCS (P = 0.007) concentrations in area samples. The full-shift TWA respirable dust (70.5 +/- 8.7 vs 300.0 +/- 88.3 µg/m3 with P = 0.007) and RCS (32.9 +/- 8.2 vs 120.8 +/- 20.2 µg/m3 with P < 0.001) exposures for grinding were also significantly reduced under Setting 2. Although Setting 2 controlled the RCS exposure for grinding and area samples to levels below the OSHA PEL, neither Setting 1 nor Setting 2 appeared to help reduce exposures for the polishing task, with the full-shift TWA RCS exposure for polishing still near the OSHA PEL under both settings. Setting 3 had elevated respirable dust concentrations in the area samples compared to Setting 2. However, it maintained the same level of exposure control as Setting 2 for the respirable dust during grinding (P = 0.881), and had significantly lower respirable dust (P < 0.001) and RCS (P = 0.031) exposures for polishing than Setting 2. The RCS concentrations from all the samples under Setting 3 were lower than the action level of the OSHA silica rule, driven by the reduced respirable dust exposure that resulted from the combined engineering control measures as well as the low silica content in the stone countertop products used during this site visit. Conclusions and Recommendations: The RCS exposures for Setting 3 were all considerably lower than the action level of the OSHA silica rule, which can be partially attributed to "Elimination" and "Substitution" in the hierarchy of controls. By working with more stone countertop products that have less or no crystalline silica, the average silica content of all the samples in Setting 3 is only 8.1%. Developing stone countertop products with low or no crystalline silica without introducing other hazards would adhere to the top of the hierarchy of controls and could be effectively incorporated in a layered, overall control strategy. The following combination of engineering controls and work practices were found to be the most effective at controlling individual RCS exposures for grinding and polishing tasks: (1) designating dust extractors for the grinding task as evaluated in Setting 2 and Setting 3
  
  and (2) training workers to position themselves and workbenches to consistently perform the grinding and polishing within the dust extractor's hooded enclosure as evaluated during polishing tasks in Setting 3. Using this combination of engineering controls and work practices consistently maintained individual RCS exposures to levels below the OSHA PEL for grinding and polishing tasks. This evaluation had limitations that could influence the generalizability of the findings. Sampling occurred over 3 days under each of the three specific settings of engineering control measures for comparing their performance on reducing RCS exposures, which may not be representative of other times or seasons at the site when different settings of the control measures may be implemented. The number of hours an employee works can also vary by season, due to changing demand for the product. In accordance with OSHA worker protection policies, until feasible engineering controls are implemented and proven effective, respirators should continue to be used to protect workers against exposures above recognized occupational exposure limits and the employer should ensure that the company respiratory protection program follows OSHA standards [CFR 2006].
  
  
• Subjects:
  Air Pollutants, Occupational Dust Engineering Occupational Health Safety Silicon Dioxide Ventilation
• Keywords:
  Airborne Dusts Control Methods Crystalline Silica Engineering Control Engineering Controls Grinding Equipment Respirable Crystalline Silica Respirable Dust Stone Countertop Stone Products
• Series:
  Engineering and Physical Hazards Survey Reports
• DOI:
  https://doi.org/10.26616/NIOSHEPHB2024DFSE1618
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Genre:
  Field Study
• Place as Subject:
  Ohio ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DFSE - Division of Field Studies and Engineering ; EPHB - Engineering and Physical Hazards Branch
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-32
• NIOSHTIC Number:
  nn:20069255
• Citation:
  Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB Report No. 2024-DFSE-1618, 2024 Feb ; :1-32
• CAS Registry Number:
  Quartz (SiO2) (CAS RN 14808-60-7)
• Federal Fiscal Year:
  2024
• NORA Priority Area:
  Construction ; Manufacturing
• Peer Reviewed:
  False
• NAICS and SIC Codes:
  327991 - Cut Stone and Stone Product Manufacturing - (NAICS)
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:bf7690694282cd481a169b8ae462ec680982d89df6d6e3bcee098f4ae9d73681cddf152974571f3542374ac4d21a1b93abb4f55681976c4151f31d6b6e8f1629
• Download URL:
  https://stacks.cdc.gov/view/cdc/174853/cdc_174853_DS1.pdf
• File Type:
  [PDF - 1.84 MB ]