Exposure to Respirable Crystalline Silica During Five OSHA Table 1 Tasks and the Effectiveness of Dust Controls, the Contribution of Background Silica Dust to Personal Exposures, and the Use of a Photometric Instrument to Assess Silica Dust Exposure

Details

• Personal Author:
  Cothern EJ
• Description:
  Occupational exposure to respirable crystalline silica (RCS) has become a global public health concern and has been identified as one of the world's most significant causes of occupational disease, with much of the exposures occurring in the construction industry. In 2016, the Occupational Safety and Health Administration (OSHA) enacted a new silica standard for construction with a permissible exposure limit (PEL) of 50 µg/m3 and an action level (AL) of 25 µg/m3. This new standard also provided the construction industry with the OSHA Table 1: Specified Exposure Control Methods When Working With Materials Containing Crystalline Silica, which accommodated employers in the construction industry by offering a guideline to achieving compliance to the standard by using specified dust-control measures and work practices. However, researchers have found that dust controls do not always reduce silica exposure below occupational exposure limits and the current studies confirm this finding. Study 1: Personal silica exposures were measured while construction workers conducted five OSHA Table 1 tasks using dust controls to assess the effectiveness of the dust control measures at reducing silica dust below the PEL. This research was conducted at a northern Colorado construction site during the build of a water sanitation plant (July 2020-November 2020) and included personal and area silica air sampling while construction workers performed core drilling, cutting with a walk-behind saw, grinding, dowel drilling, and jackhammering. In addition, environmental conditions (i.e., wind speed, relative humidity, temperature) were recorded every 30 minutes during the personal silica air monitoring so that potential determinants of silica exposure could be evaluated. Of the construction workers that participated in this study, 24 of 51 (47.1%) had the potential to be exposed over the AL of 25 µg/m3 and 15 of 51 (29.4%) had the potential to be exposed over the PEL of 50 µg/m3 for an eight-hour time weighted average (TWA) when the silica exposures were extrapolated to eight hours. When the silica exposures were extrapolated to four hours (with an additional four hours of no exposure), then 15 of 51 (29.4%) of workers sampled would have been exposed over the AL and 8 of 51 (15.7%) would have been exposed over the PEL. The mean silica concentration for all tasks was 85 µg/m3 (standard deviation [SD] = 176.2) and the mean sample time was 127 minutes. The mean silica concentration for the five tasks included: core drilling 11.2 µg/m3 [5.31], cutting with a walk-behind saw 126 µg/m3 [115], dowel drilling 99.9 µg/m3 [58.7], grinding 172 µg/m3 [145], and jackhammering 23.2 µg/m3 [5.19]. A multiple regression analysis showed that location (p < 0.001), task (p = 0.001), and temperature (p = 0.002) were significant predictors of silica dust concentrations, but relative humidity was not. A two-sample t-test showed that silica dust concentrations were significantly (p < 0.01) higher at wind speeds = 1 m/s compared to wind speeds > 1 m/s. A two-sample t-test also showed that silica dust concentrations were significantly (p < 0.01) higher among partially enclosed environments compared to outdoor locations. Based on the results of this study, exposure to hazardous levels of respirable crystalline silica can still occur with the OSHA-mandated controls fully implemented, thus increasing the risk of silica-related illnesses. Study 2: The goal of this study was to evaluate the contribution of background silica dust to personal silica exposures while employees conducted five OSHA Table 1 tasks and was performed at a northern Colorado construction site. A total of 15 area silica samples were collected over 13 days in tandem with 51 personal task-based silica samples with an average area sampling time of 187 minutes. At least one area sample was collected on each of the 13 sampling days. Of the 15 area samples, only four collected silica masses that were greater than the laboratory's reporting limit of 5,000 ng (5 µg), and included measurable background silica concentrations of 23 µg/m3, 5 µg/m3, 40 µg/m3, and 100 µg/m3. Due to data censoring (i.e., non-detects) in the area samples (73.3%), there was not a sufficient number of data points to determine with statistical certainty if silica background concentrations significantly contributed to worker exposure. However, the four measurable background silica samples may have contributed to worker exposure since 14 of 15 of the personal silica samples that exceeded the OSHA PEL occurred on the four days when the background silica levels were measurable. These results suggest a possible correlation between background silica concentrations and the higher personal silica dust exposures. Study 3: The goal of this study was to evaluate the utility of performing real-time dust monitoring to estimate RCS airborne concentrations during construction tasks. Personal air monitoring using a TSI SidePak AM520 personal aerosol monitor was performed on a northern Colorado construction site during the build of a water sanitation plant during five OSHA Table 1 tasks. Each construction task was sampled once; sample time ranged from 14 minutes to 40 minutes, with a mean sample time of 27 minutes. Prior to task-based air monitoring, the TSI SidePak and an SKC disposable respirable parallel particle impactor (PPI) were co-located on the construction site for 334 minutes to measure the area respirable dust concentration to determine an aerosol-specific correction factor for the TSI SidePak monitoring results. A comparison of respirable dust collected by the SKC PPI to the TSI SidePak AM520 showed that the direct reading instrument was underestimating respirable dust, therefore, the correction factor was applied to the respirable dust sampling results. In addition, bulk material samples were collected during the performance of the five tasks so that the percent silica could be determined for each task-specific material. The adjusted TSI SidePak mean respirable silica dust concentrations (µg/m3) (standard deviation [SD]) for the five tasks included: core drilling 12 µg/m3 [2.46], grinding 918 µg/m3 [1134.08], cutting with a walk-behind saw 36 µg/m3 [79.67], jackhammering 27 µg/m3 [23.24], and dowel drilling 66 µg/m3 [77.65]. While the silica exposure results from this study cannot be directly compared to the OSHA eight-hour TWA silica PEL of 50 µg/m3, the data are useful to observe the variability of silica exposures that occur during a task to determine if worker personal behaviors affect exposure and to determine if dust controls are effective. Employing direct-reading instruments to assess exposure also reduces the cost burden on employers by reducing the number of gravimetric samples. [Description provided by NIOSH]
• Subjects:
  Construction Industry Dust Occupational Health Safety Silicon Dioxide
• Keywords:
  Construction Industry Control Methods Crystalline Silica Direct-reading Methods Dust Control Equipment Dust Exposure Exposure Assessment Monitoring Systems Respirable Dust
• Publisher:
  Colorado State University
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Dissertation
• Place as Subject:
  Colorado ; OSHA Region 8
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-93
• NIOSHTIC Number:
  nn:20068813
• Citation:
  Fort Collins, CO: Colorado State University, 2021 Fall; :1-93
• CAS Registry Number:
  Quartz (SiO2) (CAS RN 14808-60-7)
• Federal Fiscal Year:
  2022
• Performing Organization:
  University of Colorado, Denver
• Peer Reviewed:
  False
• Start Date:
  20070701
• Source Full Name:
  Exposure to respirable crystalline silica during five OSHA Table 1 tasks and the effectiveness of dust controls, the contribution of background silica dust to personal exposures, and the use of a photometric instrument to assess silica dust exposure in real time
• End Date:
  20250630
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:b42c19ae2a34c129f1b42d983b7cd34c4f1c5d956e49dd94923d997f35c8ffd9d3f71c6874b1168ab1fc3f63cc9a214dfb083d26874ebc21acbcd6371ed908b6
• Download URL:
  https://stacks.cdc.gov/view/cdc/207388/cdc_207388_DS1.pdf
• File Type:
  [PDF - 836.20 KB ]