Projects - Concrete & masonry

Evaluation of Equipment with Dust Control for Concrete Grinding

Sampling was conducted to assess silica and respirable dust exposures to masons during work on a campus library. Initial exposures were above the Washington state 8-hour permissible exposure levels. Dust control measures, consisting of a vacuum and shrouded grinders, were then installed and exposures were resampled. After use of dust control, exposures were significantly reduced. It was concluded that, with these measures, exposures were low enough that a half-face air-purifying respirator with a HEPA filter could replace the powered air-purifying respirator.

Dust Control During Mason Cleanup

Cleanup on construction projects can produce significant dust and silica exposure. At the International Masonry Institute apprenticeship training facility, two dust control strategies were evaluated during cleanup activities: 1) use of sweeping compound to reduce dust during sweeping; and 2) use of squeegees rather than brooms and an industrial vacuum with HEPA filtration to remove dirt piles. Personal exposures were lower with sweeping compound than without controls, and lower with a squeegee/vacuum system than with sweeping compound.

Engineering Controls for Silica Dust

This NIOSH-funded study assessed the effectiveness of commercially available local exhaust ventilation (LEV) systems for controlling respirable dust and crystalline silica exposures during concrete cutting and grinding activities. In a randomized block design, implemented under controlled field conditions, three ventilation rates (0, 30 and 75 CFM) were tested for each tool and LEV system used by workers engaged in tuck point grinding a brick wall, surface grinding a concrete wall, cutting paver block and brick, and cutting concrete block. With the exception of the hand-held saw, the use of LEV resulted in a significant reduction in respirable dust exposure, although exposures remained 0.5 to 2.5 times the permissible exposure level. Nonetheless, this dust control alternative reduces the risk of workers developing disease, allows workers to use a lower level of respiratory protection, protects workers during short duration work episodes, reduces exposure to nearby workers, and reduces cleanup-associated dust exposures.

G. Croteau, S. Guffey, M. Flanagan, and N. Seixas. The Effect of Local Exhaust Ventilation Controls on Dust Exposures During Masonry Activities. AIHA Journal 63:458–467 (2002)

Gerry Croteau thesis

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Wet Concrete Sawing and Drilling

This study was an effort to characterize workplace exposures to silica and respirable dust in order to develop new or enhance existing respiratory protection policies. The study was conducted at ten different construction sites. Four tools were evaluated: walk-behind and hand-held slab saws, core drill, and wall saw. The 8-hour exposures for the 13 samples were found to be at or above the permissible exposure level in five cases. Water appeared to be effective in reducing emissions during concrete cutting and drilling. However, the potential for overexposures to silica when working in an enclosed environment still existed, both for the tool operator and adjacent workers. Therefore, when cutting concrete inside using water for dust suppression, this study recommended that saw operators and others in the area wear respiratory protection.

Flanagan ME, Loewenherz C, Kuhn G. Indoor wet concrete cutting and coring exposure evaluation. Appl Occup Environ Hyg. 2001 Dec;16(12):1097-100.

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Silica Dust Exposures During Selected Construction Activities

This study characterized exposure for dust-producing construction tasks. Eight common construction tasks were evaluated for quartz and respirable dust exposure by collecting 113 personal task period samples for cleanup; demolition with handheld tools; concrete cutting; concrete mixing; tuck-point grinding; surface grinding; sacking and patching concrete; and concrete floor sanding using both time-integrating filter samples and direct-reading respirable dust monitors. The geometric mean quartz concentration was 0.10 mg/m3 (geometric standard deviation [GSD]54.88) for all run time samples, with 71% exceeding the threshold limit value. Activities with the highest exposures were surface grinding, tuck-point grinding, and concrete demolition (GM[GSD] of 0.63[4.12], 0.22[1.94], and 0.10[2.60], respectively). Factors recorded each minute were task, tool, work area, respiratory protection and controls used, estimated cross draft, and whether anyone nearby was making dust. Factors important to exposure included tool used, work area configuration, controls employed, cross draft, and in some cases nearby dust. More protective respirators were employed as quartz concentration increased, although respiratory protection was found to be inadequate for 42% of exposures. Controls were employed for only 12% of samples. Exposures were reduced with three controls: box fan for surface grinding and floor sanding, and vacuum/shroud for surface grinding, with reductions of 57, 50, and 71%, respectively. Exposures were higher for sweeping compound, box fan for cleanup, ducted fan dilution, and wetted substrate. Construction masons and laborers are frequently overexposed to silica. The usual protection method, respirators, was not always adequate, and engineering control use was infrequent and often ineffective.

Flanagan M.E., N. Seixas, M. Majar, J. Camp, M. Morgan. Silica Dust Exposures During Selected Construction Activities. AIHA Journal 64:319–328 (2003).

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The Efficacy of Local Exhaust Ventilation for Controlling Dust Exposures During Concrete Surface Grinding

This study assessed the effectiveness of a commercially available local exhaust ventilation (LEV) system for controlling respirable dust and crystalline silica exposures during concrete grinding activities. Three different dust collection shroud configurations were tested during surface grinding by cement masons at six commercial construction sites. Data obtained with a direct reading respirable dust monitor were adjusted to remove non-work task-associated dust exposures and were subsequently used to calculate the exposure reduction achieved. The application of LEV resulted in a reduction in the overall geometric mean respirable dust exposure from 4.5 to 0.14 mg/m3, a mean exposure reduction of 92%. Despite the effective control of dust generated during surface grinding, 22% of the samples collected while LEV was being used were greater than the 8 hour time-weighted average permissible exposure limit, and 26% greater than the threshold limit value for respirable crystalline silica.

Croteau G., M. E. Flanagan, J. Camp and N. Seixas..The Efficacy of Local Exhaust Ventilation for Controlling Dust Exposures During Concrete Surface Grinding. Annals of Occupational Hygiene 2004 48(6):509-518.

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Development of an ACGIH Construction Industry Silica Exposure Database Overview

A silica monitoring data compilation project was initiated through the American Conference of Governmental Industrial Hygienists Construction Committee. Personal silica exposure monitoring data was collected and analyzed from 13 private, research and regulatory groups. An effort was made to collect as much information as possible about task, tool, environmental and control conditions. Results from 1,374 personal quartz samples reported had a geometric mean (GM) of 0.13 mg/m3 and a GSD of 5.9. Highest exposures were reported for abrasive blasters, surface and tuckpoint grinders, jackhammers, and rock drills. Results were considerably higher for short term samples (up to 2 hours) than for mid term (2-6 hours) or longer (over 6 hour) samples. For nearly all exposure variables, a large portion of variable categories were at or over the quartz occupational exposure limit of 0.05 mg/m3. The data variability within task and tool was very large, with some very high exposures reported for a broad spectrum of tools. These results indicate that respiratory protection commonly used on construction sites is often inadequate for the exposures encountered. Further understanding of the conditions leading to high exposures will require more detailed documentation of the sample characteristics following database design recommendations or systematic surveys of exposure in this complex industry.

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Work on the Edge: Factors Affecting Respirable Dust Exposures During Concrete Grinding

Tom Sultze Thesis

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