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 358-16a, 2014 Oct; :1-47
Workplace exposure to respirable crystalline silica 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 construction materials, such as brick, block, mortar and concrete. Construction tasks that cut, break, grind, abrade, or drill those materials have been associated with overexposure to dust containing respirable crystalline silica. Fiber-cement products can contain as much as 50% crystalline silica and cutting this material has been shown to cause excessive exposures to respirable crystalline silica. NIOSH scientists conducted this study to develop engineering control recommendations for respirable crystalline silica from cutting fiber-cement siding. Detailed characterization of the dust generated from cutting fiber-cement siding was conducted in a laboratory setting. Respirable dust was sampled and analyzed using a variety of instruments based on both a real-time direct reading technique and gravimetric methods. The dust size distribution and the silica distribution in the dust of different sizes were analyzed in detail for cutting fiber-cement siding from four major manufacturers. The generation rate of respirable dust was analyzed and compared for cutting fiber-cement siding using different power tools (a power shear, four miter saws, and three circular saws), different blades, differing the saw cutting feed rate, and cutting different numbers of boards in the stack. It was found that two circular saws with a 4-tooth polycrystalline diamond-tipped (PCD) blade of 18.4 centimeter (cm, 7.25 inch) diameter generated the least amount of dust under the same test conditions. A local exhaust ventilation (LEV) system was also tested for all the power saws used in the laboratory evaluation. The generation rate of respirable dust and dust removal efficiency were recorded for each power saw when used with the LEV operating at different volumetric flow rates. In most test conditions of the miter saws, the dust removal efficiency was about 65% or lower, even at the highest test flow rate of the LEV (3.97 cubic meter per minute, m3/min; or 140 cubic feet per minute, CFM). The three circular saws evaluated in this study featured a built-in dust collection container or shroud, which served as a hood and partially enclosed the saw blade for collecting dust while cutting. The dust removal efficiency for the circular saws was greater than 78% even at a low flow rate of 0.83 m3/min (29 CFM). The results from the laboratory evaluation suggested that connecting a dust-collecting circular saw to a basic shop vacuum with built-in air filters had the potential to provide a simple and low-cost engineering control measure for the dust generated from cutting fiber-cement siding. Four field surveys were conducted to validate the effectiveness of the engineering control measure suggested from the laboratory evaluation. The survey results showed that the 10-hour time weighted average (TWA) exposure to respirable crystalline silica for the workers who mainly cut fiber-cement siding on the job sites was well under control, with the 95% upper confidence limit being only 24% of the NIOSH Recommended Exposure Limit (REL) of 0.05 milligrams per cubic meter (mg/m3). This engineering control measure effectively reduced occupational silica exposures, and provided an effective, simple and low cost solution for workers cutting fiber-cement siding.
Control-technology; Engineering-controls; Construction-materials; Construction-industry; Construction-workers; Dusts; Silica-dusts; Fibrous-dusts; Respirable-dust; Dust-control; Dust-control-equipment; Respiratory-protective-equipment; Respiratory-protection; Quartz-dust; Cements; Concretes; Cutting-tools; Sampling; Vacuum-equipment; Ventilation; Exhaust-ventilation; Control-equipment; Control-systems; Dust-collection; Work-practices; Air-samples; Air-sampling; Time-weighted-average-exposure; Exposure-levels; Exposure-limits; Cyclone-air-samplers; Permissible-limits;
Author Keywords: Respirable dust; Respirable crystalline silica; Fiber-cement siding; Engineering control; Siding Contractors