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NIOSH Publication No. 2009-115:Control of Hazardous Dust When Grinding Concrete |
April 2009 |
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SummaryConstruction workers are exposed to hazardous dust when using handheld electric grinders to smooth poured concrete surfaces after forms are stripped. The National Institute for Occupational Safety and Health (NIOSH) found that exposures could be reduced if a local exhaust ventilation (LEV) shroud was attached to the grinder. Description of ExposureBreathing dust that contains crystalline silica can lead to the development of silicosis, a deadly lung disease. No effective treatment exists for silicosis, but it can be prevented by controlling workers’ exposure to dust containing crystalline silica. Exposure to crystalline silica has also been linked to lung cancer, kidney disease, reduced lung function, and other disorders [NIOSH 2002a]. Workers in the construction industry may breathe dust that contains silica during various tasks including cutting brick and block, tuckpointing masonry, using a jackhammer to break concrete or rock, or grinding concrete. A NIOSH [2001] study found that workers grinding concrete to smooth poured concrete surfaces after forms are stripped were exposed from 35 to 55 times the NIOSH recommended exposure limit (REL) for airborne dust containing crystalline silica. NIOSH evaluated the use of LEV shrouds on handheld concrete grinders to see whether they reduce worker exposure to dust [Echt and Seiber 2002; NIOSH 2002b]. NIOSH StudyThe concrete finishers in the NIOSH studies were responsible for smoothing poured concrete walls and columns. The LEV system consisted of a grinder that was equipped with a ventilation shroud, a length of flexible corrugated hose, and a portable electric vacuum cleaner that
GrindersThe grinders used were rated at either 10,000 or 11,000 rpm: Metabo model W7-115 Quick 10,000-rpm grinder and Metabo model 11025 grinder (Metabowerke GmbH; Nürtingen, Germany); Bosch model 1347A grinder (Robert Bosch GmbH; Stuttgart, Germany); and Milwaukee model 6153–20 grinder (Milwaukee Electric Tool Corp.; Brookfield, WI). The grinders were fitted with 4-inch diameter diamond cup wheels (PW series, Pearl Abrasive Co.; Commerce, CA). LEV shroudsFour LEV shrouds were used in the study. The shrouds were selected based on their rugged appearance, how easily they could be mounted on the grinders, and their availability for purchase. The shrouds used were Vacuguard (Pearl Abrasive Co.; Commerce, CA), Dustcontrol (Transmatic Inc; Wilmington, NC); and “full-dust shroud” and “cut (edging) shroud” (Sawtec; Oklahoma City, OK). Vacuum cleaners and hosesThe grinder/shroud pairs were connected via 1.5-inch (inside diameter) corrugated flexible hose to two types of industrial vacuum cleaners (DC 2700 and DC 3700; Dustcontrol AB, Norsborg, Sweden). The manufacturer reports that the DC 2700 vacuum has a maximum flow capacity of 112 cubic feet per minute (190 cubic meters per hour), and a maximum negative pressure of 84 inches w.g. (21 kPa). The DC 3700 has a maximum flow capacity of 188 cubic feet per minute (320 cubic meters per hour) and a negative pressure of 96.5 inches w.g. (24 kPa).
ControlsNIOSH and its partners have developed recommendations to protect workers from exposure to crystalline silica dust during construction activities [NIOSH 1996; Echt and Seiber 2002; NIOSH 2002a; Heitbrink and Collingwood 2005]. Some of the benefits of using the dust control noted in this report include reducing worker exposure to hazardous dust and potentially allowing for use of less protective respiratory protection, reduced cleanup time, and reduced cleanup exposures.
The vacuum cleaner should draw at least 10 amps if it is used as part of a ventilated grinder system, so it can over-come filter loading. Some vacuum cleaners are equipped with a pressure gauge that indicates when the air flow rate is too low to be effective. If the vacuum cleaner does not have a pressure gauge, workers can monitor the air flow by looking at the dust plume. If dust is escaping under the shroud, the dust collected on the pre-filter needs to be dislodged or the vacuum cleaner bags or filters need to be changed. HoseA 1.5- or 2-inch diameter hose with a relatively smooth interior and a length of no more than 15 feet should provide adequate air flow. The hose should have as few elbows or turns as possible. A study on tuckpoint grinders [Heitbrink and Collingwood 2005] reported that 2-inch diameter hoses provided better air flow than smaller (e.g., 1.5 inch) diameter hoses. Dust has a greater tendency to settle in larger diameter hoses and should be cleared before and after each use. ShroudThe shroud can be purchased with the grinder, separately, or as a unit with the vacuum cleaner and hose. The shroud should totally enclose the spaces around the exhaust entry point for the hose. The exhaust shroud should have an entry point for the hose matching the diameter of the hose. Work practices
Since NIOSH last investigated concrete grinders in 2002, several grinder manufacturers have introduced tools with dust controls. Studies since the NIOSH investigation show the effectiveness of LEV controls in reducing respirable dust when using concrete grinders [Croteau et al. 2004; Akbar-Khanzadeh et al. 2007]. RespiratorsWorkers and employers should be aware of the high risk of dust exposure in poorly ventilated areas (such as in corners or inside buildings). This may result in increased exposure to hazardous dust.
*Code of Federal Regulations. See CFR in references.
AcknowledgmentsThe principal contributors to this publication were Alan Echt of the Division of Applied Research and Technology, NIOSH and John J. Whalen under contract with the U.S. Public Health Service, Division of Federal Occupational Health. ReferencesAkbar-Khanzadeh F, Milz S, Ames A, Susi PP, Bisesi M, Khuder SA, Akbar-Khanzadeh A [2007]. Crystalline silica dust and respirable particulate matter during indoor concrete grinding—wet grinding and ventilated grinding compared with uncontrolled conventional grinding. Occup. Environ. Hyg 4:770–779. CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office. Office of the Federal Register. Croteau GA, Flanagan ME, Camp JE, Seixas NS [2004]. The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding. Ann. Occup. Hyg 48(6):509–518. Echt A, Seiber K [2002]. Control of silica exposure from hand tools in construction: grinding concrete. Appl Occup Environ Hyg 17(7):457–461. Heitbrink WA, Collingwood S [2005]. Protecting tuckpointing workers from silica dust: draft recommendations for a ventilated grinder. The Center to Protect Workers’ Rights, Silver Spring, MD [www.cdc.gov/elcosh/docs/d0600/d000683/d000683.html]. NIOSH [1996]. NIOSH Alert: Request for assistance in preventing silicosis and deaths in construction workers. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, DHHS (NIOSH) Publication No. 96–112. NIOSH [2001]. In-depth survey report of four sites: exposure to silica from hand tools in construction chipping, grinding, and hand demolition at Frank Messer and Sons Construction Company, Lexington and Newport KY; Columbus and Springfield, OH. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Survey Report No. EPHB 247–15. NIOSH [2002a]. NIOSH hazard review: Health effects of occupational exposure to respirable crystalline silica. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2002–129. NIOSH [2002b]. In-depth survey report of control of respirable dust and crystalline silica from grinding concrete at Messer Construction, Newport, Kentucky and Baker Concrete Construction, Dayton, Ohio. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Survey Report No. EPHB 247–21. For More InformationThe information in this document is based on NIOSH field studies. More information about silica hazards and controls is available on the NIOSH Web site at www.cdc.gov/niosh/topics/silica/default.html. To receive more information about occupational safety and health topics, contact NIOSH at Telephone: 1–800–CDC–INFO (1–800–232–4636) or visit the NIOSH Web site at www.cdc.gov/niosh For a monthly update on news at NIOSH, subscribe to NIOSH eNews by visiting www.cdc.gov/niosh/eNews. Mention of any company or product does not constitute endorsement by NIOSH. In addition, citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these Web sites. This document is in the public domain and may be freely copied or reprinted. NIOSH encourages all readers of the Workplace Solutions to make them available to all interested employers and workers. As part of the Centers for Disease Control and Prevention, NIOSH is the Federal agency responsible for conducting research and making recommendations to prevent work-related illnesses and injuries. All Workplace Solutions are based on research studies that show how worker exposures to hazardous agents or activities can be significantly reduced. Control of Hazardous Dust When Grinding ConcreteDHHS (NIOSH) Publication No. 2009-115April 2009Safer • Healthier • People™ DEPARTMENT OF HEALTH AND HUMAN SERVICES
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