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Control measures for silica exposures for tuckpointing.

Heitbrink-WA; Collingwood-S
NIOSH 2005 Nov; :1-52
During building renovation, mortar removal with a right angle grinder causes worker exposures to respirable crystalline silica as high as 5 mg/m3, 100 times the NIOSH REL. To control this exposure, vacuum cleaners can be used to exhaust 80 cubic feet per minute (cfm) from a hood that: partially encloses the grinding wheel. Prior laboratory studies found that exhaust rates beyond 80 cfm do not yield further reduction in dust emissions. The ability of vacuum cleaners to function as air movers and air cleaners was studied in the laboratory. Flow rate decreased linearly with increased vacuum cleaner static pressure measured just upstream of motor's inlet. As particle collection devices, the tested vacuum cleaners allowed no more than 0.2% of the particles larger than 1 microm to penetrate the vacuum cleaner. For particles smaller than 1 microm, the aerosol penetration through the vacuum cleaner was less than 5%. Field trials were conducted to evaluate the ability of vacuum cleaners to maintain this flow and to evaluate the exposure outcomes of using these control measures. Air flows were calculated from the vacuum cleaner static pressures that were measured and digitally recorded with a data-logging pressure transducer. The vacuum cleaners, outfitted with 2-inch hoses, maintained an exhaust volume greater than 80 cfm for a longer time period than those equipped with 1.5-inch diameter hose. As mortar debris was collected in the vacuum cleaner, flow rates for the vacuum cleaners equipped with 2-inch hose decreased from 95 cfm to 65 cfm and for those quipped with 1.5-inch diameter hose, the air flows decreased to 40 cfm. Clearly, the vacuum cleaners failed to maintain an air flow of 80 cfm. During the field trials, worker exposure to respirable dust and respirable crystalline silica was monitored. Geometric mean respirable dust and respirable crystalline silica exposures were, respectively, 1.07 and 0.06 mg/m3. When mortar removal was performed without ventilation, the geometric mean respirable dust and respirable crystalline silica exposures, measured by OSHA compliance officers, were, respectively, 12 and 1.2 mg/m3. Apparently, a control system consisting of a grinder hood connected by hose to a vacuum cleaner can provide an order of magnitude reduction in worker exposure to crystalline silica. Concurrent aerosol photometer and flow rate measurements overlaid on real-time video suggests that exposure reduction is limited by work-practices, the inability of the vacuum cleaners to maintain an air flow of 80 cfm, and a variable gap between the bottom of the hood and the mortar.
Construction-industry; Construction; Construction-workers; Construction-equipment; Respirable-dust; Silica-dusts; Cements; Concretes; Dusts; Dust-particles; Dust-control-equipment; Dust-control; Dust-exposure; Engineering-controls; Control-technology; Masons
Publication Date
Document Type
Final Grant Report
Funding Type
Fiscal Year
NTIS Accession No.
NTIS Price
Identifying No.
NIOSH Division
Priority Area
Personal Protective Technology
Source Name
National Institute for Occupational Safety and Health
Performing Organization
University of Iowa
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division