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Laboratory evaluation of ventilated shrouds for mortar grinding.

Heitbrink W; Watkins D
American Industrial Hygiene Conference and Exposition, June 2-7, 2001, New Orleans, Louisiana. Fairfax, VA: American Industrial Hygiene Association, 2001 Jun; :36
As brick buildings age, mortar deteriorates and needs to be replaced. Before replacing the mortar, the existing mortar is removed to a depth of 1.5 to 3 cm. Typically, an 11-cm diameter grinder, operated at 10,000-12,000 rpm, is used to remove mortar, causing worker exposures to respirable crystalline silica concentrations as high as 10 mg/m3. Also, a tool resembling a router can be used to remove mortar. For four different shrouds, the effect of exhaust flow rate upon respirable dust emissions was experimentally evaluated. To conduct this testing, a small brick wall was built and enclosed in a hall-shaped, ventilated test chamber. The grinder was mounted on a mechanical trolley which moved the grinder horizontally down the wall at constant velocity of approximately 1 m/min and the mortar was removed at a fixed depth cut of 1.2 or 2 cm. A vacuum cleaner equipped with high efficiency filters exhausted air from the shrouds to a location outside of the enclosure. The vacuum cleaner's exhaust air flow was varied by controlling the voltage applied to the vacuum cleaner. An air flow rate of 1.3 m3/sec was drawn through the test chamber and past mixing baffles and into an exhaust duct. A time-of-flight aerosol spectrometer was used to measure the respirable dust concentration in the duct. Dust emissions per volume of mortar removed were plotted as a function of exhaust flow rate. For uncontrolled grinding, respirable dust emissions were 20 mg/cm3 of mortar removed. As flow rates increased, respirable dust emissions were reduced to under 0.2 mg of respirable dust per cm3 of mortar removed. For the 11- cm diameter grinding wheel and the router, 80 and 40 cfm, respectively, were the minimum exhaust volumes which provided this emission reduction. Further flow rate increases did not provide useful emission reduction.
Ventilation; Workers; Work-environment; Work-areas; Exposure-levels; Dusts; Dust-exposure; Respiration; Respirable-dust; Silica-dusts; Silicates; Exhaust-ventilation; Aerosol-particles; Aerosols; Engineering-controls; Control-technology
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American Industrial Hygiene Conference and Exposition, June 2-7, 2001, New Orleans, Louisiana
Page last reviewed: March 25, 2022
Content source: National Institute for Occupational Safety and Health Education and Information Division