During exterior building renovation, deteriorated mortar is removed with a grinder to a depth of 1-2 cm and replaced with new mortar in a process termed """"""""tuckpointing."""""""" Typically, the grinders used in tuckpointing are 10 cm in diameter with a rotational speed of 10,000-12,000 rpm. During mortar removal, worker exposures to respirable crystalline silica are as much as 5 mg/m3, a level 100 times the NIOSH REL and approximately 50 times the OSHA PEL. Because of these excessive exposures to respirable crystalline silica, workers are at risk for developing silicosis. Dust control is achieved by partially enclosing the grinding wheel with a ventilated shroud. To exhaust air from the shroud, a vacuum cleaner can be used, functioning as an air mover and particulate collection device. Recently, vacuum cleaner bags and final filters have become commercially available for wet-dry vacuum cleaners. If these bags and filters are shown to efficiently collect respirable dust, wet-dry vacuum cleaners may be a useful control option for dust control during mortar removal. They could also meet the size and weight requirements for equipment to be used on scaffolding that may be only 0.8 meters wide, as well as providing a cost-effective option in a competitive, cost-conscious industry. Using laboratory and field evaluations, the proposed work will test the capability of wet-dry vacuum cleaners to provide the needed exhaust ventilation and dust collection. In the laboratory phase of the study, the particulate collection efficiency of wet-dry vacuum cleaner filter bags will be studied. For the vacuum cleaners to maintain exhaust flow rates necessary to capture the dust, the filter bags must efficiently collect enough dust to keep the final filters from becoming clogged. The relationship between pressure loss and exhaust flow rate will also be studied to characterize the ability of the vacuum cleaners to move air. Laboratory studies have shown that an exhaust rate of 2.2 m3/min (80 cubic feet per minute [cfm]) is needed for optimal control of the dust. The field phase of this project will focus on the overall dust exposure implications of using four wet-dry vacuum cleaners and one vacuum cleaner with reverse-pulsing filters that discharge the dust into a collection bag.
