Research to practice: Evaluations and recommendations for local exhaust ventilation designed to reduce respirable crystalline silica and dust exposures experienced during mortar removal

Tuckpoint grinding, a process of removing deteriorated mortar from in between bricks with a hand-held grinder during masonry restoration, results in excessive exposures to crystalline silica. To control this exposure, local exhaust ventilation comprised of a ventilated shroud, flexible hose and a vacuum cleaner can be used. Prior laboratory studies reported that ventilation rates beyond 80 cfm do not yield greater capture of dust. This study evaluates the effectiveness of local exhaust ventilation in reducing respirable dust exposures during tuckpoint grinding, the ability of vacuum cleaners to serve as air movers and air cleaners and the ergonomic implications to using the modified grinder. During field trials, geometric mean respirable dust and respirable crystalline silica exposures from 22 subjects performing tuckpoint grinding were 1.07 and 0.06 mg/m3 respectively. In comparison, compliance officers monitored 37 workers who did not use ventilation during grinding and their exposures were 12 and 1.2 mg/m3. Vacuums outfitted with 2'' diameter flexible hose were able to maintain flow rates above 80 cfm for longer periods than when equipped with 1.5'' hose. Video exposure monitoring revealed work practices and environments that contribute to both effective and incomplete dust capture by the ventilation system.;In the laboratory, vacuum cleaners were examined. For particles larger than 1 μm, the vacuums tested were at least 99.8% efficient. For particles smaller than 1 μm the efficiency was greater than 95%. For the large amount of silica laden aerosol captured during grinding, the vacuums tested might become a point source for respirable silica dust emissions.;An ergonomic evaluation comparing the modified grinder to the old method via surface electromyography indicates no indicates no increase in forceful exertions of the forearm flexors and extensors. It did take longer to grind the same amount of mortar with the modified grinder. Workers rated their perceived exertion as being greater with the modified grinder.;During tuckpoint grinding, local exhaust ventilation provides order of magnitude reduction in exposure to crystalline silica. Education and training should be provided on the use and limitations of local exhaust ventilation and component selection as part of a comprehensive silica control program for tuckpoint grinding.