Abstract:
This study assessed the effect of work characteristics on dust exposures during concrete grinding activities, with and without local exhaust ventilation (LEV). Particular attention was paid to the differences between work on flat surfaces where the shroud of the LEV system made a good seal, and on the edge where the seal was in partial contact with the surface. Under controlled field conditions, four union apprentices performed surface grinding tasks on concrete walls using LEV and three apprentices performed the tasks without LEV. Fourteen permutations of the four factors (surfaces (flat, right edge, left edge), handle orientation (vertical, right, left), and grinder speed (full and half speed) and LEV) were considered. The tasks were randomized and each task was performed for two minutes. The apprentices performed the 14 tasks and then repeat the set of tasks twice, totaling 42 trials. Breathing zone samples were collected with a direct reading aerosol monitor which recorded respirable dust levels every five seconds. ANOVA statistical models were run for tasks with LEV, without LEV and a combined model. The most important factor in worker respirable dust exposure was LEV. Using the LEV reduced the subject's exposure by 91% (p< 0.001). Grinder wheel speed was also important. Tasks at half speed showed a 35% reduction in respirable dust (p< 0.001). Using LEV, exposure on the right edge was significantly less (p=0.02) than on the left edge or flat surface. This is likely due to the dust collection port on the LEV shroud being directly in line with grinder emissions. Without LEV, the surface is not significant, exposures on the right and left edges being almost equal. Grinding with the handle oriented to the right was significant (p=0.002) possibly because the subject is further from the grinding wheel and the handle may actually block some of the dust from reaching the breathing zone. This study found that workers can reduce their dust exposure by using LEV, and grinding at a slower speed on the edge. Orienting the handle to the right or vertically on the right edge with LEV will reduce a workers exposure, as will orienting the handle to the left or vertically on the left edge