The effect of debris accumulation on and filter resistance to airflow for four commercially available vacuum cleaners.

Mortar removal with right-angle grinders can cause excessive exposure to respirable crystalline silica. To control this dust exposure, vacuum cleaners need to exhaust 2.3 m(3)/min (80 cubic feet per minute) from the grinder's exhaust hood. Maintaining this airflow while collecting as much as 15.9 kg (35 lb) of debris in the vacuum cleaner has been problematic. A laboratory study was conducted to evaluate how mortar debris affects vacuum cleaner airflow and filter pressure loss. Four vacuum cleaners were tested. Two of the vacuum cleaners used vacuum cleaner bags as a prefilter; the other two vacuum cleaners used cyclones to reduce the amount of debris that reaches the filter. Test debris was collected by a masonry restoration contractor during actual mortar removal using a grinder fitted with a hood. The hood is attached to a vacuum cleaner with cyclonic pre-separation. The vacuum cleaner fan curves were obtained experimentally to learn how pressure loss affects vacuum cleaner airflows. Then, 15.9 kg (35 lb) of mortar removal debris was sucked into the vacuum cleaner in 2.27-kg (5-lb) increments. Before and after adding each 2.27-kg (5-lb) increment of debris, vacuum cleaner airflows were measured with a venturi meter, and vacuum cleaner static pressures were measured at the inlet to the vacuum cleaner motor, and before and after each filter. The vacuum cleaners equipped with cyclonic pre-separation were unaffected by the mass of debris collected in the vacuum cleaner and were able to maintain airflows in excess of 1.98 m(3)/min (70 cfm) throughout the testing program. As debris accumulated in the vacuum cleaners that used bags, airflow decreased from 2.3 m(3)/min (80 cfm) to as little as 0.85 m(3)/min (30 cfm). This airflow loss is caused by the increased airflow resistance of the bags that increased from less 0.03 kPa/m(3)/min (0.1 inches of water per cfm) to 16.7 kPa/m(3)/min (1.9 inches of water/cfm). Apparently, vacuum cleaners using bags should be used in applications where adequate dust control can be achieved at airflows less than 0.85 m(3)/min (30 cfm). Vacuum cleaners with cyclonic pre-separators provided superior and cost-effective dust control compared with vacuums with bags when dust loading was high and when more than 30 cfm of airflow is needed for dust control.