Heitbrink William A, Santalla-Elias Javier
Department of Occupational and Environmental Health, College of Public Health, The University of Iowa, Iowa City, Iowa 52241, USA.
J Occup Environ Hyg. 2009 Jun;6(6):374-84. doi: 10.1080/15459620902905412.
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.
使用直角磨轮机清除灰浆会导致可吸入结晶二氧化硅的过度暴露。为控制这种粉尘暴露，真空吸尘器需要从磨轮机的排气罩排出2.3立方米/分钟（80立方英尺/分钟）的废气。在真空吸尘器收集多达15.9千克（35磅）碎屑的同时保持这种气流一直存在问题。进行了一项实验室研究，以评估灰浆碎屑如何影响真空吸尘器的气流和过滤器压力损失。测试了四台真空吸尘器。其中两台真空吸尘器使用真空吸尘器袋作为预过滤器；另外两台真空吸尘器使用旋风分离器来减少到达过滤器的碎屑量。测试碎屑由一名砖石修复承包商在实际使用配有排气罩的磨轮机清除灰浆过程中收集。该排气罩连接到一台带有旋风预分离功能的真空吸尘器上。通过实验获得真空吸尘器的风扇曲线，以了解压力损失如何影响真空吸尘器的气流。然后，将15.9千克（35磅）的灰浆清除碎屑以2.27千克（5磅）的增量吸入真空吸尘器。在每次添加2.27千克（5磅）碎屑增量之前和之后，用文丘里流量计测量真空吸尘器的气流，并在真空吸尘器电机的入口处以及每个过滤器之前和之后测量真空吸尘器的静压。配备旋风预分离功能的真空吸尘器不受真空吸尘器中收集的碎屑质量的影响，并且在整个测试过程中能够保持超过1.98立方米/分钟（70立方英尺/分钟）的气流。随着碎屑在使用袋子的真空吸尘器中积累，气流从2.3立方米/分钟（80立方英尺/分钟）降至低至0.85立方米/分钟（30立方英尺/分钟）。这种气流损失是由袋子的气流阻力增加导致的，该阻力从小于0.03千帕/立方米/分钟（0.1英寸水柱/立方英尺）增加到16.7千帕/立方米/分钟（1.9英寸水柱/立方英尺）。显然，使用袋子的真空吸尘器应在气流小于0.85立方米/分钟（30立方英尺/分钟）时能够实现充分粉尘控制的应用中使用。与使用袋子的真空吸尘器相比，当粉尘负荷较高且粉尘控制需要超过30立方英尺/分钟的气流时，带有旋风预分离器的真空吸尘器提供了更优越且具有成本效益的粉尘控制。
