Dust Control Handbook for Industrial Minerals Mining and Processing

EXAMPLES OF SECONDARY DUST SOURCESThe following are a few examples that were documented in actual field studies and willdemonstrate the impact that secondary dust sources can have on a worker's respirable dustexposure [Cecala and Thimons 1987; USBM 1988; Cecala and Thimons 1992].Dusts from Outside Sources Traveling Inside StructuresWhen dusts from outside sources travel inside structures, every worker inside the structure isimpacted. Most bagging operations at mineral processing plants use an exhaust ventilationsystem to draw the dust generated from the bagging process down into the fill hopper and awayfrom the breathing zone of the bagger (refer to Chapter 6—Bagging). It is important that the airbeing drawn into this exhaust ventilation system, commonly called makeup air, be clean air. Atone operation, the makeup air was drawn directly from the bulk loading area outside the mill.The dust generated from this bulk loading process traveled through an open door into the mill,substantially contaminating the workers inside the mill. During periods when bulk loading was3not performed, the bag operator's average dust exposure was 0.17 mg/m . As trucks were loaded3at the bulk loading area, the worker's average exposure increased to 0.42 mg/m due to thiscontaminated air (Figure 8.9). As this study demonstrates, if outside air is used as makeup air, itmust be from a location where the air is not contaminated.Figure 8.9. Increase in a worker’s respirable dust exposure inside amineral processing facility while bulk loading was being performed outside.Personal Dust Exposure from Differences in Job Function Work PracticesDuring an evaluation of four different dust control systems at a mineral processing operation, itwas determined that substantial variations occurred in the respirable dust exposure of twoworkers based upon their personal work practices in performing their same job function. In thiscase, these two workers were loading bags of product on a bag filling machine and thenControls for Secondary Sources 215