Engineering Controls Database
Dust Protection for Bag Stackers
| Mineral processing plants in the United States process material that is finely ground and placed into bags for shipping to the consumer. These bags normally range from 50 to 100 pounds in weight. Once the material is placed in these bags, a worker, known as a bag stacker, loads the bags onto pallets. A bag stacker is exposed to dust that is mainly released by the force from loading the bag onto the pallet. The two main sources are the dust on the outside of the bag and the dust that escapes from inside the bag as it is loaded. | |
| The main hazard of exposure to mineral dusts is pneumoconiosis. When very fine dust particles are breathed, they can accumulate in the lungs, and this can result in disease. Tissue reactions such as fibrosis, or scarring, of lung tissue can result from the inhalation of certain dusts. The Mine Safety and Health Administration's (MSHA) records indicate the bag stacker's dust exposure is one of the highest of all workers at mineral processing operations. | |
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MSHA regulations require that exposures for airborne contaminants including respirable dust and total dust be controlled insofar as feasible, by prevention of contamination, removal by exhaust ventilation, or by dilution with uncontaminated air. Personal respirator protection is not acceptable except when engineering controls are being developed or for occasional entry into hazardous atmospheres to perform maintenance or investigation. This NIOSH study [NIOSH 2001] dealt with controlling the bag stacker's dust exposure during use of a semi-automated palletizing machine. The worker slides the bags into position on the palletizing machine. Once an entire layer of bags is positioned, the bag stacker operates the controls on the palletizing machine to lower the layer of bags onto the pallet. An air slide is built into the semi-automated palletizing machine so the bags are easier to move. This slide uses a metal table with air jets that exit through small holes at high velocities, similar to an air hockey game. The dust problem occurs because the air slide causes dust to blow up onto the bag stacker, significantly increasing the dust exposure. NIOSH researchers believe that all operators using this type of semi-automated palletizing system need to be aware of the serious dust contamination that can occur to the bag stacker from the air slide. To control high dust exposures from air slides on semi-automated palletizing units make the following modifications (Figure 1): • Use an exhaust ventilation system with an effective hood design to capture the dust generated during the bag stacking process. The exhaust hood should be modified to make it physically impossible for the bag stacker to place his/her upper torso into the hood (Figure 2). • Use an overhead air supply island system (OASIS) to provide an envelope of clean air over the bag stacker. • Place plastic stripping around the OASIS to provide a boundary of the clean air from the system. • Modify the bag stacker's work practices to have the worker stay within the envelope of clean air provided by the OASIS.   |
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Cecala A, Zimmer J, Smith B, and Viles S [2000]. Improved dust control for bag handlers. Rock Products (4) 2000:46-49. NIOSH [2001]. Hazard control. Dust protection for bag stackers. Cincinnati, OH. U.S. Department of Health and Human Services, Public Health Service, Center for Disease Control and Prevention, National Institute for Occupational Safety and Health. DHHS (NIOSH) Publication 2001-142. |
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bag stackers bag stackers mineral processing mineral processing pneumoconiosis pneumoconiosis |
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| Testing was repeated after the suggested modifications were made to the semi-automated palletizing system. The testing showed that the changes to the system had minimized the impact of air slide contamination to the bag stacker. Three product sizes of mesh bags were evaluated. No increase was found in the bag stacker's dust exposure with two of the products, and only a very slight increase was found with the other product. The changes made to the bag palletizing process accounted for the reductions of the bag stacker's respirable dust exposure to MSHA-acceptable dust concentrations. |