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A recent report evaluating silica exposure levels in the metal/nonmetal mining industry noted that bag packaging and loading are some of the occupations at the greatest risk. In addition to dust problems, the bag-stacking process is labor intensive, making lost-time injuries common due to back fatigue and strains. During the bag-stacking process, a significant amount of dust can be generated, mainly from product on the outside of the bags and from dust escaping the bag valve upon impact of the bag on the pallet. In an effort to address dust-exposure and back-fatigue issues, Malvern Minerals Co., Hot Springs, Arkansas, made two major improvements to its ground silica stacking facility. First, the company purchased a semi-automated bag palletizing system (Figure 1). With this system, the bag stacker does not lift the bags, but slides them across a metal table. Small jets of air exit through perforations in the table top (similar to an air hockey game), allowing workers to more easily slide each bag into the proper position. After each layer of bags is completed, the table slides open, and the entire layer of bags is loaded onto an underlying pallet. The table then closes, readying it for another layer of bags. After the entire pallet is loaded, the unit delivers the pallet to a shrink wrap and forklift pick-up area. In addition to this semi-automated palletizing unit, Malvern Minerals purchased an Overhead Air Supply Island System (OASIS) to lower the bag stacker's dust exposure. The OASIS takes outside air, directs it through two filters, then delivers clean air down over the bag stacker. During tests, approximately 1,600 cfm of filtered air exited the OASIS. Based on tests and modifications of Malvern Mineral's bag-palletizing operation, the following changes may help lower bag-stacker dust exposure at operations using similar equipment: * If semi-automated palletizing units are used with an air slide, make sure the air slide is not blowing dust up onto the worker. Using the OASIS in conjunction with the semi-automated palletizing unit is effective, but the OASIS device must be positioned to cover the entire range of motion for the worker. If the unit was properly positioned at Malvern Minerals, it probably would have eliminated most of the problems initially encountered. * If using a semi-automated palletizing system in conjunction with an OASIS system, consider using plastic stripping around the OASIS discharge. This helps separate the clean air from the dust-laden air around the palletizing unit and gives the worker a physical indication of when he or she is extended out past the end of the clean-air zone. * Never use an exhaust hood that creates a need for a worker to place his upper torso (breathing zone) into the hood to perform a job function. Additionally, workers should not position themselves between the dust source and the exhaust hood. This causes the dust to flow directly past the worker and significantly increases worker contamination and dust exposure.
| Author(s): | Cecala-AB, Zimmer-JA, Smith-B, Viles-S |
| Reference: | Rock Products 2000 Apr 103(4); :46-49 |
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