Reducing Bag Operator's Dust Exposure in Mineral Processing Plants

Abstract

Abstract The Bureau of Mines has been investigating various techniques to reduce dust exposures of workers at mineral processing plants. A major problem has been the exposure of the bag operator who loads mineral product into 50- or 100-pound bags at a fill station. In many cases, this worker has the highest dust exposure of the entire plant. In the past few years, the Bureau has investigated several approaches that can significantly lower bag operator dust exposure. These include bag valve modification, dual bag nozzle system, overhead air supply island (OASIS), and control of background dust sources. Five commercially available bag-filling valves were evaluated to determine their dust reduction capabilities. An extended polyethylene valve was found to be the most effective, resulting in a 62 percent reduction in operator dust exposure as compared to the standard paper valve. A dual bag nozzle system was developed that decreases product loss and significantly lowers the operator's exposure. With this system, one nozzle fills the bag, and the other nozzle exhausts excess air when filling is complete. An improved bag clamp reduces products blowback during filling, thus reducing product accumulation on the outside of the bag. The system reduces operator exposure up to 83 percent as well as significantly lowering the subsequent exposure of workers stacking the bags onto pallets. The OASIS is placed over the operator's location at the fill station and delivers an envelope of clean air over the worker that has reduced workers' dust exposures 82 to 98 percent. The number of background sources were observed to significantly contaminate the bag operator and could cause his exposure to exceed the permissible eight-hour limit in a short period of time. To keep this exposure below the permissible limit, these background sources must be identified and controlled.