Reducing workers' dust exposure during bag stacking in enclosed vehicles.

The Bureau of Mines has evaluated cost effective systems to ventilate enclosed vehicles being loaded directly with bagged product material at mineral processing plants. This evaluation included both forms of transportation: railcars and trailer trucks. The goal of this research was to lower the dust exposure of workers stacking bags in these enclosed vehicles; these workers usually have the highest dust exposures in the entire processing plant. The problem occurs because there is no mechanical ventilation inside these vehicles. As the vehicle is being loaded, dust concentrations increase to substantial levels because released dust has no means of exiting the vehicle or of being diluted with fresh air. In cases where the dust is hazardous, as with silica sand, this may present a serious health hazard. This research project was a two-step effort. The first step was a qualitative laboratory evaluation performed in a railcar to compare different types of ventilation systems (blowing, exhaust, and push-pull systems) using a methane (CH4) tracer gas technique. An exhaust system located over the snake conveyor was the most effective system at reducing gas levels in and around the bag stacker's work area. The second step then involved a field evaluation at a silica sand processing plant to determine the system's effectiveness in the actual work environment. Three different versions were evaluated in an attempt to optimize the exhaust ventilation system's effectiveness. The most effective version involved exhausting 54.5 m3/min (2000 ft3/min) through a fiberglass tube located 1.1 m past the end of the slinger at a 2.0-m height so as not to interfere with the bag stacker's job function.(ABSTRACT TRUNCATED AT 250 WORDS)