|
U.S. Department of Labor | |
||||
| Occupational Safety & Health Administration | ||||||
 |
| Safety and Health Topics > Mineral Processing Dust Control > Reducing Dust Exposure | ||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||
2Mining engineer technician. 3Supervisory physical scientist. Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA
Abstract Introduction Laboratory-scale testing Laboratory-scale results Field testing Discussion Cost considerations Conclusions Appendix.--Curtain evaluation
1. Product leakage from bag valve while on conveyor 2. Laboratory test setup 3. Fan directions and locations used for blowing system tests 4. Dust monitoring locations used for field evaluation 5. Ventilation system used for test 2 6. Ventilation system used for test 3
1. Average concentration from four sampling locations during laboratory testing 2. Dust reductions of field testing exhaust ventilation systems A-1. Effect of blowing ventilation system with and without curtain
The Bureau of Mines has evaluated a number of ventilation systems for potential application in lowering the dust exposure of workers who stack bags of mineral product material in enclosed vehicles. Workers who stack these bags in enclosed vehicles usually have the highest dust exposure among all workers in processing plants. This is because dust liberated while the vehicle is being loaded has no means of exiting the vehicle or being diluted with fresh air and thus, dust concentrations increase to substantial levels. Laboratory-scale testing was performed in a railcar to compare the effectiveness of a number of different ventilation systems in reducing the bag stacker's dust exposure. The most effective system was taken into the field to optimize its performance. The final and recommended system exhausted about 2,000 cfm through 10-ft-long, 12-in diam fiberglass tubing located 3.5 ft past the slinger at a 6.5-ft height so as to not interfere with the bag stacker's job. A 6-in-diam tube exhausted approximately 300 cfm at the snake conveyor-slinger transfer point to capture the dust generated there. With this system, dust reductions in and around the bag stacker ranged between 65 and 95 pct when loading both 50- and 100-lb bags of product into railcars and trailer trucks.
This report describes work the Bureau of Mines performed to determine a cost-effective system for ventilating enclosed vehicles as they exist today. Laboratory-scale testing was performed to determine the most effective system. This system was then tested at a mineral processing plant to optimize the technique in a working environment and to determine its effectiveness in lowering dust concentrations in enclosed vehicles during loading of bagged mineral product material. Many mineral products are packaged in 50- or 100-lb paper bags. These bags are shipped to the customer on pallets, either in railcars or trailer trucks. Bags are either loaded by full pallets using a forklift, or directly by workers inside the vehicle, using a snake conveyor. The latter case is discussed in this report. Loading bags directly into enclosed vehicles is advantageous because it eliminates the forklift and operator. However, it is disadvantageous from a health standpoint because of the dust exposure to the stackers. With direct loading, the bags travel down a flexible snake conveyor before passing into a device called a slinger, which can be raised and lowered to a convenient height for the workers unloading the bags. The stackers then take the bags from the slinger and hand-stack them onto pallets. Except for minor effects owing to outside wind currents, there is no ventilation inside these vehicles. Any dust generated during the conveying and loading process remains within the vehicle and builds to substantial levels. This can become a serious health problem. The dust generated during loading can come from a number of different sources; the two main sources are product on the outside of the bag and leakage from the bag valve. Product on the outside of the bag is due to blowback (dust created as air and product are forced out of the bag as a result of excess pressure release from around the fill nozzle during filling); the "rooster tail" of product from both the fill nozzle and the bag valve during ejection from the filling machine, and product on the conveyor belt. Leakage from the bag valve occurs from movement on the conveyor as the bag travels to the loading area. This leakage can be substantial at conveyor transfer points and during the pallet loading process (fig. 1). |
||||||||||||||||||||||||||||||||||
 Back to Top
 www.osha.gov
|
www.dol.gov | |
|
Contact Us | Freedom of Information Act | Information Quality | Customer Survey Privacy and Security Statement | Disclaimers |
||
| Occupational Safety & Health Administration 200 Constitution Avenue, NW Washington, DC 20210 |
|
|
