Dust Control Handbook for Industrial Minerals Mining and Processing

epetitive dust leaks should not simply be, "patched," but rather, the underlying cause should bedetermined and corrective action taken to both fix the leak and prevent future reoccurrences.Each process or function within mineral processing operations should have a Standard OperatingProcedure (SOP) that includes routine inspections, maintenance, and cleaning schedules. Whenequipment is cleaned and maintained on a routine basis, it can have a significant impact onminimizing dust liberation and generation.TOTAL STRUCTURE VENTILATION DESIGNThe first strategy to lower dust exposures in any structure is to have an effective primary dustcontrol plan that captures major dust sources at their point of origin, before they are allowed toescape out into the plant and contaminate workers. Most mineral processing plants control thedust by using standard engineering controls such as local exhaust ventilation systems, waterspray applications, scrubbers, and electrostatic precipitators (refer to Chapter 1—Fundamentalsof Dust Collection Systems). These engineering controls are effective at reducing and capturingthe dust generated and liberated from the primary sources at mineral processing plants; however,they do not address the continual buildup of dust from background sources, such as thefollowing:product residue on walls, beams, and other equipment which becomes airborne fromplant vibration or high-wind events;product that accumulates on walkways, steps, and access areas, and which may bereleased as workers move through the plant and by plant vibration;leakage or falling material from chutes, beltways, and dust collectors;lids and covers of screens that are damaged or when they are removed for inspection andcleaning; andproduct released because of imperfect housekeeping practices.Since most mineral processing structures can be considered closed systems, the background dustsources stated above, along with numerous other unnamed sources, can cause dust concentrationsto continually increase as the day or shift progresses inside these closed buildings. In order tokeep dust levels at safe and acceptable levels, a method needs to be used to control thesebackground dust sources. The most effective way to achieve this is to use a total structureventilation system.PRINCIPLES OF TOTAL STRUCTURE VENTILATIONThe basic principle behind the total structure ventilation design is to use clean outside air tosweep up through a building to clear and remove the dust-laden air. This upward airflow isachieved by placing exhaust fans at or near the top of the structure and away from plantpersonnel working both inside and outside the structure. The size and number of exhaust fans isdetermined based upon the initial respirable dust concentration and the total volume of thestructure. It must be noted that all the processing equipment within a mill generates heat and thisproduces a thermodynamic "chimney effect" that works in conjunction with the total structure210 Controls for Secondary Sources