Dust Control Handbook for Industrial Minerals Mining and Processing

to be pulled directly back into the ventilation system and over the operator's breathing zone. Amore effective design is to draw the recirculated air from the bottom of the enclosure, away fromthe worker's breathing zone.Generalized Parameters for an Effective SystemThe key for an effective retrofit enclosed cab filtration and pressurization system is to balancethe various components and factors. Obviously, if one is dealing with hazardous dust, the designshould be directed to the higher efficiency range. On the other hand, if one is dealing with moreof a nuisance dust, a lower range value can be chosen.Figure 9.7. Airflow pattern for intake and return at roof of cab and uni-directional airflow design.Table 9.3 shows a summary of the impact of the various critical components to an effectivefiltration and pressurization system. This table presents the calculated PF using the mathematicalmodel derived from the laboratory study (Equation 9.2). In this table, the same componentparameters have been chosen from the previous examples, being: intake air quantity (Q I ) of50 cfm, recirculation system (Q R ) of 300 cfm, a recirculation filter efficiency (η R ) of 0.7(70 percent), an intake filter efficiency (η I ) of 0.95 (95 percent), and leakage (l) of 0, 5 percent,10 percent, and 15 percent (l = 0, 0.05, 0.10, 0.15).Operator Booths, Control Rooms, and Enclosed Cabs 237