Local ventilation for powder handling: Combination of local supply and exhaust air

The performance of a modified local ventilation unit equipped with local supply and exhaust ventilation was evaluated during the manual handling of flour additive powder. The investigation tested 5 different configurations to study the effects of the exhaust opening location and local supply air on worker exposure. The measurements were done under controlled conditions in a test room. The breathing zone (BZ) dust concentration was measured by gravimetric sampling and real time monitoring. The different local ventilation configurations were also modeled numerically using computational fluid dynamics. Without local ventilation the average BZ dust concentration was 42 mg/m super3. With local exhaust only the exposure was reduced below 1 mg/m super3. The addition of local supply air further reduced the exposure to below 0.5 mg/m super3. The lowest results were achieved by locating 2 exhaust openings on either side of the contaminant source combined with local supply air.