Abstract:
Although enclosing hoods are often deemed the most effective type of hoods for industrial processes, there is little published research concerning enclosing hoods that are suitable for industrial conditions. Studies of laboratory hoods suggest that face velocity and the presence of a worker mannikin affect the level of contaminant reaching the face of the hood. No similar studies have been done with industrial hoods.
The main objective of this study was to investigate the effect of face velocity, mannikin position, and flange angle on exposure to a mannikin standing at the face of an industrial hood.
Exposure to the breathing zone of the mannikin was greatest at the lowest face velocity and decreased as velocity increased. At velocities higher than 100 feet per minutes exposure to the mannikin was indistinguishable from background levels for most conditions tested. At velocities lower than 100 fpm other variables assumed discernable importance. Exposure was higher to the mannikin in the bent position (leaning forward, hands beside the diffuser) than hen the mannikin stood straight up with its aRMS straight down. Flange angle was significant at velocities lower than 100 fpm, but its effect on exposure was confounded with another factor, the gap between the mannikin torso and the edge of the flange. At low face velocities, exposure increased greatly with decreasing distance between the source and the face of the hood.