Tracer Gas Exposure of Human Subjects Doing Simulated Work at a Benchtop Enclosing Hood in a Wind Tunnel

Local exhaust ventilation devices (LEV) are critical in protecting workers from harmful airborne contaminants. The aim of this study is to investigate the factors that affect the performance of a benchtop enclosing hood. A Freon 134ahelium mixture was released from a 9 diameter pie-pan placed on the floor of a 30 high by 36 wide hood at 2 from the hood face. Freon 134a was measured close to the nose and mouth for a simple manikin (unheated and not breathing), a complex manikin (heated and breathing), and ten human subjects at different times while they stood at the face of the hood in a wind tunnel. Air was drawn from probe openings at the manikin and human subjects\u27 faces at 0.20 lpm into 5 liter sampling bags for 20 minutes each. In a factorial study design, the manikins and the human subjects were tested at hood face velocity (Vface) levels from 100 to 220 fpm and wind tunnel cross-draft velocity (Vcross ) levels from 14 to 63 fpm. The temperature difference (Delta T) between the subject\u27s body and the environment was also recorded.;The results show that Vface plays an important role on subjects\u27 exposure. In general, the exposures decreased as Vface increased. A statistically significant effect (p \u3c 0.001) of Vface on log-transformed exposure at the nose and mouth (log Cnose and log Cmouth) was found for both the simple manikin and the human subjects; in contrast, this effect was only found on log Cmouth for the complex manikin. Cross draft velocity (Vcross) showed a highly significant effect (p \u3c 0.001) on log Cnose and log Cmouth for the simple manikin. However, for the complex manikin and the human subjects, Vcross presented no significant effects (p \u3e 0.05) on exposures (log Cnose and log Cmouth). In addition, Delta T showed no statistically significant effect on log C nose and log Cmouth (p \u3e 0.90) for either the complex manikin or the human subjects. At low Reynolds numbers (\u3c 7000), Cnose increased as Delta T increased.;For this study, it was observed that the distance between the breathing zone and the face of the hood had a large impact on exposure. Exposures dropped dramatically for the complex manikin and the humans (Cnose = 0.0 ppm) when the subjects\u27 breathing zones were just outside of the hood face. For the human subjects, the exposure increased radically from tests where the subject aligned with the hood face (Cmouth = 2.8 ppm) to the back of the head face location (Cmouth = 93.3 ppm). In addition, the human subjects\u27 body dimensions such as height, weight, and width of the shoulders had a highly significant effect on exposure (p \u3c 0.0001). The comparisons of the results between each of the manikins and the ten human subjects found that the two manikins did not differ significantly from the three human subjects with greatest exposures and were not consistently different from each other