Improving Aerodynamics and Operator Protection Performance of Biological Safety Cabinet Subject to Dynamic Influences

摘要

Because the performance of conventional class II biological safety cabinets (BSC) is easily affected by the influences of dynamic motions such as when a person walks by, sash movements, and operator hands movements, this study applies an "air-curtain" technique to BSC and tests its effectiveness in reducing the influences of dynamic motions. The air-curtain is set up across the cabinet aperture plane by having a planar jet and suction flow go through the sash nozzle and installing the suction slot at the work surface, respectively. The aerodynamic characteristics were diagnosed by using the laser-light-sheet-assisted smoke flow visualization method, and the containment performance was measured by using the tracer-gas leakage concentration method. By adjusting the jet and suction flow velocities in the appropriate regime, the flow field displays characteristics of smoothness and two dimensionality. Results of tracer-gas concentration measurement under the static situation show that cabinets both with and without air-curtain had almost no leakage. However, when the cabinet was operated under the influences of dynamic situations, as are encountered mostly in the practical uses of BSC, the leakage levels of the cabinet without air-curtain are significantly raised. For instance, the leakage concentration of a walk-by test in the no air-curtain case can be higher than 150 ppb, whereas BSC with air-curtain shows almost no leakage. The biological safety cabinet installed with the air-curtain therefore was effective in reducing the influences of dynamic motions.