Flow and Performance of an Air-curtain Biological Safety Cabinet

摘要

Using laser-assisted smoke flow visualization and tracer gas concentration detection techni-nques, this study examines aerodynamic flow properties and the characteristics of escape fromncontainment, inward dispersion, and cross-cabinet contamination of a biological safety cabinetninstalled with an air curtain across the front aperture. The experimental method partially sim-nulates the NSF/ANSI 49 standards with the difference that the biological tracer recommendednby these standards is replaced by a mixture of 10% SF6 in N2. The air curtain is set up acrossnthe cabinet aperture plane by means of a narrow planar jet issued from the lower edge of thensash and a suction flow going through a suction slot installed at the front edge of the work sur-nface. Varying the combination of jet velocity, suction flow velocity, and descending flow velocitynreveals three types of characteristic flow modes: ‘straight curtain’, ‘slightly concave curtain’,nand ‘severely concave curtain’. Operating the cabinet in the straight curtain mode causes thenair curtain to impinge on the doorsill and therefore induces serious escape from containment.nIn the severely concave curtain mode, drastically large inward dispersion and cross-cabinetncontamination were observed because environmental air entered into the cabinet andna three-dimensional vortical flow structure formed in the cabinet. The slightly concave curtainnmode presents a smooth and two-dimensional flow pattern with an air curtain separating thenoutside atmosphere from the inside space of the cabinet, and therefore exhibited negligiblynsmall escape from containment, inward dispersion, and cross-cabinet contamination.