Special considerations in the use of vertical laminar-flow workbenches.

The design, operation, and proper use of vertical laminar-flow workbenches are reviewed. Vertical-flow hoods are different from horizontal-flow units in several important ways that must be considered by operators who may have been trained to use the horizontal-flow type. Air in vertical-flow units provides practically no resistance to ingress of air propelled by body motions of the operator or passers-by or from nearby ventilation ducts. The HEPA-filtered air hits the work surface perpendicularly and must travel horizontally to reach the exhaust ducts; thus, manipulations should not be performed close to the work surface. Turbulence patterns around objects in the vertical flow hood will be different from that in horizontal-flow units. Manipulative technique is also different in a vertical-flow hood. Supplies may be arranged to the sides and the back of the area in which manipulations will be performed. Items not sterile, including fingers and hands, must be kept downstream from critical sites. Masks do not have to be worn because of the hood's glass panel. Operators must be cognizant of basic differences between vertical- and horizontal-flow hoods.