The hands of the operator must never come between the HEPA filter and the object.Ī biological safety cabinet, CAI, and CACI also use vertical unidirectional airflow to provide an ISO class 5 environment and are other examples of PECs.įigure 5-2. In horizontal laminar flow, an object or the hands of the operator must not be in back of another object. In vertical laminar flow, an object or the hands of the operator must not be above an object in the hood. Working in vertical laminar flow requires different techniques than does working in horizontal laminar flow. However, the air is blown down from the top of the workstation onto the work surface, not across it ( Figure 5-2). The vertical laminar flow workbench (VLFW) works like an HLFW in that the air is drawn in through the prefilter and is pressurized in the plenum for distribution over the HEPA filter. Inside the HLFW is an ISO class 5 area (class 100 area). Unidirectional flow is airflow moving in a single direction in a robust and uniform manner and at sufficient speed to sweep particles away from the critical processing area. The term unidirectional flow has taken the place of laminar flow in more recent publications. Laminar flow is the air in a confined space moving with uniform velocity along parallel lines. Air is pressurized here and distributed over the HEPA filter. The plenum of the hood is the space between the prefilter and the HEPA filter. Illustration courtesy of the University of Tennessee Parenteral Medications Lab.
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