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Impact of Class II Biosafety Cabinet Downflow Velocity on Cross Contamination

Background

Over the last several years, Biological Safety Cabinet (BSC) manufacturers have lowered downflow velocity while maintaining inflow velocity in an effort to increase energy efficiency, reduce exhaust system requirements and lower BSC Noise and vibration levels. However, the lowering of downflow velocity may come with a consequence of greater lateral airflow movement within the workzone creating greater potential for cross contamination. The lowering of the downflow velocity does not compromise personnel and product containment performance. Why? Primarily, by maintaining inflow velocity above a certain level as required by the standard, typically 100 fpm (.51 mps). However, the standard does not require a specific downflow velocity and can be adjusted as needed based on the design parameters of the workzone supply diffuser and grill patterns (airflow distribution) to assure compliance to the personnel and product protection requirements of NSF/ANSI 49. NSF/ANSI 49 test procedures do test for cross contamination, but only at the workzone sidewalls, which doesn’t necessarily translate into the lateral movement of airflow in the center of the workzone. The result of these lower downflow velocities may be a greater level of sample cross contamination using traditional work practice guidelines.