Continuous-Flow Bypass For Improved Fume Hood Performance

The "roll " of air which forms inside a fume hood immediately behind the sash can be a reservoir for contaminants. Air recirculates at that location rather than exiting the hood immediately. So contaminant concentrations may be higher in the "roll " than at other points inside the hood. The matter is of some concern, because the roll is close to the breathing zone of the scientist performing the work. The current project investigated a means of reducing the concentration of contaminants directly behind the sash. If this concentration is reduced, any leakage would be less hazardous to workers in the lab. The method, called the continuous-flow bypass, introduces a constant stream of air into the hood above the sash, delivering dilution air directly to the roll. The method reduced contaminant concentration by 50 to 90%, which significantly reduces the hazard potential of any leakage