An evaluation of the effectiveness of a recirculating laboratory hood

Ductless, benchtop hoods have become a popular tool for use in the control of toxic substances in the laboratory. Low price and ease of installation are major factors contributing to their increased utilization. Little objective performance data exist for these devices. One such hood was evaluated for efficacy as an engineering control in typical laboratory applications. Face velocity, flow profile, ability to retain vapors, sorptive capacity of the filter media and overall worker protection were evaluated. The manufacturer's report of an average face velocity of 30.6 cm/s (60 fpm) proved to be accurate; however, this value was found to be substandard when compared with the hood and room design criteria which must be met for this rate to provide adequate control. The hood was designed in a manner which prevented smooth flow through the hood and increased observed turbulence and rolling. The sorptive capacity of the carbon filter proved to be comparable to that reported for organic vapor respirator cartridges. Design deficiencies are discussed to improve protection offered to the worker in an as-used situation. Further work is needed to provide a quantitative measure of the protection offered by these hoods.