Fume Hood Performance: Slot Settings and Containment Testing

Abstract

Fume hoods are provided with adjustable upper, lower, and sometimes middle slots. Slot adjustments affect the fraction of air exhausted through the different slots, which in part can determine the concentration of contaminants in different strata within the hood. Since fume hoods are used to contain particulate aerosols and chemical vapors, dioctylphthalate (DOP) and sulfur hexafluoride were used as surrogates to evaluate the effect of slot settings and sash heights on aerosol and vapor containment. While slot position had little effect on the release of sulfur hexafluoride outside the fume hood, opening the upper slot from 1.25 cm (0.5 inches) to 5 cm (2 inches) increased the release of DOP tenfold to thirtyfold depending on sash height. In a variable air volume hood, lowering the sash height decreased the total volume of air exhausted and increased the contaminant (DOP) concentration inside the fume hood. A narrow upper slot and wide lower slot were found to be optimal, while the practice of lowering fume hood sashes below 30 cm (12 inches) was questioned. DOP was found useful as an alternative approach for evaluating fume hood containment.