A meta-analysis of fume hood containment studies was conducted to identify the important factors that affect the performance of a laboratory fume hood [Ahn et al. 2008]. An analysis of factors affecting the containment performance of the hoods showed that worker exposures to air contaminants can be greatly impacted by a variety of operational issues. Increasing the distance between the contaminant source and the breathing zone leads to reduced exposure. Exposures can also be reduced by limiting the height/area of the sash opening; increasing the height of the sash opening increased the risk of hood containment failure. The presence of a manikin/human subject in front of the hood caused the greatest risk of hood failure among factors studied. This indicates that containment testing should include an operator or manikin to adequately assess hood performance. Face velocity did not make a significant difference in hood performance unless it was extremely high or low (> 150 ft/min or < 60 ft/min). Several hood operating factors showed an effect but were not statistically significant, including sash movement, hand and arm movement, pouring/weighing, and thermal load.
New fume hoods specifically designed for nanotechnology are being developed primarily based on low-turbulence balance enclosures, which were initially developed for the weighing of pharmaceutical powders. The use of bench-mounted weighing enclosures, as seen in Figure 10, is common for the manipulation of small amounts of material. These fume hood-like LEV devices typically operate at airflow rates lower than those in traditional fume hoods and use airfoils at enclosure sills to reduce turbulence and potential for leakage. They also have face velocity alarms to alert the user to potentially unsafe operating conditions. Based on the hazards assessment, these fume hood-like LEV devices can be outfitted with HEPA filtration or connected to the ventilation exhaust system.
Figure 10. Nano containment hood adapted from a pharmaceutical balance enclosure
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
