Base Cabinets. Storage cabinets for flammable solvents and for acids are commonly placed beneath the fume hood, a convenient location because the solvents and acids are routinely dispensed in the fume hood. In addition, such storage cabinets frequently require connection to the exhaust air system. Base cabinet drying ovens are occasionally used but may pose a safety risk because of the location of a heat source in an area where flammable-solvent vapors may be present. Fume hoods with no base cabinets may be used to comply with ADA requirements.

Construction Materials. Fume hood construction materials should be selected for durability and suitability for the required task. The construction materials, types of finishes and surfaces, and the type of research all need to be considered. Epoxy-coated metal is typically used for fume hood and base cabinet enclosures. Nonferrous fume hood enclosures are also available for specialized research applications. The interior cabinet enclosure is typically made of an inert, nonflammable, nontoxic, synthetic material. The working surface is typically molded epoxy resin or stainless steel.

Location in the Laboratory. Although experts may disagree on the best location for a fume hood in the laboratory, all agree that the fume hood should be located so as to minimize researcher movement in front of the fume hood. The movement of people and equipment creates eddy currents of air, which decrease the efficiency of the fume hood and can expose the passerby to potentially harmful vapors drawn from the fume hood. Fume hoods should be located away from doors because doors also can create eddy currents. In the event of an accident in the fume hood, one located by the door could block the primary path of egress from the laboratory. A dual-egress design for all laboratories can minimize this problem.

Face-to-face configurations of fume hoods should be avoided due to complex air currents that may be generated by two opposing fume hoods. If a face-to-face arrangement is required, the minimum dimension separating the fume hoods should equal the length of the fume hood but should not be less than 5 feet. Fume hoods should be located as far from researcher desks as is reasonably possible. Beneficial air currents can be created if makeup air (for description see "Exhaust and Makeup Air" below in this chapter) is delivered at the end of the laboratory opposite the fume hoods.

In some research disciplines and for some laboratory activities, such as solvent distillations, researchers prefer that the fume hood be isolated in a room separate from the primary laboratory.

Special Characteristics. Many different, highly specialized fume hoods, such as explosion proof, corrosive resistant, or with filtered exhaust, are manufactured either on a routine or custom basis. Special fume hoods are required when

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