working with radioisotopes, perchlorate, and pathogens. Height-adjustable fume hoods without base cabinets are available for ADA compliance.

Ductless Fume Hoods. Many academic institutions are investigating and starting to use ductless fume hoods in their undergraduate teaching laboratories. Technically, they are not fume hoods because they do not exhaust air from the enclosure to the outside. There is currently insufficient information to recommend them as substitutes for ducted fume hoods (NRC, 1995, p. 185).

Special Ventilation Devices

The laboratory fume hood is the most commonly used device for removal of odors and vapors from a laboratory building, but other devices are also used. Canopies are used to ventilate odors from weighing activities at a balance, ozone and other toxins from plasma emission spectrometers, and excess heat from an oven or other equipment. The exhaust from many instruments, such as gas chromatographs and atomic absorption instruments, should be exhausted from the laboratories. For many instruments, the exhaust venting can be accomplished with a small flexible duct from the instrument to a larger building or fume hood exhaust duct. Numerous special ventilation requirements of instruments and common laboratory activities are frequently overlooked in the planning and design of laboratory facilities.

Laboratory Utility Services

Utility services must be provided to each laboratory. These are discussed in detail in the section "Building Services" below in this chapter.

Laboratory Casework, Furniture, and Bench Tops

Laboratory casework includes cabinets of various configurations above and below the laboratory bench. Casework comes in several different types including built-in, modular, and freestanding. Built-in cabinets below the laboratory bench typically support the bench top. Modular casework is constructed as a system of modular units typically composed of a supporting frame that independently supports the laboratory bench, upper and lower bench cabinets. Some modular casework systems also integrate the laboratory services. A ventilated reagent cabinet adjacent to a hood can be substituted for similar under-hood cabinets. The modular design has a slight initial cost premium but provides substantial savings for organizations that frequently reconfigure laboratories. The modular system allows bench heights to be changed from a standing (36 inches) to a sitting (30 inches) height without major renovations. Base cabinets can also be changed without major disruption to the laboratory.

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