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Ventilated hoods designed to confine and exhaust materials that may be flammable, irritating, corrosive, toxic, or otherwise noxious. These enclosures typically consist of a plastic or metal cabinet-like structure with an open front for handling of products; they typically include a sash to regulate the front opening, blowers to produce an inward flow of room air into the hood, and an exhaust system. Most hoods exhaust the contaminated air to the outside, but some hoods filter the air and recirculate it into the room. These hoods may work either at a constant air volume (either conventional type or by-pass type and its variations, auxiliary-air and reduced-air subtypes) or less frequently at a variable air volume (generally operate as conventional hoods). Fume hoods are intended to remove fumes as well as vapors, gases, mists, aerosols, and other particulate materials, reducing workers exposure; they offer some protection against accidental releases, minor fires, and explosions. Chemical fume hoods are mainly used for manipulation of chemicals in open containers and/or as a secondary containment for chemical laboratory equipment; dedicated fume hoods are manufactured for particular applications such as distillation and handling radioactive materials or perchloric acid. Chemical fume hoods are not biological safety enclosures; they should not be used when handling infectious or potentially infectious materials.
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