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Book - School of Science and Technology

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352 VentilationCapSuction b<strong>and</strong>Louvre ringStack louvreWind baffleStackFigure 13.4 Robertson's ventilatorFigure 13.5 Colt type MF ventilatortimes when no ventilation is required, <strong>and</strong> a weather cap, shown in the right-h<strong>and</strong>diagram, which may be opened similarly when a completely unobstructed outlet isnecessary. Such units are manufactured to provide outlet areas <strong>of</strong> between about 0.8<strong>and</strong> 2.5 m 2 . Any natural ventilators in the ro<strong>of</strong> can <strong>of</strong>fer the considerable advantage <strong>of</strong>providing smoke venting in the event <strong>of</strong> fire by encouraging rapid clearance <strong>of</strong> smoke. Ifsmoke venting is the primary purpose then the ventilators should comply with BS 7346.On an industrial scale, inlets for natural ventilation may well present a problem because<strong>of</strong> their size <strong>and</strong> possible proximity to those operatives who may not be affected directlyby excessive heat. Wall openings, provided with louvres as Figure 13.6, may be acceptable

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