Fire ventilation

Outlets should be placed where the temperature ishighest, i.e. as high as possible.The size and development of the fire (temperature ofthe smoke) and the size of the room are critical for thedetermination of the size of outlets, but 4–8 m 2 canserve as a guideline, with smaller sizes for smallbuildings and larger sizes for large or very largeindustrial buildings.Creating openings in structures takes a long time.It can often be better to make a number of smalloutlets instead of a few large openings.InletsFire ventilation is often associated with making openings tovent out fire gases. Nevertheless it is equally important, ifthe gases are to be vented out at all, that there are inletswhere air can flow in and replace the gases that flows out.It can often be more difficult to make inlets than outlets.In general inlets should be below the layer of fire gases, i.e.level with or below the fire, since hot air rises upwards andfresh air should then be filled from underneath. For practicalreasons the supply air often needs to be arranged at agood distance both from the fire and the outlets. In certaincases outlets in the form of vents in the roof can be used asinlets. This assumes, however, that the vents are placed onthe roof to adjacent rooms that are not directly exposed tothe fire or fire gases, and that there are internal openingsbetween these rooms and the rooms exposed to the fire.Since fire gases consists for the most part of fresh air thathas been supplied to the fire, heated up and expanded, thesize of the inlets in relation to the outlets will be an approximateratio of 1:1 to 2:1, i.e. inlets should be at least as largeas and up to twice as large as outlets. An attempt to makeeven larger inlets would normally have no significance. Sinceroom divides, openings between rooms and the positioningof interior furnishings, limit the flow of the air, it is51