Fire ventilation

Outlets should be placed where the temperature is
highest, i.e. as high as possible.
The size and development of the fi re (temperature of
the smoke) and the size of the room are critical for the
determination of the size of outlets, but 4–8 m 2 can
serve as a guideline, with smaller sizes for small
buildings and larger sizes for large or very large
industrial buildings.
Creating openings in structures takes a long time.
It can often be better to make a number of small
outlets instead of a few large openings.
Inlets
Fire ventilation is often associated with making openings to
vent out fi re gases. Nevertheless it is equally important, if
the gases are to be vented out at all, that there are inlets
where air can fl ow in and replace the gases that fl ows out.
It can often be more diffi cult to make inlets than outlets.
In general inlets should be below the layer of fi re gases, i.e.
level with or below the fi re, since hot air rises upwards and
fresh air should then be fi lled from underneath. For practical
reasons the supply air often needs to be arranged at a
good distance both from the fi re and the outlets. In certain
cases outlets in the form of vents in the roof can be used as
inlets. This assumes, however, that the vents are placed on
the roof to adjacent rooms that are not directly exposed to
the fi re or fi re gases, and that there are internal openings
between these rooms and the rooms exposed to the fi re.
Since fi re gases consists for the most part of fresh air that
has been supplied to the fi re, heated up and expanded, the
size of the inlets in relation to the outlets will be an approximate
ratio of 1:1 to 2:1, i.e. inlets should be at least as large
as and up to twice as large as outlets. An attempt to make
even larger inlets would normally have no signifi cance. Since
room divides, openings between rooms and the positioning
of interior furnishings, limit the fl ow of the air, it is
51