Fire ventilation

Fans can during positive
pressure ventilation (or
during the pressurising
of adjacent rooms) be
placed side by side (in
parallel) to achieve a
larger volume fl ow of
air, or to cover larger
openings, for example
doorways. The pressure
and volume fl ow
increase considerably.
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than fans powered by an internal combustion engine.
Nevertheless, the fl ow through the fi re room depends on
the geometry of the room, the size and positioning of the
outlet, the position of the fan, and the amount and positioning
of the interior furnishings.
To prevent fi re gases penetrating out through an inlet it
is important for the air fl ow to cover the whole, or as much
as possible, of the inlet. For normal openings (apartment
doors or doors to stairwells) the distance should be approximately
1 –3 metres, depending on the type and size of the
fan. It is relatively simple to fi nd a suitable distance by trial
and error, both during training exercises and fi re and rescue
operations. It can, however, be diffi cult to cover the opening
without losing a lot of the air fl ow.
It is often of little importance, however, if fi re gases is
allowed to fl ow out, for example out into a stairwell. The
fan can be placed in the middle of the opening so that as
much as possible of the air fl ow will go into the fi re area, on
the assumption that it does not obstruct the work of the fi re
fi ghting crew.
During positive pressure ventilation it is possible to place
fans in parallel, i.e. beside each other, to achieve a greater
pressure and a greater volume fl ow, or to cover large inlets,
for example a garage door.
Fans can also be placed in series, i.e. after each other.