Fire ventilation

In buildings erected
during the 1960s it is
common to fi nd outlets,
or inlets and outlets.
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Mechanical ventilation systems
Mechanical ventilation systems can designed as:
• Supply air systems. Fans supply air through the ventilation
ducts. The exhaust air is pressed out through gaps
in the room or to adjoining rooms. The system creates
positive pressure in the fi re compartments.
• Exhaust air systems. Fans suck out air through the
ventilation ducts. The supply air is drawn in through
gaps in the room or from adjoining rooms. The system
creates negative pressure in the fi re compartments.
• Closed supply and exhaust air systems. Fans connected
to the rooms, supply them with both supply air and
exhaust air through ventilation ducts.
• Open supply and exhaust air systems. Fans connected
to the rooms, supply them with both supply air and
exhaust air through ducts. The exhaust air is also
allowed to fl ow through gaps both to the surroundings
and to adjoining rooms.
Normally the spread of fi re gases to adjoining rooms in the
building would be on a small scale, as long as the mechanical
ventilation systems are in operation. If all, or parts of
the mechanical ventilation systems stop working, this can
strongly contribute to the spread of fi re gases in buildings.
This can be a problem, especially in the case of open and
closed supply and exhaust air systems, since the different
fi re compartments are often linked through ventilation
ducts. As a rule the spread of fi re gases (and also smells