The
early detection of fire is vital for any fire-fighting operation.
Smoke and heat detectors capable of detecting fire in their
incipient stages therefore play a vital role. Well-designed
detection systems should be provided in buildings for all
the floors and at all ceiling voids. For cabins of very
small size, heat detectors may be used in view of their
cost-effectiveness. If overall cost is the over-riding criteria,
then detectors must be located at least in the ‘return air’
areas where smoke can be sensed.
The
control panel in the fire alarm system plays an extremely
important role in ensuring the overall effectiveness of the
system. Typically, a building also has its own air-conditioning
system and proper inter-linking must be maintained between
these two systems to prevent fire spreading to other areas.
Perfect matching has to be made in the two systems for this
purpose.
A
recent trend has been to have a separate air-handling unit
(AHU) for every floor. The AHU normally supplies fresh air
to the supply ducts and the return air is circulated through
false ceiling voids, which are used as return air paths. Closing
the dampers located at strategic points within the air-conditioning
system prevents the spread of combustible particles. Arrangements
should also be made to activate fire signals by the provision
of alarm control panels, which start up the exhaust fans.
The control panel must also be provided with a suitable public-address
system so that instructions can be given to the occupants
of the various floors. Evacuation instructions are also transmitted
through this system during emergencies. The ‘All Call’ switch
enables the control room operator to address all floors simultaneously.
The capacity of the amplifier should therefore be suitably
designed.
Fire
in buildings usually start at one place and then spread to
other areas through shafts and other openings. Depending on
the location, quantity and type of combustible materials stored
present in and around such buildings, the fire manifest themselves
in areas rather remote from the original location. It is therefore
very important to establish the origin of fire as, by the
time fire-fighting personnel arrive at the site, considerable
confusion can already have been caused. For this purpose,
control panels must have the feature of indicating and highlighting
zones, which were in operation first. A suitable ‘mimic diagram’
should also be provided along with each control panel to enable
fire-fighting personnel to reach this zone in shortest possible
time. The layout for this must be clear in every respect and
must take into account the fact that the fire-fighting personnel
may be operating in the building for the first time. The control
panels, often referred to as the ‘nerve centers’ of the fire-fighting
systems of buildings, are therefore of crucial importance.
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