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FIRE
DETECTION AND ALARM SYSTEM
 Fire
detection systems have increased in complexity and sophistication
as technology has advanced. In particular, the increased computing
power now available through the development of low cost processors
has enabled system designers to improve functionally through
incorporating numerous features and options into the fire
detection system, both in the detector head and in the control
panel.
However,
not all installations will require the ultimate in facilities
and features, and there is still a strong demand for relatively
simple conventional systems.
There
are four elements of a fire system :
a) The Detectors
b) The Control Panel
c) The warning sounders and strobes
d) Ancillary devices such as door closers and fan shut-down
units.
Detectors
fall into two primary types, conventional or analogue.
As a further option in intelligent systems, different manufacturers
have chosen alternative approaches to providing an alarm signal
from the detector.
 Conventional
detectors & analogue sensors differ in their operation & both
need to be matched with a compatible control panel to ensure
correct operation. In both technologies, the full range of
detector types include either ionisation smoke detectors,
photoelectric smoke detectors, fixed temperature detectors
or rate - of - rise temperature detectors.
To
decide between a conventional and an intelligent system, defining
the intended application of the system is first necessary.
If the systems are used in small business environments where
only a few detectors are installed, then the fundamental decision
between a conventional and an intelligent system is relatively
easy to make. Several factors should be considered - the customer
may not need a large number of system features, and the cost
difference between conventional and analogue sensors may increase
the overall system cost appreciably. In such applications,
the requirement can usually be satisfied by a conventional
system.
However,
in medium to large installations where a large number of detectors
are involved, the decision is not between conventional and
intelligent system per se, but between the two alternative
approaches to providing intelligence.
Conventional
Detectors
When
the detector goes into the alarm state, the circuited feed
back to the control panel is activated and the panel indicates
a fire in the particular zone. While the conventional detector
may appear as little more than a simple on-off switch, signal
processing is starting to make an appearance, so that, for
instance, the sensitivity can be adjusted locally, moving
the point at which the detector goes into alarm, and the sensitivity
levels can then self-adjust to compensate as dust enters the
chamber.
Sounders
and Strobes
Once
a fire is detected, the building's occupants have to be warned
so that they can evacuate the premises. Sounders and strobes
are available in both conventional and addressable formats;
as a further refinement, addressable sounders can draw their
power either from the control panel loop, or from a separate
external power supply. Externally powered addressable sounders
are normally used in systems where a large number of sounders
are required because the amount of current can be drawn from
the loop is finite, and this might constrain the number of
warning devices that can be powered from it.
Ancillary
Devices
Interface
modules enable ancillary equipment to be monitored and controlled
by an intelligent fire system. A conventional zone module
enables a zone of up to 20 conventional two wire detectors
to be connected to an intelligent control panel via a single
module address on a loop. The module allows the user of lower
cost conventional detectors in locations that are physically
well defined, and where knowing the individual detector address
is not particularly important.
FIRE
ALARM SYSTEM COMPONENTS
- Smoke
Detectors
- Heat
Detectors
- Photo
Electric Detectors
- Fire
Alarm Panels
- Public
Address Systems
- Speakers
/ Hooters / Sounders
- Repeat
Announcing Panels
- Chordless
/ Remote Announcers
- Evacuation
Signs
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