Fire Alarm Systems - Zoning
FIRE DETECTION ZONES
SANS 10139 Section 8.6.1 clearly states that, all
buildings, other than very small buildings, need to be divided into detection
zones. Detection zones need to be small enough for a fire to be located
quickly. Even if the system is addressable detection zone indication
needs to be provided, as this often provides a quicker, albeit less specific,
indication of the location of a fire than typical addressable text displays.
Zone indicators also provide a simple "at a glance" overview of the
extent of fire or smoke spread. Do remember zone concept applicable for mainly conventional fire detection alarm system, where pin point not possible. Conventional detection systems offer a good basic system,
ideal for small applications, or projects that are tight on funds.
Do remember Zones are very important in only conventional type fire detection & alarm system.
The detectors in a zone of the building are all connected
to the same pair of wires. If any of the detectors report an alarm, only a zone
indication is shown on the control panel, meaning that the exact location of
the alarm is not shown. There could be say 10 detectors in that zone and one
cannot tell from the control panel which detector has triggered. Only the zone
will be shown. Some Fire panel brand support 18-20 nos detectors in a single zone.
The visual audio devices are wired on a separate circuit.
Advantages of a Conventional Fire Alarm System over an
Addressable Fire Alarm System are:
·
No sophisticated configuration is required and
the setup is simple.
·
Control panel and field devices are
comparatively cheaper.
·
There is compatibility of devices within a wide
range of manufacturers.
If the total floor area of the building is greater than
300 square meters, each zone should be restricted to a single storey.
If the total floor area of the building is less than 300
square meters a zone may cover more than a single storey.
For voids above or below the floor area of a room, these
may be included within the same zone of the room, provided that the voids and
the room constitute a single fire compartment.
Additional recommendations applicable to detection zones
that contain non-addressable automatic fire detectors. The floor
area of a single zone should not exceed 2 000 square metres. The
search distance that has to be travelled by anyone responding to a fire alarm
signal after entry to the zone in order for the location of the fire to be
determined visually should not exceed 60m.
Input devices:
Automatic fire detectors within any enclosed stairwell,
lift well or other enclosed flue-like structure should be considered as a
separate zone.
MCP Zones: The floor area of a single zone should not exceed
2 000 square metres, other than in the case of a zone comprising mainly a
single, open plan area e.g. an un-compartmentalised warehouse, which should not
exceed 10 000 square meters in area.
Indian Standard says, the manual call points on
each level, other than a final exit level from the stairway, should be
incorporated within the zone that serves the adjacent accommodation on that
level. A manual call point located within the stairwell at a final exit to open
air may be incorporated within the detection zone serving the stairwell.
Each input is represented by a physical ‘zone’, which
consists of wiring the circuit to one or more devices that serve a part or a
whole area.
The alarm start zones are electrical circuits connected
to field devices such as smoke or heat detectors, manual stations or sprinkler
alarm switches. The activation of any device connected to this type of zone
will cause audible signals to sound in accordance with the approved signalling
sequence.
The supervisory start zones are electrical circuits
connected to devices such as sprinkler valve monitoring switches or low
pressure sprinkler sensors. The activation of a device connected to a
supervisory start zone will obviously not cause the warning or alarm signals of
the building to sound, but will initiate a condition of monitoring problem of
the system in the Control Unit.
Alarm initiating devices:
·
The Building Code requires a separate zone for:
·
each floor area so that the area of coverage for
each zone in a building that is not sprinklered is not more than 2,000 square
metres,
·
each floor area so that the area of coverage for
each zone is neither;
·
more than one storey, nor
· more than the system area limits specified in
NFPA 13 Standard for the Installation of Sprinkler Systems,
·
each fire compartment required to have a 2 hr
fire separation,
·
each shaft requiring fire detectors,
·
each air handling system required to be equipped
with smoke detectors,
·
each contained use area,
·
each impeded egress zone, and
·
certain fire compartments as further detailed in
the Building Code
Any room or area, separated by a fire-resistant two-hour
fire separation, other than housing units also requires a separate area. As
fire separations are a primary tool for fire containment, it is logical that
this area is also identified separately.
Smoke detectors, which are required in an air handling
system, also require a separate zone for reasons similar to the axes.
Supervisory devices:
If the fire alarm system uses sprinklers as heat
detection devices, all of the following items are required to be provided with
a single zone announcement in the fire alarm control unit, and must indicate a
supervision/problem signal in the building:
·
each sprinkler system control valves,
·
loss of water pressure,
·
loss of air pressure in dry-pipe systems or
pressure tanks
·
significant changes in water levels in water
storage containers used for fire fighting,
·
loss of electrical power to fire pump, and
·
low temperature in dry-pipe systems or water
containers used for firefighting
For addressable fire detection system Zone concept is quite different. This case zone are not mandatory, mainly zone is useful for commissioning engineers to made logic equation.