Fire Alarm Systems - Zoning

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.