Fundamentals of Fire Alarm System

Overview and Design
EX.SE RVNL/KOL-PIU/E&M
Asst. Prof. KIIT University

 Safety of human life.
 Protection of costly devices.
 Continuous and smooth operation.
 Early detection of any abnormality.

 The purpose of the fire alarm system shall be
primarily to provide notification of fire alarm,
supervisory, and trouble conditions; to alert the
occupants; to summon aid; and to control fire
safety functions.
 It is suitable for highly congested and electrical
hazards where area is prone to fire.
 Places where safety of continuous operation is
important.

 The sensing device.
 Power supply.
 Control and processing unit.
 Indicating Devices.
 Wiring and Colour Code.
 Light Intensity and Sound intensity.
 Protection.

 Heat detector.
 Smoke detector.
 Rate of temperature rise detector.

 The objective of the heat detector is that it must
respond when the fire reaches a critical heat
release rate within a specified time.
 Apollo XP95 Heat Detector:(Fixed Temperature)

 Fixed temperature heat detector.
 Rate of rise heat detector.
 Another type of heat detector is flame detector.

 Fixed temperature detectors operate when the heat sensitive alloy
reaches the critical point changing state from a solid to a liquid. It
sends a low voltage signal to controller so that it can take action
accordingly.
 The most common fixed temperature point for electrically
connected heat detectors is 136.4°F (58°C). Technological
developments have enabled the perfection of detectors that
activate at a temperature of 117°F (47°C), increasing the
available reaction time and margin of safety.

Fundamentals of Fire Alarm System

 NFPA 72.[ National Fire Alarm Code]
 IS 2189 : 2008.[Selection, installation and maintenance of
the Automatic Fire Detection and Alarm System Code of
Practice]
 IS 15908 : 2011.[Selection, installation and maintenance of
control and indicating equipments for Fire Detection And Alarm
System-Code of Practice]

 For normal ceiling ,
100 sq-mm area= one heat detector.
 For large open space,
Total area is subdivided by zones.
2000 sq-mm= one zone
ceiling height 5-7m , spacing=3.5m
 Maximum no of fire detector in a zone = 20 nos.
 For false ceiling sensitivity of fire detector must be high than normal
ceiling.
 All heat detector are connected in series with isolator in proper
locations.

ASS/TSS Room, Pump
Room, Signaling Room,
Other electrical Control
room
Platform and Traction
Other room within
premises.

 A device that detects visible and invisible particles
of combustion.

 Ionization smoke detector.
 Photo-electric smoke detector.
 Projected beam (optical) smoke detector.
 Aspirating smoke detector.
 Video smoke detector.

Photoelectric Smoke Detector Ionization Smoke Detector

 For normal ceiling ,
100 sq-mm area= one smoke detector.
 For large open space,
Total area is subdivided by zones.
2000 sq-mm= one zone
ceiling height 7-10m , spacing=5m
 Maximum no of fire detector in a zone = 20 nos.

 Main Power Supply ( single phase dedicated supply only for
fire alarm). DG set (automatic/ manual ) may be separately
installed for main power supply.
 If main power supply fails changeover within 10 seconds to
back up battery supply.
 Battery back up should maintain 48.5 h normal operation
after main supply fails.

 In high rise building and special buildings a control centre
minimum floor space required is (15-20) sq-m .
 Emergency lighting module must be there.
 Control centre room shall be provided with intercon and
direct telephone facility on emergency.
 Control panel:
Acknowledge button.
Alarm cancel indication.
Isolation/Reset facility.
Related fuse/ protective devices.

 Small distance of C and I devices, manual call point from
safety staff and fire fighters. The minimum distance is 30
m from the entrance of any zone.
 Repeat control is used for multiple entrances.
 All C and I and Power supply equipments require routine
tests.
 Noise level should be low in protected area for clearance
of audible instruction.
 C and I equipment is not centralized. It is distributed
among number of sub-panels.
 Ring or loop network is more useful.
 All sub-panels are stand alone.

 Single stage continuous alarm:
Continuous alarm sound
throughout the zone or sector. This scheme is for smaller
premises.
 Two stage general alarm:
Continuous alarm for fire
affected zone and intermittent alarm in other zone through
automatic switch from control centre. This scheme is for
large and multiple entrances premises.

 The cable from the main supply and standby supply should be
fire resistant.
 Color coding is red to discriminate from other cable.
 Cables shall be exclusively for fire detection system. Multi core
shall not share other load.
 Type: Armoured or Unarmoured FRLS cables of minimum
2X1.5 sq-mm. ATC cables for conventional fire alarm and
multistand twisted pair shielded cable for addressable alarm
system.
 PVC insulated copper conductor cable of 1.5 sq-mm can also be
used.
 Mineral insulated cables with overall LSF( low smoke fume)
(It is required for High hazard industry: Oil and Hydrocarbon, Metro
rail, Jetty, Airports, Power plant)

 Cable shall be laid down in metallic/ rigid PVC condute.
 There shall not be any joint between detector to detector,
detector to alarm, detector to manual call point.
 Proper junction box is required if there is a shortage of
cable for wiring.

Red
Yellow
Yellow
• For Alarm
• For Fault
• For Isolate

 The surrounding ambient illumination level in the
vicinity of all control and indicating equipment
shall be such that visible indications can be clearly
seen, controls easily operated and any instruction
can be easily read.

 Frequency range of hooters/horns/electronic bell
is within 500 to 1000 Hz.
 Minimum sound level is 65 dB (A) . 75 dB (A) is
required for sleeping person to awake with all
door shut.
 Maximum sound level is 120 dB (A).

 Mechanical Protection:
Break Glass Unit.
or, Manual call point. Search distance
<30m from the
Entry of any zone.
 Public addressing:

 Electrical Protection:
An over-current protective device
of suitable current-carrying capacity that is
capable of interrupting the maximum short-circuit
current is used for electrical protection.

Fundamentals of Fire Alarm System

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Fundamentals of Fire Alarm System