FUNDAMENTALS OF FIRE ALARM

SYSTEM

Overview and Design

EX.SE RVNL/KOL-PIU/E&MAsst. Prof. KIIT University

INTRODUCTION

Safety of human life.

Protection of costly devices.

Continuous and smooth operation.

Early detection of any abnormality.

PURPOSE AND SUITABILITY 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 MAIN ATTRIBUTES

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

SENSING DEVICE Heat detector.

Smoke detector.

Rate of temperature rise detector.

HEAT 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)

TYPES OF HEAT DETECTOR

Fixed temperature heat detector.

Rate of rise heat detector.

Another type of heat detector is flame detector.

PRINCIPLE OF HEAT 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. 

ELECTRICAL CONNECTION

STANDARDS

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]

DESIGN STEPS 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.

CRITICALITY OF ZONE

ASS/TSS Room, Pump Room, Signaling Room, Other electrical Control

room

Platform and Traction

Other room within premises.

SMOOTH & BEAM CEILING

Correct

Wrong

SMOKE DETECTOR A device that detects visible and invisible particles

of combustion.

DIFFERENT TYPES OF SMOKE DETECTOR

Ionization smoke detector.

Photo-electric smoke detector.

Projected beam (optical) smoke detector.

Aspirating smoke detector.

Video smoke detector.

PRINCIPLE OF SMOKE DETECTOR

Photoelectric Smoke Detector Ionization Smoke Detector

DESIGN STEPS 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.

POWER SUPPLY

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.

CONTROL AND PROCESSING UNIT

CONTROL MODULE

CONTROL ROOM AND CONTROL MODULE

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.

SOME GUIDELINE 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.

DEVICES USED FOR INDICATION

Speaker.

LED light.

DIFFERENT SCHEME SOUND INDICATION BY SPEAKER

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.

WIRING

CABLES AND THEIR INSTALLATION 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.

COLOUR CODE

Red

Yellow

Yellow

• For Alarm

• For Fault

• For Isolate

LIGHT INTENSITY

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.

SOUND INTENSITY

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).

PROTECTION Mechanical Protection: Break Glass Unit. or, Manual call point. Search distance

<30m from the Entry of any zone. Public addressing:

PROTECTION

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.

Overview

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