Fire Alarm & Smoke Detection System

What is a Fire Alarm System?
A Fire alarm is basically a system consisting of electronic devices used for detecting/alerting of fire condition at an early stage.
Simply a system which detects fire and generates an alarm

Fire Detection/Alarm system consists of
Ø  Control/Repeater Panel(s)
Ø  Input Devices
Ø  Output Devices
Ø  Power Source (AC & DC)
Ø  Media to connect the devices

Control Panel:
Ø  The Control Panel is connected to the detection zones having detectors, manual call points, sounders etc using cable as media and is operated with AC or DC source.
Ø  The Panel indicates the troubles / alarms and drives the corresponding output.

Input Devices:
  1. Detectors:
a.      Ionization Smoke Detector
b.      Photo/Optical Smoke Detector
c.       Heat Detector
d.      Laser Detector
e.       Beam Detector
f.        Duct Detector

Manual Call Point (MCP)
  1. Indoor
  2. Outdoor
  3. Weather Proof
  4. Water Proof
  5. Flame Proof  etc   

Manual Call Point (MCP) Operation:
Manual Call Points are simple switches with a resistor in series and generate an alarm due to the resistor switching across the line and drawing a Current in Ma dependent on the panel.
FLP: Used in Hazardous area                       NFLP: In general areas

Output Devices
  1. Hooters
  2. Sounders/Horns
  3. Strobes/Flashers
  4. Sprinklers
  5. Modules/Relays
  6. Notification Appliances.

Connecting Medium
  1. Cable: Generally Armored cable is used in the fire alarm systems such as to withstand fire condition. Here, we have used 2 x 1.5 armored cable
  2. Wireless technology: In this there will be transmitters and receivers.

Detector based on Ionization is cheaper than the Optical Detector
It is sometimes rejected because it is more prone to false (nuisance) alarms

It includes about 1 (Ci of radioactive Americium 241 (241Am)

The radiation passes through an ionization chamber, an air-filled space between two electrodes, and permits a small, constant current between the electrodes

241Am, an alpha emitter, has a half-life of 432 years

[Half-life is the period of time it takes for a substance undergoing decay to decrease by half]
i.e it does not have to be replaced during the useful life of the detector, and also makes it safe for people at home, since it is only slightly radioactive.

Ionization smoke detectors are used in areas where fast flaming / Hazardous fires can occur and a quicker response is needed

Optical Smoke Detector

  1. An optical detector is a light sensor (generating pulses of IR LED and measuring any diffracted light)
  2. A lens to collimate the light into a beam
  3. In absence of smoke, light passes in front of the detector in a straight line

When smoke enters the optical chamber across the path of the light beam some light is scattered by the smoke particles directing it at the sensor and thus triggering the alarm

Optical smoke detectors are quick in detecting particulate (smoke) generated by smoldering (cool, smoky) fires

Less sensitive to false alarms from steam or cooking fumes generated in kitchen

Is a unit of measurement of smoke detector sensitivity

Higher concentrations of smoke result in higher obscuration levels, lowering visibility

                                                 Ionization 2.6-5.0% obs/m (0.8-1.5% obs/ft)

Obscuration ratings
                                                 Photoelectric 6.5-13.0% obs/m (2-4% obs/ft)

Hooters (FLP/NFLP) :
Hooters/Sounders are the audible warning devices which generally take an input of 12v,24vdc and 230Vac and  convert electricity to sound using buzzers, piezo crystal buzzers with the help electronic.
NFLP: Used in general Areas
FLP: Hazardous Area   

Control Module (FCM)
Principle of operation: The control module is simply a relay having an address and is capable of accepting commands and can communicate with the fire panel and turn ON the output using input supplied and can be Reset.
This Module has 2 inputs (1) Loop (2) 24v and 1 output for Hooter activation

DO’s & Don’ts:


1.      Know about the “system” before operating.
2.      Intimate the proper authorities in case of alarm/trouble in your area.

3.      Please alert your colleagues in case you notice “fire/smoke” to vacate the area and inform the respective officials.
4.      Inform Safety/Maintenance dept if you notice any “fire alarm device” tampered.

5.      Be alert and follow evacuation plan in case of “fire”.



1.      Do not mishandle/misuse the Fire Alarm initiating and detecting devices as this may tamper the life safety.

2.      Do not neglect the “fire” condition even in mock drills.
3.      Do not touch the panel if you are not authorized to do so.


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