FIRE DETECTION AND ALARM SYSTEMS

FIRE DETECTION AND ALARM SYSTEMS

The purpose of fire detection and alarm system ((which is activated either by operating manually through MCP- manual call point (or) activated through automatic detective devices like sensors)) is to detect smoke, heat or fire as early as possible depending upon the situation and initiating an alarm and triggering other appropriate actions like

• Firefighters immediately responding to the situation.

• Automatic or Manual triggering of the extinguishing process

• Evacuation of occupants etc.

FIRE ALARM DETECTORS

An alarm system may be activated by automatic detection devices or by manual operation of manual call points.

EFFECTIVENESS OF FIRE DETECTION AND ALARM SYSTEMS: A robust installation of fire detection and alarms systems should be planned and following things to be ensured for effective functioning. The fire detection and alarm systems should

• Detect the fire quickly enough as per its intended functions without errors and remain insensitive to phenomena other than those where its function is to detect

• Reliably transmit the detection signal

• Translate this signal into a clear alarm indication that will attract the attention of the user in an immediate and unmistakable way

• Indicate the location of the fire and initiate operation of ancillary services, such as fire extinguishing system, etc

COMPONENTS OF FIRE ALARMS SYSTEM:

The main components of a fire alarms system are

1. Initiating devices

2. Notification devices

3. Fire alarm control unit(Control and Indicating equipment)

4. The primary and secondary power unit

5. Auxiliary devices

 

INITIATING DEVICES: These devices may be activated by automatic detection devices or by manual operation of manual call points.

Examples are

• Smoke Detectors

• Heat Detectors

• Multisensor fire detector

• UV/IR flame detectors

These devices connected at regular points in a circuit have sensors that respond to a physical stimulus such as heat or smoke or flame.

NOTIFICATION APPLIANCES (ALARM SIGNALLING DEVICES): These are the fire alarm

signaling appliances, commonly used are of audible type, they are

• Horns

• Speakers

• Strobe lights

• Bells

• Buzzers

FIRE ALARM CONTROL UNIT (CONTROL AND INDICATING EQUIPMENT): 

This Equipment monitors the integrity of the wiring and components of the fire alarm system through which fire detectors are supplied with power. Their main functions are

1. To accept a detection signal and actuate a fire alarm signal

2. To pass on the fire detection signal, through the fire alarm routing equipment, to the fire fighting organization or automatic extinguishers

3. To monitor automatically the correct functioning of the system

4. To indicate or display the location of the alarm activation device.

PRIMARY AND SECONDARY POWER UNIT: This main power connection is the primary electrical power, the secondary power unit will act as a standby for the entire alarm system in case the main power goes off.

AUXILIARY DEVICES: The operation of auxiliary devices by the 

FIRE ALARM CONTROL UNIT like,

1. Smoke Control Systems

2. Hood Suppression Systems

3. Clean Agent Extinguishing Systems

4. Door Release Mechanisms

5. Elevator Recall

 

DETECTION ZONES AND FIRE ALARM SYSTEM

The alarm for any type of fire initiates many different activities which are to be well-coordinated, like the commencement of fire fighting operations, emergency evacuation procedures, calling the fire brigade, auxiliary operations either manual or automatic, etc, These activities are to be well co-ordinated during emergency

So, for ease of emergency procedures, the building needs to be divided into SECTORS / ZONES for easy identification of the fire and effective communication between different parties. These zones will help to identify the place of fire very quickly as this is a visual signal, external firefighters who are not familiar with the building can also proceed to the location of fire easily

GENERAL REQUIREMENTS WHILE INSTALLING FIRE DETECTION AND ALARM SYSTEMS

1. Cables for fire alarm shall be laid in metal conduits or armored to provide physical segregation from the power cables.

2. It has to be properly ensured that FIRE ALARM CALL points and FIRE FIGHTING equipment provided along the escape routes can be readily located.

3. The control room shall have the main fire alarm panel with a communication system (suitable public address system) to aid floors and facilities for receiving the message from different floors.

4. Activation of the building automatic sprinkler or fire detection system, if provided, shall automatically unlock the doors in the direction of egress, and the doors shall remain unlocked until the automatic sprinkler system or fire-alarm system has been manually reset.

 

5. Fire detection and alarm systems in buildings shall be so planned and programmed to enable operations of various systems and equipment to facilitate requirements leading to life safety, compartmentation and fire protection. 

These systems and equipment may include

o Electromechanical systems such as air handling units, pressurization systems smoke management systems,

o Creation of compartmentation through the release of the fire barrier, hold-up fire doors, etc,

o Monitoring of fire water storage tanks and pumps, pressures in hydrant and sprinkler system, etc.

6. In buildings above 30 m in height, institutional and assembly buildings along with fire alarm systems, detectors shall also be provided inside the electrical shafts, lift machine rooms, etc

7. In buildings where the automatic fire alarm system is provided, the following things should be monitored from the fire alarm panel

a. The water level in all tanks.

b. Hydrant and sprinkler pressures of respective zones as provided.

c. Pump ‘ ON/OFF’ status.

d. All isolation valves, wherever provided with a supervisory switch

e. Other requirements to meet electromechanical services interface

8. The annunciated panel should be provided near the main entrance of the control centre so that the maintenance staff easily notices if there is any fault condition or isolation and can be immediately rectified

9. If the manual call points and detectors in zones are not indicated separately in the control equipment then there can be a misleading indication of the position of the fire, hence It is strongly recommended that the circuits for the DETECTORS and the MANUAL CALL POINT shall be different in case of conventional detection systems.

10. A minimum sound level of either 65 dB (A) or 5 dB (A) above any other noise likely to persist for a period longer than 30 s, whichever is greater should be produced by the sounders at any point which can be occupied in a building. Sounders should be suitably distributed throughout the building concerning attenuation of sound caused by walls, floors ceilings and partitions.

Article by PJ Mohan

Sr.Faculty, NIFS