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OVERVIEW OF AUTOMATIC FIRE ALARM SYSTEM FUNCTIONS

1.1. General Overview

An automatic fire alarm system is a system of equipment capable of automatically detecting and notifying fire locations, according to Vietnamese Standard TCVN 5738-2001.
The system typically includes:

Fire alarm control panel
Fire detectors
Alarm devices (sirens, flashers, manual call points)
And other peripheral equipment

1.2. Functions

Automatically detect fires quickly, accurately, and promptly within the protected area.
Automatically send alarm signals, status indicators, and control signals to peripheral devices in the system to perform specific tasks.
For systems using smoke detectors, an important function is early warning, meaning it can detect and notify incipient fires or smoldering fires before flames appear.

1.3. Classification of Automatic Fire Alarm Systems

🔹 By detector operating principle:

Smoke detector system: Detects rising smoke concentration in the protected area.
Heat detector system: Detects abnormal temperature changes.
Flame/light detector system: Detects increased light intensity from flames.
Multi-sensor detector system: Combines principles of heat, smoke, or flame detection (e.g., heat & smoke or heat & flame detectors).

🔹 By technical characteristics:

Conventional fire alarm system: Identifies the fire zone/area, not exact location. One zone may include multiple detectors. Area coverage typically ranges from several dozen to 2000 m².
Addressable fire alarm system: Identifies the exact detector that triggered the alarm. One address may cover only a few dozen square meters.
Intelligent fire alarm system: An advanced addressable system capable of measuring environmental parameters (temperature, smoke concentration, etc.), and adjusting threshold settings as required. This is the most commonly used type in modern systems.

🔥 OPERATING PRINCIPLES OF THE AUTOMATIC FIRE ALARM SYSTEM

2.1. Operating States of the System

Standby state (normal, no fire)
Fire alarm state
Fault state

2.2. Working Principles

In normal (standby) mode, the control panel continuously sends monitoring signals to devices, which respond back. The system prints out status reports periodically and flags devices requiring maintenance. A standby current Io is always maintained.
In supervisory mode, if the control panel receives error signals or no response from devices, it switches to fault mode. All faults are shown on the LCD screen. Once resolved, the system returns to standby mode.
When a fire occurs, environmental factors (temperature, smoke, light) change and trigger detectors once threshold levels are reached. The detectors send signals to the control panel, including:
- Fire signal
- Address (location) of the triggered detector
The control panel processes this input based on preset programs to:
- Announce the fire location via speaker and LCD screen
- Activate alarms and perform preset functions
If the control panel also monitors other equipment (e.g., fire pumps, flow switches), any state change will be displayed, and the system will notify until the state returns to normal.

2.3. Technical Requirements

(According to TCVN 5738–2001 “Automatic Fire Alarm Systems – Design Requirements”)

The system must:

Quickly detect fires based on its designed function
Convert fire detection into clear, actionable alarms for people nearby
Have strong interference resistance, especially where signal cables run near high-voltage lines. Solutions include using shielded signal cables or routing through metal conduits
Clearly indicate all system faults
Not be disabled or compromised by the fire before detection occurs
Operate continuously and reliably under all conditions (AC and DC power)
Ensure electrical and signal compatibility between detectors and control panel
Be highly reliable, performing all expected functions without error
Avoid fault propagation: A fault in one part should not affect the whole system
Meet both general and component-specific technical standards

🔥 FIRE DETECTORS

3.1. Concept and Function

3.2. Definition:

A fire detector is a sensor device sensitive to changes in environmental factors (e.g., heat, smoke, light) during a fire.
When these factors exceed a preset threshold, the detector sends a signal to the fire alarm control panel.

3.3. Function:

Generate electrical signals once the environmental factors reach the alarm threshold
Serve as an interface between the fire’s physical characteristics and the alarm system

Signal types generated by detectors:

Contact signals (open/close relay)
Sudden changes in current values

Each detector type produces different signal formats based on its detection method.

🔥 CLASSIFICATION OF FIRE DETECTORS

4.1. By operating principle:

Heat detectors: Respond to temperature changes
Smoke detectors: Respond to increased smoke concentration
Flame/light detectors: React to light emitted by flames
Multi-sensor detectors: React to combinations of two out of the three above

4.2. By power supply requirement:

Active detectors: Operate without external power
Passive detectors: Require constant power supply

4.3. By technical specification:

Conventional detectors: Used in zone-based fire alarm systems
Addressable detectors: Used in addressable fire alarm systems

4.4. By response mode:

Fixed temperature detector
Rate-of-rise (differential) temperature detector
Combined fixed & rate-of-rise temperature detector

STRUCTURE AND OPERATING PRINCIPLE OF FIRE DETECTORS

5.1. Structure

Though different in design, most fire detectors consist of the following:

Sensor element:
- The core component that detects environmental changes
- Converts physical changes into electrical signals when threshold is reached
- Varies by detector type (heat, smoke, flame)
Signal circuit:
- An electronic circuit that transmits signals from the sensor to external systems
Casing/Base:
- Protects and fixes the detector in place within the protected area

5.2. General Operating Principle

When a fire occurs, environmental factors change (temperature, smoke, light).
These changes activate the sensor, which in turn sends electrical signals to the fire alarm control panel.
The control panel then processes and displays the fire alarm.

OVERVIEW OF AUTOMATIC FIRE ALARM SYSTEM FUNCTIONS