What is Fire Detection and Fire Alarm Systems

Frequent cases of residential fire have been a regular headache for fire departments world over. Estimates suggest at least half of the lives that are lost due to residential fires could be saved by installing early warning fire detection and Alarm systems. They are very critical part of building management system.

There are 2 types of residential fire detection systems: smoke detectors and heat detectors. The basic fire detection system in the residential area depends upon detectors which have a sensing chamber, alarm sounding device and a means of electrical power transmission. There are 2 different kinds of smoke detectors: photoelectric and ionization. Photoelectric one is responsive to fires that begin with a long period of smoldering, whereas ionization one is more responsive to flame fires. Since prediction of fire is unpredictable, for maximum protection both technologies are in use.

Photoelectric smoke detectors: these aim a light source into a sensing chamber. Smoke produced by a fire affects the intensity of a light beam passing through air. Smoke can block or obscure the beam. When smoke blocks the light beam from the light source, reduction in light reaching the photosensitive device alters its output. Change in this output is sensed by the detector circuitry and alarm is initiated. Photoelectric smoke detectors are better suited to detect slow smoldering fires.

Ionisation smoke detectors: Ionisation smoke detectors have a small amount of radioactive material between two electrically charged plates which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm. They are more suitable for detection of fast flaming fires.

Smoke detectors offer earliest possible fire detection and alarm system/warning of fire. In certain circumstances where standard fire detectors are unsuitable, special purpose detectors are used. Laser-based fire detectors are used where extremely early fire warning is desired. They are ultra sensitive to smoke being 100 times more sensitive to standard ones.

Lately, designers of fire detection & alarm systems have begun to introduce fire detectors that combine photoelectric and ionization sensor in the same unit. The units combine the advantage of both the sensors into an advanced unit that detects smoke from a broader spectrum of fire. A residential fire detection and alarm system may also include a heat detector. Heat detectors wake up when air temperature exceeds the preset range or rate of rising is beyond a preset limit, then they raise an alert when the temperature in the vicinity rises.

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