Fire Alarm Systems are designed to alert us when an emergency occurred so that we can protect ourselves, staff and the general public from the hazards due to fire .Fire alarm system generally installed in Offices, Factories, and public buildings
When the alarm is triggered, sounders will operate to warn people in the building that there may be a fire and to evacuate. The fire alarm system may also connected with the fire brigade through a central station .
In this articles, we will discuss the structure and types of the “Fire Alarm Systems”. The fire Alarm control panel is known as “ “Brain” of the system. It is the central hub where all the detector signals are connected through the wire which provide status indication to the users.
In the unit there is feature through which we can also be set up to simulate an alarm for use in routine Fire and evacuation drills, so all staff knows about the safety action during the fire .The fire detector play vital role in the fire alarm system which may be smoke detector or simple manual operated break glass units
There are different type of detector used but we will divide them into groups including Heat detectors, Smoke detectors, Carbon Monoxide detectors, Multi-sensor detectors, and Manual Call Points.
Heat detector work either on fixed temperature where it will trigger an alarm if the temperature exceeds a pre-set value or they can work on the rate of change in temperature. Heat detectors work like an electrical fuse where the detectors contain a eutectic alloy which is heat sensitive when a specific temperature is reached ,the alloy turns from a solid to a liquid which in turn triggers the alarm.
The smoke detectors has three basic types including Ionization, Light Obscuring and Light Scattering. An Ionization Smoke detector have two chambers. The first chamber is used as a reference to compensate for changes in ambient temperature, humidity or pressure. The second chamber have a radioactive source which is usually alpha particle, and this particles ionizes the air passing through the chamber where a current flows between two electrodes. When fire occurred and smoke enters into the chamber the current flow decreases. In this types of detector the drop in current flow is used to initiate an alarm.
Light Scattering Smoke Detector
The light scattering smoke detector operation is base on the Tyndall effect. In this types a photocell and light source are separated with each other by a darkened chamber so that light sources does not fall on the photocell. Due to the smoke entering into the chamber, the light from the source will be scattered and fall on the photocell. The photocell output variation is used to initiate an alarm. In the Light obscuring smoke detector, the smoke interferes with a light beam between a light source and photocell. The photocell measured the amount of light which is received .The output variation in photocell output is used to initiate an alarm. This type of detection is used to protect large areas by keeping light source and photocell positioned some distance apart.
Carbon monoxide detectors
Carbon monoxide detectors which is also known as CO fire detectors and are electronic detectors used to indicate the outbreak of fire by sensing the level of carbon monoxide in the air.Carbon monoxide is a poisonous gas produced by combustion. Carbon Monoxide fire detectors are used sensor which is more sensitive and respond more quickly. Carbon monoxide detectors have an electrochemical cell which detect carbon monoxide level but it does not sense smoke or any other combustion products.
The Multi-sensor detectors combine inputs from both optical and heat sensors and process them using a sophisticated algorithm built into the detector circuitry. They are designed to be sensitive to a wide range of fires.
A Manual Call Point or Break Glass Call Point is used to raise the alarm by breaking the glass and switch on which triggers the alarm.
Fire Alarm can be divided into four main types;“Conventional”, “Addressable”, “Intelligent Fire Systems” and “Wireless Systems”
Conventional Fire Alarm System
In a Conventional Fire Alarm System is that which are connected with severely call point by a cable to the main control .Call points and detectors are named in “Zones” so that the faire location can identify easily.
Addressable Fire Alarm system
The addressable system have same detection principle as a Conventional System except that each detector is given a set Address so that Control Panel can then determine exactly which detector or call point has initiated the alarm. The detection circuit connected with a wire as a loop and there may be connected up to 99 devices to each loop.
Intelligent Fire Alarm system
In the Intelligent Fire Alarm system, each detector have its own computer which is connected and communicate with the control panel and if there is fire occurred in any detectors region or zones the only that computer communicated with control panel and the fire brigade can easy identify the fault location .Essentially Intelligent Systems are too much complex and incorporate far more facilities than Conventional or Addressable Systems.
Wireless Fire Alarm System
The Wireless Fire Alarm System have secure, license-free radio communications to interconnect the sensors and devices with the controllers. It provide provides many unique benefits and is a full intelligent fire detection system without the need for cabling.
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