Fire alarm systems are in use since many years. Manual systems were used in all buildings with its control situated near the exit doors. A red colored device or lever represented these systems. On manually activating these systems, a loud alarm used to ring throughout the building. These systems are used today as well but their popularity has reduced.
Today, fire alarm systems have a series of automated devices interconnected through a web of wires. The main objective of these devices, especially the automated ones, is to initiate an alarm whenever a fire is detected. The main device is the control panel that connects the entire system together and controls the working of various devices.
The control panel receives inputs from the initiating devices, that is, the fire detectors, smoke detectors, etc. After processing the input, it sends a signal to the notifying devices which ring loud alarms throughout the premises to notify about the danger. The control panel can also initiate sprinklers and certain advanced devices that can send extinguishing agent in the area where fire is detected.
Most of these fire alarm systems have power backup other than the primary power supply and this keeps the premises guarded even in case of power failure. Overall, the initiating device along with the notifying device work together through the control panel to detect fire. Let us further understand the working of the initiating devices.
Getting Inside Fire Alarm Systems
The initiating devices are automatic detectors that send a signal to the control panel as soon as they detect danger. Most fire alarms come with either one or both of the following detectors:
Ionization Detectors
These detectors are provided with a source of ionizing radiation which is a little quantity of americanum-241. Alpha particles released by this agent created positively charged ions by removing electrons from the nitrogen and oxygen atoms present in the air. An ionization chamber has two plates kept at a distance of about a centimetre. Through low voltage, one of the plates is charged positively while the other is charged negatively.
The positive ions formed by the interaction of americanum-241 and oxygen and nitrogen atoms get attracted towards the negatively charged plate. The electrons removed from nitrogen and oxygen goes towards the positively charged plate. This process creates a small electric current in the detector. If this current is disturbed by any external particles, the detector sends a signal to set off an alarm. In case of fire, smoke particles neutralize the positively charge ions and break the flow of current.
Photoelectric Detectors
An incandescent bulb or LED emits light that gets converted into light beams through a lens in photoelectric detectors. A light sensor is attached at the bottom of the detector to sense the light beams. As smoke fills the room, it interrupts the flow of light beams from the lens and the smoke particles scatter the light to hit the light sensor and this act as a trigger for raising an alarm.
