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A fire alarm system recognizes a fire through multiple methods of detection. When detection devices are activated, an alarm is triggered to warn people in the building as well as notify the fire department. One of the key components of a fire alarm system are smoke detectors. These devices range in both sophistication and function. There are two basic types of smoke detectors:
The Ionization Smoke Detector which contains a small amount of radioactive material that passes between two electrically charged plates creating an ionization chamber. This configuration ionizes the air in the chamber and creates a current that flows between the plates. When smoke enters the chamber the current flow decreases. This drop in current flow initiates an alarm.
The Photoelectric Smoke Detector which works by using a photoelectric sensor and a light source. Photoelectric technology is used in light scattering smoke detectors as well as light obscuring smoke detectors. In light scattering detectors smoke enters the detector’s sample chamber and crosses the path of the light beam, light is scattered by the smoke particles, aiming it toward the sensor, which in turn triggers the alarm. The light obscuring technology measures the difference between a light source and photocell. The photocell measures the amount of light it receives and a reduction in light reaching the photocell due to smoke initiates an alarm.
Photoelectric smoke detectors are more suitable for detecting slow developing (smoldering) fires where as the ionizations smoke detectors are better suited for fast developing (flaming) fire. Although, both types of detectors can detect both types of fire, their response time will vary, depending on the actual type of fire. Multi-technology combination smoke detectors can also be used that utilize smoke detection combined with heat and/or CO detection when a standard smoke detector is not the best solution for the environment.