How Smoke Detectors And Heat Detectors Works (Fire Detectors) --Video Included

Detection of fire is the most important and essential part of a fire fighting.Here this article goes through the basic working principles of Fire Detectors

Fire Detectors Are Of 3 Type

  1. Smoke Detectors    --- Ionization/optical
  2. Heat Detectors        --- Fixed temperature/Rate of rise
  3.  Flame Detectors    -----Infra red/ultraviolet (not explained here)
How Smoke Detectors works
  •  Simply, smoke detectors are devices which sense the smoke and give the signal to fire control panel.
  •  There are of two type Photo electric Detectors and Ionization Detectors  
>  Photo electric Detectors

  •    The Optical Smoke Or Photoelectric Type Smoke Detector, uses a light source to detect smoke. 
  • The Infra-Red LED is a lens that shots a beam over a large area. 
  • If smoke is present in the room, it enters the optical chamber, having smoke particles scatter and sensor sets of the alarm.
  •  In very large areas where a smoke detector is placed, there are two optical detectors that send the straight line of infra-red beam from a sender to a receiver. 
  • Optical Smoke Detectors are less sensitive to false alarm fire, such as minor smoke from candles, cooking, steam etc.
  >Ionization Detectors
  • Ionization smoke detectors detect smoke even it is too small to naked eye
  • It is a best and cheap alternative for Photo electric detector
  • Through alpha radiation, the ionization smoke detector passes through the air-filled space container allowing flow of electrons.
  • However if any smoke gets inside the chamber and absorbs the alpha particles, it lowers the level of ionization, hurting the flow of electrodes, thus setting off the alarm.
  • More commonly placed in accommodation areas.
  Watch video for easy understanding


How heat Heat Detectors works    
  • Heat detectors works by measuring temperature range
  • If the temperature increases beyond particular range it gives alarm
  • commonly two type of heat detectors are there
    >Fixed type heat detectors
    > Rate of rise heat detectors

>Fixed type heat detectors
  • As name indicates fixed type heat detectors operate when the ambient temperature increases sufficiently to predetermined level where the heat detector will operate
 > Rate of rise heat detectors
  • A rate-of-rise heat detector operates when the ambient temperature increases over time equal to or greater than the rate of change the detector was manufactured to operate.
Most common type heat detector is 

Fusible link electromechanic heat detector 
  • An eutectic alloy is mixture of two or more metals whose melting point at a lower temperature than the individual metal.
  •  When the ambient temperature increases to the eutectic temperature, the alloy changes state from a solid to a liquid, like solder. 
  • This enables a spring held under pressure to release and make an electrical circuit to actuate an alarm. 
  • Both Fixed type heat detector and Rate of rise heat detectors are working under this principle.
To Understand in better way watch the video 




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