Fire and Gas Detection System

• The fire alarm system is designed to detect the presence of smoke, heat or flame.
• Smoke Detector


  A device that senses smoke, typically as an indicator of fire
• Smoke Detectors

  • Housed in plastic enclosures, typically shaped like a disk about 150 millimeters (6 inches) in diameter and 25 millimeters (1 inches) thick, but shape and size vary
• Commercial Security Devices

  Issue a Digital Signal to a Fire Alarm Control Panel as part of a Fire Alarm System
• Household Smoke Detectors (Smoke Alarms)

  Generally issue a Local Audible or Visual Alarm from the detector itself
• Power Sources for Smoke Detectors

  • Central Fire Alarm System powered by Building Power with Backup Generator and Battery Backup (for Large Commercial, Industrial and Residential Buildings)
  • Individual Battery Powered Units (for Domestic and Household)
  • Several interlinked Main Powered Units with battery backup (for Domestic and Household)
• If any interlinked Main Powered unit detects smoke

  All Smoke Detectors will trigger even if household power has gone out
• Smoke Detectors are usually powered by a Central Fire Alarm System which is powered by the Building Power with a Backup Generator and a Battery Backup for Large Commercial, Industrial and Residential Buildings
• For Domestic and Household, the Smoke Detectors are usually powered by range devices from individual Battery Powered Units to several interlinked Main Powered Units with battery backup
• Smoke detectors


  Devices that detect the presence of smoke and trigger an alarm
• Types of smoke detectors

  • Ionization smoke detector
  • Optical or photoelectric smoke detector
• Ionization smoke detector


  • Has an ionization chamber and a source of ionization radiation (americium-241)
  • Alpha particles from americium-241 ionize air in the chamber
  • Positive and negative plates in the chamber collect the ions, generating a small current
  • Smoke particles attach to the ions, reducing the current and triggering the alarm
  • May give false alarms if improperly placed
• Obscuration type


  1. Transmitter shoots an infrared light beam

  2. Receiver detects the light beam

  3. Circuit analyzer monitors the intensity of the light beam

  4. Smoke reduces the light beam intensity, triggering the alarm when the signal strength drops 40-90% for 5 seconds
• Types of Optical or Photoelectric Smoke Detectors

  • Light scatter type
  • Obscuration type
• The Optical or Photoelectric Smoke Detector consist of Two Types which are the Light Scatter Type and the Obscuration Type