Fire alarm system and common types of detectors

Short notes about " FIRE ALARM SYSTEM "

1. FIRE ALARM SYSTEM By : MUHMMAD FARID, AHMED MUHAMMAD, MUHMMAD ZARIA, MAHMOUD AFEFY

2. Overview Fire alarm system is installed for protection of life, property and mission. In order to a fire alarm system to be useful, it must be able to perform these functions: Detect the presence of a fire. Notify the occupants. Notify the fire department

3. BASIC FIRE ALARM TECHNOLOGY Secondary (DC) Primary (AC) Outputs Inputs 1.Main Controller (control panel)

4. 2. Classifications of fire alarm detectors

5. 3. Selection For Detectors Stage One Incipient: Products of Combustion particles are produced (<0.3 microns). No visible smoke or detectable heat. May occur for milliseconds or days. Use ionization detectors

6. Stage Two Smoldering: Visible smoke particles are produced (>0.3 microns). Little visible flame or noticeable heat. Use Photoelectric Detectors

7. Stage Three Flame: Rapid combustion produces radiant energy in the visible, and invisible (IR, UV) spectrums. Heat begins to buildup at this stage Use Spark or Flame Detectors

8. Stage Four High Heat: Uncontrolled combustion is caused by the heating of nearby combustibles to their ignition point. Use Heat Detectors

9. 4. Notification Appliances (outputs) Bells: Used if they are only for fire, or have a distinctive sound from other bell signaling devices. Often used as an external gong to indicate the flow of water in the sprinkler system. Horns: Loud and distinctive output. Often used in high-noise environments, such as manufacturing plants.

10. Sirens: Extremely loud devices generally limited in use to outdoor or heavy industrial areas. Speakers: Audible devices used in conjunction with voice

11. SMOKE DETECTOR

12. SMOKE DETECTOR A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detector consists of two parts: A sensor to sense the smoke An electronic horn to horn the people Two basic types of smoke detectors are used today ionization and photoelectric .

13. IONIZATION SMOKE DETECTOR

14. IONIZATION SMOKE DETECTOR

15. IONIZATION SMOKE DETECTOR

16. Advantages of Ionization Smoke Detectors 1. Detects invisible products of combustion. It can detect fires that are in the incipient stage 2. Provides earlier detection than other detectors such thermal detectors   Disadvantage of Ionization Smoke Detectors Has a potential for high false alarm rate , so may provide false detection if used where dusts, or high humidity are present  

17. PHOTOELECTRIC SMOKE DETECTOR The photoelectric type detector utilizes light as a detection mechanism. A photoelectric , or optical , smoke detector contains a source of infrared, visible, or ultraviolet light, a lens, and a photoelectric receiver (typically a photodiode). There are two types of photoelectric smoke detectors: Light sensing(scattering) Light obscuring(blocking)

18. LIGHT SCATTERING SMOKE DETECTOR

19. Advantages of Light Scattering Photoelectric Smoke Detectors Sensitive to visual particles of smoke Detects smoldering low heat fires Disadvantages of Light Scattering Photoelectric Smoke Detectors Early contamination by dust causing reduced sensitivity Must be cleaned regularly

20. LIGHT OBSCURING SMOKE DETECTOR (BEAM SMOKE DETECTOR)

21. Advantages of Beam Smoke Detectors Cover a large area economically Quick acting in high atriums Disadvantages of Beam Smoke Detectors Correct alignment needs to be maintained

22. PHOTOELECTRIC SMOKE DETECTOR CIRCUIT

23. COMPARISON SENSOR TYPE IONIZATION SENSORS PHOTOELECTRIC SENSORS   USAGE Ionization sensors are designed to recognize fast-burning, flaming fires through the small amounts of smoke they produce. Photoelectric sensors are better at detecting smoldering fires that generate lots of smoke. Price $2.48 to $24.32 $14.90 to $106.91   Typical locations Clean rooms Computer rooms Mechanical air ducts Locations where sensitive detection methods are needed   Cargo Handling Areas, loading Bays etc. Atriums and corridors Computer rooms Photographic Rooms (Dark/Developing/Copying) Lift Shaft Electrical equipment rooms Warehouses

24. PLACEMENT OF SMOKE DETECTORS Smoke detectors should either be placed in the center of the ceiling, or on the wall 6-12 inches below the ceiling

25. DETECTOR SPACING

26. PEAKED OR SLOPED CEILINGS

27. FLAME DETECTOR

28. Flame Detector Designed to detect & respond to the presence of a flame or fire. It can include sounding an alarm, deactivating a fuel line and activating a fire suppression system. A flame detector can often respond faster and more accurately than a smoke or heat detector.

29. Flame Detector Circuit

30. Optical flame detectors

31. 1. Ultraviolet Detectors UV often included to minimize false alarms which can be triggered by other UV sources. Emitted at the instant of ignition within 3–4 milliseconds .

32. 2 . Infrared False alarms can be caused by other hot surfaces and background thermal radiation in the area. The usual response time of an IR detector is 3–5 seconds.

33. 3. Infrared Thermal Cameras Infrared (IR) cameras can be used to detect heat and with particular algorithms can detect hot-spots within a scene. These cameras can be used in complete darkness and operate both inside and outside.

34. 4. UV/IR These detectors are sensitive to both UV and IR wavelengths. Detect flame by comparing the threshold signal of both ranges. This helps minimize false alarms.

35. 5. IR3 flame detection Triple-IR flame detectors compare three specific wavelength bands within the IR spectral region. IR3 detectors can detect at up to 65m (215ft) in less than 5 seconds. Most IR detectors are designed to ignore constant background IR radiation.

36. Applications Hydrogen stations. Gas-fuelled cookers. Industrial heating and drying systems. Domestic heating systems. Industrial gas turbines.

37. Advantages Detection distance Sensitivity Speed of response Reliability Disadvantages Narrow field of vision. Expensive. Difficult to maintain.