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SMOKE DETECTION SYSTEMS

SMOKE DETECTION SYSTEMS. IDENTIFY PARTICLES OF COMBUSTION MOST COMMON TYPES ARE PHOTOELECTRIC AND IONIZATION. PHOTOELECTRIC DETECTORS. PHOTOELECTRIC DETECTORS. PARTICLES OF COMBUSTION DISTORT A LIGHT BEAM DISTORTED LIGHT BEAM ACTIVATES SIGNAL. PHOTOELECTRIC DETECTORS.

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SMOKE DETECTION SYSTEMS

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  1. SMOKE DETECTION SYSTEMS • IDENTIFY PARTICLES OF COMBUSTION • MOST COMMON TYPES ARE PHOTOELECTRIC AND IONIZATION

  2. PHOTOELECTRIC DETECTORS

  3. PHOTOELECTRIC DETECTORS • PARTICLES OF COMBUSTION DISTORT A LIGHT BEAM • DISTORTED LIGHT BEAM ACTIVATES SIGNAL

  4. PHOTOELECTRIC DETECTORS

  5. PHOTOELECTRIC DETECTORS

  6. IONIZATION DETECTORS • USE A PIECE OF OF RADIOACTIVE MATERIAL (ALPHA RADIATION) • The alpha particles generated by the americium ionize the oxygen and nitrogen atoms of the air in the chamber. • To "ionize" means to "knock an electron off of." • When you knock an electron off of an atom, you end up with a free electron (with a negative charge) and an atom missing one electron (with a positive charge).

  7. Ionization Detectors • The electronics in the smoke detector sense the small amount of electrical current that these electrons and ions moving toward the plates represent. • When smoke enters the ionization chamber, it disrupts this current -- the smoke particles attach to the ions and neutralize them. • The smoke detector senses the drop in current between the plates and sets off the horn.

  8. IONIZATION DETECTORS

  9. IONIZATION DETECTORS

  10. HEAT DETECTORS • FUSIBLE ELEMENT • BIMETALLIC • PNEUMATIC • RATE OF RISE VERSUS FIXED TEMPERATURE

  11. Heat Detectors

  12. Rate of Rise Detector

  13. Thermistor Rate of Rise Detectors • If the air temperature increases rapidly, the change of temperature results in a change in resistance between the thermistors. • When the ratio of resistance exceeds a factory preset level, an alarm is initiated.

  14. Pneumatic Rate of Rise Detectors • Detectors use a reliable pneumatic rate-of-rise element which responds to a rapid rise in temperature of approximately 15°F per minute. • When the air within the sealed chamberexpands faster than it can escape through a calibrated vent, the resultant increase in pressure depresses the diaphragm, causing the electrical contact to close the circuit thus initiating the alarmsignal.

  15. Fixed Temperature Heat Detectors • The fixed temperature element uses a fusible alloy and an efficient heat collector. • Detectors are normally open devices and are available in either 135°F (57°C) or 194°F (90°C) ratings. • When activated, the external heat collector drops away to provide quick visual confirmation that the detector has operated.

  16. Fusible Element Heat Detectors • A spot type of fixed-temperature detectors is used mainly in unattended spaces to detect smoldering fires that increase the temperature of a detector above its design value, usually 135°F to 145°F or 185° to 200°F. • The higher temperature devices are used in spaces that may reach higher temperatures under ordinary conditions, such as boiler rooms, attics, or cooking areas.

  17. Fusible Element Heat Detectors

  18. Fusible Element Detectors • The device usually is actuated by the melting or fusing of an element made of a fusible metal alloy. • Actuated devices usually can be detected by visual examination. • In some devices, the smaller diameter part in the center drops away. In others, the dimple becomes a hole when the detector operates. • These fixed-temperature devices are often designed for one-time operation, and the whole device or the element needs to be replaced.

  19. BIMETALLIC HEAT DETECTORS

  20. BIMETALLIC HEAT DETECTORS • USES TWO PIECES OF SANDWICHED METALS THAT EXPAND AND CONTRACT AT DIFFERENT RATES WHEN HEATED • WHEN EXPOSED TO HEAT, THE METAL BENDS TO COMPLETE AN ELECTRICAL BRIDGE AND ACTIVATES THE DETECTOR

  21. UV FLAME DETECTORS

  22. UV Flame Detectors • Ultraviolet detectors respond to flaming fires emitting light in the ultraviolet portion of the spectrum. • UV detectors can respond to a fire condition in less than 10 milliseconds.

  23. UV Flame Detector Uses • The ultraviolet (UV) flame detector is extremely fast and is used in high-hazard applications, such as aircraft maintenance areas, munitions production, and other areas where flammable or explosive liquids or solids are handled or stored. • These detectors should not be used around arc welding, as they will respond to the ultraviolet light given off by the welding process.

  24. IR Flame Detectors

  25. IR Detectors • Infrared detectors respond to flaming fires emitting light in the infrared portion of the spectrum. • IR detectors can respond to a fire condition in less than 50 milliseconds. • These detectors are designed to alarm to hydrocarbon fires, while ignoring things like arc welding, nuclear radiation and x-rays.

  26. IR Detectors • The IR flame detector is ineffective for smoldering or beginning fires. • It is used where possible fires would develop quickly (fuels, such as combustible gases and liquids, or loose cotton fiber), and it is capable of protecting a large area if it is mounted high on a ceiling or wall (30 to 50 feet).

  27. TESTING FLAME-ACTUATED DETECTORS • Flame-actuated detectors should be inspected monthly for physical damage, accumulation of lens deposits, and paint. • A spot of paint on a lens can prevent the detector from "seeing" a critical area in the protected space.

  28. Testing Flame Detectors • Be sure that auxiliary functions of the flame detection system are deactivated • Inform the fire department and persons who would hear the alarm.

  29. False Alarms and Failure to Detect • False alarms or failure to detect during a test may be caused by environmental factors or the aiming of the detector. • Check that detectors are not blocked and that lenses are shielded from direct rays of the sun and other sources of IR, such as welding equipment, in the case of UV detectors.

  30. Testing IR Detectors • The dark spot or dome at the bottom center of each IR device is the lens. • Detector lenses must be kept clean to ensure the earliest possible detection of a fire. • A 250-watt IR heat lamp several feet from the detector can serve as a flame substitute in testing an IR flame detector.

  31. Cleaning UV Detectors • Keep UV detector lenses totally clean. • A gradual buildup of contaminants frequently found in high-hazard spaces (oil, gasoline, petrochemicals, salt, and dust) block UV radiation. • A layer thin enough to be undetectable to the human eye can cause a UV detector to be completely blind. • Clean lenses according to the manufacturer's instructions.

  32. Testing UV Detectors • Test feature designed into some detectors allows for checking the device. • A small UV source inside the detector housing is shielded from directly illuminating the sensor. • A test switch deactivates alarm circuits and illuminates the test lamp. • The test lamp rays pass through the front window to the sensor. • Detector response to the test indicates that the window is clean and that the sensor and electronic circuits are operational.

  33. ALARM SYSTEMS • TYPES • CENTRAL STATION • LOCAL SYSTEM • PROPRIETARY SYSTEM • VOICE SYSTEMS • INSPECT AND TEST AT LEAST ANNUALLY

  34. Fire Alarm Panels

  35. Fire Alarm Panels • Zone Indicators • Alarm Indicators • Fire • Trouble Alarm • Loss of Signal/Connection • Test and Alarm Resets

  36. Annunciator Panels • Located near main entrance of buildings • Identify zones for alarms

  37. Annunciator Panel

  38. Pull Stations

  39. Pull Stations • Activate fire alarm in building • Single action or dual action • Most types these days have method for determining activation • Break glass bar • Require key to reset

  40. INSPECTION AND TESTING • The employer shall assure that fire detectors and fire detection systems are tested and adjusted as often as needed to maintain proper reliability and operating condition. • Local Fire Codes stipulate testing requirements

  41. OSHA’s Employee Alarm Systems (1910.165) • OSHA Standards apply emergency employee alarms installed to meet a particular OSHA standard. • They also apply to discharge or supervisory alarms required on various fixed extinguishing systems or to supervisory alarms on fire suppression, alarm or detection systems if they are intended to be employee alarm systems.

  42. OSHA’s Fire Detection Systems Standard (1910.164) • Applies to all automatic fire detection systems installed to meet the requirements of a particular OSHA standard. • Example: 1910.38 Emergency Action Plans and Fire Prevention Plans

  43. NFPA 72: National Fire Alarm and Signaling Code • Addresses design, installation, testing, and maintenance of alarm systems. • Qualifications for installers, inspectors, monitoring personnel.

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