Fire Detection, Alarm, and Suppression Systems - PowerPoint PPT Presentation

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Fire Detection, Alarm, and Suppression Systems

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  1. Fire Detection, Alarm, and Suppression Systems

  2. Introduction • Recognized functions of detection and alarm systems. • To notify occupants of a facility to take necessary evasive action to escape the dangers of a hostile fire • To summon organized assistance to initiate or assist in fire control • To initiate automatic fire control and suppression systems and to sound an alarm • To supervise fire control and suppression systems to assure that operational status is maintained • To initiate a wide variety of auxiliary functions involving environmental, utility, and process

  3. Introduction • These systems may include components that operate: • Mechanically • Hydraulically • Pneumatically • Electrically • Most are state-of-the art and operate electronically

  4. Introduction • Automatic Sprinkler Systems remain the most reliable form of protection. • They result in less business interruption and less water damage than traditional firefighting intervention • Approximately 70% of all fires are controlled by the activation of 5 or fewer sprinklers.

  5. Types of Alarm Systems • Local system or protected premises fire alarm system • Is a localized system meant to be activated by manual means, (EXAMPLE:) Pull Stations in local schools.

  6. Optional Features For Local Systems • Automatic fire detection devices may be added allowing the system to sense presence of fire and initiate the signal.

  7. Four Basic Types of Automatic Alarm-Initiating devices

  8. Heat Detector • Fixed Temperature Heat Detectors • Systems using fixed temperature detectors are among the oldest in service • They are inexpensive and are the least prone to false activations • They are the slowest to react or activate of all the various types of alarm initiating systems.

  9. 3 Primary Principles in which fixed temperature devices detect heat • Expansion of heated material • Melting of heated material • Changes in resistance of heated material

  10. Fusible Devices (Fixed temperature) • Associated mainly with automatic sprinklers, but they are also used in fire detection and signaling systems

  11. Frangible Bulb (Fixed Temperature) • Holds electrical contacts apart in alarm system. The vial of liquid has a bubble in it that heats and ruptures the bulb at a predetermined temperature

  12. Continuous Line Detector (Fixed Temperature) • Detect heat over a linear area parallel to the detector rather than in one spot in which located such as the fusible link.

  13. Bi-Metallic Detector (Fixed Temperature) • Uses two metals with different thermal expansion rates. • When heated on expands faster than the other causing the strip to bend or arch making or breaking a circuit and initiating the alarm

  14. Rate-of Rise Heat Detectors • Operate on the principle that the temp in a room will increase faster from fire than from atmospheric temp. • Typically designed to alarm when the temp rise exceeds 12–15 degrees F/min. • All rate-of-rise detectors reset after activation if undamaged.

  15. Rate-of Rise Heat Detectors • Pneumatic Rate-of-Rise Detector • The most common type • A dome shaped chamber with a flexible metal diaphragm in the base. • A small hole allows air exchange during normal conditions. • During a fire, the hole is too small to allow the heated air to escape, thus forcing the metal diaphragm to contact the alarm circuit.

  16. Rate-of Rise Heat Detectors • Pneumatic Rate-of-Rise Line Detector • Consists of a system of tubing for wide area coverage. • The space in the tubing acts as the air chamber, operating the same as the pneumatic detector.

  17. Rate-of Rise Heat Detectors • Rate Compensated Detector • Designed for use in areas subject to temp changes that are slower than those under fire conditions • Consists of an outer metallic sleeve that encases two bowed struts that have a slower expansion rate than the sleeve. When heated rapidly, the outer sleeve expands, reducing tension on the inner strips, allowing contact.

  18. Rate-of Rise Heat Detectors • Thermoelectric Detector • Operates on the principle that when two wires of dissimilar metals are twisted together at one end, an electrical current is generated at the other. • Rapid heat changes generate more current and cause activation.

  19. Smoke Detectors • Because it detects smoke & not heat, it can activate more quickly. • Comes in two basic types: • Photoelectric • Ionization

  20. Smoke Detectors • Photoelectric • Sometimes called a visible products-of-combustion detector • Uses a photoelectric cell coupled with a specific light source • The photoelectric cell functions in two ways to detect smoke: • Beam Application • Refractory Application

  21. Smoke Detectors • Photoelectric • Beam Application • Uses a beam of light across the area being monitored & onto the photoelectric eye. • The cell constantly converts the light to current, which keeps the switch open. • When smoke obscures the beam, the circuit closes & the alarm activates.

  22. Smoke Detectors • Photoelectric • Refractory • Uses a light beam that does not strike the photocell and produces no current • When smoke enters the chamber, it causes the light beam to be refracted (scattered) • Light strikes the photocell causing current to flow, which closes the switch & activates the alarm

  23. Smoke Detectors • Ionization • During combustion, minute particles & aerosols too small to be seen by the naked eye are produced. • These particles can be detected by devices that use a tiny amount of radioactive material, usually americium, to ionize air molecules. • These ionized particles allow current to flow between negative & positive plates in the chamber.

  24. Smoke Detectors • Ionization • When the particulate particles of combustion (smoke) enter the chamber, they attach themselves to electrically charged molecules of air (ions), making the air less conductive. • The decrease in current flowing between the plates initiates the alarm.

  25. Flame Detectors • Sometimes called light detectors • There are 3 basic types: • UV Detectors • Detect light in the UV spectrum • IR Detectors • Detect light in the IR spectrum • Those that detect both types of light

  26. Fire Gas Detectors • When fire burns in a confined space it changes the makeup of the atmosphere within the space. Depending on the fuel some of the gasses released are: • Water Vapor (H2O) • Carbon Dioxide (CO2) • Carbon Monoxide (CO) • Hydrogen Chloride (HCl) • Hydrogen Cyanide (HCN) • Hydrogen flouride (HF) • Hydrogen Sulfide (H2S)

  27. Fire Gas Detectors • Only water vapor, carbon dioxide & carbon monoxide are produced by all fires • This makes it practical to monitor only carbon dioxide & carbon monoxide for general fire detection purposes • Uses either semiconductors or catalytic elements to sense the gas & trigger the alarm

  28. Combination Detectors • Include fixed temp/rate-of-rise, combo heat/smoke & combo smoke/fire gas. • Combination detectors are more versatile and responsive to fire conditions.

  29. Indicating Devices • A large assortment of visual & audible devices are available. • Indicators may be used singularly or in combination with other devices.

  30. Automatic Alarm Systems • A local alarm sends a signal to an off-site location which notifies the local authorities • Signals come through dedicated wire-pairs, leased phone lines, fiber-optic cable, or wireless communication links.

  31. Auxiliary System • There are three basic types: • Local Energy System • Shunt System • Parallel Telephone System

  32. Auxiliary System • Local Energy System • Municipal fire-alarm box system • Occupancy is attached directly to a hard-wired or radio-type municipal fire alarm box • When an alarm trips in the protected occupancy, it trips the alarm & sends the signal • Can be manually activated at the alarm box

  33. Auxiliary System • Shunt System • The municipal alarm circuit extends (is “shunted”) into the protected property • When an alarm is initiated on the premises, either auto or manually, the alarm is transmitted to the alarm center over the municipal system

  34. Auxiliary System • Parallel System • Does not interconnect with a municipal circuit • It transmits an alarm directly to the alarm center over a municipally controlled telephone circuit that serves no other purpose.

  35. Remote Station System • Similar to auxiliary, but is connected to the FD communications center or through an answering service by means other than the municipal system. • Can be connected via: • Leased phone lines • Dedicated radio frequency

  36. Proprietary System • Used to protect large commercial & industrial buildings, high rises, & groups of commonly owned buildings in a single location, such as a college campus or industrial complex. • Each building has its own system wired into a common receiving point. • The receiving station is staffed by trained personnel.

  37. Proprietary System • Modern proprietary systems can be complex with a wide range of capabilities: • Transmitting coded alarm & trouble signals • Monitoring building utility controls • Monitoring elevator status • Monitoring fire & smoke dampers • Performing security functions

  38. Central Station System • Similar to proprietary, but there is no on-site receiving point. The signal is transmitted to a contracted service off-site called the central station. • Typically an alarm company that contracts with individual customers. • Central station employees receive the alarm & contact the proper authorities. • Commonly connected via supervised phone lines • Central Station Systems should comply with NFPA 72, National Fire Alarm Code

  39. Auxiliary Services • Many newer systems offer auxiliary services in addition to monitoring: • Shutting down or altering HVAC • Closing smoke or fire door or dampers • Increasing air pressure in stairwells to exclude smoke • Overriding elevator controls • Monitoring operation of burner management • Monitoring refrigeration systems • Controlling personnel access to hazardous areas • Detecting combustible or toxic gases

  40. Automatic Sprinkler Systems • Automatic sprinkler protection consists of a series of sprinklers (sprinkler heads) arranged so that the system will automatically distribute sufficient quantities of water directly to a fire to either extinguish or contain it until FF’s arrive. • Water is supplied through a series of pipes

  41. Automatic Sprinkler Systems • There are two general types of coverage: • Complete • Protects the entire building • Partial / Limited Area • Protects certain high hazard areas, exit routes or places designated by code or by authority having jurisdiction