1 / 102

Fire Detection, Alarm, and Suppression Systems

Fire Detection, Alarm, and Suppression Systems. 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

Download Presentation

Fire Detection, Alarm, and Suppression Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related