Fire alarm

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Image:Wheelock mt.jpg A fire alarm is an electromechanical or electronic bell, klaxon, chime, horn, speaker, strobe light, or other device which warns people in a building of a possible fire or other condition requiring evacuation. Some horns can produce several different kinds of sounds, including the Code-3 temporal pattern (0.5 second pulse, 0.5 second pause, 0.5 second pulse, 0.5 second pause, 0.5 second pulse, 1.5 second pause), which was designed to be a distinct pattern used only for evacuation purposes. Other sound patterns include march time (0.25 second pulse, 0.25 second pause, repeat), a continuous tone, hi-lo (0.25 seconds alternating between two tones of differing frequency), siren (up-and-down sweep in frequency), slow-whoop (slow rising sweep upwards in frequency), and an electronic bell sound. Fire alarms are often very loud, sounding at between 90 and 100 decibels [1]. Firefighters have been known to have hearing problems after exposure to alarms over many years. Typically, when a fire alarm is sounded, emergency responders are summoned, the building is evacuated, people gather at predetermined assembly points, and a roll call is held.

Fire alarms may be triggered automatically by smoke detectors, heat detectors, sprinkler flow switches, or manually. Manual pull stations and manual call points are sometimes protected by glass which must be smashed to set off the alarm. Protective covers may also be placed over the station to help prevent false alarms.

The nerve center of a fire alarm system is the Fire Alarm Control Panel, where building personnel and emergency responders are able to locate the source of an alarm, pinpoint trouble or supervisory conditions, silence alarms, and reset the system.

With the advent of the Americans with Disabilities Act of 1990, fire alarm systems changed dramatically. Along with an audible alarm, fire alarm notification appliances now have strobe lights to alert the hearing-impaired.

Especially in college dorms and high schools, there has been an epidemic of students pulling the fire alarm as a prank. Since this wastes the fire department's time and resources for no reason, as well as initiates a meaningless evacuation of the building, it is often a felony offense. If performed repeatedly, and at inconvenient times (e.g. late at night), such false alarms can lead to apathy among residents, causing them to take a real alarm much less seriously, or even ignore it.

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Fire alarm horn

A fire alarm horn is a device which alerts people of an emergency, and over the years improvements have been made to these horns to NFPA standards. The horns are typically not found indoors, more for outdoor use because of the loud volume. Some outdoor horns can project as much as 115 dB, so it can alert bystanders and witnesses as well as the people who are mingling outside the building. Also it is against ADA and NFPA standards to install a horn without a strobe indoors. The strobe needs to either be on the device or within a few feet. Many companies manufacture horns, including: Wheelock, Edwards (now EST), Simplex, and many others.

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Improvements

Template:Cleanupdate In the beginning horns were made with a metal plate and an electric shock would be sent to a small metal strip which vibrates the plate, causing the horn to make a vibrating horn sound. The volume was normally loud and volume could be controlled by the tightness or looseness of the metal strip. Horns such as the Wheelock 34T had this outdated technology. However Wheelock noticed as well as other fire alarm fanatics that the horn would sometimes skip, as in cause like a skipping sound in the horn, like the typical sound of when a CD skips. Wheelock then determined the horn useless, and then started drawing up some new ideas. For example the AH multitone pictured below:

This horn is a two tone horn. And can be programmed to do either Code-3 Horn or Continuous Horn Sound. This can be used both outdoors and indoors. Another horn was to soon follow, the Wheelock MT. This horn is a multitone horn and can be programmed to do Continuous Horn, Code-3 Tone, Code-3 Horn, Slow Whoop, Hi-Lo, Siren, Bell, and Marchtime. This can mount onto an outdoor box or can be flush mounted to an indoor wall. The tone is produced using a special horn, not anywhere near the vibratone horn, and produces a high pitched chirping sound. Many horns nowadays sound like this horn.

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Piezo horn

Piezo horns produce a high pitched sound, similar to that of a home smoke alarm. The horns are usually applied in smaller rooms. These are not as loud as regular horns, as they sound in the range of 70 to 80 decibels.

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Fire Alarm Devices

Fire alarms have devices connected to them to detect the fire/smoke or to alert the occupants of an emergency. Below is a list of common devices found on a fire alarm.

  • Manual Pulls
    • Devices to allow people to manual activate the fire alarm. Usually by exits
  • Smoke Detectors
    • Mainly two types: Photoelectric and Ionization
  • Water Flow Switches
    • Detect when water is flowing through the fire sprinkler system
  • Rate-of-Rise and Thermostat (heat) Detectors
    • Detect heat changes
  • Gate Valve Switch
    • Detects when someone has turned water off to fire sprinkler system
  • Carbon Monoxide Detectors
    • Detects poisonous gas
  • Horns/Strobes
    • Visual and Audible devices to alert people of system activation
  • Mag Locks
    • Doors will shut or lockdown areas when fire alarm is activated
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See also

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Alarm manufacturers

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