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Fire Alarm -- Description

A fire alarm system detects fire, has some sort of control panel, and notifies people of the fire
By automatically shouting "Fire!," the Fire Alarm System Raises the Alarm causing people to take action.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer






What is a Fire Alarm System?

By Douglas Krantz

A Little History

Long ago, as an early method of spreading the word of fire danger, people shouted "Fire!" Depending on the circumstances, people would run away from the fire to escape, or run toward the fire to help extinguish it.

Later, to warn people to take action, the town bell or other noisemaker was also used.

Automation Using Electricity

Much later, electricity was discovered and electrical (and electronic) fire alarm systems were developed. Sometimes before people even knew about a fire, the fire alarm system would automatically raise the alarm; the fire alarm systems had become automated.

But, when all else fails, people still shout "Fire!"

How a Fire Alarm Works

Basically, to activate it, a fire alarm system uses manually operated devices (pull stations), or automatically activated devices (smoke and heat detectors, waterflow switches, etc.).

Once a fire is discovered by the fire alarm system, it tells the occupants of a building about the fire (by making lots of noise and flashing lights), and calls the fire-fighters (through automatic communication).

After that, it is up to the occupants to defend themselves from the fire, and the firefighters to try to extinguish it.

Extra Action Taken by the Fire Alarm System

Because it's automated, other actions can be taken by a fire alarm system. It can:
  • Shut down the air handling fans and the smoke dampers in the air ducts to prevent the spread of smoke and flame
  • Turn off electricity and gas in kitchens (shunt)
  • Capture the elevators
  • Turn off the electricity in computer rooms (Emergency Power Off or EPO)
  • Turn on a deluge sprinkler system to extinguish a fire
  • Activate a preaction sprinkler system to allow it to extinguish fire
  • Unlock doors to allow exit
  • Lock doors to prevent entrance
  • Close smoke barriers or smoke curtains to prevent the spread of smoke or flame
  • Release door holders on fire doors to prevent the spread of smoke
  • Activate fire suppression systems (FM200, Halon, Dry Agent, Etc.)

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Basic Fire Alarm System

Even without the other actions, the basic fire alarm system, through sound and light, tells people to take action. It is another means of shouting "Fire!"









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Douglas Krantz

Describing How It Works
writer@douglaskrantz.com
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612/986-4210

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Electrical Flow


On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at www.douglaskrantz.com/
ElecElectricalFlow.html
.