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
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.)
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!"