Answers:
it goes back to the first fire box alarm systems
the first person to spot a fire would open the box and pull the lever to sound the alarm and the nearest station would respond
if on arrival the firemen needed more equipment they would
pull the lever again this would call in help from the next nearest station
a 3 alarm fire would call the off duty men from the near by stations back on duty and they would also respond to the fire
a 4 alarm fire would be a general alert for all available units in the city to respond to the fire.
so with each alarm that sounded the number of fireman called on to respond increased.
it used to end at four alarms. but with the changes to technology the number of people and units that could be brought in has increased, though they don't ring bells anymore they have kept the terminology.
a 9 alarm fire is a disaster call for help from anyone who can send help. Military, other states, etc.
Means that it is a really big fire!!! Run!!! Doesn't each "alarm" stand for one fire station represented at a fire? Therefore, a 9-alarm fire would mean firetrucks from 9 different stations responded to a fire. That would be a pretty massive situation.
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