You often hear speak of a "Five-alarm fire", or a "three-alarm fire".
I am looking for a brief description of the severity of fires, and how
they would be classified into these "alarm" levels.

Dear samrolken-ga;

Thank you for allowing me an opportunity to answer your interesting
question.

By categorizing a fire as “one-alarm”, two-alarm”, etc. a fire
department can establish a preplanned response. This response varies
from jurisdiction to jurisdiction according to the size of the fire
department, the city and the fire.

Traditionally, fire departments are divided into areas of
responsibility. Each area has a station, (sometimes called a station
house or precinct) that watches over it. Within each station are
several more units, commonly called squads, engines, trucks and
ladders (stations in larger cities might have many more subgroups such
as medics, ambulances, chiefs, and canteens) These units are deployed
on an alarm according the to type and severity of the fire. A
one-alarm fire then, might get a response from station #2, truck #1
and one ladder #1. What you don’t normally see during an alarm that is
almost always happening behind the scenes is that the firefighters at
station #1 are also getting out of bed and scrambling to their
vehicles, since someone from station #1 must now cover station #2’s
area. An engine or a truck will gear up and drive over to station #2
and remain there until the fire is extinguished just in case another
fire happens to break out in that jurisdiction while it’s “regular”
firefighters are off fighting a fire.

The reason that I say the alarm size varies is because stations in
bigger metropolitan areas might have 10 squads, 6 trucks and 3 ladders
while others in smaller towns may have only one of each. A three-alarm
fire in New York might be measurably more disastrous than say a
three-alarm fire in Jackson, MS. On the other hand, there are
rules-of-thumb which almost all firemen recognize. As a general rule,
a one-alarm fire warrants a one-station response, a two-alarm fire
will get a two-station response, and so on. How many actual
firefighters this ends up being though depends on the department’s
available manpower and policy. Occasionally you will read about a
10-alarm fire and sometimes a fire is so huge that it can only be
measured by calling it a “multiple alarm fire”.

The historical origin of these phrases is relatively plain to see.
Early on, if someone reported a fire, one alarm rang at one station
and they went and fought the fire. If the fire got worse and they
needed help, the second alarm was sounded at the second station,
telling these men to go help. The worse the fire would get, the more
alarms would be sounded until the necessary level of manpower and
equipment was reached to combat the fire successfully.

I hope you find that that my research exceeds your expectations. If
you have any questions about my research please post a clarification
request prior to rating the answer. Otherwise, I welcome your rating
and your final comments and I look forward to working with you again
in the near future. Thank you for using Google Answers.

Best regards;
Tutuzdad-ga


INFORMATION SOURCES

I derive my information from my 21 years in law enforcement and
emergency services.

SEARCH STRATEGY


SEARCH ENGINE USED:

Google ://www.google.com

There is a lot of good information in this answer, and I appreciate
its detail and insight. However, the answer provided no links to
external information, and did not answer my question, just provided
information about the topic I asked. In any event, this satisfies my
curiosity. Thanks!