Definitions of "Five Alarm", etc..

[Meridian]

Hi,  I was hoping someone might be able to give a definitive answer.
Unfortunately, google, yahoo, and ask.com seem to have failed me.

Often newspapers/MSM report "a three alarm blaze", "five alarm blaze" or "seven alarm fire" etc.

Is there a standard definition as to exactly what this means?  Does it vary from city to city, or?

A guess that I/others I was discussing had was that maybe on a five alarm blaze, the 5 closest stations are alarmed into service? and so forth?

 

[P/Sgt]

An 'Alarm' varies from one municipality to the next, but in most major cities in North America a First Alarm will bring two Pumpers/Engines, one Aerial/Ladder, and one District/Battalion Chief.  A Second Alarm will bring another 2 pumps, 1 aerial, and another district (or higher) chief.  Each subsequent alarm will bring roughly the same complement.  Specialty apparatus such as Heavy Rescue, Haz-Mat, etc will be dispatched at a predetermined alarm level based on the nature of the incident and type of occupancy; e.g. a residential working fire going to a 2nd Alarm or higher will usually get a Rescue Squad attached; a 1st or higher alarm involving hazardous materials will always get a HazMat unit dispatched; occupancies such as hotels, hospitals, etc will usually have more apparatus on initial alarms (maybe 3 Pumpers, 1 Aerial, 1 Rescue Squad, and 1 DC for 1st Alarm).
A 5 Alarm fire in Toronto for example, would likely have the following: 10+ Pumpers (some of which may be Rescue class), 4 or 5 Aerials/Ladders/Platforms, 1 or 2 Heavy Rescues (one may be a Rescue-class Pumper), 1 Haz Mat unit (air quality monitoring, runoff water control, etc), 1 or more Air Supply units for SCBA exchange, a Rehab unit, 2-4 District Chiefs, 1 or 2 Platoon Chiefs, a Division Commander, and the on-call Staff Officer(s).  This can be reduced, added to, or changed at the discretion of the Incident Commander based on operational needs.

 

[Meridian]

Great! Solid response, much appreciated!