Five-alarm fire

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Multiple-alarm fire

Fires are sometimes categorized as one-alarm, two-alarm, three-alarm fires, or higher. The number of alarms correlates with the level of response by local authorities, with an elevated number of alarms indicating increased commitment of resources. The term multiple-alarm is a quick way of indicating that a fire was severe and difficult to contain. This system of classification is common among both fire departments and consequently news agencies

The initial dispatch is referred to as the first alarm and is typically the largest. Subsequent alarms are calls for additional units as needed, usually because the fire has grown and additional resources are needed to combat it or the incident is taking long enough that firefighters on scene need to be replaced due to exhaustion. The number of alarms doesn't necessarily indicate the size or the severity of the actual blaze so much as the size of the incident and how long and hard the fire department had to work to control it.

The units dispatched on the first and subsequent alarms depends on what resources are available in the area and so changes from department to department. Requests for units from outside jurisdictions normally don't occur in urban areas until elevated alarms are reached (third and above), but depends on the location of the incident and the condition of the authority having jurisdiction at the time of the incident.

History

The system of classification comes from the old tradition of using pull stations to alert the local departments to a fire in their area. The "box" would send a message to all local stations by telegraph that there was a fire, indicating the location as a number: (station area) - (box number), e.g. 11-2. Fires are still dispatched as "box alarms," following this tradition, with maps broken up into a grid of "box areas."