Multiple-alarm fire

One-alarm, two-alarm, three-alarm fires, are categories of fires indicating the level of response by local authorities, with an elevated number of alarms indicating an increased number of phone alarms went off during the fire. The term multiple-alarm is a quick way of indicating that a fire is severe and is difficult to contain. This system of classification is common in the USA among both fire departments and news agencies.

Definition

A common misconception is that a "3rd-alarm fire," for example, means that three firehouses responded to the fire. This is not the rule behind the naming convention, although some cities may use the number of firehouses responding for multi-alarm designations because that is the simplest way to determine an alarm number.

The most widely used formula for multi-alarm designation is based on the number of units (firetrucks for example) and firefighters responding to a fire; the more vehicles and firefighters responding, the higher the alarm designation. (Note: In most cities, a "unit" can be anything from a tanker or ladder truck to rescue vehicles to even cars driven by the chief and deputies.)