Multiple-alarm fires is a convention used in the United States to quickly communicate and understand the severity of a fire. For instance, news outlets report on incidents such as a "four-alarm fire" to indicate a blaze that is more difficult to handle than a "two-alarm fire." While it is true the higher degree of the fire alarm, the more firefighters are dispatched to battle the blaze, this is not a one alarm to one fire house relationship.
Unit Response Protocols
Fire departments have dispatch systems which receive emergency requests and coordinate the efforts of firefighters. To aid in communication, each department has a series of short codes that correspond to actual information. In New York, 10-21 means "one-alarm fire." Every degree alarm requires a different number of response units, which can be any type of vehicle including fire engines, ladder trucks and supervisor trucks. Fire companies send a different number of response units for each degree alarm, depending on the city you are in.
One Alarm Fire
When an emergency call is receive by the fire department, a discovery set of units are dispatched to the location in question, often called a "box" alarm. If the first responders confirm there is a blaze happening, a one alarm fire is issued. Once this happens, an additional set of units are dispatched to the location to battle the blaze. The exact number of units that respond varies based on your location. For instance, in Washington, DC a one alarm fire indicates six fire engines, three ladder trucks, one rescue squad, two fire chiefs and one ambulance are on scene.
Multiple Alarm Fire
First responders on the scene of a fire are the best to assess the situation's severity. They communicate the size and intensity of the blaze to dispatchers and raise the degree of the fire alarm as necessary, i.e. two alarm fire, three alarm fire. Each time the degree moves up, additional units are dispatched to the scene of the fire both to relieve units and to add support to firefighting efforts.
Fire Alarm Escalation
Theoretically, an enormous blaze can escalate the degree of a fire alarm indefinitely. However, there are norms. For instance, the New York Fire Department has a short code system that only accommodates up to a five alarm fire, assuming that most situations are handled with this level of response. However, there are instances where blazes reach 10 alarm fire level and fire companies have to respond accordingly. As fire companies contain situations, intensity lowers as does the degree of the fire alarm.
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