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How Big Is a "10-Alarm Fire"?And how does that system work, anyway?

By Daniel Engber
Posted Thursday, May 4, 2006, at 6:54 PM ET

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A firetruck. Click image to expand.

One of the worst fires in a decade hit Brooklyn on Tuesday, May 2. Hundreds of firefighters responded to what began as an eight-alarm blaze and had progressed to 10 alarms by the evening. (The fire had shrunk to two alarms on Wednesday morning.) How does that alarm system work, anyway?

The number of alarms corresponds to the number of firefighters called to the scene. But there's no simple relationship between the two. A two-alarm designation doesn't mean you're calling in two companies, two brigades, two firehouses, or twice as many people as you would call in for a one-alarm. The precise meaning of an "alarm" varies depending on the fire department. In New York City, dispatchers send out 25 units and 106 firefighters for a two-alarm fire, 33 units and 138 firefighters for three alarms, 39 and 168 for four, and 44 and 198 for five.

A "unit" can refer to any kind of firefighting vehicle: for example, a fire engine, a ladder truck, or even a civilian car—sometimes called a "buggy"—for the fire chief. In most cities, dispatchers will respond to a one-alarm fire with three or four units and then send a few more for each additional alarm. The FDNY doesn't use the "one-alarm" designation; it sends out 12 units for an "all-hands," the level just before two alarms.

When did they start using the multi-alarm ratings? Up until the 1850s, American fire departments relied on watchtowers and church bells to announce an emergency. Bells would ring throughout the city, and firefighters would check the sky for smoke to figure out where they needed to go. A couple of big cities like New York and Philadelphia had more sophisticated systems: The bells would sound out a coded message, with a certain number of rings corresponding to a particular direction or district.

Boston put the first telegraph alarm system in place in 1852. Throughout the city, the fire department installed call boxes rigged up to ring gongs in local fire stations and a central headquarters. A firefighter could consult a codebook and use a system like Morse code to relay a single message to each location. Other municipalities soon followed suit. In New York City, a pair of rings followed by another pair served as a request for another fuel wagon. Four rings in a row meant, "The chief is on the scene." In general, more rings referred to a more intense fire. A particularly big blaze was denoted by a code of four rings followed by another four and came to be known as a "four-alarm fire."

Not every city used the same codes. To this day, the Chicago Fire Department ranks its fires as "2-11," "3-11," "4-11," and so on, instead of the more familiar multi-alarm ratings. That's probably because those were the original telegraph codes: Two rings in rapid succession followed by one and then another might have referred to what was elsewhere called a two-alarm fire.

Bonus Explainer: Where does multi-alarm chili come from? The coinage was made famous by a journalist based in Austin, Texas, named Wick Fowler. He started a company selling a mix for his "Two-Alarm Chili" in 1964 and won the international chili championship in Terlingua six years later.

Got a question about today's news? Ask the Explainer.

Explainer thanks Jim Long of the New York City Fire Department and Peter Molloy of the Hall of Flame Fire Museum.

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Daniel Engber is an associate editor at Slate. He can be reached at .
Photograph of firetruck by Mario Tama/Getty.
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