When there is a structural fire an alarm is sounded. Most departments send a designated number of engines and or trucks on a response. We would send 3 engines and 1 truck and 1 battalion chief. On a second alarm there would be an additional 3 engines, 1 truck, 2 battalion chiefs and 1 deputy chief. On a third there would be 3 more engines, On a fourth 3 more engines. So on a 7th alarm fire you would have a total of 21 engines, 2 trucks, unless additional trucks were called, 3 battalion chiefs, and 1 deputy chief. In reality lots of other big chiefs would show up to watch or try to get in on the action. The response to a fire is controlled by the number of alarms so you have a progression of people and equipment responding. It is not the same response on each additional alarm.

I think Lestermount has pretty well covered this but I wanted to add a few things. I’ve never been to a seven alarm fire but I do have a few 5 alarms under my belt. The 2nd alarm is generally the largest response. In this area, a second alarm brings out a rescue truck for air bottles and support plus the additional companies, the public information officer as well as others in the command structure are paged. At some point a duty mechanic will also be dispatched. Also keep in mind that other agencies will start to get involved, EMS will respond even if there are no injuries to standby in case there are. The police will also be called in to direct traffic and control any crowd that might gather. The Red Cross may also be requested for rehab and or to aid persons displaced by an incident. In extremes of temperature transit buses may be requested to give the displaced and firefighters a place to warm up or cool off. Usually after the 2-3 alarms the type of apparatus responding begins to be less of an issue. This is why you may see fire trucks parked away from a fire with no crews. The companies are just being used for their manpower. In a large fire, crews wear out quickly and have to be rotated. A 7 alarm fire in the heat of August might only be a 4 alarm fire in October.

Also keep in mind that as companies become committed to a fire that fire protection for other areas must still be maintained. This is done through company move ups. Fire companies in other parts of town will be moved to answer calls in the areas of some of the now empty stations. Only a very large dept like FDNY (which recently had a 7 alarm fire and I suspect is the basis for this question) could handle an incident of this size without help from other departments.

When a fire department is committed to a large incident it usually calls for mutual aid from neighboring departments. This could include volunteer as well as paid departments. They may respond to the fire scene but more likely will be asked to cover empty stations.

In resonse to a fire, the fire departments of town or city will ring an alarm, first one alarm, then more as needed. A seven-alarm fire will call out seven fire departments; a big fire! Try this link for more information:

http://wwww.firehouse.com/

7 alarm fire refers to the number of fire engines that were called to the scene, the bigger the fire, the more trucks they call in. It is also used to measure chili hotness, so if it is a seven alarm fire chili, you better be prepared for fire going in and liquid magma coming out.

A really big one. This alarm indicates that many fire trucks will be sent out.

when it’s called “seven (or any #) alarm fire, it refers to the number of fire stations called to fight the fire. seven is a very large fire.

7 alarms rang in response to the fire. (7 firehouses were called, pretty big fire)