In the United States and Canada, the seriousness of a fire is classified using a system of alarms, with one-alarm fires being the least serious and five-alarm fires being the most serious. The number of alarms indicates the level of response by local authorities, with more alarms indicating a more severe fire that requires more equipment and manpower to contain. The most widely used formula for multi-alarm designation is based on the number of units, such as firetrucks, tankers, rescue vehicles, and command vehicles, as well as firefighters responding to a fire.

A five-alarm fire is the most serious type of fire, requiring a lot of assistance from the outside due to the large size of the fire. In Rochester, a five-alarm fire is the largest response. The alarms are used to bring in more equipment and manpower due to the size of the building and the amount of fire involved. A typical fire in a small structure will usually require only one or two alarms, while a large-scale fire in a commercial building would require three alarms or more.

In summary, a five-alarm fire is the most serious type of fire, requiring a large response from local authorities due to the size of the fire and the amount of equipment and manpower needed to contain it.