AUSTIN (KXAN) — It’s common to hear fire departments describe the intensity of fires as two-alarm, three-alarm or sometimes even four-alarm, but what does that really mean?

It’s easily assumed it just means that fire is really big and more firefighters need to get there to help put it out — and that’s partially correct.

Michelle Tanzola, the Austin Fire Department’s public information and marketing manager, provided AFD’s “A Civilian’s Guide to the Austin Fire Department,” which explains how the alarm levels dictate how many crews are sent to fires of varying intensities.

For single-alarm structure fires, AFD responds with 24 firefighters and two battalion chiefs. That includes four engines, two ladder trucks and a rescue unit.

If the Incident Commander feels more people need to respond, they have the authority to increase the alarm level, and for two-alarms fires, the response is doubled. If it goes to three alarms, the response is tripled, and so on.

When AFD responded to a vacant senior living facility that caught fire March 7, it ended up as a two-alarm fire due to the size of the building. Apartment-style buildings typically require two-alarm responses.

For fires that may not rise to the standard for the alarm-level response, AFD dispatches resources using a “light box” call. That can be dispatched for anything from an oven fire, smoking electrical outlet or a fire in an unattached shed or another outbuilding, but it simply means the fire doesn’t require a full single-alarm response.

Specifically, the light box call responds with three engines, one ladder truck and one battalion chief. AFD’s light box response is similar to most departments’ full structure fire calls.