Our county has where the fire ground commander will call communications and advise to have all units to leave the buildng. Communications will play a rapid high low beeping signal and announce " ALL UNITS (Address) EVACUATE THE BUILDING" All apparatus on the fire ground will then turn on sirens and blow air horns in continuance long blast unit all firefighters have cleared the building.
There is even a beeping signal for a missing fighter on the fire ground.
Yah its common to use the air horn.. we also use the HI-LO siren tones on the rigs. Its a mutual understanding in this area, that the HI LO is not used while enroute to calls, and only used as am emergency evac. Even our EMS and police don't use the HI-LO tones, so its very recognizable on any of our MA scenes. Hear the tone.. report to command and take roll call. Works good!
We use the "high low" siren for our evacuation signal. At the same time the dispatcher will set off an "EVAC" tone over the radio and then state "All companies operating at (blank) by order of command evacuate the building"
We use the radio command "Abandon, Abandon, Abandon" followed by the SOS signal on the air horns.
SOS equals three short, three long, and three more short horn blasts, then a short wait, then a repeat of the SOS. What that means in real life is that if we hear more than a couple of shorts (the "Charge the Supply Line signal) then everyone bails out, we get a PAR, and we determine why the bailout was ordered.
In our area, all of the FD's use the radio first(Main Street Command to all Companies operating at 1234 Main Street, exit the structure immediately and get a PAR). This message is followed by long blasts of all the apparatus operating on scene.
1. In the event of a dangerous situation in a fire building that requires an immediate evacuation of firefighters all trucks will blow sirens and air horns for a period of not less than 30 seconds.
2. Upon hearing this signal, all firefighters in the building will immediately exit using the quickest route.
3. Once outside all members will meet with the Chief or Officer in charge for an immediate head count to insure all personnel are accounted for.
4. This command is to be initiated only by the Chief or Senior Officer. This signal is to be used only when there is a threat to the men inside or in the near proximity of the building.
5. Firefighters outside the building will conform to a defensive attitude when this signal is given - then report to the Chief of Officer in Charge for head count. “Defensive attitude” means all equipment and personnel are withdrawn to an area outside of the collapse distance or height of the wall of the structure involved.