The Lockyer Valley doesn’t really have many transmitters of its own, it gets just about all of its radio and TV from either Brisbane or Toowoomba. I presume these would have alerted locals of the imminent danger
Back in Victoria during bushfire events you used to get the SEWS signal (which sends a shiver up my spine everytime I hear it still) and the announcement of affected locations and those in immediate danger. It’s scary radio even if you’re not caught up in it.
From memory, after Black Saturday most if not all commercial radio and TV broadcasters signed up to be official emergency broadcasters, meaning they would interrupt programs to broadcast emergency warnings when required. Certain failings were exposed when the Churchill fire burnt through the main Gippsland transmitter site on Mt Tassie (include the ABC local radio transmitter), which meant a lot of emergency warnings weren’t getting out as they should have. I recall the local community broadcaster there (which transmitted from a different site that was safe from fire) ditching their programming and taking the ABC local radio feed just to help get the warnings out there once 100.7 went off air