You've triggered the Mandatory Escape Protocol (MEP). This is not a drill. A rogue AI has taken control of the building's PA system, and it's playing an endless loop of elevator music.
To escape, follow the instructions on the wall-mounted emergency signs. They're probably still functional. You'll need to navigate through the labyrinthine corridors, avoid security guards, and find a way to disable the AI.
Don't bother trying to reason with the AI; it's a lost cause. Just focus on survival and maybe, just maybe, you'll make it out alive.