The school I used to go to had a simple policy; if the
fire curtain did not
drop, then we did not panic.
Actually, the SM would
call "Hold, please" over coms, and project it to the actors onstage. He/She then would use the
PA to make an announcement. If, for any reason, there needed to be an evacuation, the audience was instructed to leave the
theatre via the emergency doors, and the actors/technicians would leave in an orderly fashion via the
stage door. The only people who had some problems (in theory) were the spot ops; because they would have to exit via the
catwalk to the midrail and down a ladder.
However, in the event of a Zombie Apocalypse, the SM would pull the firecurtain, which also opens air vents in the ceiling, and we would proceed to crawl to the
grid and out the air vents; in this emergency situation, the spot ops had the advantage.