Incindre: I've been a fire warden at several different buildings and I've never seen the point of hardcore sirens in the stairwells; make it dangerous IMO.
My reasoning is, people are only in the stair wells because they're evacuating anyway, and the last thing you want is loud noise impairing people's ability to think rationally in an already stressful situation.
Also, single file down the stairs people! Often the Firewardens have to get back up those very stairs you're clogging 3 abreast.
Lots of folks use the stairs for exercise or for moving between a few floors quickly, I know when I was able bodied I used the stairs in preference to elevators.