It is certainly possible to belt safely - but how many of them do? You can avoid harm - if you're sensible about it and don't overdo things. But how many roles even allow that these days? I've worried for a long time that musicals themselves are becoming unrealistically demanding vocally, with huge ranges to be traversed, at full volume. Two excellent shows come to mind (both mega-hits), Les Misrables and Miss Saigon. How long can anyone sing those parts before wearing out? One line alone (Ellen's "Chris, what's haunting youuuuuuuuuuuuuuuu" in Miss S, sung in the chest register) performed daily and twice on Wednesdays & Saturdays would do enough damage on its own, and the show is full of them.

I used to fight regular battles with my girls, trying to get them to sing it in head-register (no, I wanna be dramatic) until - where I could - I finally refused to play that duet. I also spent more hours of my life than I can remember transposing scores down and re-modulating key changes. But that was a theatre academy. The big bad Real World doesn't work like that. And when you're playing rehearsal piano or harp in the orch pit in the professional shows, you have no power over what happens onstage. All you can do is play, sigh, and collect your paycheque.

Just catch a listen to Good Morning Baltimore from the musical Hairspray. And don't get me wrong: I'm not being snobby. I think this is a great show number. It's upbeat, catchy, and carries you along on a tide of enthusiastic good-time spirit that is huge fun to listen to. But I wouldn't give you tuppence for what her voice is going to sound like in a year's time, especially if she (or someone) has to perform this 8 times a week.

http://www.youtube.com/watch?v=9TodPbIXnKw

When I hear that abrasive opening uh-uh-OH it just makes my throat ache; ditto the lyric "start" which begins high, is held for several bars and then modulates UP. No voice can go there too often and survive unscathed. Even operatically-trained performers with strong technique can come a cropper if they take on roles which demand this sort of singing. Listen to Joan Diener at the beginning of Man Of La Mancha. Then listen to her at the end of it - and I'm only talking about the cast recording. I heard on the grapevine (or read somewhere?) that she ruined her voice playing Dulcinea, and she seems never to have done anything with great success after that show (though I only have the fallible Wiki word on that).

Interesting take in one of the obits: On the popular original cast album, Ms. Diener sings in chest and head voices, and the two qualities suggested an inner struggle — a fight for the soul of the woman. She was of both heaven and earth.
The song "Aldonza" remains a frank, blistering tirade of self-recognition and self-abnegation in which angry, broken Aldonza refutes any elevated labels other than "kitchen slut" and "whore." Ms. Diener spat out that she was "spawned in a ditch" and "born on a dung heap — to die on a dung heap."

Those lines were not written to be sung moderately, and she was riveting - but at what cost?