I have a quick tip for all you singers out there (especially the ones at noisy bars). Put an earplug in one of your ears. It helps you monitor how healthily you’re singing. I’ve been doing it for years now, and I gotta say it’s a godsend. I can feel where the threshold of “destructive pushing” is, and I simply don’t cross it.
[Bonus fact] Most people have one ear that is far better at determining intonation. It shouldn’t take much experimentation to determine which ear to plug and which to leave open.