I'd suggest contributory negligence. The closely supervised worker on a factory floor should be told when to wear hearing protection etc. and can try to claim if he can show hearing loss attributable to the job. The musician is a) probably self employed b) engages in many different noisy activities and c) often controls his or her own noise exposure. It's most likely a lot harder making a claim for negligence stick in such circumstances. I did have one of those phone calls a while back, and genuinely missed part of the caller's opening sentence. I said, 'pardon, could you repeat that' and they hung up on me.... :-) The reason I posted the link was that it seems to relate, at least as I read it, to one production of one work in one venue not an incremental effect over a period of time. It has nothing to do with the fact that I happen to think that anybody forced to listen to Wagner deserves compensation...