At some point something is so loud it stops being "sound" and starts being "shock" and imparts so much energy it can break things or set things on fire.
If you want to draw a distinction, ~194 dB is probably the place to do it (in Earth atmosphere). That's where the sound pressure oscillates between 0 and 2 atm and any louder would necessarily distort.
Regarding the distortion, the error due to wrongly assumed superposition becomes noticeable before that. At this point, the non-linearity of soundwaves becomes glaringly obvious.