I found an archive post from Kottke talking about how loud the Krakatoa volcano was–apparently loud enough to burst the eardrums of people 40 miles away. From the article linked in that post:
The human threshold for pain is near 130 decibels, and if you had the misfortune of standing next to a jet engine, you’d experience a 150 decibel sound. (A 10 decibel increase is perceived by people as sounding roughly twice as loud.) The Krakatoa explosion registered 172 decibels at 100 miles from the source. This is so astonishingly loud, that it’s inching up against the limits of what we mean by “sound.”
The Kottke post also talks about how loud a Saturn V rocket is–“At very close range, the sound from the Saturn V measures an incredible 220 db, loud enough to melt concrete just from the sound“–and then finishes with an incredible fact that sperm whale calls reach 174 decibels?!