A few years ago I brewed an English bitter, 2 days later when fermentation really took off, I heard some hissing from the carboy (I had taped the bung on the top because it wouldn’t stay in the carboy). I went to investigate to find the airlock clogged and krausen barely escaping from the sides of the bung.
I took the tape off, and POP! the bung shot to the ceiling, and krausen got everywhere. On the ceiling (10 feet), and everything within a 5 foot radius, even up into my sinus’s, and in my eyes. The velocity of that yeast gunk was way more violent than I had anticipated.
That was a fun day. I don’t tape my bungs down anymore, and have been using blow-off hoses ever since.