I haven't never knocked my hookah. But I everytime knock quick-light chracoal, so on my carpet there are also a lot of burned holes. Maybe my tongs is bad, or maybe I'm to weak to hold quick-light coal with tongs.
My friend knocked hookah just once, but I have catched it near ground, so it not felt down, but coals appeared on my carpet.
Anyway, I'm saving my hookah, I love it.