The energy to toss the block up in the air comes from the energy that is stored in the form of compressed air in the cylinders. I will admit that was a pretty impressive block toss! These diesels are probably 18:1 at 100 psi, with big displacements. There really is a lot of energy there.
As for the block failure, damn that was cool. I watched the video several times. I’m inclined to think the failure is from fatigue of the block. When your up at crazy alternating stress levels, things can fatigue pretty quickly.
It could be a big ignition in the crankcase (2 stroke) but I doubt it as that would have sent a lot of shrapnel around and into the audience, not that a block flying around is not dangerous enough!
Awesome vid, thanks for posting, plus rep! :thumbup