If you put a spark inside a full gas/petrol can, not much happens. Not enough oxygen. Half full? Still not such a big deal. But empty the can, leaving behind j

If you put a spark inside a full gas/petrol can, not much happens. Not enough oxygen. Half full? Still not such a big deal. But empty the can, leaving behind just the fumes and the oxygen, and you have yourself a bomb. My understanding is that the rocket here is a similar problem. It's a giant tube of explosive material. I wouldn't want to tap it with a hammer. And they've got it falling to earth at supersonic speeds, then calmly setting itself down on a barge at sea in 3m waves.