Joe has a great example of what even a small detonation will do to steel plate.
PSI is sometimes a misleading measure.
Take air pressure. 14 PSI doesn’t sound like much but put a human sized door between 14 PSI and a vacuum and you have 21 tons of pressure.
That’s how the slight breeze on a small sail can produce over 10 tons of pressure, pulling along a boat on the water.
Or how a little bitty amount of unconfined Boomerite can blow the crap out of welded steel plate.
But it wasn’t unconfined, the 600 gm of chalk dust tamped ( not sure that is the right word ) it . Ie.. it provided the resistance needed for the wave to become destructive rather than vent . I suspect it would be interesting to see the same target shot with nothing on top of the boomerite .
I think you’d get the same effect, tamped or untamped… It’s the near instantaneous overpressure than does it!