Bet the owner of the safe gets sued.
If the case can be made that the fireworks were actually a form of booby trap, he’ll go to prison. But I doubt it can.
And, frankly, a safe is the “safest” place you can put them. It is very responsible. Sometimes you can’t protect people from their own stupid acts.
I’ll bet the problem is that these were professional grade fireworks and, while some fireworks are legal for individual purchase in NH, these sort probably require a license to use or even possess.