It depends on how far from the bomb you are. For any reasonable bomb there's a distance where duck and cover helps. It takes less overpressure to kill you wit

It depends on how far from the bomb you are. For any reasonable bomb there's a distance where duck and cover helps. It takes less overpressure to kill you with flying debris than to kill you directly. When the bomb is big enough this no longer applies, but in this realm adding more power to the boom doesn't do much to increase the damage area. There's no point in such a bomb unless you detonate it at high altitude--that means rockets, and you need a lot of rocket to lift such a bomb.