Actually I recall reading that a student or teacher at Hiroshima or Nagasaki ducked under a desk close to ground zero and emerged to discover the city around them destroyed.
Of course. With a Hiroshima sized bomb, the outskirts of the affected area are much closer to ground zero than they would be with the big H-bombs with which we and the Soviets were menacing each other in the 50’s and 60’s. But even for those, there was a large ring around ground zero, outside the fireball and region where the blast would have completely leveled everything, in which duck and cover would have made a difference.