[The_Reader_David]

Why does everyone evaluate duck and cover against being at ground zero (where it's pointless for even smaller asteroids or any nuclear weapons)? The point is to improve one's chances if one is on the outskirts of the area effected.

I leave you to consider the question with the aid of the Earth Impact Effects Program from Imperial College, London and Purdue University. I think you'll find that duck and cover would be helpful in a variety of circumstances involving a half-mile wide asteroid.

[Williams]

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.