explosion (high in the air, or near the ground).

All nuclear explosions cause light, heat and blast, which occur
immediately. In addition, explosions that are on or close to the ground
would create large quantities of dangerous radioactive fallout
particles, most of which would fall to earth during the first 24 hours.
Explosions high in the air would create smaller radioactive particles,
which would not have any real effect on humans until many months or
years later, if at all.[2]


WHAT WOULD HAPPEN IN AN ENEMY ATTACK

If the U.S. should be attacked, the people who happened to be close to a
nuclear, explosion--in the area of heavy destruction--probably would be
killed or seriously injured by the blast, or by the heat of the nuclear
fireball.

People a few miles away--in the "fringe area" of the explosion--would
be endangered by the blast and heat, and by fires that the explosion
might start. However, it is likely that most of the people in the fringe
area would survive these hazards.

People who were _outside_ the fringe area would not be affected by the
blast, heat or fire. Department of Defense studies show that in any
nuclear attack an enemy might launch against us, tens of millions of
Americans would be outside the fringe areas. To them--and to people in
the fringe areas who survived the blast, heat and fire--radioactive
fallout would be the main danger. Protective measures against this
danger can be taken.