"There at least three different types of credible nuclear threats that exist today—two more than during the Dr. Strangelove days.
Scenario 1 is the fear that set the original civil defense program in motion—an apocalyptic exchange between the United States and Russia or China involving hundreds of thermonuclear weapons. The U.S. population would theoretically have a 20- to 30-minute warning before the multi-megaton bombs began bursting in air, spreading radioactive fallout in overlapping lethal circles and the lights started going out—for good.
Scenario 2 is the nuclear terrorist scenario, i.e., the detonation of a smaller, 10-kiloton device in a major American city. Those fortunate enough not to be among the tens of thousands killed during the initial blast would have a short time to protect themselves from the subsequent, less serious fallout.
Scenario 3 is the recently emergent North Korea scenario, involving the airburst of a 100- or 150-kiloton device over an American city, perhaps Los Angeles, with, hopefully, a 30-minute warning. The result, according to NUKEMAP,would range from an estimated 195,000 to 241,000 deaths and 510,000 to 629,000 injuries from both the blast and radioactive fallout, depending on the bomb’s yield."