Radioactive Fallout Will be The Killer
Like the more than 160 million Americans who live within the danger zones, your greatest concern following a nuclear attack comes from radioactive fallout. That's the main reason you will need a well-constructed, underground bomb shelter. It's true that taking shelter under the coffee table or in the basement will increase your chances for short-term survival, but these structures will not keep you alive. Only an underground bomb shelter will guarantee your survival. Once you understand the penetrating abilities of radiation via fallout, you will be far more motivated to build a shelter underground. The concept is fairly simple - separate yourself from fallout with at least 36 inches of dirt (or varying amounts of other materials such as concrete, lead, etc.)
While the initial blast could kill a million people, tens of thousands more will die from radioactive dust which will drift for several hundred miles downrange from the point of detonation. The track it follows, just as in a volcano eruption and even the weather, is one relevant to the jet stream, a prevailing pattern of winds and weather coming from the west or north west. In other words, the fallout will most likely travel from west to east.
Fallout will begin appearing within 5 minutes (or less) after the initial blast. Depending on the size of the bomb, type of detonation (underground, ground level, or air burst) and height of the mushroom cloud which, as mentioned earlier, is filled with radioactive debris, gamma-charged dust particles can travel across several states before falling to the ground. As time goes by, the radioactive energy literally burns itself out as the powdery surface left will return to near normal levels. This can take as long as several weeks, but typically should not last more than 4 or 5 days. The immediate blast area will be uninhabitable for thousands of years. A lot of factors will play in determining the level or radiation at different intervals of time and distance from the blast. Included are weather, temperature, wind speed, and size of the weapon. You best defense against fallout? A carefully planned, well-constructed, and fully stocked underground bomb shelter.