Nuclear Blast

"A nuclear blast is an explosion with intense light and heat, a damaging pressure wave, and widespread radioactive material that can contaminate the air, water, and ground surfaces for miles around. A nuclear device can range from a weapon carried by an intercontinental missile, to a small portable nuclear device transported by an individual. All nuclear devices cause deadly effects when exploded.
Hazards of Nuclear Devices:
The danger of a massive strategic nuclear attack on the United States is predicted by experts to be less likely today. However, terrorism, by nature, is unpredictable.

In general , potential targets incluse: 

• Strategic missile sites and military bases.
• Centers of government such as Washington, DC, and state capitals.
• Important transportation and communication centers.
• Manufacturing, industrial, technology, and financial centers.
• Petroleum refineries, electrical power plants, and chemical plants
• Major ports and airfields.

The three factors for protecting oneself from radisontion and fallout are distance, shielding and time. 

•  Distance - the more distance between you and the fallout particles, the better. An underground area such as a home or office building basement offers more protection than the first floor of a building. Shielding - the heavier and denser the materials - thick walls, concrete, bricks, books and earth - between you and the fallout particles, the better.
• Time - fallout radiation loses its intensity fairly rapidly. In time, you will be able to leave the fallout shelter. Radioactive fallout poses the greatest threat to people during the first two weeks, by which time it has declined to about 1 percent of its initial radiation level..."
  Nuclear blast