After the shock wave has passed by, depending on your proximity to ground zero, you may have to worry about immediate threats due to fires and collapsing structures.
Your next largest problem is lethal nuclear radiation from late time Radioactive Fallout.
Within a few minutes the fireball will generate a Mushroom Cloud, taking radioactive debris and vapor up to the top of the atmosphere.
- Fortunately, the Fallout from the Mushroom Cloud can take many minutes to many hours before it reaches the ground, giving you time to go to or to find suitable shelter.
Survival Step 2: The first few minutes. DUCK - STAY DOWN. Let the Shock wave pass.
Survival Step 3: The first few hours. FIND A SUITABLE FALLOUT SHELTER.