
See here for the High-Yield Detonation Effects Simulator - an experiment based on public data and showing the destructive zones of large explosions.
This calculator shows the distribution of radioactive fallout by wind from nuclear bomb blasts of various yields (explosive force). The contours depict calculated radiation doses 96 hours after a nuclear bomb's detonation.
Select location, wind direction, wind speed and yield. (Requires Java, which you can download here).
Imagine you live within:
3km: Immediate fatalities are 100% due to blast waves, ground temperatures of thousands of degrees celsius and lethal doses of X-rays.
5km: Acute radiation sickness begins rapidly and is usually fatal. Immediate symptoms include nausea, vomiting, diarrhoea, bleeding from nose and mouth, low blood pressure, stroke and cardiovascular shock.
8km: Immediate fatalities are 50%. All exposed skin is severely burnt and symptoms above appear soon after.
20km: Blast waves are felt - windows may shatter, causing injury. Acute radiation sickness may lead to severe gastrointestinal symptoms, bleeding, immunosuppression and heightened risk of leukemia, lymphoma, thyroid and bone cancer.
80km: The bomb flash blinds everyone for up to an hour. Those looking at the blast will have permanent visual deficit.
Later: Psychological trauma, panic, devastation of economy, disruption of food, water, sewage and medical facilities and mass evacuation cause widespread disruption.