Look at the graph in http://www.epa.gov/radiation/docs/er/planning-guidance-for-r..., pages 29, 31, and 32. You can be well outside the 'minimal damage' zone, but inside the 'dangerous fallout' zone for miles.

For an extreme non-nuclear example, read http://en.wikipedia.org/wiki/Kaprun_disaster#The_disaster: "12 passengers from the rear of the train who successfully broke a window followed the advice of another escaped passenger who had been a volunteer fire fighter for 20 years, and travelled downward past the fire and below the smoke."

You may be hosed either way, but choices you make can have huge effects on your chances.