I'm an independent filmmaker and am trying to describe the damage done by a 25Mt nuclear device going off at ground level... especially the point at which victims might survive the initial blast wave. All of the information I have found is based on an altitude-triggered explosion. Is there anyway of even roughly saying 'okay, at six miles--or nine miles, or whatever--from ground zero they'll be pretty sure of immediate survival'? I'd like the script to be as accurate as possible, obviously, rather than make a stupid guesstimate.
Thank you.

What may help you is a publication by the US Government:

"The Effects of Nuclear War" (Washington: Office of Technology Assessment, Congress of the United States, 1979).

The Effects of Nuclear War (http://www.fas.org/nuke/intro/nuke/7906/)