Billy T: I do not know what assumptions and calculations you used. This site http://nuclearweaponarchive.org/Russia/TsarBomba.html Provided the following data about the USSR test of a 50MT weapon. This weapon was built and tested for political purposes. It was not considered a usable weapon due to serious practical problems relating to delivery, stock piling, and cost/benefit considerations. For various reasons, many smaller weapons are more useful than one big one. The article said nothing about fire storm effects, which do not seem to be mentioned in any article I have ever read about nuclear weapons, probably due to such effects only theoretically occurring within the radius of absolute destruction (this is a guess on my part). Note that “ordinary houses” were severely damaged (not totally destroyed) out to 35km (about 22 miles). this is about half the distance from Washington to Baltimore. The total destruction range of 25km is about 16 miles. Note this is for a 50MT weapon that is not expected to be used in a nuclear war, rather than the more practical weapons in the 1 to 5 Megaton range. Your calculations seem to indicate far worse effects than actual test results. You are scaling thermal effects from 50MT to 5MT (with a factor of 32%), and refer to igniting dark paper and brown leaves. This is not the material which results in fire storm effects. 32% might be correct for scaling temperature effects. I have long since forgotten how to scale blast and pressure effects, but believe that a 32% factor is a gross over estimate. I seem to remember a total destruction area about 3 to 5 miles in diameter (1.5 to 2.5 miles in radius), which would suggest a linear scaling from 50MT to 5MT. This suggests that “ordinary houses” would survive beyond three to five miles. I am not trying to minimize the horror of a nuclear war. We would lose one third to one half of our population, 50 to 100 major cities, and most of our major manufacturing facilities. The US would probably take 50 to 100 years to recover. However, it would not be the end of our civilization. My previous post only pointed out that the US would still have the basic requirements to start the recovery, while the USSR would be without such resources. We would have many compete libraries, paved roads from coast to coast, machine tools, small manufacturing facilities, many automobiles & trucks, and trained technical personnel, while the USSR would not have such items necessary for starting to rebuild a modern technological culture because all such items in the USSR were (still are, I think) concentrated in their major cities.