Doing some rough calculations, in order for this to work how the author proposes, I would estimate that the "fusion
bomb", at a very minimum, would have to vaporize steel up to about 100ft away. (Based on the dimensions of the core, the depth of the basement levels, and this quote: "
In the cellar, from all of the 47 ultra strong steel pillars, the steel was melted completely more than over 20 meters length." -
http://members.surfeu.fi/11syyskuu/soldier4.htm)
Now also based on the dimensions of the building, I estimate that the farthest distance the people in the stairway could be from the "fusion
bomb" is around 150ft. So if it vaporizes steel at 100 feet, I do not think it would be possible for humans to survive at 150 feet.
We also have to keep in mind that the "fusion
bomb" was supposed to direct its energy upward. Here is the author describing the
bomb:
"The thermonuclear bomb used was a “pure” hydrogen bomb, so no Uranium or Plutonium at all. The basic nuclear reaction is Deuterium + Tritium > Alpha + n. The ignition of this is the Fine part, either with powerful beam array or antimatter (in a very certain way to get the necessary directed-energy effect, in order not to level the adjacent blocks of high-rise buildings, too)." - http://members.surfeu.fi/11syyskuu/soldier2.htm
If he believes the blast would be powerful enough to "
level the adjacent blocks of high-rise buildings" unless properly directed, then I think we can assume that people 150 ft or less from the
bomb would not be able to survive.
Later on, he describes the effect of the "fusion
bomb":
"In its way upwards the heat and pressure waves partially penetrated about 100 floors of concrete and steel. Ten million+ degrees of heat from a hydrogen bomb sublimised all water within concrete in a moment. Water exploded momentary into 24-fold volume and totally pulverized the concrete. Even people and computers that were there disappeared into heath and light, that is why almost nothing of them was foud in the ruins." - http://members.surfeu.fi/11syyskuu/soldier5.htm
If the
bomb vaporized the water in the concrete, it would do the same to any people unfortunate enough to be in its path. The odds of survival would have to be extremely low in that situation. He states that almost nothing is found of the people in the building, but we have just over a dozen people who survived the collapse in this stairwell.
From what I have heard the stairway walls were only constructed of fire-rated sheetrock. That will hold off a fire for a couple of hours, but I don't think it would offer any protection from a "fusion
bomb."
-Make7