The version I heard was that the top floors were allowed to have
insufficient insulation around the steel because the city did not
want asbestos to be used. Asbestos already put in the thing was
allowed to remain, but the upper floors got an inferior material
and the design was not hacked (maybe it could not have been) to
allow for thicker layers. Dunno which version is true. Dunno
whether even the original design using asbestos all the way up
would have sufficed what with all that jet fuel.

Oy.