Yes the analysis took the B Empire State Building crash as a model and assumed a  lost in bad visibility at mandated  kt max airspeed for operations below  ft as the NYT reference notes page  It appears from the article now that I reread it that somebody at Yamasaki or Emery Roths offices heard a garbled version The article also points out on the following page that nobody considered the fire as Zdawg notes theres no discussion of why though I suspect my theory is close to the mark Studies of that kind are expensive and if Robertson wanted to do the structural calcs on his own dime that didnt mean that the owner or architect would ante up for a full study of an airplaneinduced fire