Impact and Initial Blast Points

http://en.wikipedia.org/wiki/World_Trade_Center#Destruction
The first tower was hit just above the 1100 foot level & the 2nd tower was hit just above the 900 foot elevation.
77x12'=924feet & 93x12'=1116feet or 900'+ & 1100'+

http://en.wikipedia.org/wiki/Collapse_of_the_World_Trade_Center#Initial_opinions_and_analysis

http://desertshapes.blogspot.ca/2013/07/peter-lance-investigations-and-reports.html