Why explosives could not have been used:
"Since their inception in the late 1800s, blasting engineers have understood that building implosions work best when the forces of gravity are maximized. This is why blasters always concentrate their efforts on the lowest floors of a structure. While smaller supplemental charges can be placed on upper floors to facilitate breakage and maximize control as the structure collapses, every implosion ever performed has followed the basic model of obliterating structural supports on the bottom few floors first, "to get the structure moving.""
"...for explosives to be considered as a primary or supplemental catalyst, one
would have to accept that either, a) dozens of charges were placed on those exact impact floors in advance and survived the violent initial explosions and 1100+ degree Fahrenheit fires, or b) while the fires were burning, charges were installed undetected throughout the impact floors and wired together, ostensibly by people hiding in the buildings with boxes of explosives. There is no third choice that could adequately explain explosives causing failure at the exact impact points."
“The chemical properties of explosives and their reaction to heat render scenario A scientifically impossible and scenario B remarkably unlikely, as we know of explosive compound that could withstand such force and/or hear without detaching from the columns or simply burning off prior to detonation.
There are other problems with both scenarios: Given the consistent weight distribution around the outer perimeter of each structure, one would have needed access to a prohibitively large quantity of load-bearing I-beam columns to allow “cutter charges” to initiate failure. Those columns would have needed extensive preparations, also known as “pre-burning”, to allow the explosives to perform their function. And in order to prepare the columns you first had to be able to see the columns, which means at least partially removing the outer-perimeter interior walls of all blast floors, including furniture, plumbing, conduit lines, insulation, etc.
All of this would have been performed within 55 minutes between plane impact and collapse – working in an environment of unspeakable heat and destruction – or have been performed completely undetected, in advance, on multiple floors in both buildings while suffering no adverse effects from planes’ impact with these same areas.
This is impossible.”
-Brent Blanchard
"Director of field operations at Protec Documentation Services...
Protec is one of the world’s most knowledgeable independent authorities on explosive demolition, have performed engineering studies, structure analysis, vibration/air events in more than 30 countries. These include the current world record-holders for documents the work of more than 20 explosives contractors who perform structure blasting as a primary source of revenue…"
http://www.implosionworld.com/Article-WTC STUDY 8-06 w clarif as of 9-8-06 .pdf
Plus, how could they have placed all those explosives in there without them knowing?
"The demolition of the Washington DC Convention Center in 2004 involved preparations that
went on for months. Massive crews were at work, placing explosives around ~500 columns and doing other preparation work. The crews and activity were highly noticeable to people in the area."
Wrecking Corp. Razes Washington Convention Center | Construction Equipment Guide Story
http://www.911myths.com/html/wtc_power_down.html
And this was on a project MUCH smaller than the WTC buildings!