9/11 fire-fighters: explosives in building

The video below recently came out of fire-fighters witnessing explosions in the LOBBY of the buildings after they were hit by the planes. In the LOBBY of the buildings??? Professor Stephen Jones found military grade explosives throughout the debris, this now confirmed by many others. From an engineering perspective the 3 buildings that fell on 9/11 were clearly assisted by explosives, fire alone could not have caused such collapses. In proper demolition style weakening of the central columns at the base by explosion was required before the whole thing could be systematically taken down. It looks like this is what the fire-fighters in the video below witnessed and were injured by,

http://www.youtube.com/watch?v=Q8DRVqSSyb8&feature=related