This is a discussion at the firehouse by the firemen that were at the trade center when it collapsed.
There was 2 guys that were filming a documentary about firemen and it so happend that they did that on that day, september 11 2001.
Later, the following months, that docu was put together and released to the public by i guess CNN or someone like that. 
This is a part that they cut out, it shows the fireman talking about when they just ran away from the WTC and talking about how it looked and sounded like there was explosions floor by floor and the building was coming down like it was a professional demolition.
I may later post the complete official docu, where you will be able to see how nicely this important part was cut out.