"Did investigators consider the possibility that an explosion caused or contributed to the collapse of WTC 7?
Yes, this possibility was investigated carefully. NIST concluded that blast events inside the building did not occur and found no evidence supporting the existence of a blast event.
In addition, no blast sounds were heard on the audio tracks of video recordings during the collapse of WTC 7 or reported by witnesses."
9/11/2001 radio broadcast: "...I was just standing there, ya know... we were watching the building [WTC 7] actually 'cuz it was on fire... the bottom floors of the building were on fire and... we heard this sound that sounded like a clap of thunder..."
"Somebody grabbed my shoulder and I started running, and the shit's hitting the ground behind me, and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it..."