According to the NIST report at 10:18 a pressure pulse occurred inside WTC1. NIST had no explanation for the event. Several floors were involved.
The pulse started a fire at the 92nd floor north side that quickly moved towards the NW corner. At 10:24 the fire crossed the corner moving south. For a short time we see smoke from the entire width of 92W (starting near the center opposite to the core) indicating that the windows were blown out. After some seconds the smoke disappeared again. At 10:27 (the next time CNN shows a close up of the top floors) about 2/3 of the west side showing heavy smoke and some spots of fire.
The fire at 92 was ignored in the NIST report.
At 10:18 CNN aired the event live:
The aerial photographs of the inward bowing used by NIST were taken at 10:22. The tilt of the antenna happened also at about that time.
The Lucia Davis video of the firefighters...http://www.youtube.com/watch?v=0YvrKfWkxdw
... was taken at about 10:15 but, of course, the watch of the firefighter might be wrong for 2-3 minutes. The angle of the shadows in the street confirm the time within some minutes.
The video was taken at 67 Murray St (found by Yougene Debs). After the loud noise of an explosion the firefighters thought "Seven's exploding" and turn the heads towards the towers.
This is a little strange in itself because the fires in WTC7 were started after the WTC1 collapse.
There were reports of exploding cars but I'm not sure if these reports came prior to the WTC1 collapse. At least the cars in the parking area along North End Ave were not on fire at that time. Some rare videos from the bottom of WTC7 at that time show no burning cars but ATF personnel.
The "working hypothesis" of the FBI at that time was a car bomb in the basement of the towers. Several News channels reported it.
Finally that pressure pulse is the second unexplained event at that time. At about 4 seconds after the onset of the collapse of WTC2 two darting flames emerged from the south side of WTC1 IZ. Immediately after that a huge fire developed across the south side. Now - after 75 minutes burning in the SW half of the impacted floors - the fire swapped to the SE half. A new fire started at 105 SE corner.
After that event only one 911 call from the upper floors of WTC1 was made (connected). NIST noted a sharp decrease of 911 calls from above the burning floors.
Is it possible to connect these events by some further research or maybe by known details e.g. burning cars etc.? Or to delimit the possible meanings?