The diesel fuel was on fire
There is no visual evidence that conclusively shows these fires. There was almost no video or images taken inside the building or from the south, on the adjacent streets to the east and west probably because the twin towers had collapsed and the area was evacuated except for emergency personnel... who were not taking pics. However this is not proof that there were fires. There was one bit of new footage of a reporter and cameramen who wandered in and one can see some intense flames licking out of the lower windows on the east side of WTC 7 below floor 8. But what was burning is hard to tell. The flames were intense and the smoke black and this could be from a number of sources.
The prevailing winds blew from the NW where the pics and well known vids were taken and this had the effect of causing a low presure on the south face which can be seen in some images to be obscured by smoke for the full height. Was this smoke from WTC 5&6? Hard to tell, but the prevailing winds would have THAT smoke pushed south and east over the WTC campus. Very little to work with here.
There were reports that all the diesel was recovered. No explanation of how or where it was recovered from. It is highly unlikely that the tank was intact after a 200,000 ton building had come down over it and it was buried just below grade as several engineering drawings show. Since the diesel was pumped up through the sub station to floors 6&7 AND had it's own power source it is reasonable to believe that when the power was interrupted the pumps ran continuously supplying diesel to those floors whether it was burned in the generators or poured onto the floor and combusted in the air. Maybe.
NIST refused to examine anything below floor 8. I would therefore immediately consider that there was something going on down there they didn't want people to know about.
The 3 transfer trusses and 8 cantilever girders failed
These trusses and girders topped off at 104' above grade... the very same distance that the upper section collapsed down at FF. Coincidence? Those structure were there in place of columns resting on bedrock... this is analogous to a bridge span which has two towers (columns) supporting the span. The area below these structures had very few columns and was structurally transparent as it were. These structures supported 42 stories of core above and the core was supporting the inside end of the floor plates. If these structures DID fail we'd see exactly what we saw. Not proof, but a logical place to look for failure.
AE911T states that 8 floors of columns had to be destroyed at once for a 100' FF. But destruction of THESE structures in the location they were would produce a 100' ff.
The engineer of the building, Irwin Cantor stated that the tower came down as a result of his trusses failing. He speculated that diesel fires had done it. That's a pretty good expert to refer to.
Electrical explosions/fires ignited the diesel
Con Ed issued a report that 8 large 13.8 kv feeds (from wtc 7's sub station presumably) were lost beginning at the moment AA11 hit tower 1. Coincidence? Rodriquez reported explosions in the sub basement at the moment AA 11 hit the 94th floor... Coincidence or was it from shorts in electrical switch gear connecting/controlling WTC 1's power and its source bldg 7 con ed sub station.
Explosions were heard well before tower 1 came down and this led to bldg 7 being evacuated... Jennings and Hess confirmed that there were no occupants in the building when they arrived before 10. They were told on a cell phone to get out as there had been explosions in the building.
They experienced explosions below them IN the core area where the electrical equipment and day tanks were located when they descended the stairs before 10 am. Coincidence?
Transformers rather frequently explode and sound like bombs. One did last week in our own neighborhood and had everyone rushing out to the street. Con Ed came and replaced it.
Old and massive transformers are cooled by flammable oil and do explode. Circuit protection is notoriously slow and so shorts down stream can kick off an explosion. We've all see blackouts take one power station down after another in cascading failures.
Deputy fire commission reported that he observed explosions of what he thought was electrical equipment. Not a bad guess.
There was no power in the building shortly after 9am. Why? This disabled the sprinkler and elevators and hampered efforts to deal with the emergency.
The observed collapse sequence showed first a 1 minute period of the entire viable (25 stories or so) building swaying east to west... operative word being ENTIRE. This means it was *swaying about some location below flr 20 something. Was there anything special at that elevation? No there was down at flrs 6&7
Then the east penthouse collapsed right down through the entire core region. It was supported by column 79 and 80 and they were above transfer truss 3. Coincidence?
Then the west penthouse fell down.. it was above transfer trusses 1 and 2... Coincidence?
These observations support a structural failure low down in the building... and the MOST likely region was floors 1-7 where there were lots of massive electrical and flammable oils located. The sub station did not have the newer dielectric coolant.
"The oil-filled tank often has radiators through which the oil circulates by natural convection. Some large transformers employ electric-operated fans or pumps for forced-air or forced-oil cooling or
heat exchanger-based water-cooling.[SUP]
[73][/SUP] Oil-filled transformers undergo prolonged drying processes to ensure that the transformer is completely free of
water vapor before the cooling oil is introduced. This helps prevent electrical breakdown under load. Oil-filled transformers may be equipped with
Buchholz relays, which detect gas evolved during internal arcing and rapidly de-energize the transformer to avert catastrophic failure.[SUP]
[61][/SUP] Oil-filled transformers may fail, rupture, and burn, causing power outages and losses. Installations of oil-filled transformers usually includes fire protection measures such as walls, oil containment, and fire-suppression sprinkler systems.
Here's an example of a sub station exploding:
https://www.youtube.com/watch?v=fzbQjd_Oo4Q
I speculate that the reason for the NIST explanation was to provide cover the the potentional wrongful death lawsuits that could (and should) be brought against PANY, LERA, Irwin Cantor, Giuliani Advisers who pushed for the OEM, assorted engineering firms and contractors who were associated with these unusual designs which were not built to NYC DOB codes...and other parties associated with this project including con ed which sold (I presume) the air rights over its facility (when vacant land was available across the street. Anything and everything associated with this had to be kept out of a court room.