Evidence for Squibs can be found here:
High-Velocity "Demolition Squibs" Are Visible in the Twin Towers' Collapses

It has been argued that the squibs were compressed air and that if it was from explosives, the squibs would be instantaneous like in a regular demolition. It has also been argued that the speed of the squibs is consistent with air being squeezed out by the falling floors above.

This argument has been handily countered in 9/11 Research 's Building a Better Mirage article:

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NIST attempts to explain away without disclosing evidence for or even accurately describing this demolition feature: energetic jets of dust emerging symmetrically from the Tower's faces.

[NIST's] fourth paragraph addresses the jets of dust, often called "squibs." It reads:
The falling mass of the building compressed the air ahead of it, much like the action of a piston, forcing material, such as smoke and debris, out the windows as seen in several videos. (p 146/196)
NIST conceals the nature of the energetic ejections by describing them only as material "forc[ed] ... out the windows". It does not mention any resources for examining this evidence, such as these video frames showing dust ejections from the North Tower.
When one examines these ejections, it becomes obvious that NIST's piston theory does not begin to explain them, for a number of reasons including:
* No photographs show evidence of the alleged piston moving down inside of the Towers, and the thickness of the dust clouds indicate that the floors were being pulverized well above the ejections.
* The ejections appear at regular intervals on all visible faces of the North Tower, a pattern much too regular to be explained by the piston theory.
* The North Tower's ejections are very energetic and focused, blasting through single openings on each face. This challenges the piston theory to explain how the relatively even application of pressure caused by falling floors could be contained by all but single windows in the middle of each face.
* The ejections appear to contain thick dust such as of pulverized concrete and gypsum, which would not be generated until after a floor had already collapsed and ejected its air.
NIST thus attempts to explain away only two of the six features of controlled demolition enumerated in the Conclusion of this essay, and in the essay's earlier version critiquing the NIST's Draft Report.
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In post 32 in the WTC Collapses thread, KennyJC has implied that I'm saying that the explosives were going off slowly. I'm not sure why he has come to that conclusion, but I made it clear that I said nothing of the sort. 9/11 Research certainly never says anything of the kind:
High-Velocity "Demolition Squibs" Are Visible in the Twin Towers' Collapses