September 11 · source record · webpage

FAQs — NIST WTC Towers Investigation

National Institute of Standards and Technology · 2021

AI-verified citationSRC-NIST-TOWERS-FAQ

identifier / locator: Created September 2011; updated September 10, 2021; page updated April 5, 2022
url: https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-towers-investigation
verification note: Fetched live 2026-08-26; the residue-testing answer (Q29), floor-capacity figures (Q18), piston/dust answer (Q32), core-standing observation (Q31), propagation statement (Q10), and the seismic-record answer (Q30) quoted verbatim by question number.
reliability notes: Agency self-explanation; authoritative for NIST's position only.
Carries the explicit statement that NIST did not test the steel for explosive or thermite residues, together with NIST's reasoning — a passage both sides of the public argument misdescribe in opposite directions.

Evidence drawn from this source

Supports· strongSEP-E014

what the source states: "Once the collapse had begun, the propagation of the collapse was readily explained without the same complexity of modeling." The supporting argument given is a capacity comparison: "The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case)."
what we infer: Confirms directly that no end-to-end simulation of either tower's total progression was produced, and that the agency's position rests on an engineering judgment supported by a capacity argument. That is a defensible position and a real gap in the auditable record — which is why SEP-C012 grades the existence of a model rather than the physics.
limitations: An agency FAQ restating a position, not a technical publication.

Undermines· strongSEP-E015

what the source states: "There were no seismic signals that occurred prior to the initiation of the collapse of either tower. The seismic record contains no evidence that would indicate explosions occurring prior to the collapse of the towers."
what we infer: Directly contradicts the explosive-demolition account, which requires detonations immediately before initiation. Recorded here with its correct attribution: this negative finding is the agency's, citing the seismic record — it is commonly and wrongly attributed to the observatory that produced the underlying measurements.
limitations: The agency's characterization of the seismic record rather than the seismologists' own publication, which this case has not obtained.

Qualifies· moderateSEP-E016

what the source states: Asked whether the steel was tested for explosives or thermite residues: "NIST did not test for the residue of these compounds in the steel." The reasoning offered: "Analysis of the WTC steel for the elements in thermite/thermate would not necessarily have been conclusive. The metal compounds also would have been present in the construction materials making up the WTC towers, and sulfur is present in the gypsum wallboard that was prevalent in the interior partitions."
what we infer: A passage both sides misdescribe in opposite directions, which is why it is recorded verbatim. "The investigation found no thermite" is false — it did not look. "Therefore thermite" is equally unsupported. The gypsum-as-sulfur-source argument is this agency's, made here; it is not the FEMA metallurgists' explanation, though it is frequently attributed to them.
limitations: The agency's justification for a methodological choice, not an independent assessment of whether the choice was sound.