:''From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse.'' <ref>https://www.nist.gov/el/faqs-nist-wtc-towers-investigation</ref> | :''From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse.'' <ref>https://www.nist.gov/el/faqs-nist-wtc-towers-investigation</ref> |