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The report determines that the actual culprit in the collapse was the combustion of ordinary building furnishings: "These uncontrolled fires had characteristics similar to those that have occurred previously in tall buildings." If the sprinkler system in WTC 7 had been working, it is likely that "the fires in WTC 7 would have been controlled and the collapse prevented."

The report also suggests that current engineering standards for coping with fire-induced thermal expansion need to be re-examined, particularly for buildings like WTC 7 that have long, unsupported floor spans.
A key factor in the collapse, NIST concluded, was the failure of structural "connections that were designed to resist gravity loads, but not thermally induced lateral loads." According to Sunder: "For the first time we have shown that fire can induce a progressive collapse."

Spurred by conspiracy theorists' questions, investigators did look specifically at the possibility that explosives were involved.

"Hypothetical blast events did not play a role in the collapse of WTC 7," the report states, adding that investigators "found no evidence whose explanation required invocation of a blast event."

Moreover, the smallest charge capable of initiating column failure "would have resulted in a sound level of 130 dB [decibels] to 140 dB at a distance of at least half a mile." Witnesses did not report hearing such a loud noise, nor is one audible on recordings of the collapse.

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