Some people have suggested that the Jet fuel was the source of the molten copper or molten steel seen in the below image.

9:53.51am, 11th Sept 2001 - Molten Metal at WTC 2

The problem with this assumption is that this photograph was taken around 1 hour later than the initial impacts. According to NIST, the jet fuel would have burnt off within minutes, as would be expected. This would only leave secondary fires from a basic oxygen deficient office fire.

"The jet fuel, which ignited the fires, was mostly consumed within the first few minutes after impact. The fires that burned for almost the entire time that the buildings remained standing were due mainly to burning building contents and, to a lesser extent, aircraft contents, not jet fuel."
Key Findings of NIST’s June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster

If we now examine the video footage of this event, we will observe that it was shot moments before the collapse of the North Tower at 10:05am.

Thus, we have recorded footage of molten copper or molten steel being produced over a sustained period between 9:53am and 10:05am, 11th September 2001 at the South Tower (WTC 2). That's a full 12 minutes at temperatures exceeding 1080C and, as we have seen, totally unrelated to the jet fuel.

The isolated nature of this event would also indicate this to be a highly localised source of additional heat, strengthening the arguement for an accelerant.