Explain how 6 weeks later they were still digging out red hot metal.<quoted text>
Good point. So it actually collapsed to below the street level. What this means is buildings are mostly air space and not really solid. The weight and downward forces would multiply as each successive floor collapsed. By the time the collapse reached street level the whole weight of the upper stories were pounding what was left below. The molten steel came from the place where the plane hit.
According to a NIST report spokesman, "there was no molten steel at all".