Lets put a little perspective on the heat. Steel melts at about 1370 Celsius. We suspect the heat in the towers were anywhere from 1200 to 1800 Fahrenheit (if I recall) while burning and the extra kinetic energy added from falling. Aluminum melts at 660 Celsius. For the purpose of black body radiation calculations, converted to Kelvin, each are about
:
Steel: 1643
Aluminum: 933
Heat min: 922
Heat max: 1255
Radiated heat from steel is very high at 131,530 w/m. Aluminum is much lower, about 1/10th that of steel, at 13,677 w/m. The fires burned at 13,044 to 44,776 w/m. Point is, and from experience working in a aluminum smelter/foundry, you can get a few feet away from molten aluminum with minimal protection. Not steel. Using the inverse square law, you would need to be at more than three times farther from molten steel to molten aluminum for the same exposed volume.
Images from
Spectral Calc:
