Gavin a quick google search will give you the grades of steel used in the Twin Towers.

http://science.howstuffworks.com/engineering/structural/grade-of-steel-used-in-world-trade-center.htm

 The NYC Department of Buildings keeps and kept decent records on all buildings. Investigators were able to find the impact steel of both towers because of Department of Building records of the buildings. For governmentallly funded buildings records are extremely meticulous.

Most jet fuel is still kerosene based...im not denying there are mixtures.