This is abstracted from an e-mail I sent to SJ about a month ago:
"Right now my short list of candidates that could contribute to iron-rich microspheres in the WTC dust (I am sure Chainsaw could add a lot more!) is (in no particular order!):
Pigments and fillers used in plastics
Fly ash from the combustion of cellulose-based materials: wood, cardboard and paper
Welding fume left in the towers from construction activities
Wear particles from grinding and cutting during construction of the towers
Iron powder cores from electronics (e.g. transformer cores)
Pyrotechnic agents (including thermite!)
NYC background levels of particulate from general environmental sources"
I would like to see SJ consider these sources, ONE BY ONE, before he draws any conclusions that he has found evidence for the use of explosives or thermite in the towers.