Good question, all five people who voted to close said that it was off-topic (so at least there was a consensus for the reason).
At the moment, our On Topic help area is a little light (e.g. no help at all). There is a meta question that we can look at for right now though: What topics can I ask about here? This question seems to fall into a couple of the topics mentioned as allowed, such as aircraft systems and technology.
Perhaps it had more to do with the wording of the question. I personally feel that it is okay, but borderline too broad just because you asked about so many different things in one question.
I suspect that you would have gotten a different response if you had asked the question more along the lines of: "Would adding barium to jet fuel cause damage to the engines?" This wouldn't carry the negative connotation of being associated with the conspiracy theorists (who have a general image of being a little... unstable) and would probably attract more expert opinions.
Perhaps try focusing more on the actual question that you have without the extra background (and maybe limiting the scope to a smaller number of substances) and see if it is reopened.