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Dreamliner woes: Are sweaty passengers to blame? – Is it possible that one of the key benefits of the Boeing 787 Dreamliner, which is denser and more humid ... (more)
Interesting speculation about a potential cause/correlator with the 787 battery issues - hundreds of breathing perspiring passengers create very different environmental conditions, and especially different than during certification.
Nicotine would get everywhere and had the advantage of being visible back in the days when smoking was allowed. (See also China Airlines flight 611.)