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Actually the laptop and cell phone use on a plane during takeoff and landing ban was because they said it could interfere with the electronics on the plane. That was debunked on slashdot.org and wired magazine in the past as well.
As far as welding a gas
tank that has fumes in it, there is no way I would ever try that unless I didn't want to live or something, that is just nuts.
Note I said if there was vapor trapped. If you want to try this experiment outside not indoors at your own risk of course. Try to light gas with a real cig like dunking it in a small puddle of it. It doesn't work that that way except maybe in the movies. The real actual cig will just drown. A lit match is a whole different story though.
On a funny note though someone at work was stealing 9 volt
batteries out of smoke detectors. He got caught after having some in his pocket with coins in there and thought his pants were going to catch fire when they shorted and emptied his pockets pronto. Haha nabbed in the act.
