Magnesium burns quite readily and not just in foil form. Just check with any insurance agent about what it costs to insure a plant that machines mag. Or check with a sailor who has done flight deck duty. But that's not to say it can't be near an open flame, it takes more than a flick of your Bic.

I had never heard of titanium burning prior to this thread. I've just never worked with it. So while the links I posted do indicate that it's plausible, I think it would require that someone be pretty careless. When your pot is glowing red, it's probably close to the right temperature. I can't imagine letting my pot get there, though.