Some things lights up when strongly heated. Other flash even from weak heating. And there are those that do not burn at all. Water, for example, is not lit.
And want to know why?
Yes, because why not burning ash: water itself has turned from burning!
What do we need to burn to get water? The hydrogen gas, the same that had once been filled balloons and airships. Now to fill airships another gas - helium. Helium does not burn, so to fly on such airships safer.