content: Oxygen burn very well on its own, more of it in an enclosed space helps that along.  That's why the flame is brief, followed by regular flammable things like hair burning while the big initial fire is gone - the initial lighter burn was helped along immensely, but ran out of available fuel to burn very quickly...  Except for things like hair which continue to burn on their ow and simply do so much more efficiently in an enclosed and oxidized environment. This is also why nitrous is popular in car engines for performance junkies, because it helps the natural fuel burn along but doesn't actually explode.