For combustion to take place, enough heat needs to be
produced by the reactions to keep the temperature of the
fuel and oxygen at or higher than the material's ignition
temperature. When heat is present, chemical reactions occur
because lone hydrogen and oxygen atoms are very reactive;
they quickly combine with other molecules or atoms. This
leads to a rapid "branching chain reaction."
Though the chemical chain reaction that takes place when
hydrogen burns may seem complex, it's much simpler than the
one that takes place with other fuels. Even with a seemingly
simple fuel such as methane (CH4), more than 100
individual chemical reactions take place.
