Depends on the chemical composition. Hydrogen doesn't just combine dually with Oxygen. Just most commonly due to the abundance of both particulates. :)
Still requires a minimum energy to kick start the reaction, plus it's excessively slow unless it's kick-started via a radical chain reaction or something. That's why the Hindenburg didn't suddenly explode while they were filling it up due to a tiny microscopic leak somewhere.
Also for LDHs water's involved, kind of, but it's got more to do with metal hydroxides forming clay layers.