There has been a handful of news reports recently discussing the recent tragedy of the SpaceX rocket, where the term 'Explosion' has been used. But is that what has really happened?
In order to have combustion, three elements are needed: heat, fuel, and an oxidizing agent. The topic of redux reactions could likely span multiple posts, but for simplicity sake, an oxidizing agent is one that accepts electrons (reduced). In most cases oxygen acts as the oxidizing agent, so you have a triangle that looks a bit something like this: 
If you remove any one of these three, the fire will be extinguished.
Depending on the news source you read, the rocket was traveling anywhere about 4700 kph at a height of about 47 km. At this height, even though the air composition is roughly the same as at sea level (~21% Oxygen), the air pressure is much lower, and the molecules are spread out so far that there is not enough Oxygen to fuel the reaction.
If you watched Elon Musk's press release, he noted that a mechanical failure caused the rocket to break apart, not necessarily explode. Of course these details may change as the exact causes and details become available.
Now that you know a little more about combustion, combine the info you learned last year to safely enjoy your 4th of July holiday.