More goes into compositing a believable explosion that one would think.
Here, Kris Truini form Kriscoart Productions demonstrates how he composited a realistic explosion into a live action shot.
create a realistic epic explosion in Adobe After Effects
Although Kris doesn’t actually create the explosion, he does walk through the various elements that are needed for a composite of this magnitude, to have the shot look believable.
The explosion effects used here, come from stock practical effects that will be composted in by means of a track. Even still, there is a lot of work that needs to be done to get it looking like it belongs in the footage.
Kris walks through using the 3D Camera Tracker in After Effects to track the shot that will be used for the basis of the explosion.
Kris also shows how you can remove some actors from the shot after the explosion has happened.