In the beginning of the movie the Narrator says "We have front row seats..." the camera pans down the building they are in and shows the van with the bomb inside. Later by the end of the movie the Narrator defuses the same bomb, but Tyler kicks him out of the van, fixes the bomb, and closes the van while breaking the key in the lock and tossing it so the Narrator wont defuse it again. If the bomb had been fixed by Tyler the building they were in should have been destroyed as well.