Does anybody have a way to watch the video again? I'm curious to watch it again now that I know what happened. I haven't watched many launches before so I didn't know if what was happening was routine or not. Though, admittedly, it was weird that one second there was a rocket, then the next there was only debris...
Based on that, one can clearly see by stepping frame by frame at 3:20 disintergration of what i imagine must be second stage fueltanks. Difficult to say if it is oxygen or kerosene, but since its expanding so rapidly it would seem likely that its a oxygen tank.
But nevertheless its just guessing from me and im no expert.
edit: https://www.youtube.com/watch?v=ZeiBFtkrZEw&t=23m38s Thanks xur17!