User blog comment:Raptor of Love/Aokiji vs Akainu and the Aftermath/@comment-5386071-20121203061508/@comment-8298508-20130417051309

The reason why akainu is able to burn ace is because their power is in superiority relationship which mean "which one is stronger will be win". ref = "http://eatmanga.com/Manga-Scan/One-Piece/One-Piece-573/page-13" please look at the bottom right of the page.

But if there are no relationship between two material type from logia user that involved in a fight, then no one will be injured. For example when ace vs smoker  ref = http://www.youtube.com/watch?v=gMIvkjrmkyI