User blog comment:Miskos3/Fairy Tail Chapter 486: The Fourth Guest, Review/@comment-7418318-20160525151848/@comment-7418318-20160526085520

When Laxus took those MBP in, they didn't just damage his lungs, but ALL his organs.

That means the MBP went into his blood and spread all over his body through it.

How is an iron lung going to stop the MBP from going into the blood? Or are you saying that all of Gajeel's other organs are also turned into iron? .... hmm... though if he has a big block of iron for a brain that could explain a things. :P