Board Thread:General Discussion/@comment-6192846-20140111153519/@comment-3467648-20140718074847

Actually, it was revealed in one of the OSS albums the Body Swap technique is part of the Reincarnation art gained by these ones who were involved with the Sin and Leviantha's Disaster. Another aspect of the Reincarnation art is the inherent immortality shared by both, Elluka and Irina

With that you can conclude that both sorceresses were affected by the explosion,. The difference was Elluka ended unscathed, while Irina ended as a limbless bloody pulp. My guess is the magical blast acted as in similar fashion to the eye of a hurricane, and while Irina was near, she wasn't in the exact epicenter of the disaster.