i would like to know if you can use nitrox 50% or ean 50 to free dive to 20 m or will oxygen toxicty or lung expansions be a risk.also are there any benifits from using 50 % oxygen mix for free diving.i think that the risk of swb will be minimized slightly givin the greater volume of oxygen in the breath hold. also i dont think that breathing compressed air from a cilinder at the surface and desending to depth and returning to surface on breath hold will cause lung expansion injury or will it??? acording to boyles law it wont .please let me know what any of you espcialy the pros think and if it is benificial to prolong apnea and less risk of swb using ean 50 or 60