Chip, I think you may be misunderstanding what free diving is. It is a sport where people breath-hold dive to extreme depths, often to more than 200 feet. Pressure increases one atmosphere every 33 feet or so, so the divers must use valuable lung capacity to equalize the pressure in the mask, thus having less oxygen to continue the dive. If I understand this correctly, Steff is trying to find a way to eliminate the airspace altogether, and replace it with water, which is non-compressable, and neutral with the surrounding pressure.