Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name 'scuba', an acronym for 'Self-Contained Underwater Breathing Apparatus', was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long and/or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the likelihood and effects of nitrogen narcosis during deeper dives. (Source: Wikipedia.org, CC BY-SA)