Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in deep sea diving. Humans are not physically nor anatomically well adapted to the environmental conditions of diving. Various equipment has been developed to extend the depth and duration of human dives and allow different types of underwater work to be done. In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The environment exposes the diver to a wide range of hazards. The risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth, and the purpose of the dive.
The provision of breathing gas at ambient pressure can prolong the duration of the dive, but there are problems that may result from this technological solution. Deep diving is underwater diving to a depth beyond the norm accepted by the diving community. When deep diving, nitrogen narcosis becomes a hazard below 38 meters (98 feet). Narcosis while diving is a reversible alteration in consciousness. It is caused by the anesthetic effect of certain gases at high pressure. It is basically a temporary decline or loss of senses, movement, and numbness. Narcosis can be completely reversed in a few minutes by ascending to a shallower depth or taking timed decompression stops. Decompression stops are needed the deeper you go. Using normal scuba gear, breathing gas consumption is proportional to ambient pressure. Therefore, at 50 meters (160 feet) the pressure is a six-bar. A six-bar is when a diver breathes six times as much air on the surface.