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People Under the Sea: History - Approaches

The approaches to staying underwater longer and deeper fall into two categories. The first has been through the development of ways to provide a diver with either compressed air or other gas mixtures. This approach has taken two directions: surface supply and self-contained supply. The surface supply approach usually used a long tube, which in its simplest form ended in a regulator and mouthpiece carried by the diver. In more sophisticated systems, the tube leads into a dive suit or some larger enclosed space containing the diver. Devices in this category have included caissons (huge spaces supplied with compressed air) used mainly for bridge and tunnel work, underwater habitats used for saturation diving, diving bells and rigid-helmet diving suits. In all these devices, the diver breathes air at the same pressure as the surrounding water pressure, which puts the diver at risk for decompression problems, such as the bends and air embolism, if ascent is too fast. Special 'high-tech' mixtures, such as hydrogen-oxygen, helium-oxygen and helium-nitrogen-oxygen, are used to dive deeper than is possible with compressed air.

The "Self Contained Underwater Breathing Apparatus" (or SCUBA) is the best known self-contained breathing supply system. In fact, it is so commonplace that scuba diving has become a popular sport.

The second major approach maintained the diver at normal surface conditions of air composition and pressure. People have designed a variety of equipment to meet the challenge. This path has produced a series of heavy-walled vessels, which can maintain their internal atmosphere at or near sea level pressure and prevent the surrounding water pressure from affecting the occupants. Such vessels include the following: the bathysphere, an unpowered hollow steel ball lowered from the mother ship by steel cable; the bathyscaphe, a bathysphere with buoyancy control so that cable is not needed for descent and ascent; and the submarine, which can travel great distances in any direction under its own power. All one-atmosphere vessels require a system to both provide fresh air (usually by adding oxygen to the existing air) and get rid of exhaled carbon dioxide (with soda lime, lithium hydroxide or a similar compound that soaks up carbon dioxide). A modern extension of the one-atmosphere vessel is the self-contained armored diving suit, flexible yet able to withstand pressures at depth. In effect, the diver becomes almost like a small submarine. With these one-atmosphere suits, a diver can work at a depth of several hundred feet for hours.

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