Different Types of Diving
July 21st, 2015 by Piper Smith
Breath-hold diving (free diving, skin diving). This earliest form of diving is still practiced for both sport and commercial purposes (e.g., ama divers of Japan and Korea, pearl divers of the Tuamoto Archipelago). The breath-hold diver’s compressible air spaces are squeezed by the increased water pressure throughout the dive. Each dive, limited by the individual’s tolerance for breath-hold and the risk of drowning from hypoxia, is usually a minute or less.
Diving in a heavy-walled vessel. Heavy-walled vessels can maintain their internal atmosphere at or near sea level pressure, and so prevent the surrounding water pressure from affecting the occupants. Such vessels include: the bathysphere, an unpowered hollow steel ball lowered from the mother ship by steel cable; the bathyscape, 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 takes up CO2). 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 meters for hours.
Diving with compressed air supplied from the surface. The diver is separated from the supply of fresh air, which is kept on the surface. Air reaches the diver through a long umbilical, which in its simplest form ends in a regulator and mouthpiece carried by the diver. In more sophisticated systems the umbilical leads into a dive suit or some larger enclosed space containing the diver. Devices in this category include caissons (huge spaces supplied with compressed air, employed 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, and so is at risk for decompression problems (bends, air embolism, etc.) 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 possible with compressed air.
Diving with compressed air or other gas mixture that is carried by the diver (scuba diving). There are two principle types of scuba: open and closed circuit. Open circuit vents all expired air into the water, and is the mode used in recreational diving. Closed circuit systems, in which exhaled air is re-breathed after carbon dioxide is absorbed and oxygen added, were widely used before open circuit became available, particularly by military divers who wished to avoid showing any air bubbles. As with divers using surface-supplied compressed air, scuba divers are at risk for decompression problems if they ascend without proper decompression. Helium-oxygen and other mixtures can be used to go deeper than possible with compressed air.