Types Of Diving |
Types of Diving -- Free (Breath-Hold) Diving
Free diving, or breath-hold diving, is the earliest of all diving techniques, and has played a historic role in the search for food and treasure or in military operations. The ancient Greeks developed underwater military squads, using free divers to ambush enemy ships during the Peloponnesian Wars. Roman divers collected dye-producing Mediterranean snails to color the Emperor's rich purple cloaks. The Ama of Japan and Korea still dive for seafood, such as abalone, as they have done for centuries. Likewise, native people throughout the Caribbean and Polynesia have been diving for oysters, conch, fish and lobster for thousands of years.
What is the advantage of free diving?
The obvious advantage of free diving as a work method and a recreational activity is that it allows maximum freedom for the diver to maneuver. The obvious disadvantage is that the diver's air supply is limited to the amount of air the diver can take in and maintain in a single breath or can obtain using a snorkel-type reed or tube to the surface. The modern snorkel is an aid in breath-hold diving but doesn't supply air continuously unless the diver is very near the surface.
Types of Diving -- Diving Bells
After snorkels, diving bells were the next successful method of increasing endurance underwater. These bells consisted of a weighted chamber, open at the bottom, in which one or more people could be lowered underwater. The early use of bells was limited to short periods in shallow water, but later bells became quite popular when inventors developed methods of supplying fresh air to the bell using barrels and hoses.
Types of Diving -- Helmet (Hard-Hat) Diving
Although early diving bells provided divers some protection and an air supply, they limited the diver's mobility. In the 17th and 18th centuries, a number of devices (usually made of leather) were developed to provide air to divers and to afford greater mobility. However, most of these devices were not successful because they relied on long tubes from the surface to provide air to the diver and thus did not deal fully with the problem of providing adequate quantities of compressed air.
The first major breakthrough in surface-supplied diving systems came in the early 19th century in the form of a helmet-and-suit apparatus that consisted of a rigid helmet sealed to a flexible waterproof suit. Pressurized air was pumped down from the surface into the helmet. This type of equipment, with a few refinements, is still in use today.
In the 20th century, hard-hat divers learned that breathing mixed gases, in particular a helium-oxygen mixture, permitted them to dive to greater depths for longer periods than had been possible with regular air mixtures. Although surface-supplied diving has several advantages in terms of stability, air supply, and length of work period, major problems with hard-hat gear include severely limiting the diver's mobility, requiring support personnel on the surface, and cost. Scuba gear frees the diver from surface support and enables extraordinary mobility never before achieved in diving.
Types of Diving -- Scuba Diving
The development of self-contained underwater breathing apparatus, or scuba, provided the free-moving diver with a portable air supply which, although finite in comparison with the unlimited air supply available to the helmet diver, allowed for better mobility. Scuba diving is the most frequently used mode in recreational diving and is also widely used to perform underwater work for military, scientific and commercial purposes.
What are the two types of scuba?
The two types of scuba designs include the "open" scuba design, where the diver breathes air from a cylinder or canister and the exhaled air goes into the water and rises to the surface as bubbles. The diver must return to the surface before or when the supply of air runs out.
The "closed" scuba rig design allows a diver to reuse the same gas. A diver's exhaled breath is passed through a chemical in one of the cylinders to remove the carbon dioxide and the diver then breathes the "cleaned" gases over and over again. New oxygen is added automatically as consumed. Using this system, the diver can stay underwater longer and no bubbles come to the surface.
Types of Diving -- Saturation Diving
"Saturation diving" is a technique developed by the U.S. Navy in the late 1950s that permits divers to remain at high pressures for weeks or months without having to often undergo decompression and waste the diver's time. Researchers discovered that when a diver is underwater for a long time -- days or weeks, for example - the time needed to decompress reaches a maximum and stable point. The diver becomes "saturated" and no longer accumulates additional gas such as nitrogen or helium. In other words, decompression time for a diver who has been underwater for one day may be the same as for a diver who has been down for a week.
Divers operating in the saturation mode live underwater and work out of a pressurized facility, such as a diving bell or underwater habitat, typically for a week or more, as in NOAA's Aquarius habitat at Key Largo, Florida, or in the North Sea oil fields. These facilities are maintained at the pressure of the depth at which the diver will be working. Today, a great deal of underwater work is done using remotely operated vehicles (ROVs) that are controlled from the surface. Still, there are some underwater jobs only a human diver can accomplish.
Types of Diving -- Diving in a Heavy-Walled Vessel
Heavy-walled vessels can withstand tremendous underwater pressures and maintain their internal pressure at or near sea level pressure -- a pressure called "one atmosphere" or "one atm."
Such vessels include: the bathysphere -- an unpowered hollow steel ball lowered from the surface support 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 these vessels require a system to provide fresh air (usually by adding oxygen to the existing air) and to get rid of exhaled carbon dioxide (with soda lime, lithium hydroxide, or similar chemical compounds that take 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, a diver in one of these armored suits becomes almost like a small submarine.
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