Diving Apparatus
The first divers to use any type of diving apparatus were probably breathhold, or free divers. An Assyrian artifact from about 900 B.C. is among the earliest records of free diving gear. A frescoe depicts a swimmer breathing underwater from a goat skin. By the 5th century B.C. Greek divers used breathing tubes while in the water. The earliest record of swimming goggles is from a second century A.D. vase of Peruvian origin. Tortoiseshell goggles and breathing tubes were routinely used by free divers by the Middle Ages.
The diving bell, another early device that allowed man to descend and observe the underwater environment, is open to the water at the bottom. From its earliest use, this allowed divers to go on short forays out into the open water and return to the bell for air. However, the air inside would quickly become stale. Edmond Halley (1656-1742) finally made diving bells practical in 1716 by introducing the idea of air replenishment while underwater. More recent developments related to the diving bell include the bathysphere and bathyscaphe. These twentieth century inventions provided scientists their first glimpse of the deepest areas of the ocean. The submarine has been instrumental both in marine warfare and marine research.
Today's oceanographers use a wide variety of personal diving apparatuses for underwater exploration. In modern free diving, or skin diving, the diver carries no air supply and is equipped only with mask, fins, snorkel, and when in cold water, a wet suit. The mask allows the diver to see clearly, while the snorkel, a J-shaped tube, lets the diver breathe while swimming just below the surface of the water. Fins, flat rubber shoes that resemble duck feet, provide much better propulsion than bare feet with less effort.
In scuba diving (an acronym for Self-Contained Underwater Breathing Apparatus) cylinders of pressurized gas (usually compressed air) are strapped onto a diver's back. This air supply is connected via hoses to the diver's head gear, which includes a mask, a pressure regulator, and a mouthpiece.
There are three major types of scuba equipment. In closed and semi-closed circuit systems, known as rebreathers, exhaled air is recirculated and purified by passing through a canister of carbon dioxide absorbent, which extracts the carbon dioxide from exhaled air, making it safe to recycle. With these types of systems, divers can remain underwater for longer periods of time, but their complexity makes rebreathers potentially more dangerous. Open-circuit systems simply vent exhaled air directly into the water. They are preferred by most divers because they are relatively safe, easy to use, and less costly than other systems.
Divers use weighted belts and inflatable vests to adjust their buoyancy so they can descend in a gradual, controlled fashion, neither paddling furiously to get underwater nor sinking like a stone to the bottom. When water is cold, divers wear wet suits to withstand the chill. These full-length suits are made from a spongy rubber material that insulates against the cold water. While clinging to the body, the wet suit retains an inner layer of water, the temperature of which is regulated by the diver's body heat. A warmer alternative for very cold water is the dry suit -- so-named because it keeps the diver dry even when fully submerged. The first practical diving suit was devised by a German named Klingert around 1797. His combination of metal parts for the main body shield and leather for the sleeves and breeches was innovative, but it was extremely heavy, and the leather restricted the diver's movements.
Far more complex than snorkeling or scuba diving, is tethered diving (hard-hat diving), in which air is pumped through a hose from the surface or an immersed structure. This approach, although more expensive, is commonly used for deep-sea excavations or to repair underwater structures like oil rigs. There are many different designs available, but the classic hard-hat assembly is heavy and awkward, usually consisting of a 60-pound (27-kg) helmet connected to a rubberized body suit, an 80-pound (36-kg) weighted belt, and a 40-pound (18-kg) pair of weighted shoes. The diver controls the air supply by using valves on the belt or inside the helmet. Air is important not only for breathing, but aids in ascent and descent as well. A non-return valve allows air pressure to build in the suit so the diver can rise. The chin valve releases air into the water, allowing the diver to vent air and sink deeper.
Another type of tethered-diving apparatus is the JIM suit, a magnesium alloy and fiberglass shell invented by Joseph Peress in 1922. It is named for Jim Jarrett who made the first experimental dives using this suit in the 1920s. The JIM suit maintains the diver at a constant 1-atmosphere (sea-level) pressure and has its own 20-hour air supply. It weighs in at a massive 910 pounds (413 Kg), which helps the diver withstand the strong ocean pressure encountered at its maximum working depth -- about 2,000 ft (610 m).
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