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Scuba Essay, Research Paper

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Underwater Diving

Have you ever wondered what it would be like to swim with the fish and explore the sea floor. I am interested in water activities such as swimming, diving, and skiing. I felt that scuba was for me. Many people know that the earth is covered with water (2/3 of it anyway), but many people have never seen first hand what is below. In this essay I will talk about the history of diving right up to the present day, because it has not always been possible to swim with the fishes and survive.

Both men and women have practiced breath-hold diving for centuries. some evidence comes from thousand-year-old undersea artifacts found on land and depictions of divers in ancient drawings. In ancient Greece breath hold divers are known to have hunted for sponges(Martin,16). The story of Scyllis (about 500 B.C.) is perhaps the most famous(Martin, 6). As told by the 5th century B.C. historian Herodotus.

During a naval campaign the Greek Scyllis was taken aboard ship as prisoner by the Persian King Xerxes I.(Martin, 6)When Scyllis learned that Xerxes was to attack a Greek flotilla, he stole a knife and jumped overboard.(Martin, 8)The Persians could not find him in the water and presumed he had drowned. Scyllis surfaced at night and made his way among all the ships in Xerxes’s fleet, cutting each ship loose from its moorings by using a hollow reed as snorkel to remain undetected.(Martin, 10)Then he swam nine miles to rejoin the Greeks. It is definitely a good story, but I am not sure if it is true.

The desire to go under water has always existed. Hunting for

food, uncovering artifacts, repairing ships, and perhaps just to observe marine life. Until humans found a way to breathe underwater, however, each dive was necessarily short. Breathing through a hollow reed allows the body to be submerged, but it must have become apparent right away that reeds more than A couple of feet long do not work well.(Ketles,82) It is impossible to inhale against water pressure. This will limit the snorkel+s length.(Martin,63)Breathing from an air-filled bag brought under water was also tried, but it failed due to rebreathing of carbon dioxide. (Martin,65)Only a few breaths can be taken from a bag before the CO2 level becomes too high.

In the 16th century people began to use diving bells supplied with air from the surface, probably the first effective means of staying underwater for any length of time. The bell was held at rest a few feet

from the surface with its bottom open to water and its top portion

containing air compressed by the water pressure.(Ketles, 46)A diver standing upright would have his head in the air. He could leave the bell for a minute or two to collect sponges or explore the bottom, then return for a short while until air in the bell was no longer breathable.

In the16th century England and France crafted full diving suits made of leather and used them to depths of 60 feet.(Ketles, 52)Air was pumped down from the surface with the help of of manual pumps. Soon helmets were made of metal to withstand greater water pressure so divers could dive deeper. By the 1830s the surface-supplied air helmet was perfected well enough to allow salvage work of sunken ships.(Ketles, 52) Starting in the 19th century, two main avenues sprouted. One scientific, the other technologic, helped to accelerate underwater exploration.( Scientific research was advanced by the work of Paul Bert and John Scott Haldane, from France and Scotland. Their studies and research helped to explain effects of water pressure on the body, and also define safe limits for compressed air diving. At the same time, improvements in technology such as compressed air pumps, carbon dioxide scrubbers, and regulators, made it possible for people to stay under water for long periods of time.(Ketles, 53) There are really four mini-histories in the story of man’s

desire to explore below the sea, they correspond with each separate

method of diving.(Hull,14)The earliest form of diving (breath hold) is still practiced for both sport and commercial purposes, such as the pearl divers of the Tuamoto. The breath hold diver’s air spaces are pushed in by the increased water pressure throughout the dive. (Hull,14) Each dive, is limited by the person+s tolerance for breath-hold and the risk of drowning.

Heavy-walled vessels can maintain their internal pressure at or near sea level pressure (’one atm.’), and prevent the surrounding water pressure from affecting the divers. Such vessels include the bathysphere, which is an unpowered hollow steel ball that is lowered from a ship by steel cable, and the submarine which can travel great distances in any direction under its own power.(Hull, 19 )All one-atmosphere vessels require a system to both provide fresh air (by adding oxygen to the existing air) and get rid of exhaled carbon dioxide (with soda lime, lithium hydroxide which takes up CO2). A modern version of the one-atmosphere vessel is the self-contained armored diving suitthat is flexible yet able to withstand pressure. With these one-atmosphere suits a diver can work at a depth of several hundred feet for hours.

Diving with a compressed air supply 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 cord, which ends in a regulator and mouthpiece carried by the diver. In more sophisticated systems the air cord leads into a dive suit or some larger space containing the diver. Devices in this category include caissons (huge spaces supplied with compressed air mainly for bridge and tunnel work), diving bells, and rigid-helmet diving suits.(Hull,15) In all these devices the diver breathes air at the same pressure as the surrounding water pressure, and so is at risk for

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