Scuba diving
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Scuba diving is the use of independent breathing equipment to stay underwater for long periods of time for recreational diving and professional diving. Generally the diver swims underwater, but walking and the use of diver propulsion vehicles is possible while breathing from scuba equipment. The word 'SCUBA' is an acronym for "Self Contained Underwater Breathing Apparatus", but it is grammatically acceptable to refer to 'scuba equipment' or 'scuba apparatus' in conversation.
The two types of scuba equipment are the "open-circuit" Aqua-lung, developed by Jacques Cousteau and the "closed-circuit" rebreather.
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History of diving
Men and women have practiced breath-hold diving for centuries. Indirect evidence comes from ancient artifacts of undersea origin found on land (e.g. mother-of-pearl ornaments), and depictions of divers in ancient drawings. In ancient Greece breath-hold divers are known to have hunted for sponges and engaged in military exploits. Of the latter, the story of Scyllis (sometimes spelled Scyllias; about 500 B.C.) is perhaps the most famous, as told by the 5th century B.C. Greek historian Herodotus (and quoted in numerous modern texts).
During a naval campaign the Greek Scyllis was taken aboard ship as prisoner by the Persian King Xerxes I. When Scyllis learned that Xerxes was to attack a Greek flotilla, he seized a knife and jumped overboard. 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; he used a hollow reed as snorkel to remain unobserved. Then he swam nine miles (15 kilometers) to rejoin the Greeks off Cape Artemisium.
The desire to go under water has probably always existed: to hunt for food, uncover artifacts, repair ships (or sink them!), and perhaps just to observe marine life. Until humans found a way to breathe underwater, however, each dive was necessarily short and frantic.
How to stay under water longer? Breathing through a hollow reed allows the body to be submerged, but it must have become apparent right away that reeds more than two feet long do not work well; difficulty inhaling against water pressure effectively limits snorkel length. Breathing from an air-filled bag brought under water was also tried, but it failed due to rebreathing of carbon dioxide.
In the 16th century people began to use diving bells supplied with air from the surface, probably the first effective means of staying under water for any length of time. The bell was held stationary a few feet from the surface, its bottom open to water and its top portion containing air compressed by the water pressure. 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 16th century England and France, full diving suits made of leather were used to depths of 60 feet. Air was pumped down from the surface with the aid of manual pumps. Soon helmets were made of metal to withstand even greater water pressure and divers went deeper. By the 1830s the surface-supplied air helmet was perfected well enough to allow extensive salvage work.
Starting in the 19th century, two main avenues of investigation one scientific, the other technologic - greatly accelerated underwater exploration. Scientific research was advanced by the work of Paul Bert and John Scott Haldane, from France and Scotland, respectively. Their studies helped explain effects of water pressure on the body, and also define safe limits for compressed air diving. At the same time, improvements in technology - compressed air pumps, carbon dioxide scrubbers, regulators, etc., - made it possible for people to stay under water for long periods.
Used with permission from Lawrence Martin, M.D. Web Site of Origin: www.lakesidepress.com/abcindex.htm. The web pages containing the scuba book are inoperative at present, and have not yet been moved to a new site. The above URL is the global or index web site.
And see Timeline of underwater technology.
Diving Issues
See Diving disorders
Equipment to allow underwater breathing
The two most common types of equipment are:
- surface supplied diving, where the diver's breathing gas (usually air) is pumped down from the surface. Standard diving dress is a historically interesting type of surface supplied diving equipment.
- scuba, where the breathing gas supply is carried by the diver.
Need to see underwater
Diving masks and diving helmets solve this problem. Occasionally commando frogmen use special contact lenses instead, to avoid searchlight beams reflecting off a mask window.
Avoiding losing body heat
This causes hypothermia. Water conducts heat from the diver 25 times better than air. Except in very warm water, the diver needs the thermal insulation provided by a diving suit.
Avoiding skin cuts and grazes
Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects and marine animals and coral.
Diving longer and deeper safely
There are a number of techniques to increase the diver's ability dive deeper and longer:
- technical diving - Diving Deeper than 130 feet.
- surface supplied diving - use of umbilical gas supply and diving helmets
- saturation diving - long-term use of underwater habitats under pressure and a gradual release of pressure, over several days, in a decompression chamber at the end of a dive
Being mobile underwater
- The diver needs to be mobile underwater. Personal mobility is enhanced by fins worn on the feet and Diver Propulsion Vehicles. Other equipment to improve mobility includes diving bells and diving shots.