Diving Tools And Techniques
Diving suits and devices to help divers stay longer underwater were invented and tested as early as the fourth century B.C. Aristotle mentions artificial breathing devices for divers, and Alexander the Great supposedly dove in a primitive version of a diving bell. The first practical diving bell was invented in 1717 by Edmund Halley, the British astronomer for whom the comet is named. It had a wooden chamber with an open bottom and glass in the top or ceiling for light. Leather tubes supplied air to the occupants, and the air was furnished through casks lowered into the water as they were needed. As water flowed into the casks, it forced the air out through the tubes, in a simple form of compressed air. Steel chambers similar to Halley's invention are still used today for some types of underwater construction, except that the compressed air is supplied from tanks.
Individual diving suits to protect divers and let them move freely were first tried in the seventeenth century. In 1819, the first successful diving suit was invented by Augustus Siebe (1788-1872), an inventor of German and British extraction. He used the principle of the diving bell in fitting the diver's head into a metal helmet that was attached to a leather jacket. Air was pumped into the helmet through a hose. The system was not watertight, but the forced-air pressure kept the water below the diver's nose and mouth. Siebe followed his invention with several improvements, the last of which was made in 1830. The modern diving suit fully encloses the diver in a suit of rubberized fabric and a helmet. The unit is airtight, and the diver can regulate both air pressure and buoyancy with valves on the helmet. Diving suits for greater depths include weighted shoes, lead plates for the back and chest, and a communications line linked to a telephone at the surface. For still greater depths, metal suits with special airtight joints help divers withstand the higher water pressures. Air pressure within these suits can be properly regulated so, in fact, the suits for greater depths impose less physical stress on the diver than those for shallower waters. Self-contained underwater breathing apparatus (SCUBA) supports both skin divers and divers with gear for deeper water and eliminates the troublesome supply hoses.
Work underwater is done with special equipment that is also pneumatically powered (powered by compressed air). Drills, wrenches, and other tools require supplied air for power although standard cutting and welding torches can be used underwater. Electrically powered lights are needed at depth because light only penetrates a few yards (meters) in some waters. Underwater stations for working and habitation have been tested; depending on depth, different air supplies using mixtures of oxygen and helium or hydrogen instead of nitrogen are needed to prevent fatal bubbles in the blood stream of the diver. Divers adapt to the underwater world in stations no more than 328 ft (100 m) deep, but they can work for shorter periods of time at depths of 1,300-1,500 ft (approximately 400-650 m) in flexible suits. Underwater habitats or stations are supplied air and power by stationary surface craft.
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