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the act of work or recreation in an underwater environment. The main health effects are related to the increased pressure to which the person is subjected as the ambient pressure generally increases by 1 atm (14.7 pounds per square inch) for each 33 feet of descent below the water surface. Conditions that warrant caution about diving include obesity, diabetes, alcoholism, epilepsy, drug abuse, and respiratory disorders, including allergic rhinitis. See also decompression sickness, diving reflex.
diving(1) diving in swimming pools carries the potential hazard of neck injury, if the dive is too steep relative to the depth of the water; (2) in scuba diving the diver breathes compressed air from a cylinder, through a face mask and a closed system of tubes ('self-contained underwater breathing apparatus'). Pressure increases by 1 atmosphere (1 bar) per 10 metres of depth. Below 30 m the 'intoxicating' effect of nitrogen narcosis is a danger, avoided by the use of helium-oxygen mixtures. Hypothermia is also a hazard in cold climates; (3) in breath-hold diving the duration of immersion can be increased if the dive is preceded by vigorous hyperventilation. This depletes carbon dioxide in the body so that it will take longer to rise to the level which would normally trigger the break-point, but oxygen in the lungs and the blood can be depleted to the point of threatening consciousness. See also barotrauma, cervical spine, decompression illness.
the act of submerging underwater; diving by fish and amphibians creates an obvious need for mechanisms that allow them to be submerged under water for long periods. Most mammalian and avian orders also have aquatic species that have a similar need. Diving reflexes operate as soon as nostrils are submerged and include oxygen conservation, respiratory arrest, intense peripheral vasoconstriction, bradycardia and compression of the chest with almost complete evacuation of the lungs.