Harmful effects of rapid change from a higher- to a lower-pressure environment. Small amounts of the gases in air are dissolved in body tissues. When pilots of unpressurized aircraft go to high altitudes or when divers breathing compressed air return to the surface, external pressure on the body decreases and the gases come out of solution. Rising slowly allows the gases to enter the bloodstream and be taken to the lungs and exhaled; with a quicker ascent, the gases (mostly nitrogen) form bubbles in the tissues. In the nervous system, they can cause paralysis, convulsions, motor and sensory problems, and psychological changes; in the joints, severe pain and restricted mobility (the bends); in the respiratory system, coughing and difficulty breathing. Severe cases include shock. Recompression in a hyperbaric chamber followed by gradual decompression cannot always reverse tissue damage.
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In engineering, a type of foundation most commonly used underwater for a bridge, but sometimes used in building construction. It is a large hollow structure that is sunk down through the earth by workers excavating from inside it; ultimately it becomes a permanent part of the pier. There are three types: the open caisson, open at both top and bottom; the box caisson, closed at the bottom; and the pneumatic caisson, with an airtight chamber to accommodate submerged workers. Caisson columns, typically 2 ft (0.6 m) or more in diameter, may be used as an alternative to bearing piles. A round hole is dug or bored to a stable layer of earth and temporarily supported by a steel shell, then filled with concrete poured around a cage of reinforcing bars.
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Caisson (French for "box") may refer to: