Modern helmet diving suits usually consist of a waterproof one-piece suit made of canvas and rubber that entirely covers the wearer except for the head and hands. Heavy rubber bands seal the suit at the wrists, leaving the hands free. On the feet the diver wears leaded boots weighing about 40 lb (18 kg), and lead weights are fastened to the chest to maintain equilibrium. A metal helmet with side and front windows covers the head. A noncollapsible pipe connects the helmet to an air supply. An attached lifeline hauls the diver to the surface. Too rapid an ascent from great depths causes the diver to suffer decompression sickness. To prevent this, deep-sea divers either use an all-steel, armored diving suit or breathe a special mixture of nine gases developed by the Swiss mathematician Hannes Keller.Scuba Diving
Helmet diving has the disadvantage of restricting the diver's lateral movement because of the connection to the surface. This fact led to the development of scuba (an acronym for self-contained underwater breathing apparatus). Scuba delivers air to the diver (from tanks of compressed air) at the same pressure as that exerted by the surrounding water. In this way the diver is able to descend to great depths without feeling the ill effects of high pressure (see skin diving). A skilled scuba diver with good equipment can descend as deeply as a helmet suit diver.
Record-setting dives of over 300 ft (91 m) have been made with scuba gear, although careful scuba divers do not go below about 130 ft (40 m). Beyond this depth a condition known as nitrogen narcosis (popularly called "raptures of the deep") tends to set in. Caused by the narcotic effects of the air's nitrogen at high pressure, the condition is marked by a loss of judgment that often causes the diver to discard equipment or engage in other dangerously foolish behavior. Nitrogen narcosis also affects helmet suit divers, but not until a depth of about 200 ft (61 m).
The ancient Greeks practiced commercial and military diving, usually with little or no equipment. In the Iliad, Homer describes the use of divers in the Trojan Wars; Greek laws regulating those who dived for sunken treasure are found as early as the 3d cent. B.C. Before the introduction of modern apparatus, divers submerged with the aid of a rope and a stone weight; using the rope as a guide for position, the naked diver quickly scooped up whatever commodity was being sought.The Development of Diving Equipment
Inventors as early as the 17th cent. sought means whereby divers could stay underwater for extended periods. At that time, various types of diving dress and underwater armor attempted to supply fresh air through a surface pipe kept above the water by a float. Augustus Siebe devised the first practical diving equipment early in the 19th cent. in England. His first suit was of the open type, consisting of a helmet attached to a jacket made of waterproof material. Air was pumped to the helmet through a pipe from the surface—air pressure serving to keep the water level below the diver's head and the air finally escaping through open vents at the bottom of the jacket. The diver had to maintain a generally upright position; a fall could result in drowning because the air in the suit was likely to rush out through the vents. To correct this difficulty, Siebe later developed the closed type of diving suit that, with improvements, is still in general use. Instead of the earlier open vents, the closed type of suit had valves that let air out without letting water in, regardless of the diver's position. The limitations imposed on the helmet diver's lateral movement (because of the connection to the surface) led to early interest in alternative equipment that would permit freer movement, but the scuba apparatus was not developed by Jacques Yves Cousteau and Emil Gagnan until well into the 20th cent. In 1943 successful tests were made of the new compressed-air breathing apparatus, and it has been widely used since.Development of Diving Vessels
Several types of large metallic structures have been used as underwater diving vessels since early times. Aristotle, as early as 360 B.C., mentions sponge divers using primitive vessels. Otis Barton's bathysphere—a hollow, globular steel structure built to withstand tremendous pressure—was used in undersea exploration in the 1930s, but an attached steel cable and winch limited its mobility. The first free and self-contained diving craft was Auguste Piccard's bathyscaphe. His craft, the Trieste, descended (1960) to 35,000 ft (10,668 m), the deepest known point in the ocean.
See H. E. Larson, A History of Self-Contained Diving and Underwater Swimming (1959); J. S. Potter, The Treasure Diver's Guide (rev. ed. 1972); T. Griffiths, Sport SCUBA Diving in Depth (1991).