- The Washington Times - Thursday, July 11, 2002

The word "scuba" was coined by an American, Dr. Christian Lambertsen, who in 1939 designed a self-contained underwater oxygen breathing apparatus for the U.S. military that was used during World War II. The gear worked for shallow dives, but the gas mixture was wrong for greater depths, and divers were dying from the oxygen toxicity.
The breakthrough came in 1943, when two Frenchmen, Emile Gagnan and the famed oceanographer Jacques Cousteau, invented the demand regulator, which adjusted the air pressure automatically, supplying air as the diver needed it. Their regulator was connected to three cylinders, each holding 2,500 pounds per square inch of air. The complete equipment, or autonomous diving suit with the pressure regulator, was called the Aqua-Lung and is the basis for equipment used today.
The regulator is the key. The deeper a diver goes, the greater the pressure exerted on his body by the weight of the water. The pressure regulator compensates by supplying equal amounts of air pressure to the lungs.
The lungs typically use the necessary amounts of oxygen at these higher pressures, and the remaining gases are exhaled through a valve in the mouthpiece of the regulator. But the lungs have a limited degree of resistance to other gases passing into the bloodstream. As the air pressure climbs, greater concentrations of nitrogen (the primary component of air) pass through the lungs and into the blood.
The blood will absorb a certain amount of this nitrogen that can later be "off-gassed" from the body. But if too much nitrogen builds up, bubbles may form in the bloodstream and travel throughout the body, causing damage to various tissues. The term "bends" comes from a symptom of becoming permanently bent over when the nitrogen bubbles lodge in the lower spine and damage nerves and other tissues. Ascending rapidly from a deep dive creates dangers because not enough time is allotted for off-gassing. As the nitrogen rapidly expands in the lower pressures, the blood can actually boil.
Thus on deep, long dives, the diver must stop at certain levels for prolonged periods of time on the way up to off-gas the excess nitrogen in a slow, controlled manner.
The vast majority of recreational divers are not certified for this type of diving, called decompression diving. Recreational divers use non-decompression dive tables or computers that have conservative time and depth limits so that decompression stops are not necessary.
However, it has been found that by stopping at a depth of 15 feet for three minutes after each dive, especially after a dive of greater than 60 feet, the chances of developing decompression sickness are greatly reduced.
The deeper one dives (130 feet maximum for most recreational divers), the less time allotted for the dive. If a problem were to arise at depth, the diver could make a controlled emergency ascent to the surface with little fear of the bends.
When taking in multiple dives, limits are also laid out on the amount of surface time required for off-gassing between dives. Diving instructors say that using dive tables and computers has made scuba diving safer than bowling.
Matthew Graham

A portion of the above sidelight was derived from Mary Bellis' "The Inventors of Scuba Diving Equipment," at about.com. See https://inventors. about.com/library/inventors/blscuba.htm.

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