The word "scuba" stands for "self contained underwater breathing apparatus". This device allows persons
to dive underwater for extended periods of time. The most popular form of this apparatus is called an
aqualung, which was designed in France during World War II by Jacques Yves Cousteau. Jacques Yves
Cousteau was a French navel officer when he developed the aqualung. He is most famous for his work as an
underwater explorer. The aqualung consists of anywhere from one to three cylinders of compressed air that
is fed to an underwater diver through a mouthpiece.
Persons wishing to take up the sport of scuba diving need to be properly trained. There are several
organizations that provide training and certification in this sport, including the National Association of
Underwater Instructors (NAUI) and the Professional Association of Diving Instructors (PADI).
Because of the potential hazards of scuba diving, instructors spend much of their time teaching proper
safety techniques. This requires a full understanding of the operation and proper maintenance of diving
equipment as well as an understanding of the effects of underwater pressure on the human body. At sea level,
the air pressure on the body is 14.7 pounds per square inch (this is the equivalent of 1 atmosphere).
Every time a diver descends 33 feet underwater, the pressure increases by an additional 14.7 pounds per
"The bends," or decompression sickness, is one such hazard associated with pressure changes. The longer
you stay down and the deeper you go, the more nitrogen dissolves into your body tissues. If you ascend too
rapidly, the dissolved nitrogen comes out of solution too quickly and forms bubbles in your tissues. A diver
suffering from decompression sickness can experience severe pain (particularly in joints), dizziness, and in
severe cases, blindness, paralysis, and death.
Because of these safety concerns, the NAUI, using information provided by the U.S. Navy, has created dive
tables that specify how a given dive needs to be approached. Prior to any dive, several variables need to be
considered. These variables include dive schedule (this includes information about depth and dive time),
maximum dive time (MDT), actual dive time (ADT), residual nitrogen time (RNT), and total
nitrogen time (TNT). Using these variables and the NAUI dive tables, a person can determine how a dive must
be approached. For example, the tables will provide information about how long a given dive can last as well as
how much time needs to elapse before a second dive can be initiated. This time between dives, called surface
interval time (SIT), allows for excess nitrogen in the system to dissolve. All nitrogen leaves the body after
24 hours. If a person makes a second dive in less than 24 hours time, another table needs to be consulted, based
on the fact that nitrogen is still in the body.
In addition to the information provided by the tables, other rules or standards must also be applied. For
instance, all divers must ascend no faster than 60 feet per minute. Also, the depth of a dive must always be
considered as the deepest depth attained, even if the majority of the dive time is spent at a lesser depth. When
scuba divers plan dives that are particularly cold or strenuous, additional precautions must be followed.