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TechnologyScuba Diving
Scuba Diving
 The
self-contained underwater breathing apparatus or scuba diving
system, as we know it today, is the result of technological
developments and innovations that began almost 300 years ago.
Scuba diving is the most extensively used
system for breathing underwater by recreational divers throughout
the world, and in various forms is also widely used to perform
underwater work for military, scientific and commercial purposes.
Advantages and Disadvantages
Scuba diving has many advantages
over free diving, mixed gas, helmeted, saturation, and other
forms of “technical” diving. Scuba divers have great
freedom of movement under water because they swim with fins
and without heavy equipment; The gear is relatively inexpensive,
simple to operate and maintain, and requires a small support
crew, or none at all.
Despite all of these apparent advantages,
recreational scuba also has its drawbacks. These
include no direct link between the diver and the surface;
no method of communicating with the diver or monitoring his
activities; limited dive time (since the diver must carry
all of his air in a tank); and limited depth (since decompression
diving is normally avoided due to the limited quantity of
air in the tanks).
Essential Equipment
 In
addition to a mask and fins, basic recreational scuba
equipment consists of a cylinder of compressed air attached
to a two-stage "demand regulator." The regulator lowers the
air pressure in “steps” from the cylinder and dispenses it
to the diver as needed.
Cylinders for scuba diving are made
of steel or aluminum alloy, and are designed to operate safely
at pressures ranging from 2,250 to 3,500 psi (pounds per square
inch). As a means of comparison, air pressure at sea level
is only about 15 psi. One of the most commonly used types
of diving cylinders is made of aluminum alloy, and has a capacity
(the quantity of gas that can be compressed into the cylinder)
of 80 cubic ft. The amount of time that it takes a diver to
use up all of the air in the dive cylinder is dependent on
several factors, including, the diver’s breathing rate, and
the depth to which the diver descends (the deeper the dive,
the greater the amount of air used). All cylinders used by
scuba divers should be inspected internally at least once
a year for damage and corrosion.
 The
primary function of the “demand regulator” attached to the
diving cylinder is to reduce the high-pressure gas supplied
by the scuba cylinder to the ambient pressure surrounding
the diver at depth. If the diver were to breath compressed
air directly from the cylinder, it could easily rupture his
lungs. The reduction of air pressure from the diving cylinder
to the diver is accomplished in two steps. The first stage
of the regulator, which attaches to the cylinder valve, reduces
the high pressure in the cylinder to an intermediate pressure
approximately 140 psi over ambient pressure. This intermediate
pressure fills a low-pressure hose that connects the first
stage of the regulator to the second stage. The second stage,
contained in the diver’s mouthpiece, reduces the intermediate
pressure to the ambient pressure. The regulator is known as
a “demand regulator” because it only supplies air when the
diver “demands” it; that is, gas flows through the regulator
only when the diver inhales.
Critical for Safety
 Other
devices, while not directly involved in the breathing circuit
of the recreational scuba diver, are nonetheless
critical for safety. These include a Pressure
Gauge, depth gauge, and dive timer. These
instruments inform the diver about the amount of air left
in the cylinder, their depth in the water, and how much time
has been spent underwater. A diver who exceeds the prescribed
depth or time spent underwater, may become susceptible to
nitrogen narcosis, and/or decompression sickness, which can
be fatal.
Two additional items generally considered
essential for the scuba diver are a “BC”
or “BCD” (buoyancy compensator device) and a dive knife. Almost
all BCs are worn like a vest, and include a band for mounting
the air cylinder. The BC contains an air bladder that the
diver inflates or deflates to maintain control over buoyancy,
thereby avoiding uncontrolled ascents and descents.
In addition to the BC, few divers enter the water without a dive knife. Most divers carry them in the event that they become entangled in a line, net, or some other gear, and need to cut themselves free. A dive knife can also be used as a signaling device by banging it against a dive cylinder.
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