UNDER PRESSURE - DIVE SCIENCE
Strap on your mask and fins and dive in to the world of deep-water
science. While SCUBA (self-contained underwater breathing
apparatus) diving can open up a new world full of fascinating
underwater creatures, it can also be very dangerous. Here
are a few of the most common problems divers face:
Have you ever swum to the bottom of a swimming pool and noticed
that your ears begin to hurt? That uncomfortable feeling is
caused by the weight of the water and air above you. As you
get deeper, the amount of water over your head increases and
so does the pressure. Although divers sometimes experience
pain from the increased pressure underwater, the real problems
occur when a diver surfaces improperly. Divers breathe compressed
air through a regulator, which ensures that the air breathed
into their bodies is at the same pressure as the surrounding
water. But if they breathe compressed air underwater and then
ascend, holding their breath, the pressure around them decreases,
so that their lungs expand. Air sacs in the lungs can then
rupture, causing an air embolism, in which bubbles of air
enter the blood stream and may block circulation to the brain.
Despite how it sounds, “the bends” is not a new
dance craze or a wild ride at your local amusement park. It
is a potentially life threatening condition resulting from
underwater pressure changes. Because 80% of the air we breathe
(both directly and through scuba tanks) is nitrogen, our blood
is always full of dissolved nitrogen. However, as a diver
breathes via a tank underwater, the blood in his or her body
can hold more nitrogen due to the increased water pressure.
If the diver then returns to the surface of the water too
quickly, the blood can no longer hold as much nitrogen at
this lower pressure. As a result, nitrogen is forced out of
the blood as tiny bubbles in the tissues, potentially causing
severe joint pain (hence the name “the bends”),
as well as dizziness, paralysis and even death. Divers can
easily avoid these problems by limiting the depth of their
dives and their time underwater and by following a few simple
diving safety guidelines, such as following a pre determined
dive plan and making a slow controlled ascent.
Although marine mammals, such as whales, dolphins
and seals breathe air just like us, they don’t get the
bends. When marine mammals dive, they hold their breath for
staggering amounts of time. Sperm whales have been known to
hold their breath for almost two hours when diving for food.
Because they take air at the surface of the ocean, marine
mammals do not get extra nitrogen in their blood and therefore
have no danger of the bends. This also explains why people
can free-dive (dive without tanks) without worrying about
getting the bends. Although the average person has a difficult
time holding their breath for more than a minute or two, some
highly trained free divers can hold their breath for up to
five minutes as they dive to depths well over 100 feet (30
Did you know that the record for the deepest
underwater filming by a diver was recently set at 350 feet
(106.68 meters) by renowned diver, Howard Hall, during the
making of Coral Reef Adventure?
THE DIVE LOCKER
Are you ready to make the plunge into the deep blue? Every
diver needs to make sure they have the right gear, so let’s
take a look at diving equipment.
The mask and snorkel
Unlike fish and marine mammals, humans require some help to
see clearly underwater. This is where the scuba mask comes
in. Because each of us is unique, masks vary in size, shape,
lens color and even eyeglass prescription. The snorkel, although
never used underwater (or you would end up with a mouthful
of water), is important for surface swims back to the dive
boat. The snorkel allows divers to breathe easily at the surface
in spite of waves.
Fins and Wetsuit
Short of a nice layer of blubber and a powerful tail fluke,
fins and a wetsuit are the only things that keep a diver warm
and swimming properly. Because a dive in the tropical waters
of the Caribbean is so different from a dive under the ice
in Antarctica, wetsuits and fins come in a wide range of styles
and thicknesses to accommodate changes in water temperature
and ocean currents. A good wetsuit is essential for any diver,
as the body loses heat much more quickly in water than in
air. Likewise, a good pair of fins enables a diver to swim
using far less energy and effort.
The Buoyancy Compensator (or BC)
Do you ever wonder how fishes hover effortlessly in the ocean
while we must work tirelessly to stop ourselves from sinking
to the bottom? The fish’s secret is a small air bladder
that they can inflate or deflate to adjust their buoyancy.
Divers have a special rugged vest called a buoyancy compensator
that has a built-in air bladder to make it possible to adjust
buoyancy. The Buoyancy Compensator, or “BC” in
scuba lingo, also holds the diver’s air tank in place
and hooks directly to the tank with a special hose. As divers
descend they are compressed, effectively making them heavier
for their volume than at the surface. BCs are used to overcome
this effect so divers are able to stay at neutral buoyancy.
The average recreational diver breathes compressed air. The
air is contained in a tank that divers carry on their backs.
The typical tank is made of aluminum, weighs about 14 kg (31
pounds) empty and holds 2,265 L (80 cubic feet) of air at
1360 kg (3000 pounds) per square-inch (psi) (about the same
amount of air as would fit in a telephone booth).
Don’t try to breathe compressed air directly from a
scuba tank or your lungs might take a beating due to the intense
air pressure! Fortunately divers have developed a special
mouthpiece and valve, called a regulator, that reduces the
pressure from the tank to a pressure equal to surrounding
water. The regulator also contains a special valve that efficiently
provides air only when the diver inhales. The regulator actually
consists of two separate pieces. The first stage attaches
to the tank and reduces the pressure to a safe breathing level.
The second stage supplies the air through a small mouthpiece
Ever wonder how divers always seem to know how much air they
have left and at what depth and in which direction they are
swimming? The secret is the numerous gauges that divers carry
as part of their standard equipment. Typically, divers carry
a gauge that tells them the air pressure in the tank, a gauge
that tells them their depth and a compass for navigation.
These gauges are often arranged on a single console that clips
to the diver’s BC. Nowadays, many divers carry a handheld
dive computer that automatically calculates the amount of
time a diver can safely stay underwater depending on the depth.
Before computers, divers had “dive tables” to
calculate bottom time for various depths.