Light and Vision
Changes in perception of
senses occur as a result of the differences between the two different types
of breathing medium – water and air. Let us see how these changes affect
divers under water.
Beginners find it impossible
to determine size and distance under water which leads to exaggeration
of the size of fish and other objects. When experienced divers have doubts
about the extent of something, they always make a comparison by taking
it in their hands. This is certainly a good method because muscular senses
remain unchanged under water.
According to certain laws
in physics, colors lose their brightness with the increase of depth – red
disappears below 8 meters, orange – below 10 m, yellow – below 20 m and
at greater depth everything looks bluish, greenish or grayish. For instance,
if a person hurts himself at a depth of 20 meters, his blood will seem
black. Illumination restores the brightness of colors regardless of depth
and amateurs are astonished by the diversity of patterns in a world which
looked monotonous and dull before.
You may wish to consult the
Section for more details on light and vision under water.
Sound and Hearing
Sounds under water, in contrast
to those in the air, can be heard at greater distance. For example, the
whir of a boat’s engine is heard earlier under water than in the air. If
the boat is 15 to 20 meters away, a diver would think that it is above
his or her head. Disorientation under water is also a significant problem
because the location of the source emitting sound waves is hard to be determined.
However, this confusion can be overcome after some practice.
A curious phenomenon, explained
with the density of the water and speed of sound waves, was observed by
some divers working in an underwater laboratory - “Our voices became
funny and unusually loud, shrilling and resonant so that we could not recognize
our own voice laughter. Entering the underwater habitat for the first time,
everyone burst into laughter as he heard his unpleasant voice. It was like
a recording tape set to fast-motion”.
Sometimes, hearing might
fail because of outer factors – noise of working engines, noise of air
in decompression chambers or that of instruments. However, the most common
problem among divers is the middle-ear squeeze.
You may wish to consult the
Section for more details on sound and hearing under water.
Three semicircular canals
which control the sense of equilibrium (balance) are located in the inner
ear. These canals, filled with fluid, contain ciliated cells and freely-rolling
particles of calcium carbonate, called ear sand. When one's head
is tilted, gravity forces the particles to shift and irritate the neighboring
cilia. Consequently, the ciliated cells, send information to the central
nervous system which orientates to the new position of the body. Thus,
balance is achieved.
According to Archimedes’
principle, objects appear lighter in water than they are in the air.
During their stay under water, divers take no pains in order to keep their
position. Because of the reduced weight of the whole body, ciliated cells
cannot be irritated by the ear sand to the same extent as they are irritated
out of water. That is why they do not send any commands for the change
of position. This leads to the state of loose muscles and weightless body
which is typical of both divers and astronauts.
With closed eyes, one who
is at rest under water quickly loses his or her sense of body position
in space. This concerns especially people with neutral
buoyancy. Research data show that a swimming diver with his eyes closed
determines his body location with an error of 17°± 8°. Orientation
also depends on the position of the body – lying on the back, head relaxed
backwards, is considered unfavorable.
A diver has to use outer
factors which signal his body location. He relies mainly on his eyesight
(following the light layer of water above him), air bubbles, which always
go up, buoys and other light objects showing the way to the surface.
Divers, suffering from sinusitis,
orientate themselves much better for the vertical position of their bodies.
This phenomenon can be explained with the difference in pressure that they
cannot equalize immediately. They feel pain in the sinuses which suggests
an increase of pressure or that they sink.
Sense of Touch
The nervous endings, located
under the skin, react to warm and cold, to pain and touch. This sensitivity
is of significance because it helps to determine any changes in the surrounding
water and to react to them. The sense of touch is reduced and the feeling
of pain almost disappears under water. This is due to the fact that water
cools the skin and thence – the sensitive cells, and lowers their sensitivity.
It is well-known that frozen fingers are insensitive and unable to feel
pain. This phenomenon was used by renowned Russian surgeon Pirogoff, who
conducted amputation of limbs without anesthetic after freezing them in
snow. The reduced sense of pain under water should be taken into consideration
because divers might get hurt (without being aware of that) and not take
Feelings of warm and cold
remain unchanged under water. The heat capacity of water is 4 times greater
than that of air. Moreover, its thermal conductivity is 25 times greater
than that of air. This means that human body loses heat much faster in
water than in air. So, abrupt thermal differences can do irretrievable
harm to the human organism. That is why divers should trust their “first”
and “second shivers”. The former, which are typical when entering water,
signal the beginning of cooling. “Second shivers” that are felt later mean
danger of overcooling – heat production cannot compensate for heat loss
any more! On the other hand, during dive preparation, a diver in a wet
suit who has been exposed to the hot sun for a long time might become overheated.
These two conditions are named Hypo- and Hyperthermia
and are discussed in the following subsection.
Smell and Taste
The nose in the mask cannot
perform its normal function but it can give information on the state of
air the diver breathes. Smell of oil, dust or something musty signals that
the apparatus was poorly charged by the compressor. Raised water pressure
and increased waste of energy are some of the reasons for changes in taste.
Students who have had appetite in the first days of diving activities,
later become “capricious”. They prefer salads, fruit, yogurt and juices
to fish, meat and bakery. These changes are confirmed by divers living
in underwater habitats and decompression chambers.