Page created by
Heather C. Hopkins
Last updated 11/25/2009
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Pressure
and
Scuba
Diving:
First,
what
is
pressure in physics terms? Pressure is a force acting on
a unit of area, or, Pressure = Force/Area. Atmospheric pressure
is caused by the weight of the atmosphere, which is different at
various altitudes. Basically, divers know that pressure increases
as depth
(underwater) increases. Similarly, pressure decreases at higher
altitudes.
Hydrostratic pressure is the force acting due to fluids at rest (or
static). Immersed divers experience increased pressure due to the
force of water acting upon them. This is also known as
compression.
Decompression, the opposite of compression, is when a diver
experiences
decreasing pressure as he or she ascends towards the surface of the
water. In this case, air expands and fills a larger volume.
Compression or decompression can cause damage in
a person's body,
due to unequal
air pressures. This damage is known as barotrauma (see dangers
section for more information).
Illustration
of
Boyle's Law, courtesy of
http://www.antonine-education.co.uk/New_items/STA/Gas%20Laws/Gas_Laws.htm
The
process that occurs during compression and
decompression is portrayed by Boyle's
Law.
This
law is expressed as PiVi=PfVf,
and
describes
pressure as being inversely proportional to volume when
temperature is constant. Boyle's Law
explains why divers will feel a "squeeze" or discomfort in their ears
as they descend. The squeeze is caused by an unbalanced, greater
amount of pressure outside an air space (the ears, for example).
It is necessary to reduce the discomfort in the ears by adding air to
the space with various equalization techniques. Boyle's Law also
explains why a diver should never hold their breath underwater, because
air expands during ascent, and if the air has no way of being released,
the pressure may burst air sacs in the lungs (see dangers
section for more information). |