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Glossary
A
Absolute Pressure: (See also ata.) The pressure referenced
to zero pressure. Absolute pressure is the
total pressure from all sources. In diving, it is equal
to water (hydrostatic) pressure plus air (atmospheric)
pressure.
Actual Dive Time (ADT): The total time spent
underwater from the beginning of descent until the
return to the surface at the end of the dive. The precautionary
safety stop need not be included in the
dive time.
Adjusted Maximum Dive Time (AMDT): The
Maximum Dive Time for a specific depth minus the
Residual Nitrogen Time for the repetitive dive letter
group and that depth.
Air Embolism: See Arterial Gas Embolism.
Air: The mixture of gases that surrounds the earth–the
earth’s atmosphere. Air consists of approximately
21% oxygen and 78% nitrogen, the balance being
trace gases including argon, carbon dioxide, and
others.
Algorithm: The formulas or procedures for solving a
problem in a certain number of steps. In diving,
algorithm usually refers to a particular set of formulas
used to establish decompression status, as in
a dive computer, or to devise decompression and
dive tables.
Ambient Pressure: The total surrounding pressure.
See absolute pressure.
Analysis, Gas: The measurement of separate component
gases in a gas mixture. In recreational nitrox
diving, analysis is for oxygen content only.
Argon: A colorless, odorless, inert gaseous element
that constitutes about one percent of the air.
GLOSSARY
Arterial Gas Embolism (AGE): The obstruction of
arterial blood flow by an air bubble or bubbles.
Blockage of a vessel in the brain usually results in
paralysis and other neurological deficits. AGE is normally
caused by a lung overexpansion injury that
allows air bubbles to escape into the circulation.
ata: The abbreviation for atmospheres absolute; the
total pressure expressed in multiples of one atmosphere.
Atmosphere: The gaseous envelope surrounding the
earth (or any celestial body). Also, the unit of pressure
equal to the pressure of the air at sea level. One
atmosphere is equal to 1.01325 bars, 760 millimeters
of mercury (mmHg), or 14.696 pounds per
square inch (psi).
B
Bar: The metric/S.I. unit of pressure equal to one million
dynes per square centimeter or about 750
mmHg. One atmosphere of pressure is equal to
1.01325 bars.
Bends: See Decompression sickness.
Best Mix: The gas mix chosen for optimal balance of
nitrogen and oxygen content for a given nitrox
dive. The best mix provides the lowest concentration
of nitrogen that, at the same time, will keep the
diver within the permissible oxygen partial pressure
limit.
Bottom Time: The dive time from the moment of
descent to the beginning of direct ascent to the surface
or to the precautionary safety stop. See also
Actual Dive Time.
Boyle’s Law: The statement of the relationship
between the volume and density of a gas and its
pressure. Boyle’s law states: “At constant temperature,
the volume of a gas varies inversely with
absolute pressure, while the density of a gas varies
directly with absolute pressure.”
GLOSSARY