102 NAUI Nitrox Diver
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.
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 bar.
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 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.”
C
CNS: Central nervous system
CNS Oxygen Toxicity: The toxic effects on the central
nervous system of breathing high-pressure oxygen.
CNS oxygen toxicity results from relatively short
exposures to high partial pressures of oxygen and
may present as a range of signs and symptoms, up to
epileptic-like convulsions.
Contingency Maximum Operating Depth: The depth
range for a specific gas mixture that gives an oxygen
partial pressure exceeding 1.4 ata and up to 1.6 ata.
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