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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.
Continuous-flow Mixing: A method of blending
enriched air nitrox in which oxygen is mixed with
air at the intake of the compressor. The blend is
monitored using in-line oxygen analysis, and the
oxygen flow and content are adjusted to achieve the
desired mix.
Convulsion: The involuntary, abnormal contraction
or series of contractions of the muscles. Convulsions
are the terminal sign of CNS oxygen toxicity.
Cylinder Markings: Markings used on scuba
cylinders are of several types. Legally required markings
for working pressure, hydrostatic testing, etc. are
stamped into the metal on the shoulder of the
cylinder. To designate nitrox cylinders, the standard
marking is a green band on a yellow cylinder or
green band with a yellow border. Nitrox cylinders are
also labeled with specific information about each fill.
D
Dalton’s Law: The statement of the relationship of
the pressure exerted by each gas in a mixture to the
total pressure. Dalton’s law states: “The total pressure
exerted by a mixture of gases is equal to the
sum of the pressures exerted by each of the gases if
it alone were present and occupied the volume.”
DClEM: Defence and Civil Institute of Environmental
Medicine, Canada (now Defence Research and
Development Canada, Toronto). Since 1939, the
DCIEM/DRDC has conducted research in all areas
of human protection and performance in extreme
environments. It is best known in general scuba
diving for development of the DCIEM dive tables.
DCS: See Decompression sickness.
Decompression: The reduction of pressure or the
release from compression. As used in diving,
decompression means a controlled reduction of
pressure or ascent in the water.
Decompression Sickness (DCS, Bends): The
disorder marked by neurological deficits, pain, and
sometimes death caused by release of nitrogen gas
bubbles in various tissues of the body. DCS results
from a too-rapid decrease in ambient pressure after
being in a pressurized environment.
Dedicated Cylinder: A scuba cylinder prepared for
use with a specific gas. A dedicated nitrox cylinder
will have been properly cleaned (including the
cylinder valve) and then reassembled using oxygencompatible
parts.
Dive Computer: An electronic instrument that monitors
time and depth and uses a mathematical algorithm
to calculate and display dive time, depth, and
decompression information.
Dive Profile: Also called dive schedule. An abbreviated
statement giving the depth and duration of a
dive. It is expressed as depth/time (for example, 21
meters/40 minutes or 70 feet/40 minutes).
Dive Schedule: An abbreviated statement giving the
depth and duration of the dive. See Dive profile.
E
EAD: See Equivalent air depth.
EAN: Enriched air nitrox. Any nitrogen-oxygen mixture
containing more than 21% oxygen.
NAUI Nitrox Diver
GLOSSARY