GLOS Glossary 103
Glossary
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.”
DCIEM: 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.
In 2014, the DCIEM became the DRDC (Defence
Research and Development Canada).
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 toorapid
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 oxygen-compatible
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.
EANx: A way to express the oxygen content of a specific
enriched air nitrox mix. The “x” is replaced with the
oxygen percentage of the mix. EAN32 would be a
nitrox mixture that is 32% oxygen.
Enriched Air Nitrox (EAN, Oxygen Enriched Air): Any
nitrogen-oxygen mixture containing more than 21%
oxygen.
Equivalent Air Depth (EAD): The depth at which air
would have the same nitrogen partial pressure as the
oxygen enriched air that is being used for the dive.
For example, a diver using a nitrox mix containing
32% oxygen at 24 msw (80 fsw) is exposed to an inert
gas level equivalent to 20 msw (64 fsw) if breathing
air.
F
Fire Triangle: The three components needed to start a
fire and keep it burning: oxygen, fuel, and a source of
ignition.
40% Rule: The rule that allows scuba and other breathing
gas equipment to be used without special oxygen
cleaning if it will be used with oxygen enriched
mixtures that do not exceed 40% oxygen content.