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(commonly nitrogen) in the breathing gases at
depth. The condition is alleviated by ascending to a
shallower depth or by changing the components of
the breathing mixture, as in trimix.
Ingassing: The diffusion of additional dissolved gasses
into the tissues as ambient pressure increases.
M
Maximum Dive Time (MDT): Also called the nodecompression
time or no-decompression limit
(NDL). The length of time that may be spent at a
given depth without being required to make a
mandatory decompression stop during ascent to the
surface.
Maximum Operating Depth (MOD): The maximum
depth to which a particular gas mixture can
be used without exceeding the oxygen partial pressure
limit. In normal diving the maximum PO2 is
1.4 ata.
MDT: See Maximum Dive Time
Membrane Separation: The process of separating
gases by forcing a gas mixture through a differentially
permeable membrane that allows some gases
to pass more readily than others.
MOD: See Maximum Operating Depth.
msw: Meters of seawater. The pressure exerted by one
msw equals 1/10 bar.
N
Narcosis: See Nitrogen narcosis and Inert gas narcosis.
Nitrogen Narcosis: A semi-stuporous condition
caused by the elevated partial pressure of nitrogen
in the breathing mixture at depth. The condition is
alleviated by ascending to a shallower depth or by
diluting the nitrogen in the breathing mixture, as
in trimix.
Nitrogen: the colorless, odorless, tasteless gas that
makes up approximately 78% of the air. Nitrogen is
metabolically inert and is responsible for narcosis
and decompression sickness in diving.
Nitrox (EAN, Enriched Air Nitrox, Oxygen-
Enriched Air): A term generally used for a mixture
of oxygen and air or oxygen and nitrogen with
an oxygen percentage greater than 21%. The term
has also been used in habitat diving for nitrogenoxygen
mixtures with an oxygen content less than
21%.
No-decompression Dive: A dive that does not
require a decompression stop during ascent. The
term “no-required-decompression dive” is also used
to remind divers that all dives involve decompression,
even though decompression stops may not be
required.
No-stop Dive: Another term for no-decompression
dive.
NOAA: The National Oceanic and Atmospheric
Administration, a U.S. government agency created
in 1970 within the Department of Commerce. NOAA
is a science-based agency that has the responsibility
to predict changes in the oceanic and atmospheric
environments and living marine resources.
NOAA Nitrox I and NOAA Nitrox II: Two standard
mixes of enriched air nitrox that were first used by
the National Oceanic and Atmospheric
Administration in research diving. NOAA Nitrox I and
NOAA Nitrox II are EAN32 and EAN36, respectively.
O
OCEANx Calculator: A NAUI product that allows a
diver to easily determine oxygen exposure limits
and to perform equivalent air depth conversions for
oxygen-enriched air mixtures.
NAUI Nitrox Diver
GLOSSARY