GLOS Glossary 105
Glossary
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 nitrogen-oxygen 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.
Offgassing: The diffusion of dissolved gasses from
the tissues and their elimination from the body as
ambient pressure is reduced.
Oxygen: An element that is found free as a colorless,
odorless tasteless gas comprising 21% of air.
Oxygen combines readily with most elements and
is a constituent in many organic compounds and
minerals. Almost half of the composition of the
earth’s outer crust is oxygen in various mineral
compounds. In respiration, the oxygen we breathe is
metabolized in our bodies to sustain life.
Oxygen Clean: Refers to the cleanliness and absence of
contaminants in equipment that has been prepared
for oxygen service. Common contaminants include
those that can serve as a source of combustion such
as petroleum-based lubricants, soot, dust, metal
particles, etc.
Oxygen Cleaning: The process by which equipment
is prepared for oxygen service. “Formal” oxygen
cleaning follows very strict cleaning, handling, and
documentation procedures. “Informal” oxygen
cleaning uses the same cleaning techniques but is not
as rigorous regarding handling and documentation.
Oxygen Compatible: Refers to lubricants or
components that are designed for use in highoxygen
environments. Materials that are not oxygen
compatible may be subject to ignition or rapid
degradation in a high-oxygen environment.
Oxygen-Enriched Air (EAN, Nitrox, Enriched Air
Nitrox): Air to which oxygen has been added) or
from which nitrogen has been removed) to produce a
mixture with an oxygen percentage above 21%.
Oxygen Exposure Limit: The maximum time that the
diver can be exposed to a certain partial pressure of
oxygen. NOAA has published a table of single-dive
oxygen exposure limits and 24-hour oxygen exposure
limits for a PO2 range of 0.6 ata to 1.6 ata.
Oxygen Service: Denotes equipment that has been
specially cleaned and prepared for use with oxygen.
Oxygen Toxicity: Short or long term deleterious
physiological effects of exposure to elevated partial
pressures of oxygen.
P
Partial Pressure: The portion of the total gas pres-sure
exerted by a single gas in a mixture of gases. See
Dalton’s Law.