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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.
GLOSSARY
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 pressure
exerted by a single gas in a mixture of gases.
See Dalton’s law.
Partial Pressure Mixing: The mixing method by
which gases are serially combined using proportions
of each gas to determine the composition of
the resulting mixture. Each gas is added to the containing
cylinder so that its partial pressure gives it
the desired fraction of the resulting mix.
PO2: Partial pressure of oxygen.
Pressure: Force acting on a unit of area. See also
Absolute pressure and Gauge pressure.
Pressure, Atmospheric: The measure of the weight
of the surrounding “column” of air. One atmosphere
is equal to 1.01325 bars, 14.7 pounds per
square inch (psi), 33 fsw, or 760 millimeters of
mercury (mmHg).
Pressure Gradient: The difference in pressure
between two separate locations. Used in diving to
describe the driving force on a gas that causes it to
move in or out of a body tissue.
Pressure Swing Absorption: A method of separating
gases in a mixture using the adsorption properties
of a porous material, usually a “molecular
sieve” over which the gas mixture is passed. In
nitrox blending by pressure swing absorption, the
adsorbing material removes nitrogen from the air
flowing over it.
GLOSSARY