87
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.
fsw: Depth (or pressure) measured in feet of seawater.
The pressure exerted by one fsw is approximately
equal to 1/33 of a standard atmosphere.
G
Gas Analysis: The measurement of separate component
gases in a gas mixture. In recreational nitrox
diving, analysis is for oxygen content only.
Gas Fraction: The quantity of a single gas in a mixture
of gases expressed as a decimal fraction of the
whole. Gas fractions are used in mathematical calculations.
Gas Laws: The physical statements that predict how
GLOSSARY
an ideal gas will behave with changes in pressure,
temperature, and volume.
Gas Percentage: The quantity of a single gas in a
mixture of gases expressed in relation to 100 representing
the whole mixture. Gas percentages must be
converted to gas fractions in mathematical calculations.
For example, a mix that is 32% oxygen has
an oxygen fraction of 0.32.
Gas Tension: The equivalent of partial pressure for a
dissolved gas.
Gauge Pressure: The pressure indicated by a gauge
that ignores atmospheric pressure. Depth gauges,
which show hydrostatic pressure in msw or fsw, are
examples of gauge pressure read-out.
H
Henry’s Law: The statement of the relationship of the
pressure of a gas on a liquid to the solubility of the
gas in the liquid. Henry’s law states: “The amount
of gas that will dissolve in a liquid at a given temperature
is directly proportional to the partial pressure
of that gas on the liquid.”
Hypoxia: A deficiency in the amount of oxygen reaching
the tissues of the body and the condition
brought on by that deficiency.
I
Ideal Gas Laws: The description of the relationship
of temperature, pressure, and volume of a theoretical
“ideal” gas, that is, one with molecules of negligible
size moving randomly and colliding with
completely elastic collisions. The behavior of a real
gas more closely approximates that of an ideal gas
when it is at relatively low pressure and high temperature.
Inert Gas Narcosis: A semi-stuporous condition
caused by the elevated partial pressure of inert gases
GLOSSARY