Cited Passage
This means that after any dive, it takes six hours
for the 60-minute compartment to return to its starting
amount of nitrogen, and 12 hours for the 120-minute half-
time compartment to return to starting pressure—equilibra-
tion with ambient pressure on land. From another perspective, oxygen can significantly
enhance decompression. Decompression requirements are
dictated by the on-gassing of inert gases. By breathing 100
percent oxygen, the inert gas gradient is significantly
increased, thus increasing inert gas elimination from the
body. For example, pure oxygen can be used to shorten
decompression on the 20 and 10 fsw stops. In addition,
high oxygen content mixtures can also be used to shorten
decompression from the 30 fsw stop and deeper. Mixes
rich in oxygen have proven to substantially improve
decompression outcome when used as a supplemental
decompression gas from both air and nitrox dives. 3.3.4.2 Decompression Sickness
Decompression sickness (DCS, also known as “the
bends”) is the result of inadequate decompression follow-
ing exposure to increased pressure. During a dive, the
diver’s body tissues absorb nitrogen from the breathing gas
in proportion to the surrounding pressure. If the diver
ascends too quickly, the nitrogen may come out of solu-
tion and form bubbles in the body’s fluids and tissues. WARNING
ALTHOUGH DECOMPRESSION SICKNESS MAY
OCCUR AS A RESULT OF VIOLATING ACCEPTED
SAFE DIVING PRACTICES, IT CAN ALSO OCCUR
EVEN WHEN THE ACCEPTED GUIDELINES ARE
BEING FOLLOWED PRECISELY. Bubbles form after many dives, often with no symp-
toms; these are called silent bubbles. It’s probably not
true that asymptomatic bubbles form after every dive;
however, they are not uncommon. Bubbles cause dam-
age in several ways: they can block blood and lymph cir-
culation, depriving vital areas of oxygen and waste
removal; extravascular bubbles can compress and stretch
blood vessels and nerves creating pain, damage, and dis-
ability; as foreign invaders to the body, bubbles can pro-
voke a cascade of defenses including blood coagulation,
release of vasoactive substances from cells lining the
blood vessels, and the body’s immune system reacts by
coating the bubbles with lipoproteins, which then dena-
ture and release circulating fat emboli. Bubbles do not
pass from body tissues into veins, unless the veins are
already torn. Bubbles, even though tiny, are too big to
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