current certification level: diving enriched can extend your bottom
times, reduce your surface intervals, and generally make your dives more
enjoyable.
So what is nitrox?
In the broadest sense, nitrox is any gas blend of oxygen and nitrogen
other than air. Air, of course, is basically a mix of 21 percent oxygen
and 79 percent nitrogen. For divers, nitrox is any gas blend with more
than 21 percent oxygen. Generally for recreational divers this is a
blend of either 32 percent or 36 percent oxygen, sometimes abbreviated
EANx32 or EANx36.As we all know, nitrogen is the cause of diving maladies such as
decompression sickness and nitrogen narcosis. We learned in our PADI Open
Water Diver course that our bodies use up oxygen when we breathe. However,
because nitrogen is not used by our bodies, nitrogen saturates our tissues.
This happens whether we are on the surface or on a dive.
Our regulators are designed to deliver air to us at whatever pressure we are
at. That’s why our bottom times become shorter and shorter the deeper we go.
As our regulators deliver more and more air to us as we descend, more and
more nitrogen is absorbed into our tissues. The more nitrogen we absorb on a
dive, the more dangerous and difficult it becomes for us to return to the
surface.
Why? The answer is simple. While we can tolerate some excess of nitrogen in
our tissues, exceeding the safe limits prescribed by our dive tables and
computers can result in the dissolved nitrogen in our tissues coming out of
solution and forming bubbles that produce symptoms such as joint pain,
coughing, rashes, headaches, paralysis, unconsciousness, or worse. This is
what we divers call decompression sickness and our non-diver friends call
the bends.
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So what good is nitrox?
By reducing the amount nitrogen in our breathing gas, we do not
absorb as much nitrogen on our dives. Gas blends with just 32
percent or 36 percent oxygen can sometimes nearly double the time a
diver can spend at depth before reaching the safe limits of excess
nitrogen.
In addition, because we absorb less nitrogen on our dives, even if
we do not stay down longer than air would permit, as enriched air
divers, we can shorten our surface intervals and still have enough
time to enjoy the next dive. In some cases, we can actually do more
dives in a single day than we could safely do if we dived with air.
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So why doesn’t everyone dive nitrox?
We started out this discussion by saying that the PADI Open Water Diver
Manual warns beginners not to use cylinders marked enriched air unless they
are properly trained. The reason for this warning has to do with a little
problem known as oxygen toxicity.
Believe it or not, oxygen, which we need to stay alive, can cause a diver to
convulse when pressures increase on descent. This generally happens when the
partial pressures of oxygen exceed 1.6 atmospheres. Although the convulsions
themselves are not life-threatening, the convulsions often cause a diver to
lose the regulator, aspirate water, and drown.
When breathing air on a dive, we would have
to descend to depths below 200 feet before oxygen toxicity becomes a
problem. However, using nitrox or oxygen on a dive can cause us to reach
depths that are potentially dangerous very quickly.
So is nitrox dangerous?
When I started diving nitrox in the
early 1990s, only technical diving agencies taught nitrox diving. The
general belief at the time was that nitrox was dangerous and experimental. I
recall being told horror stories of divers convulsing and drowning because
they grabbed the wrong cylinder or didn’t properly mix their nitrox. Most
recreational divers were convinced that nitrox was only for risk-takers.
Today things are much different. PADI and many other recreational training
agencies now teach recreational divers to use enriched air. Even students in
the PADI Open Water course are allowed to use enriched air on their final
dive under the direction of an Enriched Air instructor.
So what changed? First, procedures for properly blending enriched air and
marking cylinders have reduced the chance of mistakenly using the wrong gas.
Oxygen analyzers have become plentiful, reliable, and affordable. Training
materials and instruction are far superior compared to 20 years ago as well.
Finally, and perhaps most importantly, nitrox is also available at most
resorts and major dive centers. Because it is so readily available, nearly
every active diver is likely to be exposed to nitrox at some point. |
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Common Nitrox Misconceptions
Divers use Nitrox to increase safety.
This is not true. Recreational divers use nitrox to extend bottom time.
Technical divers use nitrox to shorten decompression time.
Nitrox is safer than air.
This is not true. More complex dive planning offsets any slight safety
improvement.
Nitrox makes you feel better.
There is some empirical evidence that using nitrox helps prevent
headaches and gives the diver more energy due to the higher oxygen
percentage. However, this is not true for everyone. Developing
proper breathing and buoyancy techniques, staying in shape, and pacing yourself on every dive are likely
to be far more effective.
You can dive deeper on nitrox.
This is totally false. Breathing more than 21 percent oxygen requires that
you stay at a shallower depth. Use nitrox for shallow dives. Use air for
deep dives above 130 feet.
Nitrox reduces the risk of nitrogen narcosis.
This is also not true. Oxygen is just as narcotic as nitrogen under
pressure. Use extreme care when diving nitrox at deeper depths. |
In part, the availability of nitrox is why your Open Water Diver manual
includes the warnings it does. It’s not that nitrox is so dangerous; it’s
that you are likely to see it and you need to be trained before using it.
That’s where the PADI Enriched Air Diver course comes in.
What will I learn in the PADI Enriched Air
Diver course?
In the
PADI Enriched Air Diver course, you will learn how to safely dive
nitrox. This means learning how to calculate maximum operating depths and
maximum exposure times to avoid issues with oxygen toxicity. It means
learning to calculate equivalent air depths and planning enriched air dives
using special tables and log pages. It also means learning to properly
analyze the contents of your cylinder and how to properly mark your nitrox
cylinder to avoid confusing it with a bottle of air. Once certified, you will be
able to plan and execute dives using blends up to 40 percent oxygen.
I’ve heard some divers use blends beyond 40
percent oxygen. Why am I limited to EANx40?
There are several reasons why using a blend greater than 40 percent is not
of much benefit to a recreational diver.
First, whenever we use a blend higher than EANx40, several serious equipment
issues come into play. Oxygen is highly flammable. Even the smallest trace
of a contaminant can cause an explosion when percentages above 40 percent
oxygen are used. For this reason, any dive equipment that comes into contact
with a blend containing above 40 percent must be “oxygen cleaned.” This can
be an expensive and laborious task. Regulators, SPGs, and cylinders all must
be cleaned if blends like this are used.
In addition, because the maximum operating depth is so shallow for blends
above 40 percent, you will probably not be able to carry enough gas with you
on the dive to realize any gain in extended bottom times. For example, a
dive to 50 feet with EANx36 gives you 220 minutes of bottom time! Chances
are you will run out of air long before you ever reach the maximum time
limit even on a repetitive dive with this blend. Using a blend above EANx36
really wouldn’t make much sense.
So why do divers use higher blends?
Blends above 40 percent are generally used by technical divers to shorten
decompression time when ascending from dives below 130 feet. This is a very
different reason from using nitrox to extend bottom time. It is also very
dangerous, since it requires the diver to switch gases during the dive.
These procedures are taught in the
DSAT Tec Deep
course.
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