Larry "Harris" Taylor, Ph.D.
This
is an electronic reprint of an article that appeared in The Flipper (Sept/Oct.
1993, p. 6-8). This material is copyrighted and all rights retained by the
author. This article is made available as a service to the diving community by
the author and may be distributed for any non-commercial or Not-For-Profit
use.
All rights reserved.
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Simply put, Nitrox is any binary mixture of nitrogen and
oxygen. The air you are currently breathing is nitrox-21. (The number refers to
the percentage of oxygen in the mix.) The Nitrox mixes most often encountered
are NOAA Nitrox I (32% O2) and NOAA Nitrox II (36% O2).
Collectively, all nitrogen-oxygen binary mixes are known as "enriched air
nitrox" (EANx) or oxygen enriched air to emphasize that the O2
concentration is higher than air. One Nitrox training agency (ANDI) uses the
marketing trademark of "safe air." Like the emergence of buoyancy compensators
and submersible pressure gauges, the entrance of Nitrox into the sport diving
community has promulgated much discussion.
As such, there is an abundance of mythology surrounding the topic. Let's
examine some of these myths.
Myth:
Nitrox is a deep diving gas:
Absolutely false! Nitrox is used primarily to extend bottom
times in the 60-90 fsw range. NOAA I has an operating depth limit of 130 fsw;
NOAA II has a limit of 100 fsw.
Myth:
Nitrox is a new, untested gas mix.
No! Nitrox has been successfully used in the scientific,
commercial and military diving communities since 1879.
Myth:
If you use this gas, you will die.
As with any diving, there are risks. The increased O2
concentration increases risk (relative to air) for oxygen toxicity at
depths below 100 fsw. The use of this gas requires that divers to rigorously
monitor depth and time.
Myth:
If I use this gas, then I cannot be treated for bends in a
chamber.
There is no medical reason for non-treatment. Oxygen "dose" is
measured in OTU's (Oxygen Tolerance Units). A typical sport dive accumulates
less than 150 OTU's. It has been medically accepted that humans can tolerate a
daily dose of 1440 OTU's. Since a typical chamber run uses about 400 OTU's (with
600 OTU's being about max per treatment), a typical diver, especially in rigidly
controlled resort situations, has more than adequate OTU reserve available for
treatment.
Myth:
If I use this equipment, I must purchase totally separate scuba gear and
everything must be oxygen cleaned. Using Nitrox will destroy my current scuba
gear.
It has been established that oxygen mixes less than 40%
O2 do not require O2 cleaning. While it might be prudent,
as long as O2 concentration is less than 40% there is no need for
separate gear. Current scuba gear can be used with EANx. Since some gas mixes
are prepared in the scuba cylinder (thus cylinder may be exposed to higher
concentrations of oxygen), it is required that Nitrox cylinders be O2
cleaned and used only for nitrox.
Advantages of Nitrox
The primary component of air is nitrogen. Nitrogen is
physiologically inert (not used by the body.) As such it just accumulates in
tissues. Decompression schedules (obligations) are based on this accumulation of
nitrogen. If we lower the percentage of nitrogen in the breathing gas mix, then
we lower our tissue accumulation of nitrogen gas and decrease our risk of
decompression problems.
There are two ways to utilize EANx. The first is termed the
"physiological" advantage. This means breathing EANx while using whatever sport
diver tables/computer (based on air) you currently use. Since you are breathing
a mix that employs less nitrogen than air, you will accumulate less nitrogen
than you would breathing air on the same dive profile. Since you have
accumulated less nitrogen than your air table/computer has calculated, you have
a "physiological" safety factor; you are at less risk for a decompression
sickness hit than you would be breathing air on the same
dive.
The second way to utilize EANx is termed the "decompression
advantage." Since decompression schedules are based on nitrogen accumulation,
divers breathing EANx (contains less nitrogen than air) will take longer to
absorb a fixed amount of nitrogen. This means that divers can stay at the chosen
depth longer on EANx than on air. This difference can be
substantial.
No Decompression Times
The increase in no-D time allowed in the 60-90 fsw range is
the primary reason for using the gas as a breathing mix within the
scientific, commercial and military diving communities.
Disadvantages
The decrease in nitrogen is accomplished by a corresponding
increase in oxygen. This increases the potential for oxygen toxicity "hits." An
oxygen toxicity hit may occur with no-warning with the severity of a
"grand-mal-type" seizure. Such an event in sport diving gear is not considered
to be survivable. It is the potential for oxygen toxicity hits that mandates
absolute discipline and adherence to established diving protocols and
procedures: the gas must be analyzed and found appropriate for the depth range
desired (requires prior planning to establish diving limits), the depth limits
of the gas mix MUST BE respected (the consequence of going too deep with EANx is
the potential for in-water seizure followed by drowning), and equipment must be
properly maintained.
Conclusion:
The use of gas mixes other than air is rapidly entering the
recreational market. The distinct advantages of EANx for shallow water diving
are substantial and will most likely give this gas a permanent place in sport
diving. The disadvantages of this gas require that divers understand what they
are doing and adhere to a level of discipline that is unfamiliar to many within
the sport diving community. The concerns about the use of EANx in the
recreational scuba community are real; the penalty of improper use can be
severe. However, the key to
successful EANx diving (as with all diving) is knowledge of the risks and
adherence to those procedures that have been established to minimize those
risks.
For those (like myself) whose diving is primarily less than
100 fsw, EANx is definitely the current breathing mix of choice. I have said it
before and I will continue to preach the "gospel" according to "Harris": In ALL
conceivable diving scenarios, the knowledgeable, physically fit diver has more
fun! Staying at depth longer, to many, means more enjoyment of Planet Ocean.
With proper training and understanding, EANx can be the doorway to more
bottom-time and thus more in-water fun!
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About
The Author:
Larry "Harris" Taylor, Ph.D. is a biochemist and Diving Safety
Coordinator at the University of Michigan. He has authored more than 200 scuba
related articles. His personal dive library (See Alert Diver, Mar/Apr, 1997, p.
54) is considered one of the best recreational sources of information in North
America.
All rights reserved.
Use of these articles for personal or organizational profit is specifically denied.
These
articles may be used for not-for-profit diving education.