Call It "High-Tech" Diving
by R.W. Hamilton, Ph. D.
A new category of diving is taking shape in the recreational diving world that sparks
considerable controversy, and is a cause of great concern. This, in general terms, is
diving deeper and staying down longer than the traditional limits. Although by no
means new, for many years it was a cause for concern more than controversy.
There was a general agreement the it was surely dangerous, was not approved by
anyone, and one could say with a clear conscience, "Don’t do it." Now methods are
coming along that, for the price of extra effort, make it possible to extend both
depth and bottom time with what is regarded by some as an acceptable degree of
risk, and in comparison with older methods, some tempting efficiencies.
This article describes the new technology, setting the stage for future articles that
explore some of these methods in more detail, but it also contains a serious caveat
about all this: It has to be done properly, or it should not be done at all.
Limits of Traditional Recreational Diving
Recreational diving is defined by the so-called "training agencies," the organizations
of diving instructors (NAUI, PADI, etc.), as no-stop scuba diving with air, to 40
meters, 130 feet. Many more experienced divers push beyond that envelope, either
by doing longer bottom times that require decompression stops or by going deeper.
Although the re are often some definite objectives for these dives, they are
nevertheless being done for fun, so it still comes under the "recreational" label. It
dies not, however, fit within the "traditional" definition. A new term is needed.
The training agencies discourage the use of the term "sport diving" because it
implies some sort of competition. A colleague mentioned that he saw two young
divers holding onto the bottom with their BCU’s inflated, then letting go and racing
to the surface. It is appropriate to discourage that sort of competition, just as it is
the equally risky practice of seeing who can swim the farthest underwater in
breathhold dives. Certainly advanced divers can practice their sport without
dangerous interpersonal competition, so the word "sport diver" does not meet our
needs. Competition is indeed a motivation, not so much for the depth and time
records&endash;since nowadays they are limited to those willing to make
exceptional efforts&endash;but to be the first in an unexplored cave, of the first to
look into a virgin wreck. "Sport" does not fit the bill here.
Two other names seem to be suitably descriptive. One is the possible overused
term "advanced" recreational diving, which already has many specific meanings,
but is perhaps valuable for its ambiguity. This applies to a diver working outside the
no-stop, 40 meter (130 feet) limit, regardless of the technique used. The other.,
"high tech" diving, relates to the new methods but does not include all situations,
since the traditional limits can easily be exceeded with standard gear.
The task of picking a single all-inclusive term can be left to others; for now, I am
calling dives outside the traditional limits "advanced", and those done outside those
limits using equipment other than standard wetsuits for thermal protection, as
"high tech."
This includes the use of dive computers and new decompression techniques, dry
suits, scooters, multiple or overpressurized tanks, as well as special gas mixtures.
Use of dry suits and dive computers within the traditional depth and decompression
limits can be considered traditional diving, although some special training is
needed. While some of these "high tech" items are relatively new to recreational
diving, many of the terms are old stuff to commercial divers.
The Need For Competence
Considering the unforgiving nature of mistakes in diving, just talking about
advanced and high tech diving has to be done with caution, lest it lead innocent
lams to the slaughter. Therefore this general topic has to lead off with a note on
competence. We cannot proceed without such a caveat.
Somehow it seems unnecessary to warn a novice skier against trying an intentional
head-over-heels flip (as some of us do them occasionally without intending to, but
that is another matter). But novice divers, it seems from the accident reports, do
equally risky things, apparently without recognition of the risks involved.
Something that may involve just a little extension beyond standard limits, if it
seduces a diver into running out of air at depth, can be a great deal more risky
than trying a flip on skis. Divers do these things. Therefore, allow me this bit of
preaching on competence.
Many things can be done with acceptable risk, even flips on skis, by someone
competent to do them. But in advanced and high-tech diving there are many things
that seem easy and indeed are easy for experts, but which can involve
unacceptable risk for ordinary divers. The bottom line is: divers must become
competent in new diving practices before sticking their necks out.
The need for proper knowledge and training is not a new idea. When numerous
commercial diving fatalities swept the early days of offshore oil exploration in the
North Sea, a number of regulations were issued that addressed proper equipment
and procedures. But they had no great impact on the safety record. The thing that
brought about a sharp reduction on fatalities was an emphasis on competence.
Although this is hard to define, it was followed by specific requirements for training,
certification, and updating of divers and their supervisors. And it has worked. Many
of the early accidents were human error, and while it is difficult to legislate that
people must not make mistakes, it is possible to ensure that they at least
know&endash;and know well&endash;the right way to o risky things.
All this is merely a prelude to a difficult task: to discuss what is happening in
advanced, high-tech, recreational diving without encouraging people to try things
they are not prepared for and thus to lead them into situations they cannot handle.
So in very general terms&endash;you heard it here&endash;don’t do it if you do
not know what you are doing.
Training, and Then Competence
What does it take to be prepared for high-tech diving? Knowledge, practice, the
right equipment and good planning.
First, a diver should have knowledge of the obvious hazards to life and health that
may exist in the high-tech diving environment. In addition to knowing when an
oxygen mix can be expected to explode, this includes an understanding of the
body’s physiological limits, first in the classic "black and white" limits, but also in
the duration of exposure as well as other environmental and physiological factors.
Necessary knowledge includes the procedures and practices to be used&endash;not
just what they are but what they mean, the consequences of deviation, and how
best to proceed when things are not going according to plan. Familiarity with one’s
equipment is also critical&endash;how it works, how to use it, how it should be
maintained, and what to do when it malfunctions.
Next is practice. And I offer this as a proverbial Catch-22: before doing a new and
dangerous thing, one must be highly experienced in it. The way around this doublebind
is practice, something one can do at any level of experience. An aspiring
advanced diver should practice all the various steps that are required, from reading
a table to connecting the apparatus. Practice things in parts, then link them
together. Practice first with everything right, then with some variables different and
finally with some things out of order. And take small steps; perhaps it is best not to
try to stage bottles and oxygen in the water the first time you use your new dry
suit. Consider the pilot of a high performance jet; it may take only a few months of
around-the-clock training to learn to fly it, but this practice must go through many
stages before real proficiency is achieved. What some world-class divers do is every
bit as challenging as flying "Top Gun"; divers have a different task, but they will be
just as dead if they screw up.
Much of the high-tech in high-tech diving has to do with equipment. It need not be
the most expensive, but it has to be right for the job. Know that it is right, and
know that it is working and in good shape. Pilots may not take their own planes
apart, but they do have to know when the aircraft needs fixing. Likewise, whether
or not you design, build, or maintain your own dive gear, you do need to know how
to tell when it is&endash;or is not&endash;right.
The last item on this list is planning, but it may be first in importance. All modern
divers get some training in dive planning, and let us hope that they all use it.
Planning a high-tech dive is no different in principle, but it can be a great deal more
complex. Not much more needs to be said here, just be sure to make planning a
fundamental part of every dive.
Getting The Technology
It is one thing to instruct new high-tech divers on the importance of learning, it is
something else to provide the necessary information.
Likewise, preaching about "the right equipment" does not make it available, nor
does it define what is needed. How does one go about getting the
information&endash;the knowledge&endash;to do advanced and high-tech diving?
There is no easy way. Some of the most experienced leaders in the scuba world are
dead set against releasing the information&endash;let alone
encouragement&endash;on the diving methods under discussion here. And they are
right. The word-of-mouth network that gives someone just enough information to
get started but not enough to do it right, is extremely dangerous.
Proper textbooks and courses are hard to come by for several reasons. First, most
recreational divers shouldn’t consider advanced, high-tech diving because they
cannot&endash;or will not&endash;get the necessary knowledge and training to do
it safely. Second, those who train divers as a profession don’t want to add to their
own woes; and the average instructor seldom has the specialized knowledge
anyway. Third, the scientific diving community, who, while diving professionally,
generally use recreational diving practices; they are not eager to see an excess of
recreational diving accidents threaten their programs. A final point is perhaps the
most important, things are not well enough developed that a crisp textbook can be
written; we basically do not know as much about this as we would like to. Even so,
"state of the art" does exist, and because high-tech diving is here to stay and is
going to be used, books and courses will become available in time. Several
university diving programs are beginning to move into advanced diving practices;
standards are being developed; and the documentation is slowly taking shape.
Organized programs are another approach. At present, virtually all of the high-tech
divers are individuals working alone. Each has his or her own equipment and
procedures, maintenance, and planning practices; only when diving with partners
will he/she follow the same dive profile as someone else. So in organized groups,
individual divers can follow the group’s practices and can gain experience with risk
reduced to the practical limit. This is not widely available yet, but it is coming.
Another tried and true way to learn new tricks is from someone who already knows
how. How do you know when your expert is telling you the right things? Obviously
you check his track record, find out how he got hid training, and how he is
regarded by the community. Our contribution is to offer more specific details in
future articles, including a review of the activities being carried out by high-tech
diving programs.
Risk
At some point, it is necessary to discuss risk. Diving is a risky enterprise. Like
anything else, the risk involved is directly related to the style of the practice. Some
automobile drivers go their entire lives without accidents, other have them all the
time. Most of the factors that influence driving risk are well-known, with
attitude&endash;the strong desire to drive safely&endash;being the most important
item. Diving is the same, and the consequences of an accident&endash;a loss of
control&endash;are just as serious as in driving. In a recent talk on fitness to
divers, Dr. Fred Bove said, "The first guy to be eliminated should be the one who
runs out of gas on the freeway." Running out of gas is more serious in diving than
in driving, but the point was made. The guy who runs out of gas or suffers frequent
fender-benders has no business in high-tech diving.
There is no such thing as perfectly safe diving, any more than there is a
decompression table with a true zero-bends incidence. The only way to be perfectly
safe underwater is to stick to cold showers. But diving can involve an acceptable
risk. Recreational diving, as currently practiced, has less risk than many other
activities, both sport and occupational, and the risk is acceptable to most. Advance
high-tech diving will involve a higher risk than routine diving, but the risk can be
kept within acceptable limits by having the right attitude, and by following
guidelines like those given above. If you don not intend to do it in a safe way, then
for goodness sake don’t do it at all.
Experience deserves a special emphasis here. Whether they be metallurgy or
medicine, practices that work on numerous occasions are generally regarded as
"acceptable." This is certainly the way decompression tables become validated, and
other diving practices might follow the same path. Although this is a complex issue,
since real depth of experience is generally lacking, the principle holds.
An Overview Of Current High Tech Diving Practice
For those who have paid their dues and bravely read the sermon, it is now time for
a brief discussion of what this is all about. As explained, any proper diving outside
the recreational guidelines is "advanced." This includes air dives in the range of 40
to about 60 meters (130- to 200 feet)&endash;more or less within Navy and
commercial limits, and those to greater depths, in some cases exceeding 90 meters
(300 feet)&endash;which almost invariable carry too high a risk to condone. Deep
air dives deserve further discussion, first to elaborate on the risks, but also to
relate what has been done.
The next methods are in a category best called "special mix diving," that is, dives
done with gas mixtures rather other than air. Of these, the most common are two
types of "nitrox" diving. Nitrox, a mixture of oxygen and nitrogen with a
composition different from air, is for use in undersea habitats and has less oxygen
than air. This method offers certain advantages, the main one being access to the
depth range of from 10 to 60 meters with very long bottom times, and little or no
decompression following excursions (depending on the depth of the habitat).
The term "nitrox" is also used for a mixture of air and oxygen more properly called
"enriched air nitrox." This method, "EANx," is useful in the range from 10 to about
35 or 40 meters, and allows greatly increased bottom times with no increase in
decompression time. It is being used by some university diving programs, is
described in the NOAA diving manual, and is beginning to be embraced by
recreational divers. There are two main hazards to EANx, both related to its oxygen
content. Since excess oxygen is being breathed, the possibility of toxicity must be
accounted for, and handling mixtures rich in oxygen is a fire and/or explosion
hazard.
Decompression tables for EANx diving can be derived from existing air tables by the
"equivalent air depth" calculation, but some advantages can come from custom
table computation.
Perhaps the most exciting of the special mix methods are "trimix" and heliox diving.
Trimix involves the use of mixtures of helium, nitrogen, and oxygen that are
appropriate for diving in the range of 50 to 100 meters. At the deeper end of this
range, a mixture of helium and oxygen, with little or no nitrogen, is better. Trimix,
or heliox diving takes considerable planning and preparation because of gas
logistics problems and in most cases, special decompression tables are needed.
Logistics applies first at the level of mixing which takes both skill and equipment,
and later at the level of breathing, since all the gas needed for a deep trimix or
heliox dive cannot normally be carried by the diver.
Still another special mix method involves the use of rebreathers. These supply gas
to the diver in a closed, or semi-closed loop from which CO2 is absorbed. They are
not readily available to recreational divers, but some scientific diving programs are
beginning to use them, and they have been used for years by many navies. In
addition to long in-water times, rebreathers offer the possibility of optimal oxygen
level to gain decompression advantages. The need for redundancy in the event of
system failure is a problem in some applications.
As mentioned, other high-tech items are having an impact on diving. Dive
computers make variable depth (multilevel) and repetitive diving more accessible,
albeit with meaningful risk of decompression sickness unless certain precautions
are taken. Dry suits are making all types of diving more comfortable, and with
proper training this is probably with less overall risk. Dry suits are essential for the
long dives possible with special mixtures.
With all of these warnings issued, and all of the described parameters met,
advanced high-tech diving offers the prepared, knowledgeable diver a chance to
experience a realm not previously accessible to humans. And there is every reason
to think&endash;as our technology and knowledge advance&endash;that we will be
able to push the envelope even further.
Bill Hamilton, a physiologist with 25 years of specialization in the diving, aerospace
and environmental fields, has spent much of his professional effort bridging the gap
between the laboratory and the field. A resident of Tarrytown, New York, he is the
principal in his consulting firm, Hamilton Research. Ltd., where his work includes
the development and assessment of commercial, institutional, and governmental
decompression procedures.
by R.W. Hamilton, Ph. D.
A new category of diving is taking shape in the recreational diving world that sparks
considerable controversy, and is a cause of great concern. This, in general terms, is
diving deeper and staying down longer than the traditional limits. Although by no
means new, for many years it was a cause for concern more than controversy.
There was a general agreement the it was surely dangerous, was not approved by
anyone, and one could say with a clear conscience, "Don’t do it." Now methods are
coming along that, for the price of extra effort, make it possible to extend both
depth and bottom time with what is regarded by some as an acceptable degree of
risk, and in comparison with older methods, some tempting efficiencies.
This article describes the new technology, setting the stage for future articles that
explore some of these methods in more detail, but it also contains a serious caveat
about all this: It has to be done properly, or it should not be done at all.
Limits of Traditional Recreational Diving
Recreational diving is defined by the so-called "training agencies," the organizations
of diving instructors (NAUI, PADI, etc.), as no-stop scuba diving with air, to 40
meters, 130 feet. Many more experienced divers push beyond that envelope, either
by doing longer bottom times that require decompression stops or by going deeper.
Although the re are often some definite objectives for these dives, they are
nevertheless being done for fun, so it still comes under the "recreational" label. It
dies not, however, fit within the "traditional" definition. A new term is needed.
The training agencies discourage the use of the term "sport diving" because it
implies some sort of competition. A colleague mentioned that he saw two young
divers holding onto the bottom with their BCU’s inflated, then letting go and racing
to the surface. It is appropriate to discourage that sort of competition, just as it is
the equally risky practice of seeing who can swim the farthest underwater in
breathhold dives. Certainly advanced divers can practice their sport without
dangerous interpersonal competition, so the word "sport diver" does not meet our
needs. Competition is indeed a motivation, not so much for the depth and time
records&endash;since nowadays they are limited to those willing to make
exceptional efforts&endash;but to be the first in an unexplored cave, of the first to
look into a virgin wreck. "Sport" does not fit the bill here.
Two other names seem to be suitably descriptive. One is the possible overused
term "advanced" recreational diving, which already has many specific meanings,
but is perhaps valuable for its ambiguity. This applies to a diver working outside the
no-stop, 40 meter (130 feet) limit, regardless of the technique used. The other.,
"high tech" diving, relates to the new methods but does not include all situations,
since the traditional limits can easily be exceeded with standard gear.
The task of picking a single all-inclusive term can be left to others; for now, I am
calling dives outside the traditional limits "advanced", and those done outside those
limits using equipment other than standard wetsuits for thermal protection, as
"high tech."
This includes the use of dive computers and new decompression techniques, dry
suits, scooters, multiple or overpressurized tanks, as well as special gas mixtures.
Use of dry suits and dive computers within the traditional depth and decompression
limits can be considered traditional diving, although some special training is
needed. While some of these "high tech" items are relatively new to recreational
diving, many of the terms are old stuff to commercial divers.
The Need For Competence
Considering the unforgiving nature of mistakes in diving, just talking about
advanced and high tech diving has to be done with caution, lest it lead innocent
lams to the slaughter. Therefore this general topic has to lead off with a note on
competence. We cannot proceed without such a caveat.
Somehow it seems unnecessary to warn a novice skier against trying an intentional
head-over-heels flip (as some of us do them occasionally without intending to, but
that is another matter). But novice divers, it seems from the accident reports, do
equally risky things, apparently without recognition of the risks involved.
Something that may involve just a little extension beyond standard limits, if it
seduces a diver into running out of air at depth, can be a great deal more risky
than trying a flip on skis. Divers do these things. Therefore, allow me this bit of
preaching on competence.
Many things can be done with acceptable risk, even flips on skis, by someone
competent to do them. But in advanced and high-tech diving there are many things
that seem easy and indeed are easy for experts, but which can involve
unacceptable risk for ordinary divers. The bottom line is: divers must become
competent in new diving practices before sticking their necks out.
The need for proper knowledge and training is not a new idea. When numerous
commercial diving fatalities swept the early days of offshore oil exploration in the
North Sea, a number of regulations were issued that addressed proper equipment
and procedures. But they had no great impact on the safety record. The thing that
brought about a sharp reduction on fatalities was an emphasis on competence.
Although this is hard to define, it was followed by specific requirements for training,
certification, and updating of divers and their supervisors. And it has worked. Many
of the early accidents were human error, and while it is difficult to legislate that
people must not make mistakes, it is possible to ensure that they at least
know&endash;and know well&endash;the right way to o risky things.
All this is merely a prelude to a difficult task: to discuss what is happening in
advanced, high-tech, recreational diving without encouraging people to try things
they are not prepared for and thus to lead them into situations they cannot handle.
So in very general terms&endash;you heard it here&endash;don’t do it if you do
not know what you are doing.
Training, and Then Competence
What does it take to be prepared for high-tech diving? Knowledge, practice, the
right equipment and good planning.
First, a diver should have knowledge of the obvious hazards to life and health that
may exist in the high-tech diving environment. In addition to knowing when an
oxygen mix can be expected to explode, this includes an understanding of the
body’s physiological limits, first in the classic "black and white" limits, but also in
the duration of exposure as well as other environmental and physiological factors.
Necessary knowledge includes the procedures and practices to be used&endash;not
just what they are but what they mean, the consequences of deviation, and how
best to proceed when things are not going according to plan. Familiarity with one’s
equipment is also critical&endash;how it works, how to use it, how it should be
maintained, and what to do when it malfunctions.
Next is practice. And I offer this as a proverbial Catch-22: before doing a new and
dangerous thing, one must be highly experienced in it. The way around this doublebind
is practice, something one can do at any level of experience. An aspiring
advanced diver should practice all the various steps that are required, from reading
a table to connecting the apparatus. Practice things in parts, then link them
together. Practice first with everything right, then with some variables different and
finally with some things out of order. And take small steps; perhaps it is best not to
try to stage bottles and oxygen in the water the first time you use your new dry
suit. Consider the pilot of a high performance jet; it may take only a few months of
around-the-clock training to learn to fly it, but this practice must go through many
stages before real proficiency is achieved. What some world-class divers do is every
bit as challenging as flying "Top Gun"; divers have a different task, but they will be
just as dead if they screw up.
Much of the high-tech in high-tech diving has to do with equipment. It need not be
the most expensive, but it has to be right for the job. Know that it is right, and
know that it is working and in good shape. Pilots may not take their own planes
apart, but they do have to know when the aircraft needs fixing. Likewise, whether
or not you design, build, or maintain your own dive gear, you do need to know how
to tell when it is&endash;or is not&endash;right.
The last item on this list is planning, but it may be first in importance. All modern
divers get some training in dive planning, and let us hope that they all use it.
Planning a high-tech dive is no different in principle, but it can be a great deal more
complex. Not much more needs to be said here, just be sure to make planning a
fundamental part of every dive.
Getting The Technology
It is one thing to instruct new high-tech divers on the importance of learning, it is
something else to provide the necessary information.
Likewise, preaching about "the right equipment" does not make it available, nor
does it define what is needed. How does one go about getting the
information&endash;the knowledge&endash;to do advanced and high-tech diving?
There is no easy way. Some of the most experienced leaders in the scuba world are
dead set against releasing the information&endash;let alone
encouragement&endash;on the diving methods under discussion here. And they are
right. The word-of-mouth network that gives someone just enough information to
get started but not enough to do it right, is extremely dangerous.
Proper textbooks and courses are hard to come by for several reasons. First, most
recreational divers shouldn’t consider advanced, high-tech diving because they
cannot&endash;or will not&endash;get the necessary knowledge and training to do
it safely. Second, those who train divers as a profession don’t want to add to their
own woes; and the average instructor seldom has the specialized knowledge
anyway. Third, the scientific diving community, who, while diving professionally,
generally use recreational diving practices; they are not eager to see an excess of
recreational diving accidents threaten their programs. A final point is perhaps the
most important, things are not well enough developed that a crisp textbook can be
written; we basically do not know as much about this as we would like to. Even so,
"state of the art" does exist, and because high-tech diving is here to stay and is
going to be used, books and courses will become available in time. Several
university diving programs are beginning to move into advanced diving practices;
standards are being developed; and the documentation is slowly taking shape.
Organized programs are another approach. At present, virtually all of the high-tech
divers are individuals working alone. Each has his or her own equipment and
procedures, maintenance, and planning practices; only when diving with partners
will he/she follow the same dive profile as someone else. So in organized groups,
individual divers can follow the group’s practices and can gain experience with risk
reduced to the practical limit. This is not widely available yet, but it is coming.
Another tried and true way to learn new tricks is from someone who already knows
how. How do you know when your expert is telling you the right things? Obviously
you check his track record, find out how he got hid training, and how he is
regarded by the community. Our contribution is to offer more specific details in
future articles, including a review of the activities being carried out by high-tech
diving programs.
Risk
At some point, it is necessary to discuss risk. Diving is a risky enterprise. Like
anything else, the risk involved is directly related to the style of the practice. Some
automobile drivers go their entire lives without accidents, other have them all the
time. Most of the factors that influence driving risk are well-known, with
attitude&endash;the strong desire to drive safely&endash;being the most important
item. Diving is the same, and the consequences of an accident&endash;a loss of
control&endash;are just as serious as in driving. In a recent talk on fitness to
divers, Dr. Fred Bove said, "The first guy to be eliminated should be the one who
runs out of gas on the freeway." Running out of gas is more serious in diving than
in driving, but the point was made. The guy who runs out of gas or suffers frequent
fender-benders has no business in high-tech diving.
There is no such thing as perfectly safe diving, any more than there is a
decompression table with a true zero-bends incidence. The only way to be perfectly
safe underwater is to stick to cold showers. But diving can involve an acceptable
risk. Recreational diving, as currently practiced, has less risk than many other
activities, both sport and occupational, and the risk is acceptable to most. Advance
high-tech diving will involve a higher risk than routine diving, but the risk can be
kept within acceptable limits by having the right attitude, and by following
guidelines like those given above. If you don not intend to do it in a safe way, then
for goodness sake don’t do it at all.
Experience deserves a special emphasis here. Whether they be metallurgy or
medicine, practices that work on numerous occasions are generally regarded as
"acceptable." This is certainly the way decompression tables become validated, and
other diving practices might follow the same path. Although this is a complex issue,
since real depth of experience is generally lacking, the principle holds.
An Overview Of Current High Tech Diving Practice
For those who have paid their dues and bravely read the sermon, it is now time for
a brief discussion of what this is all about. As explained, any proper diving outside
the recreational guidelines is "advanced." This includes air dives in the range of 40
to about 60 meters (130- to 200 feet)&endash;more or less within Navy and
commercial limits, and those to greater depths, in some cases exceeding 90 meters
(300 feet)&endash;which almost invariable carry too high a risk to condone. Deep
air dives deserve further discussion, first to elaborate on the risks, but also to
relate what has been done.
The next methods are in a category best called "special mix diving," that is, dives
done with gas mixtures rather other than air. Of these, the most common are two
types of "nitrox" diving. Nitrox, a mixture of oxygen and nitrogen with a
composition different from air, is for use in undersea habitats and has less oxygen
than air. This method offers certain advantages, the main one being access to the
depth range of from 10 to 60 meters with very long bottom times, and little or no
decompression following excursions (depending on the depth of the habitat).
The term "nitrox" is also used for a mixture of air and oxygen more properly called
"enriched air nitrox." This method, "EANx," is useful in the range from 10 to about
35 or 40 meters, and allows greatly increased bottom times with no increase in
decompression time. It is being used by some university diving programs, is
described in the NOAA diving manual, and is beginning to be embraced by
recreational divers. There are two main hazards to EANx, both related to its oxygen
content. Since excess oxygen is being breathed, the possibility of toxicity must be
accounted for, and handling mixtures rich in oxygen is a fire and/or explosion
hazard.
Decompression tables for EANx diving can be derived from existing air tables by the
"equivalent air depth" calculation, but some advantages can come from custom
table computation.
Perhaps the most exciting of the special mix methods are "trimix" and heliox diving.
Trimix involves the use of mixtures of helium, nitrogen, and oxygen that are
appropriate for diving in the range of 50 to 100 meters. At the deeper end of this
range, a mixture of helium and oxygen, with little or no nitrogen, is better. Trimix,
or heliox diving takes considerable planning and preparation because of gas
logistics problems and in most cases, special decompression tables are needed.
Logistics applies first at the level of mixing which takes both skill and equipment,
and later at the level of breathing, since all the gas needed for a deep trimix or
heliox dive cannot normally be carried by the diver.
Still another special mix method involves the use of rebreathers. These supply gas
to the diver in a closed, or semi-closed loop from which CO2 is absorbed. They are
not readily available to recreational divers, but some scientific diving programs are
beginning to use them, and they have been used for years by many navies. In
addition to long in-water times, rebreathers offer the possibility of optimal oxygen
level to gain decompression advantages. The need for redundancy in the event of
system failure is a problem in some applications.
As mentioned, other high-tech items are having an impact on diving. Dive
computers make variable depth (multilevel) and repetitive diving more accessible,
albeit with meaningful risk of decompression sickness unless certain precautions
are taken. Dry suits are making all types of diving more comfortable, and with
proper training this is probably with less overall risk. Dry suits are essential for the
long dives possible with special mixtures.
With all of these warnings issued, and all of the described parameters met,
advanced high-tech diving offers the prepared, knowledgeable diver a chance to
experience a realm not previously accessible to humans. And there is every reason
to think&endash;as our technology and knowledge advance&endash;that we will be
able to push the envelope even further.
Bill Hamilton, a physiologist with 25 years of specialization in the diving, aerospace
and environmental fields, has spent much of his professional effort bridging the gap
between the laboratory and the field. A resident of Tarrytown, New York, he is the
principal in his consulting firm, Hamilton Research. Ltd., where his work includes
the development and assessment of commercial, institutional, and governmental
decompression procedures.
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