Adventure Dominica
Recreational Scuba Diving:
An Overview
What Does 'Scuba' Stand For?
Scuba is an acronym for 'self-contained underwater breathing apparatus'.
There are several ways one can go under water (breath-hold, helmet diving, submarine, etc.). "Diving with scuba" signifies using apparatus that is completely carried by the diver and not connected to the surface, hence self-contained.
How Popular Is Scuba Diving?
An estimated 2.5-3.5 million Americans participate in recreational scuba diving. Another 500 thousand become certified each year in the United States.
In the early days of scuba diving (roughly 1950-1970), participants were predominately young men. Today the sport is enjoyed by people in all age groups and both sexes.
And why not? Just about any teenager or adult who enjoys the water and can swim, and who does not have heart or lung impairment, can learn to scuba dive.
It does not take great physical strength or unusual exercise tolerance. All it takes is the desire, plus some basic classroom and in-water training.
Scuba originally began with military and commercial applications, where it is still employed. However, by far its widest use, in terms of number of participants, is recreational.
Recreational scuba today is like other any other sport that requires specialized equipment and training, such as snow skiing, sailing, mountain climbing and horseback riding.
This section will provide an overview of recreational scuba diving, and explain how it differs from other forms of diving with scuba equipment.
Apparatus Figure 1.
Front and side view of scuba diver equipped ready to jump into the water.
She is carrying a compressed air tank, and is wearing a buoyancy
compensator (BC), mask with snorkel, and fins.
Her mouthpiece is attached to the second stage regulator, and it in turn is
attached by hose to the first stage regulator on top of the tank. The alternate
second stage regulator is shown over her left arm.
Note: this diver is not wearing a weight belt; weights are carried inside her
BC.a tank of compressed air carried by the diver on his or her back. a first
stage regulator attached to the tank that serves to lower air pressure
delivered to the diver. a second stage demand regulator and mouthpiece,
that delivers air on inhalation and closes on exhalation. a face mask that
covers the diver's eyes and nose, to allow for both underwater vision and
equalization of air pressure within the mask.
An extra second stage regulator and mouthpiece, carried by the diver in
case of emergency (when attached to a long hose, this extra second stage is
called an octopus).two submersible gauges, one to display an accurate
depth and the other to show how much air remains in the tank (or,
alternatively, a single gauge that combines both functions, e.g., as part of a
dive computer).an inflatable vest (buoyancy compensator, BC) worn to
provide a means of establishing positive buoyancy when needed.
A weight belt and weights (or some other type of weight system), worn to
compensate for the positive buoyancy of the diver and scuba apparatus. fins
to facilitate self-propulsion in the water. a wet suit or other type of body
protection to prevent hypothermia (and secondarily to prevent cuts and
abrasions under water); in cold water gloves and a hood may be worn for
hypothermia protection also.
Optional equipment for scuba diving numbers many items, such as a snorkel,
dive knife, small tank of extra air, dive computer, compass, dive lights,
writing slate, whistle, and inflatable signaling device.
Depending on the circumstances (e.g., lights for night diving, a snorkel for
surface swimming) some of these items may at times be essential, but they
are not part of basic scuba equipment.
With the basic scuba equipment a qualified diver can safely remain
underwater for anywhere from a few minutes to over two hours; the time
limit for any given dive will depend on the depth of that dive, the rate of air
consumption, and the profile of any dives made within the previous 6-12
hours.
What Is Scuba Certification?
Potential hazards that every scuba diver must be aware of include
de-compression sickness, air embolism, hypothermia, physical exhaustion,
injuries from marine life, boating accidents, sunburn, and out-of-air
catastrophes.
Despite the list of potential problems, recreational diving is actually a safe
sport if the diver is healthy and trained properly, each dive is carefully
planned and dive limits are followed.
The most serious problems, and how to avoid them, are covered in the
entry-level scuba course.The entry-level course, also known as 'basic open
water' or 'basic certification,' takes about 30 hours.
About 10 hours is spent in classroom instruction and the remainder in
supervised pool and open water diving. 'Open water' means a natural body
of water open to the sky.
Upon completion, a certification or 'C' card is issued.
The C card contains the new diver's picture; date of course completion and
signature of the instructor.
The basic open water course is fairly standard and is given under the
auspices of one of several national training agencies.
Many people are first exposed to scuba through the "resort course." This is
an introductory lesson offered at a resort or on a cruise, and is always taught
by an instructor (i.e., one who is also qualified to teach the standard open
water course).
The resort course is highly variable; it may include only a brief lecture on a
crowded bus on the way to the dive site, or a leisurely morning pool session
before the afternoon open water dive (I have seen both methods).
Because the resort course contains no textbook and very little in the way of
theory or skills testing, it does not certify for independent diving.
It is also good only for that resort and for the time you are a guest there.
If you return six months or a year later to the same resort you would have to
start all over with another resort course.(One exception is the Club Med
resort course, which offers 'Club Med Certification'.
The student completing a Club Med resort course can dive at any other
Club Med around the world, but always with a Club Med instructor and
after an initial checkout dive.)
Resort courses are fine for introduction to scuba, but anyone who has
enjoyed the experience is encouraged to take a standard certification course
and learn the necessary skills and theory.
Standard certification is also more practical.The C card allows one to rent
or buy scuba equipment anywhere in the world, and to engage in
recreational diving without supervision by an instructor.
The certification process distinguishes recreational scuba diving from most
other sports that use specialized equipment (e.g., snow skiing, mountain
climbing).Without a C card (i.e., without certification) one should not go
scuba diving (unless accompanied by a professional scuba instructor).Who
Teaches Scuba? In college the lowest academic rank is the "instructor,"
usually someone in graduate school who is assigned to teach and work
under a "professor.
"In the world of scuba the instructor is the highest level. A scuba instructor is
the only person trained and qualified to teach scuba diving. He or she works
under the auspices of one of the national scuba training agencies.
The scuba instructor can be assisted by other scuba professionals who are in
training to become a scuba instructor; they may have the title of dive master
(the entry level position for a scuba professional) or assistant
instructor.However, only someone with instructor status can teach the basic
open water course.
How Does Recreational Scuba Diving Differ From Other Forms Of
Scuba Diving?
Diving was revolutionized by the development of a workable demand
regulator, co-invented in 1943 by Jacques Cousteau and Emil Gagnan.
The "sport" of scuba diving did not catch on for another 10 years. Today the
greatest use of scuba equipment is for recreational diving.
Recreational scuba diving, as taught by national certifying agencies, is
defined as diving that: Uses only compressed air as the breathing mixture.
It is never done solo, does not exceed a depth of 130 feet, does not require
specialized training beyond the basic open water course.
Scuba equipment is also widely employed by two other types of divers,
loosely categorized as "professional" and "technical.
"By definition, these two groups are not constrained by the RSD criteria
listed above.
Professional diving is done for military, governmental, commercial, or
scientific purposes.Professional divers are paid to dive.
They have a specific mission for each dive, e.g., lay a mine or recover a
bomb (military), look for a body or a weapon (law enforcement agency),
explore for oil (commercial), map an ancient wreck or examine a new
species of fish (scientific).
Technical diving is the term for all diving that exceeds recreational limits but
is not engaged in for profit.Although many, if not most, technical divers
consider themselves involved in a recreational activity, the nature of their
diving and type of equipment used exceed the boundaries of RSD.
To be sure, there is not universal agreement on what constitutes technical
diving, and any attempt to define it tends to degenerate into heated
discussion and semantics.
For the novice or basic open water diver, the following activities can be
considered to be "technical diving."The Realm Of Technical Diving cave
diving Ice diving very deep diving (to greater than 130 feet) mixed gas diving
(using gas mixtures other than air, such as nitrox or trimix) deep-penetration
wreck diving with specialized life-support equipment (e.g., O2 re-breathers)
Much of technical diving is taught by agencies other than the national open
water certification agencies.
However, recently PADI and other national agencies became involved in
nitrox certification, although the activity is still not considered part of basic
open 'recreational diving.
'Still, the trend is to expand the envelope of technology to encompass more
and more divers, and it is conceivable that some of today's advanced
technology (e.g., rebreathers) will one day be routinely used by open water
recreational divers.
Clearly, the distinction between 'technical' and 'recreational diving' is
becoming less distinct over time.
(No matter how diving activities are classified, no one should engage in any
diving activity unless certified in that activity or else supervised by a qualified
instructor.)
What Is The Buddy System?
RSD requires that each diver be accompanied under water by a buddy who
can share air or provide other assistance.
Scuba apparatus is designed to carry an extra demand regulator.
This is required in case one diver runs out of air and has to share a single
tank with his or her buddy.
Ideally, the buddies should have similar training and skill levels; it does no
good to have a buddy who dives deeper or stays down longer than you do.
Buddies should stay close together and always be aware of each other's
location.
Why is 130 Feet The Maximum Depth In Recreational Diving?
The 130 foot limit is an arbitrary depth originally adopted by the U.S. Navy
because it gave navy divers about 10 minutes of bottom time on compressed
air; going any deeper on air made no sense to the Navy because the time
available to do useful work was simply too short.
As with many diving issues in the early days of scuba (e.g., the 'no
decompression' limits), the Navy standard was also adopted by the
recreational training agencies.
Some experienced recreational divers do go deeper than 130 feet, and yet
still stay within no decompression limits. However, since the risks of the
bends, running out of air, and nitrogen narcosis increase as you go deeper,
the training agencies feel that some arbitrary limit must be set and have
stayed with 130 feet.
Thus, although one can dive deeper and stay within no decompression limits,
diving deeper than 130 feet a) is not taught by the recreational training
agencies, and b) must be undertaken with great care and an understanding
of the increased risks.
What Is Mandatory Decompression And Why Is It Not Part Of
Recreational Scuba Diving?
"Decompression" always occurs when we go from a higher to a lower
ambient pressure.
Thus all compressed gas diving is decompression diving. When recreational
diving is referred to as "no decompression diving" it really means, "no
mandatory decompression stop diving."A decompression stop should never
be necessary within the guidelines of RSD.
A decompression stop is often necessary in dives deeper or longer than
allowed in RSD; it provides time for some of the excess nitrogen that
entered the tissues to "gas off" (diffuse into the blood stream and then be
ventilated out by the lungs), thereby minimizing risk of decompression
sickness (DCS).
Based on experiments, plus much trial and error experience, the amount of
excess nitrogen remaining in the tissues after a planned, mandatory
decompression stop should not cause DCS.
Since professional and technical divers often spend longer periods under
water and/or dive deeper than recreational divers, they must know when to
stop on ascent and how long to wait before surfacing.
By contrast, each recreational dive is planned so that the diver can ascend
continuously to the surface without encountering decompression sickness;
the diver is still decompressing on the way up, but doesn't have to stop to
allow further decompression.
The basic assumption is that diving is inherently made safer by avoiding dives
that require decompression stops.
This is both the philosophy and practice of recreational diving today.
The "no decompression stop" limits in RSD are based on maximum depth,
time under water, and extent of any preceding dives, all factors which
directly affect tissue nitrogen uptake.
The limits are set in dive tables known to every certified diver, and are
incorporated into all dive computers.
Excess nitrogen, which enters tissues due to the increased ambient pressure
under water, determines the "no-decompression stop" limits.
A non-repetitive dive (no previous dive within a specified time period,
typically 6-12 hours) to 130 feet has an allowable "actual bottom time"
(measured from the time dive commences to start of ascent) of only about
5-10 minutes for a dive to 130 feet.
Beyond this brief time span the diver risks developing decompression
sickness from a continuous ascent.
In contrast, at 35 feet, on a non-repetitive dive, the 'no decompression'
bottom time is about 205 minutes.
Although RSD is always planned for no decompression stop required, it is
routine practice to make a 3 to 5 minute "safety stop" at 15 feet before
surfacing from any dive deeper than about 40 feet.
This is a decompression stop but it is not mandatory, just added for extra
safety to the dive; hence the term safety stop. In theory, when adhering to
the recreational diving tables one should not experience DCS if a safety stop
is not made.
Nonetheless, all dives deeper than about 40 feet should incorporate a safety
stop, and it is universally practiced.
If any dive requires a decompression stop for any reason, it has exceeded
the limits of recreational diving.
Are There Different Levels Of Recreational Diving? Within the universe of
recreational diving there are many levels, based on extent of training,
experience, or both. I have already commented on the resort course, which
is not formal scuba training but just an introductory scuba experience.
The following paragraphs pertain to the certified diver.Training. One can
take several courses beyond basic open water, and they can be divided into
two "tracks."
The first track is for people who want more training but have no intention of
ever teaching scuba. With such courses as advanced diving, stress and
rescue, underwater photography, ice diving, and deeper diving (60-130
feet), one can gain additional knowledge and skills, all under the purview of
recreational diving.
The second track is for people who plan to turn professional (within the
recreational purview) and teach scuba. They will take courses leading up to
the instructor level (advanced diving, stress and rescue, dive master,
assistant instructor, instructor).
Once an individual achieves instructor level he or she is a full-fledged
professional within recreational scuba and can teach the basic certification
course.
Unless they have taken special training, scuba instructors are not trained to
exceed the recreational limits.Thus they are not technical divers and would
need further training to do mixed gas diving, for example.
Of course many scuba instructors do obtain training in these and other
technical diving skills.Experience. Most recreational divers never take more
than the basic open water course.
However, after making many dives over the years they become highly
experienced and adept in all the important skills. In recent years scuba
agencies have developed a way to recognize the more experienced divers,
by creating "dive cards" showing the number of dives obtained, in round
numbers.
Thus, with proper documentation you can get a card that shows you have
done anywhere from 50 to 5000 lifetime dives.
The utility of this type of card is that it can quickly show your level of
experience, such as when you go to rent equipment or sign on for a boat
dive.
Experience counts for much in scuba diving (as with any activity), and the
cards are a way of acknowledging this.
What Is Sport Surface-Supplied Compressed Air Diving And How
Does It Differ From Scuba?
As its name indicates, sport surface-supplied compressed air diving
(sometimes shortened to 'sport surface-supplied air,' SSSA) separates the
compressed air source from the diver.
For this reason it is not "scuba," which is self-contained (the scuba diver
always carries his/her own air source). SSSA uses a small gasoline- or
electric-powered air compressor that can sit on a boat, dock or a floating
inner tube, so it can literally go to any dive site and remain over the heads of
the divers (Figure 2).
The compressor can provide air to more than one diver at the same
time.Each SSSA diver is tethered to the compressed air source by a long
hose.The entire apparatus is sometimes called a hookah, after the Egyptian
term for a pipe that cools water, but "surface-supplied compressed air" is
the more correct term.
At the end of each hose is a second stage regulator and mouth-piece, just
like in scuba diving; exhaled air is expelled into the water.
For recreational divers this technique has been pioneered by Brownie's
Third Lung, Ft. Lauderdale, FL (1-800-327-0412).SSSA diving is limited
by the strength of the air compressor, the length of the hose and, as in scuba,
the level of diver training.
As sold by Brownies, each unit serves at least two divers; some can serve
three or four divers at 30 feet.Other units allow deeper diving, up to 90 feet
for two divers.
In principle SSSA diving is the same as professional helmet diving, except
that the depths are generally less, no helmet is worn by the diver, only
compressed air is used (professionals may used mixed gases), and the
amount of surface support (i.e., other people on the surface) may be minimal
to none.
What Is THE FUTURE OF RSD? The future is now:
The technology that exists today, mostly in the realm of technical diving, may
become part of recreational diving tomorrow.There is unending debate
within professional diving circles about most of this technology, and whether
it should enter the realm of recreational diving sooner rather than later.
Dive safety Spread of hyperbaric chambers to all popular dive sites;
development of affordable, portable hyperbaric chambers that can be
carried on a dive boat. Universal use of dive computers air integrated to the
scuba tank, eliminating the high-pressure hose connection.
Use of full-face masks that remain on the diver's face if there is any panic or
loss of consciousness (absence of a mouthpiece reduces the risk of
drowning in these situations).
Implementation of underwater voice communication technology.
Development of "heads up" displays for dive data; instead of data displayed
on a wrist device or on a dangling console, all data will appear inside the
diver's mask, available for reading with only a turn of the eye.
Critical information may flash, assuring the diver's attention. Implementation
of diver-specific algorithms (adjusted for the diver's age, weight, and
perhaps other characteristics) for dive computers.Such algorithms may
become available from studies that correlate dive accident experience with a
wide range of dive profiles in a diverse group of divers.
Extension of bottom time or distance traveled under water.
Use of nitrox, perhaps with a depth limiter to prevent diving too deep and
incurring risk of oxygen toxicity.Use of stronger tanks (carbon fiber) that can
hold higher pressures and thus more cubic feet of gas.
Underwater scooters that allow the diver to range further on a given dive
with the same amount of air.
Use of re-breathing "closed circuit" scuba technology. Much of this
technology and equipment are available now, if not for the recreational diver
than in technical circles.
Just as other once-new technology gradually became accepted (e.g., dive
computers), it seems likely that much of today's "cutting-edge" technology
will be adopted by recreational divers in the coming years.
Cost and complexity will certainly be a limiting factor, however. Many
recreational divers may not want to be burdened with more equipment or
ever more complicated and expensive technology only time and the
marketplace will tell.
Front and side view of scuba diver equipped ready to jump into the water.
She is carrying a compressed air tank, and is wearing a buoyancy
compensator (BC), mask with snorkel, and fins.
Her mouthpiece is attached to the second stage regulator, and it in turn is
attached by hose to the first stage regulator on top of the tank. The alternate
second stage regulator is shown over her left arm.
Note: this diver is not wearing a weight belt; weights are carried inside her
BC.a tank of compressed air carried by the diver on his or her back. a first
stage regulator attached to the tank that serves to lower air pressure
delivered to the diver. a second stage demand regulator and mouthpiece,
that delivers air on inhalation and closes on exhalation. a face mask that
covers the diver's eyes and nose, to allow for both underwater vision and
equalization of air pressure within the mask.
An extra second stage regulator and mouthpiece, carried by the diver in
case of emergency (when attached to a long hose, this extra second stage is
called an octopus).two submersible gauges, one to display an accurate
depth and the other to show how much air remains in the tank (or,
alternatively, a single gauge that combines both functions, e.g., as part of a
dive computer).an inflatable vest (buoyancy compensator, BC) worn to
provide a means of establishing positive buoyancy when needed.
A weight belt and weights (or some other type of weight system), worn to
compensate for the positive buoyancy of the diver and scuba apparatus. fins
to facilitate self-propulsion in the water. a wet suit or other type of body
protection to prevent hypothermia (and secondarily to prevent cuts and
abrasions under water); in cold water gloves and a hood may be worn for
hypothermia protection also.
Optional equipment for scuba diving numbers many items, such as a snorkel,
dive knife, small tank of extra air, dive computer, compass, dive lights,
writing slate, whistle, and inflatable signaling device.
Depending on the circumstances (e.g., lights for night diving, a snorkel for
surface swimming) some of these items may at times be essential, but they
are not part of basic scuba equipment.
With the basic scuba equipment a qualified diver can safely remain
underwater for anywhere from a few minutes to over two hours; the time
limit for any given dive will depend on the depth of that dive, the rate of air
consumption, and the profile of any dives made within the previous 6-12
hours.
What Is Scuba Certification?
Potential hazards that every scuba diver must be aware of include
de-compression sickness, air embolism, hypothermia, physical exhaustion,
injuries from marine life, boating accidents, sunburn, and out-of-air
catastrophes.
Despite the list of potential problems, recreational diving is actually a safe
sport if the diver is healthy and trained properly, each dive is carefully
planned and dive limits are followed.
The most serious problems, and how to avoid them, are covered in the
entry-level scuba course.The entry-level course, also known as 'basic open
water' or 'basic certification,' takes about 30 hours.
About 10 hours is spent in classroom instruction and the remainder in
supervised pool and open water diving. 'Open water' means a natural body
of water open to the sky.
Upon completion, a certification or 'C' card is issued.
The C card contains the new diver's picture; date of course completion and
signature of the instructor.
The basic open water course is fairly standard and is given under the
auspices of one of several national training agencies.
Many people are first exposed to scuba through the "resort course." This is
an introductory lesson offered at a resort or on a cruise, and is always taught
by an instructor (i.e., one who is also qualified to teach the standard open
water course).
The resort course is highly variable; it may include only a brief lecture on a
crowded bus on the way to the dive site, or a leisurely morning pool session
before the afternoon open water dive (I have seen both methods).
Because the resort course contains no textbook and very little in the way of
theory or skills testing, it does not certify for independent diving.
It is also good only for that resort and for the time you are a guest there.
If you return six months or a year later to the same resort you would have to
start all over with another resort course.(One exception is the Club Med
resort course, which offers 'Club Med Certification'.
The student completing a Club Med resort course can dive at any other
Club Med around the world, but always with a Club Med instructor and
after an initial checkout dive.)
Resort courses are fine for introduction to scuba, but anyone who has
enjoyed the experience is encouraged to take a standard certification course
and learn the necessary skills and theory.
Standard certification is also more practical.The C card allows one to rent
or buy scuba equipment anywhere in the world, and to engage in
recreational diving without supervision by an instructor.
The certification process distinguishes recreational scuba diving from most
other sports that use specialized equipment (e.g., snow skiing, mountain
climbing).Without a C card (i.e., without certification) one should not go
scuba diving (unless accompanied by a professional scuba instructor).Who
Teaches Scuba? In college the lowest academic rank is the "instructor,"
usually someone in graduate school who is assigned to teach and work
under a "professor.
"In the world of scuba the instructor is the highest level. A scuba instructor is
the only person trained and qualified to teach scuba diving. He or she works
under the auspices of one of the national scuba training agencies.
The scuba instructor can be assisted by other scuba professionals who are in
training to become a scuba instructor; they may have the title of dive master
(the entry level position for a scuba professional) or assistant
instructor.However, only someone with instructor status can teach the basic
open water course.
How Does Recreational Scuba Diving Differ From Other Forms Of
Scuba Diving?
Diving was revolutionized by the development of a workable demand
regulator, co-invented in 1943 by Jacques Cousteau and Emil Gagnan.
The "sport" of scuba diving did not catch on for another 10 years. Today the
greatest use of scuba equipment is for recreational diving.
Recreational scuba diving, as taught by national certifying agencies, is
defined as diving that: Uses only compressed air as the breathing mixture.
It is never done solo, does not exceed a depth of 130 feet, does not require
specialized training beyond the basic open water course.
Scuba equipment is also widely employed by two other types of divers,
loosely categorized as "professional" and "technical.
"By definition, these two groups are not constrained by the RSD criteria
listed above.
Professional diving is done for military, governmental, commercial, or
scientific purposes.Professional divers are paid to dive.
They have a specific mission for each dive, e.g., lay a mine or recover a
bomb (military), look for a body or a weapon (law enforcement agency),
explore for oil (commercial), map an ancient wreck or examine a new
species of fish (scientific).
Technical diving is the term for all diving that exceeds recreational limits but
is not engaged in for profit.Although many, if not most, technical divers
consider themselves involved in a recreational activity, the nature of their
diving and type of equipment used exceed the boundaries of RSD.
To be sure, there is not universal agreement on what constitutes technical
diving, and any attempt to define it tends to degenerate into heated
discussion and semantics.
For the novice or basic open water diver, the following activities can be
considered to be "technical diving."The Realm Of Technical Diving cave
diving Ice diving very deep diving (to greater than 130 feet) mixed gas diving
(using gas mixtures other than air, such as nitrox or trimix) deep-penetration
wreck diving with specialized life-support equipment (e.g., O2 re-breathers)
Much of technical diving is taught by agencies other than the national open
water certification agencies.
However, recently PADI and other national agencies became involved in
nitrox certification, although the activity is still not considered part of basic
open 'recreational diving.
'Still, the trend is to expand the envelope of technology to encompass more
and more divers, and it is conceivable that some of today's advanced
technology (e.g., rebreathers) will one day be routinely used by open water
recreational divers.
Clearly, the distinction between 'technical' and 'recreational diving' is
becoming less distinct over time.
(No matter how diving activities are classified, no one should engage in any
diving activity unless certified in that activity or else supervised by a qualified
instructor.)
What Is The Buddy System?
RSD requires that each diver be accompanied under water by a buddy who
can share air or provide other assistance.
Scuba apparatus is designed to carry an extra demand regulator.
This is required in case one diver runs out of air and has to share a single
tank with his or her buddy.
Ideally, the buddies should have similar training and skill levels; it does no
good to have a buddy who dives deeper or stays down longer than you do.
Buddies should stay close together and always be aware of each other's
location.
Why is 130 Feet The Maximum Depth In Recreational Diving?
The 130 foot limit is an arbitrary depth originally adopted by the U.S. Navy
because it gave navy divers about 10 minutes of bottom time on compressed
air; going any deeper on air made no sense to the Navy because the time
available to do useful work was simply too short.
As with many diving issues in the early days of scuba (e.g., the 'no
decompression' limits), the Navy standard was also adopted by the
recreational training agencies.
Some experienced recreational divers do go deeper than 130 feet, and yet
still stay within no decompression limits. However, since the risks of the
bends, running out of air, and nitrogen narcosis increase as you go deeper,
the training agencies feel that some arbitrary limit must be set and have
stayed with 130 feet.
Thus, although one can dive deeper and stay within no decompression limits,
diving deeper than 130 feet a) is not taught by the recreational training
agencies, and b) must be undertaken with great care and an understanding
of the increased risks.
What Is Mandatory Decompression And Why Is It Not Part Of
Recreational Scuba Diving?
"Decompression" always occurs when we go from a higher to a lower
ambient pressure.
Thus all compressed gas diving is decompression diving. When recreational
diving is referred to as "no decompression diving" it really means, "no
mandatory decompression stop diving."A decompression stop should never
be necessary within the guidelines of RSD.
A decompression stop is often necessary in dives deeper or longer than
allowed in RSD; it provides time for some of the excess nitrogen that
entered the tissues to "gas off" (diffuse into the blood stream and then be
ventilated out by the lungs), thereby minimizing risk of decompression
sickness (DCS).
Based on experiments, plus much trial and error experience, the amount of
excess nitrogen remaining in the tissues after a planned, mandatory
decompression stop should not cause DCS.
Since professional and technical divers often spend longer periods under
water and/or dive deeper than recreational divers, they must know when to
stop on ascent and how long to wait before surfacing.
By contrast, each recreational dive is planned so that the diver can ascend
continuously to the surface without encountering decompression sickness;
the diver is still decompressing on the way up, but doesn't have to stop to
allow further decompression.
The basic assumption is that diving is inherently made safer by avoiding dives
that require decompression stops.
This is both the philosophy and practice of recreational diving today.
The "no decompression stop" limits in RSD are based on maximum depth,
time under water, and extent of any preceding dives, all factors which
directly affect tissue nitrogen uptake.
The limits are set in dive tables known to every certified diver, and are
incorporated into all dive computers.
Excess nitrogen, which enters tissues due to the increased ambient pressure
under water, determines the "no-decompression stop" limits.
A non-repetitive dive (no previous dive within a specified time period,
typically 6-12 hours) to 130 feet has an allowable "actual bottom time"
(measured from the time dive commences to start of ascent) of only about
5-10 minutes for a dive to 130 feet.
Beyond this brief time span the diver risks developing decompression
sickness from a continuous ascent.
In contrast, at 35 feet, on a non-repetitive dive, the 'no decompression'
bottom time is about 205 minutes.
Although RSD is always planned for no decompression stop required, it is
routine practice to make a 3 to 5 minute "safety stop" at 15 feet before
surfacing from any dive deeper than about 40 feet.
This is a decompression stop but it is not mandatory, just added for extra
safety to the dive; hence the term safety stop. In theory, when adhering to
the recreational diving tables one should not experience DCS if a safety stop
is not made.
Nonetheless, all dives deeper than about 40 feet should incorporate a safety
stop, and it is universally practiced.
If any dive requires a decompression stop for any reason, it has exceeded
the limits of recreational diving.
Are There Different Levels Of Recreational Diving? Within the universe of
recreational diving there are many levels, based on extent of training,
experience, or both. I have already commented on the resort course, which
is not formal scuba training but just an introductory scuba experience.
The following paragraphs pertain to the certified diver.Training. One can
take several courses beyond basic open water, and they can be divided into
two "tracks."
The first track is for people who want more training but have no intention of
ever teaching scuba. With such courses as advanced diving, stress and
rescue, underwater photography, ice diving, and deeper diving (60-130
feet), one can gain additional knowledge and skills, all under the purview of
recreational diving.
The second track is for people who plan to turn professional (within the
recreational purview) and teach scuba. They will take courses leading up to
the instructor level (advanced diving, stress and rescue, dive master,
assistant instructor, instructor).
Once an individual achieves instructor level he or she is a full-fledged
professional within recreational scuba and can teach the basic certification
course.
Unless they have taken special training, scuba instructors are not trained to
exceed the recreational limits.Thus they are not technical divers and would
need further training to do mixed gas diving, for example.
Of course many scuba instructors do obtain training in these and other
technical diving skills.Experience. Most recreational divers never take more
than the basic open water course.
However, after making many dives over the years they become highly
experienced and adept in all the important skills. In recent years scuba
agencies have developed a way to recognize the more experienced divers,
by creating "dive cards" showing the number of dives obtained, in round
numbers.
Thus, with proper documentation you can get a card that shows you have
done anywhere from 50 to 5000 lifetime dives.
The utility of this type of card is that it can quickly show your level of
experience, such as when you go to rent equipment or sign on for a boat
dive.
Experience counts for much in scuba diving (as with any activity), and the
cards are a way of acknowledging this.
What Is Sport Surface-Supplied Compressed Air Diving And How
Does It Differ From Scuba?
As its name indicates, sport surface-supplied compressed air diving
(sometimes shortened to 'sport surface-supplied air,' SSSA) separates the
compressed air source from the diver.
For this reason it is not "scuba," which is self-contained (the scuba diver
always carries his/her own air source). SSSA uses a small gasoline- or
electric-powered air compressor that can sit on a boat, dock or a floating
inner tube, so it can literally go to any dive site and remain over the heads of
the divers (Figure 2).
The compressor can provide air to more than one diver at the same
time.Each SSSA diver is tethered to the compressed air source by a long
hose.The entire apparatus is sometimes called a hookah, after the Egyptian
term for a pipe that cools water, but "surface-supplied compressed air" is
the more correct term.
At the end of each hose is a second stage regulator and mouth-piece, just
like in scuba diving; exhaled air is expelled into the water.
For recreational divers this technique has been pioneered by Brownie's
Third Lung, Ft. Lauderdale, FL (1-800-327-0412).SSSA diving is limited
by the strength of the air compressor, the length of the hose and, as in scuba,
the level of diver training.
As sold by Brownies, each unit serves at least two divers; some can serve
three or four divers at 30 feet.Other units allow deeper diving, up to 90 feet
for two divers.
In principle SSSA diving is the same as professional helmet diving, except
that the depths are generally less, no helmet is worn by the diver, only
compressed air is used (professionals may used mixed gases), and the
amount of surface support (i.e., other people on the surface) may be minimal
to none.
What Is THE FUTURE OF RSD? The future is now:
The technology that exists today, mostly in the realm of technical diving, may
become part of recreational diving tomorrow.There is unending debate
within professional diving circles about most of this technology, and whether
it should enter the realm of recreational diving sooner rather than later.
Dive safety Spread of hyperbaric chambers to all popular dive sites;
development of affordable, portable hyperbaric chambers that can be
carried on a dive boat. Universal use of dive computers air integrated to the
scuba tank, eliminating the high-pressure hose connection.
Use of full-face masks that remain on the diver's face if there is any panic or
loss of consciousness (absence of a mouthpiece reduces the risk of
drowning in these situations).
Implementation of underwater voice communication technology.
Development of "heads up" displays for dive data; instead of data displayed
on a wrist device or on a dangling console, all data will appear inside the
diver's mask, available for reading with only a turn of the eye.
Critical information may flash, assuring the diver's attention. Implementation
of diver-specific algorithms (adjusted for the diver's age, weight, and
perhaps other characteristics) for dive computers.Such algorithms may
become available from studies that correlate dive accident experience with a
wide range of dive profiles in a diverse group of divers.
Extension of bottom time or distance traveled under water.
Use of nitrox, perhaps with a depth limiter to prevent diving too deep and
incurring risk of oxygen toxicity.Use of stronger tanks (carbon fiber) that can
hold higher pressures and thus more cubic feet of gas.
Underwater scooters that allow the diver to range further on a given dive
with the same amount of air.
Use of re-breathing "closed circuit" scuba technology. Much of this
technology and equipment are available now, if not for the recreational diver
than in technical circles.
Just as other once-new technology gradually became accepted (e.g., dive
computers), it seems likely that much of today's "cutting-edge" technology
will be adopted by recreational divers in the coming years.
Cost and complexity will certainly be a limiting factor, however. Many
recreational divers may not want to be burdened with more equipment or
ever more complicated and expensive technology only time and the
marketplace will tell.
There are no local, state or federal
laws regulating recreational scuba
diving. Some regulations apply to
certain aspects of equipment, such as
tank inspection and air compressor
maintenance, but there are no
regulations regarding divers.
New applicants for certification may
be required to obtain medical
clearance if they acknowledge a
problem on their health questionnaire,
but there is nothing to compel an
applicant to admit an active medical
problem.
On the other hand, relatively few
physicians are familiar with scuba
diving, so an encounter between
diver-with-medical-question and a
physician may not result in correct
advice or information. Even when
physicians are knowledge-able in this
area, there is apt to be disagreement
about what disqualifies people from
diving.
WHO IS FIT FOR DIVING?
Before discussing medical conditions
that might prohibit diving, it will be
useful to discuss fitness in a general
sense.
Diving requires at least a sound mind,
heart and lungs. Beyond these basics,
much has been written about physical
fitness for diving, including the
subjects of exercise, nutrition, and
physical stamina.
Clearly one does not have to be an
athlete or body builder to dive. On the
other hand, diving is not
recommended for true "couch
potatoes" either.
It is probably risky to be sedentary in
life style Ä overweight, no exercise,
no routine physical exertion on the job
or otherwise Ä and then go diving.
Diving physicians believe that the
more physically fit the individual, the
less risk in diving. There are several
cogent reasons for scuba divers to be
physically fit.
1) Diving can be strenuous. It can
require sudden bursts of physical
exertion such as when swimming
against a current, climbing onto an
unsteady boat, or rescuing a buddy.
Obviously the more fit you are, the
better you can handle heightened
physical requirements. Many a diver
has "tired out" and had to be rescued
because he didn't have the stamina for
unexpected physical stress.
2) Physically fit people tend to use
less air than the unfit. Hyperventilation
and panic stress reactions are more
likely to occur in the physically unfit.
3) Physical fitness reduces the risk of
heart attack, which is a major cause of
diving fatality.
4) Physical fitness may reduce the risk
of developing DCS. Apart from the
exercise jocks, how does someone
know if they are physically fit?
Sophisticated exercise testing can give
numbers to go by, but such tests are
cumbersome, expensive and hardly
necessary (with the exception of
testing for underlying heart disease). In
truth, if the question is just about
overall physical fitness, and not about
underlying heart disease, you are
probably the best judge. You are
probably physically fit for scuba diving
if you can swim several laps in the
pool without difficulty (the basic
swimming test for enrollment into a
scuba certification course), ride a
bicycle for half an hour, or jog a half
mile without collapsing. Certainly if
you perform aerobic exercise regularly
you are probably physically fit.
You are probably physically unfit if
you don't regularly exercise, or you
are short of breath with simple efforts
like stair climbing or brisk walking, or
you exceed 20% of your ideal body
weight and/or smoke heavily. In other
words, the question of physical fitness
for an activity like scuba diving is
mostly one of common sense.
Common sense suggests that, since a
scuba diver's life may depend on
heavy physical exertion at some point,
you should not be grossly overweight,
should not smoke, and you should
engage in some aerobic exercise on a
frequent basis. The exercise could be
bicycling, running, swimming, racquet
sports, or any other aerobic activity.
(Exceptions to this recommendation
are physically impaired people who
may take special training to go scuba
diving; see below.)
CAN ONE DIVE WHILE TAKING
A DECONGESTANT?
Generally, yes. Decongestants are
commonly employed to clear up nasal
inflammation and to help shrink
mucous membranes in the head. They
are not treatment for infection of ears
or sinuses, but only for symptomatic
relief of mild head congestion.
Over-the-counter decongestants
commonly employed include
Dimetapp, Sudafed, and various
acetaminophen (Tylenol) preparations
combined with an antihistamine. Some
caveats: you should feel well, not have
any side effects from the medication
(such as drowsiness or dizziness), and
be able to clear your ears without
difficulty.
WHAT CONDITIONS SHOULD
PROHIBIT DIVING?
Table 1 lists conditions that physicians
involved in dive medicine generally
regard as permanently prohibitive of
scuba diving. Table 2 lists conditions
that are self-limiting or treatable, and
that would prohibit diving only until
resolved or adequately treated. Table
3 lists chronic conditions that might or
might not prohibit diving, depending
on a medical assessment. In reviewing
these lists, keep in mind the following:
As explained above, scuba diving can
be a physically demanding activity
when everything goes well; it can
become more so when there are
adverse conditions such as waves,
current, poor visibility, faulty
equipment, etc. People not in good
health should not dive. The problem is
in defining "good health." From the
diver's point of view, he or she should
feel well, not be fatigued, and have no
medical problem that might affect
diving.
laws regulating recreational scuba
diving. Some regulations apply to
certain aspects of equipment, such as
tank inspection and air compressor
maintenance, but there are no
regulations regarding divers.
New applicants for certification may
be required to obtain medical
clearance if they acknowledge a
problem on their health questionnaire,
but there is nothing to compel an
applicant to admit an active medical
problem.
On the other hand, relatively few
physicians are familiar with scuba
diving, so an encounter between
diver-with-medical-question and a
physician may not result in correct
advice or information. Even when
physicians are knowledge-able in this
area, there is apt to be disagreement
about what disqualifies people from
diving.
WHO IS FIT FOR DIVING?
Before discussing medical conditions
that might prohibit diving, it will be
useful to discuss fitness in a general
sense.
Diving requires at least a sound mind,
heart and lungs. Beyond these basics,
much has been written about physical
fitness for diving, including the
subjects of exercise, nutrition, and
physical stamina.
Clearly one does not have to be an
athlete or body builder to dive. On the
other hand, diving is not
recommended for true "couch
potatoes" either.
It is probably risky to be sedentary in
life style Ä overweight, no exercise,
no routine physical exertion on the job
or otherwise Ä and then go diving.
Diving physicians believe that the
more physically fit the individual, the
less risk in diving. There are several
cogent reasons for scuba divers to be
physically fit.
1) Diving can be strenuous. It can
require sudden bursts of physical
exertion such as when swimming
against a current, climbing onto an
unsteady boat, or rescuing a buddy.
Obviously the more fit you are, the
better you can handle heightened
physical requirements. Many a diver
has "tired out" and had to be rescued
because he didn't have the stamina for
unexpected physical stress.
2) Physically fit people tend to use
less air than the unfit. Hyperventilation
and panic stress reactions are more
likely to occur in the physically unfit.
3) Physical fitness reduces the risk of
heart attack, which is a major cause of
diving fatality.
4) Physical fitness may reduce the risk
of developing DCS. Apart from the
exercise jocks, how does someone
know if they are physically fit?
Sophisticated exercise testing can give
numbers to go by, but such tests are
cumbersome, expensive and hardly
necessary (with the exception of
testing for underlying heart disease). In
truth, if the question is just about
overall physical fitness, and not about
underlying heart disease, you are
probably the best judge. You are
probably physically fit for scuba diving
if you can swim several laps in the
pool without difficulty (the basic
swimming test for enrollment into a
scuba certification course), ride a
bicycle for half an hour, or jog a half
mile without collapsing. Certainly if
you perform aerobic exercise regularly
you are probably physically fit.
You are probably physically unfit if
you don't regularly exercise, or you
are short of breath with simple efforts
like stair climbing or brisk walking, or
you exceed 20% of your ideal body
weight and/or smoke heavily. In other
words, the question of physical fitness
for an activity like scuba diving is
mostly one of common sense.
Common sense suggests that, since a
scuba diver's life may depend on
heavy physical exertion at some point,
you should not be grossly overweight,
should not smoke, and you should
engage in some aerobic exercise on a
frequent basis. The exercise could be
bicycling, running, swimming, racquet
sports, or any other aerobic activity.
(Exceptions to this recommendation
are physically impaired people who
may take special training to go scuba
diving; see below.)
CAN ONE DIVE WHILE TAKING
A DECONGESTANT?
Generally, yes. Decongestants are
commonly employed to clear up nasal
inflammation and to help shrink
mucous membranes in the head. They
are not treatment for infection of ears
or sinuses, but only for symptomatic
relief of mild head congestion.
Over-the-counter decongestants
commonly employed include
Dimetapp, Sudafed, and various
acetaminophen (Tylenol) preparations
combined with an antihistamine. Some
caveats: you should feel well, not have
any side effects from the medication
(such as drowsiness or dizziness), and
be able to clear your ears without
difficulty.
WHAT CONDITIONS SHOULD
PROHIBIT DIVING?
Table 1 lists conditions that physicians
involved in dive medicine generally
regard as permanently prohibitive of
scuba diving. Table 2 lists conditions
that are self-limiting or treatable, and
that would prohibit diving only until
resolved or adequately treated. Table
3 lists chronic conditions that might or
might not prohibit diving, depending
on a medical assessment. In reviewing
these lists, keep in mind the following:
As explained above, scuba diving can
be a physically demanding activity
when everything goes well; it can
become more so when there are
adverse conditions such as waves,
current, poor visibility, faulty
equipment, etc. People not in good
health should not dive. The problem is
in defining "good health." From the
diver's point of view, he or she should
feel well, not be fatigued, and have no
medical problem that might affect
diving.
Q: My doctor tells me I have
hypertension. Is it a problem for me to
continue diving.
A: Hypertension, or high blood
pressure, is one of the most common
medical conditions seen in the diving
population - no surprise, really, since it
is a common medical condition in the
general population.
Strict criteria for hypertension can vary
depending on the reference cited, but
normal blood pressure is generally
accepted to be a systolic pressure
below 140 and a diastolic pressure
below 90 mm Hg, depending on age
(cited as systolic first and diastolic
second - e.g. "120 over 80," by your
doctor). A thorough medical evaluation
should be performed to find a treatable
cause for hypertension; in most cases,
however, none will be found.
Basically, two different sets of
complications face a person with
hypertension: short-term and long-term.
Short-term complications are generally
due to extremely high blood pressure;
the most significant is the risk of a
stroke due to rupture of blood vessels
in the brain (called a cerebrovascular
accident). Long-term detrimental
effects are more common: they include
coronary artery disease, kidney
disease, congestive heart failure, eye
problems and cerebrovascular disease.
Fitness and Diving Issue
As long as the individual's blood
pressure is under control, the main
concerns should be the side effects of
medication(s) and evidence of
end-organ damage.
Divers who have demonstrated
adequate control of blood pressure
with no significant decrease in
performance in the water due to the
side effects of drugs, should be able to
dive safely.
A recent report in a diving medical
journal citing several episodes of acute
pulmonary edema (i.e., lungs congested
with fluid) in individuals with
uncontrolled hypertension while they
were diving. Regular physical
examinations and appropriate screening
for the long-term consequences of
hypertension such as coronary artery
disease are necessary.
Medication Used in Treatment
Mild hypertension may be controlled
with diet and exercise; however,
medication is often necessary. Many
classes of drugs are used to treat
hypertension, with varying side effects.
Some individuals must change
medications after one drug appears to
be or becomes ineffective. Others
might require more than one drug taken
at the same time to keep the blood
pressure under control.
Classes of drugs known as
beta-blockers often cause a decrease
in maximum exercise tolerance and
may also have some effect on the
airways. This normally poses no
problem for the average diver. ACE
(angiotensin converting enzyme)
inhibitors are the preferred class of
drugs for treating hypertensive divers; a
persistent cough is a possible side
effect.
Calcium channel blockers are another
choice, but lightheadedness when going
from a sitting or supine position to
standing may be a significant side
effect. Diuretics are also frequently
used to treat hypertension. This
requires careful attention to hydration
and electrolyte status.
Most anti-hypertensive medications are
compatible with diving as long as the
side effects experienced by the diver
are minimal and their performance in
the water is not significantly
compromised. Any diver with
long-standing high blood pressure
should be monitored for secondary
effects on the heart and kidneys.
For more information on
cardiovascular conditions, see the
complete article by Dr. James L.
Caruso on Cardiovascular Fitness and
Diving from the July/August 1999 issue
of Alert Diver.
DAN reviews its guidelines on how
soon divers may fly after diving.
Q: I am a dive instructor in Venezuela.
First, after making multiday repetitive
dives, is an extended surface interval
beyond 12 hours before flight
considered enough? Second, driving to
altitude after diving is one of our peak
topics.
Since our closest dive training site is a
bay surrounded by mountains, after
diving we must drive through a
mountain pass nearly 1,000 feet / 305
meters above sea level, and then to
Caracas, nearly 3,300 feet /1000
meters above sea level.
Waiting 12 hours after recreational or
training dive activities is not the local
practice and, as far as I know, there
have not been any reports of
decompression sickness (DCS). Is our
practice safe?
A: DAN Research is currently at work
on the question of how long scuba
divers should wait before flying after
diving. The U.S. Navy tables
recommend that you wait at least two
hours before you board a plane after
making a single no-decompression
dive; the U.S. Air Force says you
should wait 24 hours.
Current DAN FAD Recommendations
DAN's original recommendations for
flying after diving based on maximum
altitude exposure of 8,000 feet / 2,440
meters (the cabin pressure of
commercial airliners) are:
A minimum surface interval of 12 hours
is required before ascent to altitude in a
commercial jet airliner (altitude up to
8,000 feet).
Divers who plan to make daily, multiple
dives for several days or make dives
that require decompression stops
should take special precautions and
wait for an extended surface interval
beyond 12 hours before flight. The
greater the duration before flight the
less likely decompression sickness is to
occur.
Current Research
Realizing that just about all current
recommendations for flying after diving
are based mostly on "best guess" and
not hard data, Dr. Richard Vann and
Dr. Wayne Gerth launched DAN's
Flying After Diving study in 1993 at
F.G. Hall Hypo/Hyperbaric
Laboratory at Duke University Medical
Center. The data so far suggest that the
original recommendation of waiting 12
hours or more after making single
no-decompression dives is reasonable.
In addition, current research suggests
that it may be wise to wait 17 hours or
more after making repetitive dives.
However, the research is as yet
incomplete and further work is
continuing.
More specific data on DAN's FAD
recommendations are scheduled for a
future issue of Alert Diver.
The one unshakable truth is that the
longer the surface interval after diving,
the less the risk of DCS when flying
afterward. Remember chamber trials
are conducted within a relaxed, dry
environment unlike the open water,
where the multiple stresses of diving
conditions may adversely affect the rate
of inert gas uptake and elimination.
Extended surface intervals allow for
additional denitrogenation and may
reduce the likelihood of developing
symptoms. For those diving heavily
during an extended vacation, it may not
be a bad idea to take a day off at
midweek, or save the last day to buy
those last-minute
hypertension. Is it a problem for me to
continue diving.
A: Hypertension, or high blood
pressure, is one of the most common
medical conditions seen in the diving
population - no surprise, really, since it
is a common medical condition in the
general population.
Strict criteria for hypertension can vary
depending on the reference cited, but
normal blood pressure is generally
accepted to be a systolic pressure
below 140 and a diastolic pressure
below 90 mm Hg, depending on age
(cited as systolic first and diastolic
second - e.g. "120 over 80," by your
doctor). A thorough medical evaluation
should be performed to find a treatable
cause for hypertension; in most cases,
however, none will be found.
Basically, two different sets of
complications face a person with
hypertension: short-term and long-term.
Short-term complications are generally
due to extremely high blood pressure;
the most significant is the risk of a
stroke due to rupture of blood vessels
in the brain (called a cerebrovascular
accident). Long-term detrimental
effects are more common: they include
coronary artery disease, kidney
disease, congestive heart failure, eye
problems and cerebrovascular disease.
Fitness and Diving Issue
As long as the individual's blood
pressure is under control, the main
concerns should be the side effects of
medication(s) and evidence of
end-organ damage.
Divers who have demonstrated
adequate control of blood pressure
with no significant decrease in
performance in the water due to the
side effects of drugs, should be able to
dive safely.
A recent report in a diving medical
journal citing several episodes of acute
pulmonary edema (i.e., lungs congested
with fluid) in individuals with
uncontrolled hypertension while they
were diving. Regular physical
examinations and appropriate screening
for the long-term consequences of
hypertension such as coronary artery
disease are necessary.
Medication Used in Treatment
Mild hypertension may be controlled
with diet and exercise; however,
medication is often necessary. Many
classes of drugs are used to treat
hypertension, with varying side effects.
Some individuals must change
medications after one drug appears to
be or becomes ineffective. Others
might require more than one drug taken
at the same time to keep the blood
pressure under control.
Classes of drugs known as
beta-blockers often cause a decrease
in maximum exercise tolerance and
may also have some effect on the
airways. This normally poses no
problem for the average diver. ACE
(angiotensin converting enzyme)
inhibitors are the preferred class of
drugs for treating hypertensive divers; a
persistent cough is a possible side
effect.
Calcium channel blockers are another
choice, but lightheadedness when going
from a sitting or supine position to
standing may be a significant side
effect. Diuretics are also frequently
used to treat hypertension. This
requires careful attention to hydration
and electrolyte status.
Most anti-hypertensive medications are
compatible with diving as long as the
side effects experienced by the diver
are minimal and their performance in
the water is not significantly
compromised. Any diver with
long-standing high blood pressure
should be monitored for secondary
effects on the heart and kidneys.
For more information on
cardiovascular conditions, see the
complete article by Dr. James L.
Caruso on Cardiovascular Fitness and
Diving from the July/August 1999 issue
of Alert Diver.
DAN reviews its guidelines on how
soon divers may fly after diving.
Q: I am a dive instructor in Venezuela.
First, after making multiday repetitive
dives, is an extended surface interval
beyond 12 hours before flight
considered enough? Second, driving to
altitude after diving is one of our peak
topics.
Since our closest dive training site is a
bay surrounded by mountains, after
diving we must drive through a
mountain pass nearly 1,000 feet / 305
meters above sea level, and then to
Caracas, nearly 3,300 feet /1000
meters above sea level.
Waiting 12 hours after recreational or
training dive activities is not the local
practice and, as far as I know, there
have not been any reports of
decompression sickness (DCS). Is our
practice safe?
A: DAN Research is currently at work
on the question of how long scuba
divers should wait before flying after
diving. The U.S. Navy tables
recommend that you wait at least two
hours before you board a plane after
making a single no-decompression
dive; the U.S. Air Force says you
should wait 24 hours.
Current DAN FAD Recommendations
DAN's original recommendations for
flying after diving based on maximum
altitude exposure of 8,000 feet / 2,440
meters (the cabin pressure of
commercial airliners) are:
A minimum surface interval of 12 hours
is required before ascent to altitude in a
commercial jet airliner (altitude up to
8,000 feet).
Divers who plan to make daily, multiple
dives for several days or make dives
that require decompression stops
should take special precautions and
wait for an extended surface interval
beyond 12 hours before flight. The
greater the duration before flight the
less likely decompression sickness is to
occur.
Current Research
Realizing that just about all current
recommendations for flying after diving
are based mostly on "best guess" and
not hard data, Dr. Richard Vann and
Dr. Wayne Gerth launched DAN's
Flying After Diving study in 1993 at
F.G. Hall Hypo/Hyperbaric
Laboratory at Duke University Medical
Center. The data so far suggest that the
original recommendation of waiting 12
hours or more after making single
no-decompression dives is reasonable.
In addition, current research suggests
that it may be wise to wait 17 hours or
more after making repetitive dives.
However, the research is as yet
incomplete and further work is
continuing.
More specific data on DAN's FAD
recommendations are scheduled for a
future issue of Alert Diver.
The one unshakable truth is that the
longer the surface interval after diving,
the less the risk of DCS when flying
afterward. Remember chamber trials
are conducted within a relaxed, dry
environment unlike the open water,
where the multiple stresses of diving
conditions may adversely affect the rate
of inert gas uptake and elimination.
Extended surface intervals allow for
additional denitrogenation and may
reduce the likelihood of developing
symptoms. For those diving heavily
during an extended vacation, it may not
be a bad idea to take a day off at
midweek, or save the last day to buy
those last-minute
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