Compiled
and edited by Jeffrey Bozanic
This month's
question was raised by Ron Ryan, NAUI 7205L, the Supervisor of the Catalina
Hyperbaric Chamber. His concern stems from the fact that different tables
permit a varying number of repetitive dives to be made, from a maximum
of one repetitive dive within any twelve hour period on one end of the
scale to tables which license the divers to make an unlimited number
of repetitive dives at the other end of the continuum.
A secondary issue
involves the stamina of the divers involved. All divers experience some
degree of physical and mental effort during the course of a dive. Beginning
divers may find that one openwater dive is all they can handle in a
day, without becoming so spent, either physically or mentally, that
they are incapable of making an additional dive with a reasonable margin
of safety. Experienced divers, on the other hand, may be capable of
four or five or even more repetitive dives within a day's activities
without undue fatigue. Of course, the physical conditions of the waters
in which the divers are diving and the type of work done by the divers
during the dive affect the energy expended and consequently the fatigue
levels of the divers as well. These factors are not easy ones to quantify
or factor into repetitive dive tables use.
A third concern
is that of individual diver physiology. Every diver varies in some degree
from one another. Physiological factors such as obesity, fitness, and
past incidents of decompression sickness affect one's susceptibility
to decompression sickness. It is impossible for dive tables to incorporate
all of these factors for any individual diver. Limiting the daily number
of repetitive dives might introduce a measure of protection which does
not exist at the present.
Related to the
physiology concern is the question of multi-day repetitive diving. While
one or more repetitive dives may be made on a single day without manifestation
of decompression problems, cause for worry may exist when a high level
of repetitive dive activity extends over a longer time frame. This stems
from the theoretical possibility that nitrogen dissolved in the body
has not off-gassed to the degree predicated by repetitive diving tables,
and builds up in the body tissues over time. As this affects tissue
compartments with long half-times, use of tables which are based on
a shorter half-time model may exacerbate this problem. Recently published
data bolsters the concern of multi-day repetitive diving.
Hill and Gilliam
(1990) documented the diving activity of recreational divers aboard
the cruise ship Ocean Quest for a one year period. This resulted in
a database of 77,680 dives, 43% of which were conducted using decompression
tables. The average diver made three (3) dives per day, every day for
four consecutive days. Seven (7) cases of decompression sickness were
recorded among the tables users. All of the dives which resulted in
a case of decompression sickness were conducted within the no-stop limits
of the tables used. Pertinent to the question above, all cases of decompression
sickness occurred during the fourth day of diving activity.
Other elements
further complicate the problem of deciding what is a reasonable level
of daily diving activity. Some of these include training, equipment
used, diver health factors, etc.
Only one written
response from the membership was received. That response mirrors the
verbal comments received while researching this question. Basically,
the membership feels that given our current level of knowledge regarding
diving physiology, that this question is unanswerable as posed. There
are too many variables to consider, and the data to promote any definitive
maximum number of dives does not exist.
Despite the inability
to define a limit, students should be informed of the general concerns
outlined above when discussing repetitive diving. Besides concerns with
personal comfort and fatigue levels, the potential problems with conducting
repetitive dives over multiple days should be addressed. And, as always,
it is incumbent upon the diving professional to remain abreast of new
developments in diving medicine, and modify their views as new information
becomes available.
References:
Hill, R.K. and
Gilliam, B.C. 1990. A comparison of the incidence of decompression sickness
in men and women divers using decompression tables and diving computers
for 77,680 dives. In Proceedings of the American Academy of Underwater
Sciences Tenth Annual Diving Symposium: Diving for Science... 1990.
Pp. 157-162.
QUESTION: "HOW
MANY REPETITIVE DIVES SHOULD BE ALLOWED IN ANY 24-HOUR PERIOD? WHY?"
A. I find this
question rather intimidating, insofar as it is a big question for a
little person. I do not presume to know, or understand, all the factors
involved in "creating" tables with various tissue groups and
models... just whose tissue group(s) and models anyway? I do know that
there are many DCS injuries which occur within the No-Decompression
limits as indicated on the tables -- any tables -- and as such I would
be very unwilling to "push" these published limits. The number
of dives managed within a 24-hour period would depend on all the factors
that are usually discussed; depth, time, temperature, physical fitness,
etc... but we know that staying within the limits does not guarantee
a safe profile.
I have just taken
several lines to say that there is no answer -- at least none available
to the average "sport" diver.
--Struther MacFarlane,
NAUI 6676; Toronto, Ontario, Canada(As a private professional educator,
has taught all levels from introductory to serving as ITC Director.
Recipient of the NAUI Canada Gold Pin and Special Recognition Awards.)
A. In order to
make a responsible recommendation that is credible certain facts must
be assumed. Presently the so-called "conventional wisdom"
would like to see divers doing only two or three dives a day. However,
several recent studies (including my own) present huge data bases of
diver populations doing far greater numbers of repetitive dives daily
with virtually no incidence of decompression sickness. Regional factors
such as cold water obviously have to be considered along with the individual
physiological status. The question is simply too broad.
Practically speaking, divers do anywhere from 4 to 12 repetitive dives
routinely on liveaboard dive vessels and as a group have the lowest
incidence of DCS of any diver population. With the acceptance and widespread
use of multi-level computers, this type of multi-level exposure has
actually gotten safer due to accuracies of time/depth instruments and
adoption of more conservative decompression models as a basis of computer
programming. Australia has adopted a law that limits repetitive
diving to four a day, and it is exceedingly unpopular with a large segment
of the liveaboard divers who justifiably feel unreasonably restricted.
Interestingly, no decline in incidence of DCS has been proven to that
group.
Certainly to attempt "square table" format dives much beyond
four dives per day if any depth is attained will be virtually self-restrictive.
But the multi-level diver with a computer in good working order should
be allowed to dive within those reasonable limits. It has to be a matter
of informed personal choice. I always shudder when I hear that some
agency is about to issue another "limit" to sport divers and
their freedom. It is not the place of NAUI or any agency to attempt
to regulate the diving practices of experienced certified divers. The
sport cannot be forever geared to the "lowest common denominator":
the entry level diver.
All arguments to the contrary, the certified sport diver has to be responsible
for himself in such judgements and adopt a diving profile consistent
with his health, ability, and computational capabilities given site
conditions. Please let's not fuel the fire of a so-called "standard"
that might result in an ordinance similar to the Australian rule. I
have routinely made 5-7 dives a day for most of the last two years and
had no incidence of DCS personally or with any sport divers accompanying
me. Far more important than numbers of dives is ascent rate and duration
of "safety stops."
--Bret
Gilliam, NAUI 3234; Brunswick, Maine
A. Without including
depth and time this is a hypothetical question. If we are talking about
a shallow coral reef there is no limit. If it is down the wall one dive
may be too much. It is the duty of a NAUI Instructor to make this difference
clear to each student and to be certain that they are proficient in
use of the dive tables. They must be able to chart their dives and stay
within the no-decompression limits. NEVER should recreational divers
be encouraged to engage in stage decompression diving.
--Roy Damron, NAUI
207; Kona, Hawaii
A. Philosophically,
this question illustrates an important problem in teaching. More important
than attaching numbers is the need to ensure that both instructors and
students appreciate the "whys" of what they are doing. If
divers truly understand the issues they can make their own intelligent
decisions regarding repetitive diving. Providing only "whats"
or "hows" is a disservice to those who look to us for knowledge.
Instructionally, I like the standard that no more than two dives per
day (three with one night dive) can count towards certification. Learning
is improved if students have some time to reflect on what they did instead
of just rushing through the motions. Novices also expend far more energy
per dive than an experienced diver does- especially important in the
less forgiving temperate to cold environments. If we want students to
respect moderation, we had certainly better demonstrate it.
--Neal
Pollock, NAUI 7068; Vancouver, British Columbia, Canada"Should
the certification title Skin Diving Leader be changed to Skin Diving
Instructor? Should Skin Diving Leaders, Assistant Instructors, and/or
Divemasters be given the right to vote? Why/why not?"
A. For the last
few years I have watched the position of Assistant Instructor dwindle,
both in responsibility and scope to the point that he/she is rendered
virtually useless. The real problem is that, unfortunately, there is
no money to be made by the AI to compensate for costs incurred to retain
certification, ie. cost of membership; and I see insurance becoming
mandatory in the not too distant future. Also, in most cases they are
not compensated for the costs associated with the open water check out
dive. For myself who, at least in the past, performed valuable services
for the Instructor, it is hard to comprehend the fate of the AI.
You ask if the Skin Diving Leader title should be changed to Skin Diving
Instructor? I am of the opinion that the position of SDL should never
have been created. At the time this position was created the AI's duties
were being lessened and insurance was becoming an issue with no way
for the AI to pay the inherent cost. Here were perfectly capable persons,
already in leadership postures, needing a way to recoup the insurance
premium so they could retain REAL RESPONSIBILITY in the jobs they were
already doing within our organization.
I believe that it is now time to rectify a mistake. Let's get rid of
the SDL position, and put the responsibilities where they belong in
the AI's hands. Now the AI has some source of income in that he/she
can give classes by teaching skin diving a much needed area of instruction.
The AI then changes from being alone and helpless, to becoming a real
team member in promoting safety and diving education.
--L.C.
Campbell, NAUI Z 7091; Klamath Falls, OR(Assistant Instructor helping
certify over 150 persons per year through Aqua Toys. Has been diving
for over 30 years.)
