So what do you know about narcosis?
THE MOUNT-MILNER TEST
In 1965 a research project was conducted by professional diver Tom Mount and psychyatrist
Gilbert Milner to determine the effects of anticipated behavior modeling in diving
students with respect to narcosis. Three control groups of four students with equal
male/female ratios were trained in identical dive classes except:
Group One was taught that a diver would get narcosis at 130 fsw, and much emphasis
was placed on the extremely high probability of narcosis with SEVERE symptoms.
Group Two was taught of the existence of narcosis, the symptoms and depths of occurance
begining at 100 fsw, but were not subjected t an intimidating lecture, as in Group One,
that narcosis was an absolute barrier.
Group Three was well educated on narcosis with three full hours of lecture on symptoms,
risk, danger and known research. They were told that divers with strong will power as
postulated by Miles (1961) could mentally prepare themselves and greatly reduce the
effects.
Prior to the open water dives all students were given two dives to 30 fsw and two to
100 fsw to develop good breathing techniques.
Before the actual dives fo testing purposes, the students were taken on a 50 fsw dive
where the test were performed so a mental/dexterity familiarity could be achieved with
the format of the test problems. Changes were then made in the test so they could not
be performed from memory. The tests consisted of handwriting evaluations, peg-board
testing, math and ball bearing placement in a long-necked narrow bottle, etc.
In the initial test depth of 130 fsw, divers in Group One had minor to above average
narcosis problems while Group Two and Three divers had little affect on test scores.
At 180 fsw test depth, two Group One divers dropped from the exercise due to severe
narcosis problems and were removed fom the dive. All Group Two divers were affected
although still functioning at about 50% test levels. Group Three divers had minor
impairment.
At the 200 fsw test depth, all divers in Group One and two from Group Two were dropped
due to severe narcosis and apprehension. Group Three divers actually showed slight
improvement in test scores.
At the 240 fsw test depth, one diver was dropped from Group Two and one diver from
Group Three due to severe narcosis. The remaining Group Two diver and three Group
Three divers showed levels of impairment but again scores and performance showed
improvementover the previous depth level. One diver, a female from Group Three,
registered her highest scores on all tests at the 240 fsw level.
Concurrent testing of experienced deep divers showed 7 out of 10 divers with no
decrease in performance or scores at the 200 fsw test level. The three divers with
decreased perfomance finished the testing (2 with perfect scores) but required
additional time than was usual. At 240 fsw, 5 out of 10 performed all tests with
no decreased performance. One diver had problems with the ball bearing test but
perfect scores on the peg board, math and handwriting. The other two showed up to
42% deficits and had problems completing the tests.
The bvious conclusions include a subjective validation to both "adaptation" and
the negative influence of "modeling" behavior in those groups of divers preconditioned
that narcosis was inevitable and severe. The Group Three divers with little prior
diving experience were satisfactorilystill performing at the 200 fsw level and
three divers continued to perform (with one showing improvement still) at the 240 fsw
test level.
If we teach our children that all dogs will bite, we can safely assume that when
presented with a specimen even as lowly as a toy poodle (which should probally be
shot on sight anyway), we can expect a high fear index. Likewise, if we teach our
dive students that narcosis is a finite, unyielding biophysical wall, then we can
logically expect such conditioning to impair thier performance beyong a more
realistically educated diver lacking preconcieved phobias and suggestions. Education
is the key to performance and safety.
CONCLUSION
Depth limitation largely becomes a decision based upon narcosis levels and available
gas supply (until the O2 toxicity range is entered). Most divers will be able to
function well in excess of the so-called 130 fsw (39.4 m) limit with even a little
practice.
All divers should exercise prudence and reasonable caution in all aspects of deep
diving but partiicularly so when it comes to narcosis. Experience is vital before
attempting progressively deeper dives. Ideally, the diver should be seeking out the
benefit of training by a competent, well experienced deep diving instructor before a
penetration below sport diving depths. Don't try to obtain field experience on your
own or with another buddy. The historical record provides too many fatalities or
near misses due to narcosis to warrant such a risk.
Narcosis Symptoms
Light headedness
Euphoria
Drunkenness
Impaired neuromuscular coordination
Hearing sensitivity or hallucination
Slowed mental activity
Decreased problem solving capacity
Overconfidence
Short term memory loss or distortions
Improper time perceptions
Poor judgement
Loss of consciousness
Levity or tendency to laughter
Amnesia
Loss of mechanical dexterity
(Gilliam, Bret, Deep Diving, 1995,Watersport Publishing Inc.)
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