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So what do you know about narcosis?

THE MOUNT-MILNER TEST

Research Project:
In 1965, a research project was conducted by professional diver Tom Mount and psychiatrist Gilbert Milner to determine the effects of anticipated behavior modeling in diving students with respect to narcosis.

Control Groups:
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 occurrence beginning at 100 fsw, but were not subjected to 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.

Tests
Before the actual dives for 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.

Test Depth 130 fsw
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.

Test Depth 180 fsw
At 180 fsw test depth, two Group One divers dropped from the exercise due to severe narcosis problems and were removed from the dive. All Group Two divers were affected although still functioning at about 50% test levels. Group Three divers had minor impairment.

Test Depth 200 fsw
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.

Test Depth 240 fsw
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 improvement over 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
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 performance 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.

Subjective Valuation
The obvious 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 satisfactorily still performing at the 200 fsw level and three divers continued to perform (with one showing improvement still) at the 240 fsw test level.

Education
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 probably 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 their performance beyond a more realistically educated diver lacking preconceived 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.

Exercise Prudence
All divers should exercise prudence and reasonable caution in all aspects of deep diving but particularly 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

(Gilliam, Bret, Deep Diving, 1995, Watersport Publishing Inc.)

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This page was last updated on February 27, 1999.