Despite the large amount of experimental data obtained from exposures of human subjects to simulated chamber dives in excess of 400 msw, only six men really dived in open sea, in that depth range (Janus IV, 460 msw open sea dive Oct. 1977). An excursion dive even took place down to 501 msw during the same diving operation.
Until now more than 40 divers have been exposed to depths of 400 msw or deeper during the French deep diving experiments.
During the Atlantis III dive at Duke University, three subjects were successfully compressed down to 686 msw.
In 1983, the Deep Dive Development Project demonstrated that both diving and hyperbaric welding tasks can safely and efficiently take place on a routine basis at 300 msw.
Safe working dive to 400 msw is considered physiologically feasible provided that technical and medico-physiological aspects are carefully evaulated, controlled and tested in an onshore trial dive.
We shall discuss the main topics to be taken into account in the definition of the human factors programme for working dives to 400 msw
This essential aspect is mainly based on professional and medico/physiological criteria as well as divers' training. The professional criterion chiefly covers an extensive professional and technical experience in the various tasks intended to be done at depth. Moreover, it also includes an acceptable sociable attitude which is essential to create a team spirit.
On the medico/physiological side, despite various trials, it has not yet been possible to establish sure selection criteria for very deep divers. Nevertheless apart from the standard medical examination for divers the selection will essentially consider the following topics:
Central Nervous System (Clinical Neurological Examination, Neuropsychological evaluation, Electroencephalography)
Lung function evaluation
Cardiovascular adaptation to muscular work (Maximum Oxygen Uptake)
Cochleo-vestibular system evaluation (Electronystagmogramme and audiometry).
A minimum level of training appears to be necessary for deep diving. Apart from the technical training, it should include:
Some physical training (ventilatory work against breathing resistances)
Emergency medical training for divers
Exposure to pressure in an onshore controlled environment.
Different researchers have reported some potential minor and reversible changes in the Central Nervous System both during and after deep diving. This leads to careful evaluation of the Central Nervous System reactions by means of standardized batteries of tests.
During the compression phase to depths of 400 msw, an adequate compression profile enables minimization of the so-called ‘High Pressure Nervous Syndrome’ which is to be carefully controlled on the other hand during an onshore trial dive by means of neurophysiological investigation techniques
In the post dive period, a complete CNS follow-up programme is expected to provide valuable information on the neurological short term effects.
As gas density increases with depth, it leads to a modification of the gas flow in the bronchial tree (dynamic resistances). As a consequence, the maximum expiratory outputs are decreased and the work of breathing increased to maintain adequate outputs necessary for alveolar ventilation, particularly during muscular exercise.