Objective
The project is intended to demonstrate that hydrogen diving, which increased the diver's efficiency and therefore the reliability of his operations, can be implemented at lower cost and under optimum safety conditions using conventional helium diving equipment without any major costly system modifications.L%
The first experimental dive was conducted at the Comex Hyperbaric Experimental/Centre in Marseilles in January/February 1994.
Four professional divers were placed in living chambers pressurised with a heliox mixture (H2, O2) to a simulated depth of 350 msw.
From this life support level, the divers then made daily 6-hour excursions breathing a hydreliox mixture (H2, He, O2) on each of the 8 days.
- 4 excursions at 335 msw.
- 4 excursions at 365 msw.
i.e. +/- 15 msw with respect to the life support depth in order to simulate diver operations above and below the diving bell.
No hydrogen narcosis was detected in the psychometric tests run with hydreliox. Overall, the diver's performance improved as the dives progressed - a proof that the learning process was not inhibited by the change in the breathing mixture.
The physical exercises, calibrated using an arm-type ergometer, proved much easier than when breathing heliox, thanks to the enhanced breathing facility procured with hydreliox, a finding echoed by all the divers.
As far as the isobaric counterdiffusion phenomenon was concerned, no hydrogen bubbles were detected in the blood circulation of any of the four divers on their return from the excursions at 335 msw. However, Doppler and Echo-Doppler tests did reveal bubbles in the blood circulation one of the four divers-always the same one-after each excursion at 365 msw; the level did not call for any therapy and all the bubbles disappeared naturally after 18 hours breathing heliox.
The demonstrations carried out at sea at 210 metres during the HYDRA 12 operation in June 1996 have proved that hydrogen diving is feasible on industrial scale, using equipment designed for traditional helium diving.
The fact that no technical nor physiological incidents occurred during the whole of the operation at sea proves once again that we have perfect control over this new innovative method for manned subsea intervention.
It has now become obvious that in areas of medium depth at which divers usually operate with helium, hydrogen will clearly improve their performance :
- Improved efficiency
- Greater working capacity
- Greater security.
The indirect effect of the above factors is that manned subsea intervention has become much more reliable.
The second effect induced by the improvement in the divers' performance is an increase in their productivity because they can work faster with hydrogen than with helium. The diving equipment will therefore be immobilised for shorter periods and the overall cost of an intervention will thus be lower. This points is important in the current economic environment with the need for drastic decreases in the costs of producing offshore hydrocarbons.
The technical requirements to implement this new diving method will be limited mainly to the surface gas reclaim system for the closed breathing circuit. We have used the same equipments as those designed for helium and adapted the electric components and the oxygen automatic make-up.
All diving methods currently used for undersea operations, whether for short-term interventions or long-term saturation diving, involve the use of helium-base breathing mixtures.
Adding hydrogen to the breathing mixture diminishes the deep diving limitation factors (High Pressure Nervous Syndrome, Breathing gas density).
Hydrogen diving, developed in recent years as a saturation technique, may be adapted as a supplement to helim saturation diving to take advantage of the physiological comfort it provides for the divers.
The mixed diving technique covered by this project is organized as follows :
- Divers are confined under pressure in saturation chambers pressurized with a heliox mixture at a pressure equivalent to the undersea operation depth.
- Immersion work is carried out using a "hydreliox" (H2-He-O2) breathing mixture.
The advantages of this "helium in/hydrogen out" technique is that it can be implemented in existing facilities used for conventional helium diving without major changes in the heavy equipment.
The project involves five major phases :
PHASE 1 : BIBLIOGRAPHIC SURVEYS
Concerning gas exchanges involving isobaric counterdiffusion.
PHASE 2 : SPECIFICATION OF EXPERIMENTAL PROCEDURES AND TEST FACILITIES
The test facilities are defined to obtain a configuration representative of operational deep-sea diving units found on most existing diving support ships.
The experimental procedures are specified to investigate gas transfer phenomena when the breathing mixtures are changed, and especially the permissible hydrogen partial pressure gradients according to the diving depth and duration.
PHASE 3 : EXPERIMENTAL DIVES
Experimental dives are performed in a hyperbaric simulator at pressures corresponding to deep-sea operation depths (below 200 msw).
These dives are used to determine the permissible hydrogen partial pressure gradients according to the diving depth and duration. The divers are submitted to a Doppler examination to quantify the hydrogen-helium isobaric counterdiffusion as they return to the helium saturation caisson.
PHASE 4 : SPECIFICATION OF METHODOLOGICAL PROCEDURES
Based on the results obtained during the experimental dives, we specify the general procedures for implementing mixed diving at sea, notably :
- The composition of the hydreliox breathing mixture necessary according to the heliox saturation life support level, the immersion depth and the duration of the operational dives.
- The precautions necessary when to the living chambers.
PHASE 5 : QUALIFICATION OF RESULTS AT SEA
The diving bell is modified to supply the hydreliox mixture, with a gas reclaim system adapted to breathing closed circuit.
Several hydreliox working dives are performed to verify that there are no technical or financial constraints that could prevent widespread use of this new diving technique.
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DEM - Demonstration contractsCoordinator
13321 Marseille Cedex
France