Objective
This project is intended to qualify the diver's breathing equipment with a view to industrialising mixed "H2-helium" diving from diving facilities rated for conventional helium-based diving. This new method will augment the efficiency and working capacity of divers, thereby increasing the dependability of undersea operations. Through the use of specific breathing equipment, this method could be implemented in optimum conditions of safety on existing diving platforms with no major costly modifications.
The main innovation is the use of a H2-based breathing mixture when divers are working in water, whereas on the surface platform they live in saturation caissons pressurised with helium. This technique allows divers to benefit from the "ergonomic" properties of H2 but restricts the H2 content to a very low level; this means that the heavy equipment designed to operate with helium need not to be modified and safety problems arising from the utilisation of H2 are substantially simplified.
The complete closed circuit breathing system was specifically designed for hydrogen mixtures and was approved by the "Bureau Veritas International" on the basis of the most stringent criteria stipulated in the North Sea Regulations imposed by the Norwegian Petroleum Directorate (N.P.D.). It then successfully passed the tests at sea, in real working conditions during the HYDRA 12 operation (June 1996).
The laboratory tests have demonstrated that whatever the performances demanded :
- standardised slow or very fast breathing rates (simulating
breathhlessness),
- diver above or below the diving bell,
- the "hydrogen gas reclaim system" still had the capacity to ensure sufficient gas supplies to maintain breathing resistance within the limits stipulated in the regulations.
All of the tests were carried out with the system on a "single and universal adjustment" whatever the depth between 70 and 310 metres. This point is particularly important because our experience has proved that operational performance tends to decrease when using systems that require constant readjustment. Technicians rarely have the means on work sites to create the laboratory conditions required to optimise operating parameters and thus adjustments become approximate and sometimes are far from being optimal, thus leading to poor results.
The "hydrogen gas reclaim system" has been proved to be reliable during different implementations in conditions of human intervention :
- Dives to - 120 m in the hyperbaric simulator to approve the "bell" procedures.
- Dives to - 60 m at sea on the INPP (National Institute for Professional Diving) barge to approve the diving procedures.
- HYDRA 12 operation at - 210 m to approve procedures and operational equipment.
The technicians at the surface and the divers all apprreciated how easy the system was to use and adapt to any situation.
All diving methods currently used in undersea operations, whether for short-term interventions or long-term saturation diving, involve the use of helium and oxygen based breathing mixtures.
Adding hydrogen to the breathing mixture diminishes the deep diving limitation factors (high pressure nervous syndrome, breathing effort) and enhances the overall physiological comfort (articular pains reduced, reversion to nasal breathing etc...).
Developed in recent years, hydrogen diving has demonstrated all these special features, the mixed hydrogen-helium technique takes advantage of the "ergonomic" qualities of hydrogen without the need for major changes to the heavy diving equipment.
In conjunction with appropriate breathing equipment, this technique could be applied to all undersea operations at depths of 150-350 meters; furthermore, it could be implemented on all the existing diving facilities designed for conventional helium-based diving.
The breathing equipment is being qualified inthe context of promoting mixed "hydrogenhelium" diving. This new method significantly enhances the working capacity and efficiency and hence the safety and the reliability of personnel working undersea on oil production rigs. The method should be all the more favourably received in that the diver's breathing equipment will have been previously qualified and certified and its marketing will therefore be much quicker.
The improved physiological comfort provided by hydrogen will very substantially diminish fatigue and could increase working duration in immersion by as much as 50 %; moreover, this gain in "productivity" does not entail any increase in the operating costs nor any large capital outlay.
The breathing system must comply with the criteria in force in the profession:
- DIVER'S HELMET
* The breathing resistance must not be greater than 14 hPa both for inhalation and exhalation, irrespective of the breathing rate
* Carbon dioxide must not be retained in the helmet.
* The inhaled gas temperature must comply with the physiological standards as a function of the depth.
- GAS RECLAIM SYSTEM
* Elimination of the carbon dioxide and keeping the residual partial pressure no higher than the maximum acceptable value stipulated by the standards.
* Re-oxygenation of the mixture to compensate for the diver's metabolic oxygen consumption, and holding the partial pressure within the minimum/maximum limits specified by the standards.
* Boosting the pressure of the regenerated breathing mixture to make up for the pressure drops in the umbilical cord and breathing tube, and supplying the helmet regulating system with enough pressure and flow for normal operation of the pressure regulating valve.
The project involves three major phases :
1. Adapting the closed-circuit breathing loop for the hydreliox mixture.
2. Simulator functional breathing tests.
3. Qualification and rating of the complete breathing system.
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DEM - Demonstration contractsCoordinator
13321 Marseille Cedex
France