Divers working on undersea oil production installations are faced with a series of limiting factors caused by the subsea environment and generated by the hydrostatic pressure and the gases diluting the oxygen in the pressurized breathing mixtures. This situation has led to the use of the following different types of gas as a function of the immersion depth:

• Air down to 50 metres; however below this depth, nitrogen narcosis effects are hazardous for the diver.
• Nitrox (an oxygen/nitrogen mixture) for long saturation dives near the surface.
• Nitrogen trimix (an oxygen/nitrogen/helium mixture) for bounce dives down to 150-180 metres. This mixture is not in common use on offshore rigs.
• Heliox (an oxygen/helium mixture) for all types of bounce dives and saturation diving.

Though the use of helium in the 1970's was a major breakthrough for deep-sea diving, it did not completely eliminate all the effects of pressure on the diver's organism and the diver's performance decreased as the depth increased.

A TECHNOLOGICAL BREAK THROUGH FOR DEEP DIVING EFFICIENCY AND WORKING SAFETY

Today, divers who work on underwater oil production installations are subject to various limitations inherent to the use of the helium breathing mixtures developed in the 1960's.

As early as 1982, COMEX launched an ambitious research programme called HYDRA that was undertaken to increase the safety and working capacity of deep-divers. The new hydrogen breathing mixture substantially increased the performance of divers. The effectiveness of hydrogen was clearly demonstrated in world record-setting dives: in 1988, six divers went down to 534 metres off Cassis (HYDRA 8) and in 1992, a depth of 701 metres was reached in our Hyperbaric Research Centre (HYDRA 10).

The aim of HYDRA 12 - a world premiere- was to demonstrate the industrial feasibility of the new "Helium IN / Hydrogen OUT" diving technique. Inside the saturation chambers on board the ships, divers breathed the standard helium mixtures but they were supplied with a hydrogen mixture when working on the seabed. With this new diving technique, hydrogen can be used - without high alteration costs - on all the existing major deep diving support vessels equipped to operate with helium.

In addition, for this operation, COMEX has designed and developed an innovative closed circuit breathing system which feeds the diver working on the seabed with hydrogen. The divers connect pipe sections by bolting together flanged spool pieces on a working platform submerged at 210-220 metres. This depth is typical of the current human helium working depths and will therefore provide a meaningful comparison between helium and hydrogen.

HYDRA 12 OPERATION : A SUCCESS 16/28 JUNE 1996

On Friday, June 28, 1996, the four COMEX professional divers left their saturation chambers after 12 days of confinement.

According to HYDRA 12 operation plan, from June 17 to June 21, they achieved eight working dives at a depth of 210 metres:

• four dives with the standard helium mixture "heliox",
• four dives with a new hydrogen mixture "hydreliox", rich in hydrogen.

On a repetitive basis, they connected various spool pieces on a sea-floor working platform with the aim of comparing their performances when using alternatively both breathing mixtures. Each dive lasted from 2 to 6 hours depending on the type of work required.

During these operations, divers breathing the hydrogen mixture demonstrated a higher efficiency with regard to task analysis and a greater working capacity when the manipulations demanded sustained effort. The ergonomic effectiveness of hydrogen was thus clearly demonstrated in actual open sea working conditions. It is now proved that hydrogen is the best component in breathing mixtures for mid-deep or very-deep dives.

The "helium to hydrogen" and "hydrogen to helium" switches were perfectly mastered at both physiological and technical levels.

After hydreliox dives, the Doppler ultra sound tests showed no circulating bubbles in the divers' cardiovasculary system. This proves beyond doubt a perfect hydrogen dosage within the breathing mixture.

Besides, the "surface loop" closed-circuit breathing system worked perfectly giving evidence of its total reliability and demonstrating how easy it could be to add an "hydrogen out" deck container package on a classic helium-diving support vessel The saturation equipment was that of INPP, normally used for professional deep divers' training in their Marseille base.

These results focus on the qualities of diving under hydrogen and the development capacities of this new "Helium In/Hydrogen Out" technique on board large diving vessels operating on offshore petroleum production fields (North Sea, Brazil, Gulf of Mexico).

The HYDRA 12 operation was sponsored by the European Community (Direction de l'Energie) in the frame of the THERMIE programme and co-financed by the "Fonds de Soutien aux Hydrocarbures" (State Fund for Hydrocarbon exploration and production new technologies) through the "Comite d'Etudes Petrolieres et Marines (Direction des Hydrocarbures et des Carburants du Ministere de l'Industrie)".

After the success of the HYDRA 12 offshore dive hydrogen demonstration, COMEX is now focusing on a new research with hydrogen decompression system. This programme is studying the decompression rate with hydrogen breathing gas compared to helium decompression rate.

First animal model tests performed, seem to indicate that decompression with hydrogen will be faster than helium decompression with the same security (very low decompression illness risk). This programme will be continued with professional divers' tests to determine hydrogen decompression tables faster and safer than actual helium table.

For further information contact: Comex S A 36, Boulevard des Oceans - 13275 Marseille Cedex 9 France. Tel: (33) 91 23 50 00

Fax: (33) 91 23 50 21.