Gas mixer to help safeguard deep-sea divers

A specially designed electronic gas mixer has been ordered by Bibby Offshore for use on its new diving/construction support vessel DSV Bibby Sapphire.

A specially designed MG50-2ME+SOA electronic gas mixer has been ordered by Bibby Offshore from Witt Gas Techniques for delivery in early September 2006 for use on its new diving/construction support vessel DSV Bibby Sapphire.

This gas mixer is a stationary system that will be used to mix oxygen with heliox, the breathing gas made from oxygen and helium, used by deep sea divers working at depths up to 300m.

It will mix the correct percentage (user defined) of oxygen and heliox for the required depth; the deeper the depth the less oxygen is required in the gas.

It has a better than +/-1% absolute mixing precision.

It will have two gas inlets, one of which is oxygen and the other heliox.

From the inlets it will mix the heliox with the required oxygen content.

It has a built in oxygen gas analyser to monitor the oxygen levels in the mixture, whilst pressure switches monitor the gas supply pressure.

A touch screen control is used to input the correct mixtures.

From the mixer the gas goes to a compressor and onto the storage tubes for use by the divers.

DSV Bibby Sapphire operates in the North Sea and Worldwide.

The vessel deploys divers to depths between the surface and 300m.

The deeper the depth the divers are deployed to, more decompression is required.

It operates a diving technique to maximise the working time of the divers, which involves them living at a pressure equivalent to the water pressure at which they are working.

The divers live in a 15 man saturation dive chamber onboard the vessel and transfer at the same pressure to a diving bell, which is then deployed to the working depth.

The divers can operate at this depth for periods up to eight hours.

They return to the bell, which returns to the surface and they transfer back to the chamber and continue to live at this pressure.

This pattern is repeated until the job is complete or they have reached the time limit imposed for this cycle, which is 28 days including decompression.

A storage pressure of 11bar absolute at 100m working depth would require a decompression of approximately 5 days.

The 94m-long DSV Bibby Sapphire is fitted with a DP class 2 dynamic positioning system and has a transit speed of 15 knots.

It also includes a heavy lift crane, 850m2 working deck space, a helideck, fire fighting capability and accommodation for up to 197 persons.

Carl Long, General Manager, Witt Gas Techniques said: "Our gas mixers are used in a wide variety of industries from ranging from food production to welding".

"This particular gas mixer is a derivative from a mixer used to supply high purity (synthetic) air in hospitals, so it has to be very reliable and it has a number of built-in safety features, including an optical alarm being triggered if the inlet pressure is too low and the system automatically shuts down".

"We have previously supplied mixers for professional diving, with one of our mixers being used on Jacques Cousteau's research vessel Calypso".

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