Swapping from back gas to a decompression cylinder, or from decompression cylinder to decompression cylinder is an area where GREAT CARE needs to be taken to ensure that you don't end up breathing the wrong gas either too deep or too shallow with potential ramifications for your decompression obligations or oxygen toxicity.
It is equally as important as testing your gas mixes before you dive. The importance of getting it right cannot be over emphasised, too many people have got it wrong and not been able to tell the story afterwards. The sections Which Decompression/Stage Cylinder?, Decompression Cylinder Marking Template for 50% Nitrox and the Decompression Cylinder Marking Template for Oxygen should be read in association with this page.
A regulator must never be colour coordinated to indicate the mix which it is attached to in case the wrong regulator were to be attached to the wrong bottle, likewise mouthguards must never be used! If you should mount decompression cylinders bi-laterally, make sure that you never associate one side with one mix eg left deeper, right shallower but use visual identification. Otherwise you may one day mount the wrong bottle on the wrong side and end up breathing the wrong mix!
Decompression bottles should be kept pressurised but turned off during the dive until it comes to the time to use them, this prevents any accidents since they cannot be physically breathed until you have turned them on.
The procedure is as follows and assumes that the tank is carried on the left hand side. One diver will swap regulators first and then the second diver will do so in anything but calm, clear still water when both can swap at the same time...so in the UK it is safe to say that it should always be in sequence.
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1.
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First diver checks his depth on his gauge, goes to his deco cylinders, checks the depth markings and picks the correct bottle for the stop depth he is at. |
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2.
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He removes the regulator which is bungied to it side and takes it in front of him. |
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3.
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Whilst looking at the pressure gauge he briefly presses the purge button. This should clear any debris in the regulator and at the same time the pressure will be seen to drop on the gauge indicating that he has taken the regulator from the bottle he is looking at. He will then recheck the operating depth on the bottle he is looking at and the depth he is at. |
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4.
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He will turn the tank on, remove the regulator from his mouth and but the decompression regulator in, before passing it's hose behind his head. |
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5.
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He will then clip off his primary regulator, signal ok to his buddy, which should be returned. |
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6.
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During each step, the divers buddy should maintain a constant check that the correct bottle and regulator has been chosen and be prepared to intervene/signal if necessary. |
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7.
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The second diver will then do a gas switch, when he starts breathing the new gas, the stopwatch will be started |
When restowing
the regulator from a decompression cylinder, it may be easier to detach
the tail (bottom clip) and move it in front of you where you can see what
you are doing and have easy access to the bungies etc.
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Hit
Counter Complements of http://www.digits.com.
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Diving can be
a hazardous sport and the information contained within this site is
not intended to replace formal training. |
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© Copyright H Beasley 15 March 2003