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Old 16th April 2006, 14:29   #6 (permalink)
nigelh
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Current Rebreather/s:
Inspiration Vision
Other CCR

Other Rebreather/s:
Inspiration Classic
Other CCR
 
Join Date: Mar 2005
Location: Brighton, Sussex, UK
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Re: A guide about setpoint selection for deep dives

I'm having problems with some of the text and a few of the deductions.
Quote:
1. For Gas management, we should use the rule of 1/3rds. At the end of the dive, a CCR diver should still have at least 1/3 of the oxygen cylinder left.
This is a conceptual misunderstanding of rule of thirds. My reserve should not depend on my cylinder size but my gas usage plan. Also I would prefer to have a specific size of reserve on a CCR as my usage is so small.
Quote:
5. For the Oxygen exposure, a competent CCR diver should always stay within reasonable limits and should select a setpoint lower than 1.1 for the bottom part of the dive, maybe increasing this setpoint during the decompression phase.
This is complete twaddle contradicting what most agencies teach and negating much of the benefit of CCrs. We are not seeing divers dropping like flies on 1.3 bar ppO2s. There may be a case for reducing it on longer dives or in repetative dive situations but as a general rule it has a good track record with no reported problems.
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Last edited by nigelh : 16th April 2006 at 14:33.
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