Hello,
Can someone at TDI please give me the definitive answer on whether or not the deco proc course requires doubles or not?
Yes, or no; Can the deco proc course be taught with a single tank and single deco/stage cylinder if the stage/deco cylinder is breathable at deepest depth?
Thanks,
brrrrr........
Course may be taught with a single and an H or Y valve. Final gear configuration will depend on local conditions, depths at which course is to be conducted, and duration of dives and all members of dive team staying within acceptable gas management rules.
The original poster dives on the east coast... well, for a point of reference, the majority of our instructors in North America teaching this course on open-circuit would have candidates on manifolded doubles. I've been teaching it for many years and can only recall two students who did it on high-volume singles and an H valve.
As to the question raised by OP about redundancy being supplied by deco gas that can be breathed at maximum depth... Not the best plan at all for two reasons.
Optimal decompression. Decompression Procedures is normally taught in conjunction with Advanced Nitrox which allows for high-oxygen content decompression gas to be used. This practice is commonplace because we believe it optimizes off-gassing.Having a deco gas and bottom gas delivering the same, or very similar partial pressures of inert gas on ascent is out of sync with that practice. In some cases, deco is taught as a stand-alone and in this case, the maximum allowable nitrox mix will reflect that allowed under the auspices of the student's basic nitrox training. Usually then, air will be used as a back mix and something like EAN39 as a decompression.
Concerning CNS toxicity. Not having a redundant BOTTOM GAS (that's to say a mix with an MOD equal to or exceeding maximum target depth for the dive) breaks standards and good sense. Bailing out to a hot mix is neither tolerated by standards nor is it an acceptable practice.
Having said all that, in practice, the course COULD be conducted no deeper than the MOD of EAN39 and that COULD be used in the event of a primary gas failure (simulated or real), but it would make OOA buddy drills complex and untenable.