Really stupid question... Why dive thirds with doubles?

[DA Aquamaster]

How exactly will you know when the increase in CO2 doesn't make a difference? How does one gauge when skip breathing will retain just enough CO2 to not be problematic?

Exactly. Especially given the highly narcotic properties of CO2.

Thinking it is doable at PO2 upwards of 1.0 also implioes doing it at greater depths and greater ENDs. So in effect, it potentially is working counter to any attempt to limit END - trimix, decreased MOD, etc.

Personally I'd prefer to turn the dive a couple hundred feet sooner, or take a stage to extend the penetratiopn than deal with the extra narcosis caused by elevated CO2 levels from skip breathing. But to each his own.

My major beef here is that we should not be promoting a practice without also fully informing people of the problems that may result. Personally, I think many of the issues where divers report being excessively narced at a reasonable END around 100 ft are potentially related to CO2 retention.

In cave diving, the rules related to training (1/6ths in doubles at Intro), peer pressure (real or just imagined), and/or in some cases a personal ego driven need not to be the person who turns the dive on gas and/or the desire to push the penetration on a given amount of gas a few hundred feet farther all contribute to the number of skip breathing divers out there who are, in my opinion, placing themselves and their teams at risk with elevated CO2 levels and uneccesarily impaired judgment at any given END.

Then we as a community make a bad situation worse by coveting low SAC rates and associating them with being a "better" diver. If adiver wants to improve SAC rate, they need to do it through increasing fitness, not through skip breathing. Similarly, if they need more distance for any given SAC, they need to bring more gas.

 

[marchand]

Skip breathing to improve SAC just does not work.

All I'm saying that what you said here is not true. Skip breathing does stretch your gas significantly. Its not just a couple hundred feet difference; depending on the dive it can easily add up to over a thousand feet, which for me is the difference between having to swim three stages, or just two into devils. I'm not saying that there aren't trade offs or risks, because there definitely are. I can tell a difference in the amount of narcosis, but it has never been enough for me to justify adding a stage bottle.

In my opinion, where skip breathing is dangerous is using is to effectively lower the PO2 of the gas you are breathing. For example, diving air below 250' and using skip breathing to avoid oxtox.

 

[ScubaDocER]

All I'm saying that what you said here is not true. Skip breathing does stretch your gas significantly. Its not just a couple hundred feet difference; depending on the dive it can easily add up to over a thousand feet, which for me is the difference between having to swim three stages, or just two into devils. I'm not saying that there aren't trade offs or risks, because there definitely are. I can tell a difference in the amount of narcosis, but it has never been enough for me to justify adding a stage bottle.

In my opinion, where skip breathing is dangerous is using is to effectively lower the PO2 of the gas you are breathing. For example, diving air below 250' and using skip breathing to avoid oxtox.

I agree with DA that skip breathing to improve your SAC rate does not work as part of an organized, planned dive. If you are skip breathing as part of an emergency plan such as a loss of gas situation, then it is better than the alternative if you and your buddy do not have enough gas to exit as a team. But to use skip breathing as part of your dive plan seems concerning to say the least. If you are able to penetrate into a cave a thousand feet further using skip breathing alone then that is some impressive diving my friend. I guess I would suggest that if you are already diving with doubles and 2 stages and you still do not have enough gas to complete your planned dive without skip breathing, then perhaps the dive is not worth doing in your current configuration. A RB may be in order. Or a scooter. Or a different dive plan. It might be easier to just place stages in the cave on one dive, and then come back the next dive and complete your extended range dive. This seems more sensible than avoiding carrying a third stage by skip breathing.

BTW, it is not only the narcotic properties of the elevated CO2 that may cause you problems, but the acidosis associated with the elevated CO2 may become an issue as well. Again, I don't know how long you will be skip breathing, nor what your measurable CO2 levels will be, but I would caution anyone against using this as part a formal dive plan. The benefits don't seem to outweigh the risks IMHO.