Pony for high O2 EAN on 15' safety-stop.

[TSandM]

Breathing a high-oxygen mix at shallow stops will definitely reduce your nitrogen load. The question is whether the risk-benefit ratio falls to the positive.

Positives: Reduced likelihood of DCS (which is already very low, especially if you are following good ascent procedures -- and if you can't follow good ascent procedures, you have no business on high O2 mixes). Shorter surface intervals, but you'd need decompression software to know by how much. Probably shorter time to fly, but I don't think anybody will endorse this with the data that are currently available.

Negatives: Need for another bottle and deco reg, O2 cleaned. Difficulty finding high O2 mixes if you don't have tech training. Need to do a gas switch. Need for a multi-gas computer or decompression software, to know what you are actually DOING to your loading with the amount of O2 you're breathing.

Risks: Total body O2 toxicity (primarily pulmonary). It is not benign to breathe high O2 mixes for long periods without a break. This is something you learn in a deco class. And the worst risk, CNS toxicity. Should you get distracted by something and lose precise control of your depth, you can easily run your ppO2 up into toxic levels, and a seizure underwater is rarely survivable.

For someone with the appropriate training and the necessary skills (and we do a LOT of training to be sure we have those necessary skills!) the balance may swing positive, especially for repetitive deeper dives or multi-day trips. But for people who haven't had the training, the risks are just too high. I'm really surprised a hyperbaric doc would recommend this.

 

[Rhone Man]

I think the upsides are marginal (reduce ppN2 from about 1.2 ATA to 0.0 ATA for 3 minutes), and the downsides are considerable (cost and trouble of maintaining a rig compatible with EAN70, and the risk that sooner or later, some idiot will take a hit from the pony at depth and end up in a world of trouble).

If you are really that worried about it, much safer to breathe pure O2 topside for a few minutes after you get out. Pretty much the same upside, but much lower cost and risk.

 

[muddiver]

Another school of thought is that you can use the benifits of a richer O2 mix by doing your ascent on it instead of just doing a safety stop on the richer mix. If you dive 21% to 36% as a bottom gas, you could carry a 30 or 40 cu pony of say 40% and use it as an ascent mix when you get to 70' to the surface. The MOD for 40% is actually approximately 82' at a PO2 of 1.4.

But because the MOD of 40% is 99' at 1.6, it is still a acceptable bailout for the majority of the recreational diving depth range. If you plan to dive deeper than 99' than you may want to modify your mixes to satify your safety requirements.

 

[paddler3d]

If you do what muddiver says, you can get around most of the equipment O2 issues. You'll still have to O2 clean your bottle though.

 

[RJP]

However, a recreational diver carrying such a pony (filled with EANx70) would have to realize that the gas in the pony would not be available below the maximum operating depth (or MOD) for the O2 content...

Nor would it be available without some sort of Advanced Nitrox/Deco Theory or other tech-type c-card.

 

[paddler3d]

If I owned my own boat. I would figure out how to do it. My buddy and I looked at doing it on his boat, but it was too small. My vision would be to have a hang bar with a few regs available one it with O2. To me, that would swing the PITA factor to a positive.

 

[kanonfodr]

Eeee....carrying a pony bottle of 70% scares the crap out of me, and I'm not one of the smarter divers on this board!! I would suggest Pyle stops as mentioned above. I know I feel a lot better when I do 1 minute ascents with a deep stop while controlling my ascent rate vs. a shot to the surface and chilling at 15 feet.

Peace,
Greg

 

[Wookie]

Wow. I'm reading all these folks who suggest what a pain it is to reduce your exposure to DCS. I'd like to suggest what a pain it is to spend 4 or 5 days in the chamber running table 6's because you took a type 2 hit for no good reason.

First, though, if you're going to use nitrox over 40%, take an advanced nitrox class. An instructor will be able to give you the do's and don'ts of diving using high partial pressures of oxygen, and will also evaluate your diving skills to ensure you can maintain your depth properly while distracted, and evaluate your propensity for running out of gas at depth. I might also suggest that a lower percentage of nitrox (40%) will get you on a flush-out gas earlier than a higher percentage, and therefore start the "flush" earlier than a shallower gas.

I agree with the suggestions for slower ascent rates and half or "Pyle" stops. You will get more bang for your buck utilizing anything to slow your ascent than the gas you choose.

At the end of the day, I use all those things (I fill my own pony) to avoid DCS. I spent those days in the chamber, and would rather not have a repeat.

Above all, have fun
Frank

 

[Indian Valley Scuba]

I saw a reference to a dive computer in one of the earlier posts that "might have deep stop options". Heck, you don't need a computer do to that....a depth gauge and a watch will work fine. I won't start a "recipe battle" here with how many minutes at each stop or how deep the stops should but, but just use your head, and don't rely on that fancy watch and some guy's mathematical interpretation of you body you have on your wrist - it is far more likely to let you down than you are.

 

[Packhorse]

Wow. I'm reading all these folks who suggest what a pain it is to reduce your exposure to DCS. I'd like to suggest what a pain it is to spend 4 or 5 days in the chamber running table 6's because you took a type 2 hit for no good reason.

Are you suggesting there is something wrong with the algorithms in the majority of recreational tables/ computers?

If not why bother with 70% O2 for rec diving?

Sure for deco diving high EAN mixes are great but for rec diving on EAN to start with IMHO its just unnecessary and a pain.