40% O2 mix at the safety stop

[hypertech]

Anything over 40% needs to be an O2 clean reg. I haven't bought any myself as I am certified to 40%, but I understand the gas is pretty expensive too.

 

[TSandM]

Oxygen isn't expensive; the supply is essentially infinite, and there are many applications for it, so it's readily available. What you may have difficulty with is finding someone who will fill your bottle for you, though. Most tech diving shops will require you to present proof of Advanced Nitrox training for mixes richer than 40%.

There is no question that breathing O2 on a 15 foot stop offgases you faster than continuing to breathe backgas. The question is what the magnitude of the benefit really is. The incidence of DCS on recreational profiles where proper procedures are followed is extremely low. Controlling one's ascent and doing some combination of stops on the way up is probably of FAR greater benefit than breathing O2. Technical divers do it because it markedly shortens their decompression time, but for us recreational folks, our "deco" time is pretty minimal anyway.

The risk of breathing pure oxygen underwater is, quite simply, death. Oxygen toxicity most commonly manifests as seizures, which can occur without any premonitory symptoms. VERY few people survive seizing underwater, and only then if a savvy and very skilled buddy is IMMEDIATELY at hand. Yes, the likelihood of seizing while breathing off a hang tank at ten feet is very low, but so is the DCS risk, and DCS from a recreational dive is EXTREMELY unlikely to be lethal. You have to ask yourself, "What am I trying to accomplish?" and also, "What is the possible price I'll pay for it?" For me, O2 on recreational dives just doesn't pencil out on a risk-benefit analysis.

 

[RiverRat]

Controlling one's ascent and doing some combination of stops on the way up is probably of FAR greater benefit than breathing O2.

Yep you got it. Most DCS hits on rec. profiles I think are a direct result of wicked ascent rates. Don't quote me but I think that's the main issue. Especially when some agencies are still teaching 60 fpm ascent rates

I always practiced 30 fpm and started stopping or slowing down earlier in my profiles. Like 30, 20, 10 and real slow from 10 ft. to the surface. Adding in a deep stop is not a bad idea either on a deep recreational dive. Have to be carefull there so you don't ongas by stopping too long. But if you're diving a computer it'll compensate just as it would for a multi-level dive. And if you are diving a multi-level dive then you don't need a deep stop as you've covered it with the profile anyway, or should have.

If you're contemplating NEEDING O2 at your stop then you may be pushing NDL's (and gas reserves) and it would be a good time to think about more training. If you're diving doubles (or a big single) and pushing it then you can really get in trouble and need to RUN to a DECO course

 

[OldNSalty]

I am not contemplating needing it, I have no desire to be forced into deco and enjoy my diving in < 130 ft - plenty to see. I don't own my on boat so it was really just an academic question as the concept was brought up to me by someone with sufficiently more knowledge on the topic so I really wasn't in a position to argue the point with him.

 

[Bismark]

Oxygen isn't expensive; the supply is essentially infinite, and there are many applications for it, so it's readily available. What you may have difficulty with is finding someone who will fill your bottle for you, though. Most tech diving shops will require you to present proof of Advanced Nitrox training for mixes richer than 40%.

There is no question that breathing O2 on a 15 foot stop offgases you faster than continuing to breathe backgas. The question is what the magnitude of the benefit really is. The incidence of DCS on recreational profiles where proper procedures are followed is extremely low. Controlling one's ascent and doing some combination of stops on the way up is probably of FAR greater benefit than breathing O2. Technical divers do it because it markedly shortens their decompression time, but for us recreational folks, our "deco" time is pretty minimal anyway.

The risk of breathing pure oxygen underwater is, quite simply, death. Oxygen toxicity most commonly manifests as seizures, which can occur without any premonitory symptoms. VERY few people survive seizing underwater, and only then if a savvy and very skilled buddy is IMMEDIATELY at hand. Yes, the likelihood of seizing while breathing off a hang tank at ten feet is very low, but so is the DCS risk, and DCS from a recreational dive is EXTREMELY unlikely to be lethal. You have to ask yourself, "What am I trying to accomplish?" and also, "What is the possible price I'll pay for it?" For me, O2 on recreational dives just doesn't pencil out on a risk-benefit analysis.

Lynne, thank you very much for your input. Hopefully everyone will take this advice from a medical doctor. To the rest of those making comments about using 02 for "deco" on NDL dives, print this page out and glue it to your foreheads. Do not mess with 100% 02 unless you have the proper training and have demonstrated the proper skills to be able to use it safely. Any cavalier advice about using it for any other reason is handing people bullets for a gun and not providing the training necessary to safely handle that gun. As far as references to what divers were doing 10 years ago compared to now, 02 for decompression has been around a lot longer than that. Do some research and you will find that studies on breathing 02 will go back further than most peoples birthdates on SB.

It seems like there has been a trend for many people want to adapt techniques developed and used in technical diving for every day recreational diving. While those on the frontier of any sport who consistently push the boundaries of knowledge and training will constantly set the bar for those that follow, many of these techniques and skills are not for beginner divers. That is one of the reasons we have training and certification levels. Simply put, while any new diver can benefit from learning to back kick, some of these techniques, like accelerated 02 decompression require seriously higher skill levels to be done safely. The problem as I see it is that their are many who do not seem to understand the different levels of risk associated with various technical diving skills. The downside to a bad back kick is next to negligible, the downside to using hi pp02' is death. If you want to use the skills and techniques from technical diving, for god's sake, take the training necessary to use them safely. Don't just take anecdotal advice from anyone on the bloody internet! Would you take flying lesson's online? How about skydiving lessons? Find a good instructor and learn to do it safely and enjoy the benefits.

rant over..........

 

[mrlipis]

But how does that affect a 100% O2 deco stop bottle? I mean if pure O2 is breathed at 5m we're talking PPO2 of 1.5. Is that unsafe?

There is an accumulative effective of O2 over the course of a day. I don't have a table with me so I don't remember the limits but It would be possible to push yourself over the limit at a safety stop while taking in 100%. Unlikely but I suppose possible.

Bruce

 

[Sideband]

Would you take flying lesson's online? How about skydiving lessons?

It is only recomended that one of those two classes be an online course. It can be either one. If your flight class is online then you want really good bailout skills and if your bailout skills suck you better know how to fly.

 

[hypertech]

If you want to use the skills and techniques from technical diving, for god's sake, take the training necessary to use them safely. Don't just take anecdotal advice from anyone on the bloody internet! Would you take flying lesson's online? How about skydiving lessons? Find a good instructor and learn to do it safely and enjoy the benefits.

rant over..........

I agree with what you said, but I can't let a good rant go by

I'm a pilot and I don't see any reason why a person couldn't learn from book and the internet how to do flight planning. I wouldn't want to go throw them into a cockpit and expect them to manage task loading and execute a landing in one piece, but as far as the information processing that goes on during preflight - I don't see a problem.

Unless I grossely misunderstand the task here, I think we are deciding at what depth and what mix one would need to change a regulator/mix to be safe, then actually performing the task requires very little special training. What we are talking about is properly understanding the parameters and limitations of a dive profile. If that's the case, then learning by book or internet certainly seems reasonable. You just need to make sure your source is sound. I wouldn't trust a web forum as my sole source of info, but a lot of this probably could be self taught with the proper resources.

 

[RiverRat]

You just need to make sure your source is sound. I wouldn't trust a web forum as my sole source of info, but a lot of this probably could be self taught with the proper resources.

I think the "right" individual, a "technically minded" individual would have no problem figuring it out. But it's pointless. You need a card anyway to get your bottles cleaned, labelled and filled, get on boats (well tech dives). Even if one did go ahead and start bringing a bottle of O2, held a good stop etc. and pulled it off I don't think its a good idea. I mean what if one uses a "pony" with O2 and someone else grabs it? Rare it would happen but still there is a chance. I learned a LOT in my classes. I'm STILL learning stuff I had no clue about. I'd say "self teach" the academic portion beforehand. Do plenty of research. Buy gear if you want (although it's best to sometimes to wait and get advice). But before you start messing around, especially if you're mixing in with recreational divers, go take the damn course.

 

[MauiScubaSteve]

Personally I think no stop open water diving should not require hang bottles. Gas management people; plan your dive and dive your plan.

I have seen a boat on Oahu that hangs regs (or used to). That was because their questionable guide/instructors were taking noob/tourist divers on dives way above their skill level, but the captain was one of the 500psi nazi's (return with 500psi or you don't get to do the second dive). The guides would bring the heaviest breather back to the hang bar with 500psi and then put them on the hang reg.

In recreational no stop single tank diving, which is in my opinion the basic scuba that we discuss in this forum, hanging regs or tanks are just there so you can break the rules you should have learned in your OW training!