40% O2 mix at the safety stop

[nereas]

I've carried a pony with pure oxygen in case we missed the hang bottle on the way back up. But you are right, usually it should be filled with air or EAN.

Carrying a single bottle of 100% O2 is probably not a very good idea.

When I carry a single bottle, like this, it normally has EAN 50 in it. And then, I am normally wearing my twin tanks, as well.

 

[RiverRat]

Fortunately most of the rest of the world other than America doesnt insist on nannying and allows people to make their own choices so cards aren't needed.

I could do without some of the "nannying" But I've seen and heard of some really stupid things done by divers not only during the course of their regular diving, but in classes that they probably shouldn't have been in yet. The nannying helps to keep some of these folks alive. Unfortunately it impacts us all to some degree. Is the rest of the diving world really that laid back?

 

[nereas]

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

Based on current tables and guidelines, you would only reach the 100% CNS limit after diving at a ppO2 of 1.6 ATAs for 45 mins.

That takes either a really rich mix, or else a really deep dive, or both, followed by pure O2 at the safety stop. It's not possible without going into deco, first.

 

[String]

The nannying helps to keep some of these folks alive. Unfortunately it impacts us all to some degree. Is the rest of the diving world really that laid back?

Darwin does a good job of that too.

Here ive never been asked for a nitrox card and never been asked for qualifications to get a fill, get on a boat, enter a quarry. You turn up and take your chances - nobody else involved.

 

[Blackwood]

I won't buy into the argument that bouyancy control is a tech skill. I will buy into the argument that people who don't have the skills to do something shouldn't do it.

I don't think there is anything about this that requires tech training. The requirements are pretty simple: did you have a conservative dive, are you above 15-20 feet, can you maintain your depth at 15 feet adequatly when next to a line and or a hose anchored to the boat? Can you change your reg without freaking out (after all, breathing from alternate air is an open water skill)? If the answers to those questions are yes, then you can decide if you want to grab that reg or not.

No, holding depth is not a "tech skill". But rescuing a toxing diver is hardly a common "rec skill."

Carrying a single bottle of 100% O2 is probably not a very good idea.

... why?

What if I'm in San Diego diving the Yukon. Say an hour at 90 feet. For that profile, O₂ makes perfect sense, and personally I'd rather have it with me (i.e. slung) than leave it somewhere I may not be able to return to.

 

[Bismark]

It would make more sense to use the EAN 40 in your tank during the actual dive, rather than use it as a hang-tank during your safety stop.

Any level of O2 higher than 21% in a hang tank will indeed give you some added off-gassing than plain air. But the difference, for NDL diving, is rather insignificant.

So your friend had good intentions, however his math was way off. The main benefit of a safety stop is to give your bloodstream a chance to scrub your body of compressed nitrogen, before your return to surface pressure.

The safety stop itself is much more significant than whatever is in the hang tank.

If you use EAN 40 in your tank, then you should not dive deeper than 100 ft.

And with EAN 40, if you drift down to 130 ft, then you would be dangerously close to experiencing an oxygen toxicity siezure. And any deeper than that and you would probably die. So you need to be careful about what you are doing when you have EAN 40, or any other nitrox, in your tank. They teach you all about this in a nitrox class.

Since we are on a more technical bent here (no pun intended) I agree with a lot of what you are saying however, your two paragraphs demonstrate, in essence, what I think is the nature of the problem with learning this type of thing from the internet. Not trying to pick on you here, but you have essentially just told someone that they would probably die if they breath 40% 02 at 130 ft and that they should dive no deeper than 100' on 40%, PP02's of which are about 2.0 and 1.6 respectively. However, you have over simplified the issue with breathing high pp02's in attempt to make it easily understood in a single post on the internet. I am sure you have done this with the best of intentions but the end result may not be what you intended. I am sure you know that a quick survey of the literature, including some of the original studies of breathing 02 and oxygen toxicity, demonstrated the vast range of various peoples ability to tolerate 02 in high concentrations. It is not so cut and dry as 1.6 pp02 is okay and 2.0 will kill you. The variables in many of Paul Bert's experiments were so all over the map, that it was difficult to come to any hard and fast rules. Instead, we have a dopted a "range" of use based on statistical analysis. Will you tox at 2.0? Maybe. Will you tox at 1.6? Maybe. Will you tox at 1.2? Maybe. There is no hard and fast rules, as the variables are too difficult to narrow down. We have however adopted some generally accepted "policies" regardings higher pp02's at depth, but even the various training agencies disagree on this. I rember hearing somewhere over 20 years ago in some basic diver training somewhere, (must be getting old, memory is acting up) that "breathing oxygen at 2 atmosphers was lethal". I remember being suitably impressed and scared but I had no idea what the hell the person telling me meant! Sometimes information in small amounts can cause more problems than just telling someone to take a class or a course and learn it more thoroughly.

To the OP, take a nitrox course from a reputable agency and from a reputable instructor and learn the full meal deal. Any thing else will just confuse the issue for you at a later date. Considering the law of primacy and learning, if this thread was your first exposure to understanding the use of 02 in diving, we may have already confused you.

 

[Bismark]

A good dive shop, which has oxygen, can fill those, yes.

But they will want to see from you either (1) a DAN oxygen provider card or (2) a stage deco card, showing that you are at least some kind of trained tech diver or oxygen provider.

I was under the understanding that medical 02 bottles had a different regulator/first stage connection and most dive shops did not have this fitting.??

 

[Tomeck]

50% is better than 40% or 100% for decompression stop, because the time of decompression stop is shorter.

 

[Bismark]

Can't follow the link, but I'm, interested so what was it about.



I won't buy into the argument that bouyancy control is a tech skill. I will buy into the argument that people who don't have the skills to do something shouldn't do it.

I don't think there is anything about this that requires tech training. The requirements are pretty simple: did you have a conservative dive, are you above 15-20 feet, can you maintain your depth at 15 feet adequatly when next to a line and or a hose anchored to the boat? Can you change your reg without freaking out (after all, breathing from alternate air is an open water skill)? If the answers to those questions are yes, then you can decide if you want to grab that reg or not.

I didn't argue that buoyancy control is a tech skill. I said that it was difficult for new and inexperienced divers to do. Nor do I say that you need tech training to learn good buoyancy skills. However, it is emphasized in tech training for the reasons I previously stated.

Some of the most skilled divers I know have never taken tech training, yet have no difficulty with buoyancy control. They have developed this skill through experience, which, by definition, the inexperienced diver does not have. Tech training will help develop buoyancy control skills, but so should any decent recreational training regimen..........that is a different post however...........

 

[Bismark]

50% is better than 40% or 100% for decompression stop, because the time of decompression stop is shorter.

Again, good intentions but faulty information presented in a much to summary-like fashion.