Nitrox vs. Regular Air?

[Age]

Actually it is not recommended to ascend with a toxing diver. During the seizure the airway will be closed so ascending will cause lung damage/ AGE as the expanding gas has nowhere to go. The preferred method is to stay with the diver until the seizure stops and then ascend.
As far as I know there has only been a handful of successful rescues of divers having O2 convulsions. Much better never to get into that situation in the first place.

Although it is counter intuitive that is also very true. Thank you for reminding me. I've just read the relevant section in my new NAUI book that also, interestingly points out that because the person has been breathing a high PPO2 in the first place he or she remains well oxygenated. That's worth remembering if your impulse is to save the diver before the convulsions are over.

 

[Blackwood]

.....that would be the least of your worries.

Hence the "if it were possibly" caveat

Could be done in a chamber. Pure O₂ at 4ATM for an hour, and drop the pressure to 1ATM in the matter of a few seconds. I betcha the subject will get bent (among other things).

AAs far as I know there has only been a handful of successful rescues of divers having O2 convulsions.

I know of exactly 2 cases. One, a guy toxed at 20 feet after switching to deco gas. Fortunately, he was only at 20 feet. I think they kept him in control, completing deco.

The other is the 'famous' case in which Andrew Georgitsis rescued a guy who switched to the wrong mix at depth (150 feet, if I recall).

I can't think of anyone I'd rather be in the water with if I were to tox than A.G.

 

[espenskogen]

Yah. That has been re-thought by some. If it isn't soluble, it doesn't go into solution. If it doesn't go into solution, it doesn't have to come out of solution. Breathe in, breathe out.

That said, any gas we breathe under pressure can bend us. Due to the solubility and metabolic properties of oxygen, we tend to treat it as not contributing to DCS. But if it were possible to suck on pure oxygen at 150 feet for an hour, it could bend us. So can nitrogen and helium.

Anyway, as you said, what to believe is up to the individual. Personally, I won't penalize myself for breathing helium.

Fair enough - I guess that's one school of thought.

In the same water, sure. Narced at 30, more narced at 50.

But many people will operate better at 50 meters in the Red Sea or French Polynesia than they will at 30 meters in cold murky Redondo or UK waters. And, of course, it varies from dive to dive.

There has been argued that peoples ability to operate better in clear calm water is to do not so much with the physiological narcosis, but more to do with the psychological effect of diving in a hostile environment (if you can call it that)

I tend to agree that for many recreational dives helium is overkill. However, it may sometimes have merit.

And there is more to it than risk. This is an anecdote that my trimix instructor passed along. Two divers (I can't remember their names) dove the same wreck for years on air. One day, they were convinced to try mix (pun intended ). After the dive, they came up talking about all these things they saw that they had never noticed or remembered before. Portholes, railings, etc.. On a wreck they'd hit a hundred times!

Risk be darned, I dive to see the underwater world. But If I can't remember it, what was point?

Would I dive mix to 90 feet? No. 110? Maybe. Am I penetrating?

Yeah, I get you. At 110, it's starting to have a purpose I suppose. If you're penetrating, then presumably you'd be carrying redundancy, and technically, you're now doing a tech dive. (Yes, the pun was intended there as well) (I guess there are dives overhead which could be border line recreational - If you don't penetrate more than 8-10 meters for example but it's close enough to tech). Generally, Tech divers are better trained, and have a better understanding of the risks than recreational divers (Assuming you can group divers into these distinctions). Being in an overhead environment, you're doing stuff complicated enough for the haze at 30 meters to add a not inconsiderable risk, and I would probably use mix under those circumstances as well.

But it seems the point where both you and I would choose mix is relatively far away from the average recreational dive - Either in terms of depth, or the complexity of the tasks performed. I could see why one would use mix in a cave dive as well - Just to make it less likely to make a mistake that could turn into a fatal one in an overhead environment.

It seems we're more or less on the same page though...

 

[espenskogen]

Hence the "if it were possibly" caveat

Could be done in a chamber. Pure O₂ at 4ATM for an hour, and drop the pressure to 1ATM in the matter of a few seconds. I betcha the subject will get bent (among other things).

Yes, but I suspect the severity of an oxygen bend would be less than a bend from an inert gas, since the body will metabolize the oxygen, and hence reduce the bubble size until it's gone.
Could have some nasty short term effects though.

 

[mempilot]

I don't agree with using Trimix for Recreational diving. Narcosis is not a significant problem at depths of 40 meters or less, and if you dive deeper than 40 meters, then it's per definition a tech dive (or a stupid dive, should you try to do it with a single cylinder and no deco). You increase the bend risk significantly by mixing helium into your mix, and should you get a hit, it's likely to be more severe. Sounds like a great idea for the average recreational diver, doesn't it?

IANTD offers a recreational trimix course which mates up pretty well with deeper NDL dives. Remember, NDL has nothing to do with depth. You can do a NDL dive to 140, 150, etc. The definition of 'tech' diving isn't really depth related either. Most have adopted the term 'overhead environment' to signify technical diving in most cases. While deep can cause decompression obligation, which would be considered technical under this definition, depth along with time is what puts you there, not depth by itself. Performing a normal slow ascent with He is not dangerous. The problem stems from the fact that many divers ascend too quickly even on air or nitrox. They get away with it most of the time. This 'most of the time' would not be as forgiving with helium, since He offgasses quicker than other inert gasses. The average recreational diver wasn't deemed able to handle Nitrox many years ago either. Trimix to recreational depths (just a squirt is all it takes to eliminate narcosis), is a great tool for divers that want to do dives a the deep end of their NDL abilities, perform work (video etc), and do so with a clear head.

Trimix does solve narcosis, but narcosis is not a problem within recreational diving limits. There are a number of courses aimed at NDL diving which makes little sense. Recreational Trimix is just one of them. Normoxic trimix does make some sense, but that is aimed for tech diving with a depth limit of 65m, which is still anything but recreational.

How is that you can make a comment like, "narcosis is not a problem within recreational diving limits."? Are you an authority on dive related incidents? Narcosis is a factor in incidents and accidents. It often times can be the dissappearing evidence after the fact.

Also, how can you say that recreational trimix is one of the courses aimed at NDL that makes no sense and say that normoxic trimix does? You do not understand trimix. Recreational trimix is normoxic trimix by definition of the gas and curriculem. Normoxic Trimix courses assume you have already taken decompression training. The trimix training is identical to recreational trimix. If you don't believe, I will show you the materials for the two courses. I have taken all of them. Which of them have you taken to be such a knowledgeable source on any of this? BTW, you can use what you learned in Normoxic trimix on dives in the NDL ranges. We do it all the time.

So you wonder what kind of diving I do? Not recreational diving on Trimix, that's for sure. The antagonists of Nitrox back in the day said don't use the voodoo gas, you're all going to die!!

I'm not sure what your point is here?? Are you backing my line that the antagonists got it wrong and that you now have it wrong about trimix?

I'm saying use the right gas for the job. If you are diving deep enough for narcosis to be an issue, then by all means use trimix. But if you are a recreational diver doing 20 - 30 meter dives, the question is whether to use nitrox 21, 32 or 36. The operative word here is risk management. You use Trimix on deep tech dives because on these dives, the risk of not using Trimix is higher than the risk of using it. Trimix in itself is no goal.

How about 35 to 40 meters? You say risk management like putting 10% He in a tank is going to somehow raise the risk by some huge degree. Hardly. I agree, trimix is no goal. Safe diving is.

The discussion in this thread was related to the benefits of nitrox which is to either reduce the bend risk by reducing the amount of inert gas in your system, or to increase the bottom time by reducing the amount of inert gas in the mix.

Right. And my statement was that trimix does this and one more thing, reduce narcosis. Simple true statement. You sound foolish attacking that simple true statement with uneducated(untrained) responses.

As for my education - This might be news to you, but most peoples perception of offensive ba****ds like you is that you might be the one lacking in education. Besides, it's not me who's got the following fitness challenge on his profile: Trying to get past 3rd grade reading level.: ) and counting...

The question of your education was not pointed at anything other than that related to diving. I'm not sure how I've been offensive, but you borderline on it. Try to add a little humor to your life. You might actually be a little less annoying.

 

[mempilot]

In the TDI training I did, the mantra was 'A fast ascent on air and you'll hurt. On Trimix, you will almost certainly die'

What TDI training was that? Please tell us your level of certification.

 

[TSandM]

I've been narced enough in cold water at 90-100 feet that I couldn't swim in a straight line (midwater no visual references).

the impairment at 30 meters don't warrant the increased risk of helium in my opinion. (And certainly not for a type of diving, where the majority of participants have less than 20 dives a year, and less than brilliant buoyancy control)

Having frankly hallucinated at 100 fsw, and acted on it, and luckily not been in a position where I could hurt myself with what I did, I strongly disagree that the impairment at 100 fsw is not enough to merit doing something to reduce it. I do, however, agree that the use of helium in deeper recreational dives is ONLY safe if the diver has experience and good technique in controlled ascents, and can manage problems at depth without having to accelerate the trip to the surface. To me, that means doubles and a facility with valve shutdowns and air-sharing, and carrying spare equipment (eg. masks). So 30/30 or 25/25 are not gases to be blithely used by anybody who wants to go deep, unlike Nitrox, which requires no additional diving skills but just book learning. At least this is my opinion.

 

[espenskogen]

What TDI training was that? Please tell us your level of certification.

That would be the advanced trimix course.

 

[espenskogen]

IANTD offers a recreational trimix course which mates up pretty well with deeper NDL dives. Remember, NDL has nothing to do with depth. You can do a NDL dive to 140, 150, etc. The definition of 'tech' diving isn't really depth related either.

Sorry, think you've got it wrong here. Although Tech is usually a reference to overhead environment, recreational diving is defined as no-stop diving to a depth of no more than 40 meters with most mainstream agencies (Apart from BSAC which operates with 50 meters and deco - which in my book is tech, but that's a different discussion). So maybe a NDL dive to 150 feet would not fall into the tech category by default, but it would fall outside of the recreational diving category, so make of it what you will.

Most have adopted the term 'overhead environment' to signify technical diving in most cases. While deep can cause decompression obligation, which would be considered technical under this definition, depth along with time is what puts you there, not depth by itself. Performing a normal slow ascent with He is not dangerous. The problem stems from the fact that many divers ascend too quickly even on air or nitrox. They get away with it most of the time. This 'most of the time' would not be as forgiving with helium, since He offgasses quicker than other inert gasses. The average recreational diver wasn't deemed able to handle Nitrox many years ago either. Trimix to recreational depths (just a squirt is all it takes to eliminate narcosis), is a great tool for divers that want to do dives a the deep end of their NDL abilities, perform work (video etc), and do so with a clear head.

Maybe so, if you are doing 150ft dives as NDL's - But since 5 minute bottom time is on the low side to do any work, I kind of assumed we were discussing the depth limits of the mainstream recreational agencies when we were discussing recreational diving. I totally agree that a normal slow ascent with helium is not dangerous. But pop down to an average tourist dive centre, and see how many recreational divers do a normal slow ascent.
Divers who are competent enough to go down the tech route would probably be totally safe with recreational trimix, but these divers tend to go down the tech route. If your buoyancy is not good enough to hold formal deco stops, I would suggest helium might not be the best idea in the world.

How is that you can make a comment like, "narcosis is not a problem within recreational diving limits."? Are you an authority on dive related incidents? Narcosis is a factor in incidents and accidents. It often times can be the dissappearing evidence after the fact.

Yes, narcosis is indeed a factor, and if all divers dived recreational trimix, I dare say the outcome of a lot of the incidents might have been fatal. Or maybe some incidents would never have happened, but some that hasn't happened might have. It would be interesting to get the views of a dive doc in regards to this matter - Given that a lot of the chamber rides around the world are due to rapid uncontrolled ascents on air or nitrox, what do you reckon the outcome would be if all these were on trimix?

Also, how can you say that recreational trimix is one of the courses aimed at NDL that makes no sense and say that normoxic trimix does? You do not understand trimix. Recreational trimix is normoxic trimix by definition of the gas and curriculem. Normoxic Trimix courses assume you have already taken decompression training. The trimix training is identical to recreational trimix. If you don't believe, I will show you the materials for the two courses. I have taken all of them. Which of them have you taken to be such a knowledgeable source on any of this? BTW, you can use what you learned in Normoxic trimix on dives in the NDL ranges. We do it all the time.

Because a recreational dive tends to be shallower than 30 meters for the majority of divers - A few do 40 meters, and it starts to make sense to dive trimix, but then it starts making sense to add in 10-15 minutes of stops, and actually have time to look around as well.

I'm not sure what your point is here?? Are you backing my line that the antagonists got it wrong and that you now have it wrong about trimix?

No, I have never argued that trimix hasn't got a purpose, but not in shallow diving. Trimix is a deep(ish) gas - Nitrox is a shallow gas, so I'm saying the antagonists had it wrong, and one ought to use the right gas for the dive in question.

How about 35 to 40 meters? You say risk management like putting 10% He in a tank is going to somehow raise the risk by some huge degree. Hardly. I agree, trimix is no goal. Safe diving is.

As I said - At those depths it's starting to make sense if you tend to get put out by mild narcosis. Each to their own. I would use mix if I was doing something vaguely complicated, like penetration, but not for a nice dive over the reef looking at the pretty fishes.

Right. And my statement was that trimix does this and one more thing, reduce narcosis. Simple true statement. You sound foolish attacking that simple true statement with uneducated(untrained) responses.

You're clearly not reading what I'm saying. You made a statement which pretty much said that there was no point in Nitrox - Trimix is the way to go. That is a false statement - You have the greatest benefit of Nitrox in fairly shallow water - You have the greatest benefit of Trimix in fairly deep water. See my point?

The question of your education was not pointed at anything other than that related to diving. I'm not sure how I've been offensive, but you borderline on it. Try to add a little humor to your life. You might actually be a little less annoying.

That's funny, because it came across as if you were relating it to your comment about being able to read a simple sentence.

The reality of the matter however, is that there is not an issue with my education. Or yours, I'm sure - Your profile looks fairly impressive. What it an issue though, is your arrogance. I've never disagreed that Trimix has a purpose. You might not agree, but I'm telling you, your original post came across as if you meant people should forget about Nitrox and go for Trimix instead (and your subsequent posts came across as if someone disagreed with you, they were stupid). To use Trimix safely requires CONSIDERABLY more in-water time than using Nitrox, so by throwing out the trimix comment, not only did you come across as a little bit of a cyberdiver with big words and little knowledge (although I understand this is not the case..) but you also potentially made divers with insufficient dive experience to use trimix safely think that they ought to go and do a trimix course instead of the nitrox course they were considering.

So in the spirit of making peace, I will agree with you that on dives to the deeper end of the recreational depths, for divers with sufficient experience and skill to do it safely, trimix is not a bad idea. (Be that on an NDL dive or a deco dive). But let's be clear, we're talking about maybe the top 5% of the diving population in terms of skill and knowledge here.

 

[espenskogen]

Having frankly hallucinated at 100 fsw, and acted on it, and luckily not been in a position where I could hurt myself with what I did, I strongly disagree that the impairment at 100 fsw is not enough to merit doing something to reduce it. I do, however, agree that the use of helium in deeper recreational dives is ONLY safe if the diver has experience and good technique in controlled ascents, and can manage problems at depth without having to accelerate the trip to the surface. To me, that means doubles and a facility with valve shutdowns and air-sharing, and carrying spare equipment (eg. masks). So 30/30 or 25/25 are not gases to be blithely used by anybody who wants to go deep, unlike Nitrox, which requires no additional diving skills but just book learning. At least this is my opinion.

Ok, cool - Never really had issues with narcosis until hitting 45 m, but I know some people get it worse than others, so that's fair enough. Totally agree with the rest of your comments though.