Nitrox - 1.40 or 1.60 PO2?

[Bismark]

My approach is consistent and conservative; it has served me well for almost forty (40) years of diving.

I do not suggest that I will not learn and understand more about tis or any other subject. However, in my first post (which apparently you did not read) I stated that I am making my first two dives tomorrow using EAN and NOT following air tables or computer set to 21% O2.

We are taught to dive within our limits and this is what I am doing. When I gain an appropriate amount of experience diving EAN, I will be able to set new limits. If you teach new divers other than to dive within their limits, it is you who are doing the disservice to divers. I would not let you teach my children to dive.

And yes, I am a recreational diver and very PROUD of it!

You are being very defensive for no reason. I am not attacking you personally and you are entitled to your opinion. However, what do you expect to learn from "experience" by diving nitrox? The science and the math won't change. You have chosen to adopt a "trust me" approach to diving nitrox and then "understand more about it" at a later date. Kind of backwards as far as I am concerned but to each his own. However, I find it surprising that you would state that you would not let me teach your children. Where did that come from? Do you feel more comfortable passing on agency recommendations as the gospel without understanding what is going on? Is that what you want for your children also? Again, this is entirely your choice and it is your family.

Also, where is this "teach new divers other than to dive within their limits" stuff coming from? What exactly do you think I am teaching? Where have I said that I am teaching divers to diver outside their limits? Do you think the math involved in nitrox diving is so complicated that the average diver can not understand it? No offense but you are the product of a diving industry that at one time perpetuated the myth that the math involved with "the devils gas" was entirely too complicated for the average diver and if you just "trust us" you will be okay. I am not an advocate of that position and do not encourage it in my instruction. If you feel more comfortable with that type of training for your family then their are several online nitrox classes that you will be happy with.

Finally, your profile states that you have logged between 250-500 dives in your stated 40 years of experience. That works out to something like 10-15 dives a year. Do you feel this is adequate experience to decide who should teach diving to your children?

Congratulations on being a recreational diver. So am I.

 

[Ben_Ayers]

One question comes to mind. There has been anecdotal evidence that suggest it may be possible to actually develop a sensitivity to high O2 PP over an extended period. Does anyone believe this could be a factor as mixed gas diving becomes more prevalent?

In Dick Vann's presentation for the Dan Tech Diving Workshop, he mentioned a study done by Schaefer on free divers becoming less sensitive to elevated CO2 levels when doing a lot of diving. After a 3 month layoff their sensitivity to increased CO2 had returned to normal. I wonder if your mentioned increase in O2 sensitivity could actually be attributed to insensitivity to Co2 leading to a lower tox threshold.

He also discussed a study done by Donald where a single diver breathed 100% O2 at 70' twice a week for 19-20 total dives. Times for onset of symptoms ranged from 7 -148 minutes - the graph didn't seem to show increasing sensitivity, it was all over the place.

Other tidbits from the workshop/convention that I found interesting:

Dr. Morris (sp) presentation on the Shaw accident and how gas density can lead to "effort independent exhalation" and elevated CO2. The physiologic mechanism of this was enlightening.

Static lung loads, negative and positive.

A non-fatal o2 hit (1.3) and the diver was on Cialis.:shocked2: Vann et al did studies with rats showing increased cerebral blood flow and accelerated O2 seizures on Cialis in rats at 6 ATA.

I hope they can do further studies on other meds, as decongestants seem to be a common theme. Further, if ED medications cause increased CBF, it stands to reason perhaps BP meds would do the same.

A big thanks to Gene Hobbs and others for trying to get quality information to divers!

There is a link to the Dan workshop in Gene's post, I think on page 2 of this thread.

Thanks,
Ben

 

[Anti-Hero]

In Dick Vann's presentation for the Dan Tech Diving Workshop, he mentioned a study done by Schaefer on free divers becoming less sensitive to elevated CO2 levels when doing a lot of diving. After a 3 month layoff their sensitivity to increased CO2 had returned to normal. I wonder if your mentioned increase in O2 sensitivity could actually be attributed to insensitivity to Co2 leading to a lower tox threshold.

He also discussed a study done by Donald where a single diver breathed 100% O2 at 70' twice a week for 19-20 total dives. Times for onset of symptoms ranged from 7 -148 minutes - the graph didn't seem to show increasing sensitivity, it was all over the place.

Other tidbits from the workshop/convention that I found interesting:

Dr. Morris (sp) presentation on the Shaw accident and how gas density can lead to "effort independent exhalation" and elevated CO2. The physiologic mechanism of this was enlightening.

Static lung loads, negative and positive.

A non-fatal o2 hit (1.3) and the diver was on Cialis.:shocked2: Vann et al did studies with rats showing increased cerebral blood flow and accelerated O2 seizures on Cialis in rats at 6 ATA.

I hope they can do further studies on other meds, as decongestants seem to be a common theme. Further, if ED medications cause increased CBF, it stands to reason perhaps BP meds would do the same.

A big thanks to Gene Hobbs and others for trying to get quality information to divers!

There is a link to the Dan workshop in Gene's post, I think on page 2 of this thread.

Thanks,
Ben

I also watched the video of the Shaw accident and found the WOB, and static loading very interesting.

Was the diver who went to 70' twice a week on 100% 02, in a warm, dry chamber, just sitting? There is also speculation that chamber rides in relation to partial pressures don't accurately take into account physical exertion or environmental factors like cold water.

Interesting none the less.

 

[Gene_Hobbs]

Dr. Morris (sp) presentation on the Shaw accident and how gas density can lead to "effort independent exhalation" and elevated CO2. The physiologic mechanism of this was enlightening.

It was Dr. Simon Mitchell... They also published a paper on the analysis that goes a little deeper than his presentation. (Another ASEM article so it is free as well):

Mitchell SJ, Cronjé FJ, Meintjes WA, Britz HC (February 2007). "Fatal respiratory failure during a "technical" rebreather dive at extreme pressure". Aviat Space Environ Med 78 (2): 81–6. PMID 17310877.

This link and the link to the YouTube video of his fatality are on wikipedia: David Shaw (diver)

A big thanks to Gene Hobbs and others for trying to get quality information to divers!

Thanks Ben! Always good to hear our work is appreciated!

 

[Papa_Bear]

I really enjoy these types of discussions, thanks to everyone who is trying to contribute! I always learn something even if it because I am researching my own point of view!

The last post is interesting in what effect skip breathing might have with Co2 build up delaying toxicity? One of the reasons I like Nitrox is as an old time diver and a Photographer I tend to skip breath and don't get the associated head ache with the enriched air and I have always assumed it was the higher O2 levels that are washing out the Co2 evening all things out in my blood.....???? Nitrox is invaluable in cave and survey diving that I have done and it is the only way I can get in 5 or 6 dives a day with my camera!

 

[garyfotodiver]

You are being very defensive for no reason. I am not attacking you personally and you are entitled to your opinion. However, what do you expect to learn from "experience" by diving nitrox? The science and the math won't change. You have chosen to adopt a "trust me" approach to diving nitrox and then "understand more about it" at a later date. Kind of backwards as far as I am concerned but to each his own. However, I find it surprising that you would state that you would not let me teach your children. Where did that come from? Do you feel more comfortable passing on agency recommendations as the gospel without understanding what is going on? Is that what you want for your children also? Again, this is entirely your choice and it is your family.

Also, where is this "teach new divers other than to dive within their limits" stuff coming from? What exactly do you think I am teaching? Where have I said that I am teaching divers to diver outside their limits? Do you think the math involved in nitrox diving is so complicated that the average diver can not understand it? No offense but you are the product of a diving industry that at one time perpetuated the myth that the math involved with "the devils gas" was entirely too complicated for the average diver and if you just "trust us" you will be okay. I am not an advocate of that position and do not encourage it in my instruction. If you feel more comfortable with that type of training for your family then their are several online nitrox classes that you will be happy with.

Finally, your profile states that you have logged between 250-500 dives in your stated 40 years of experience. That works out to something like 10-15 dives a year. Do you feel this is adequate experience to decide who should teach diving to your children?

Congratulations on being a recreational diver. So am I.

The one who is defensive is you, sir. Your profile states you are an instructor; therefore, you are a professional, not a recreational diver. I have learned the math involved concerning EAN; the physics involved with diving does not change. We do, hopefully, learn additional information concerning this activity, and others as well, with the passage of time. I choose to be conservitive - that is my choice.

The OP is, apparently, a new recreational diver. I maintain that the discussion should remain within the limits of the question asked. Someone who is new at a particular activity, like me with EAN, should take things slowly and carefully. Discussions involving tech diving with long multi-stage decompressions or suggestions to do other than what one was initialy taught may, in my opinion, cause someone serious issues.

It is all a matter of risk management. The risks that should be incurred by a new, recently trained diver (or anyone who has just acquired a new knowledge skillset) must be less than those incurred by a more experienced person. One must learn crawling before walking or running. This is mere prudent common sense.

As for my judgement as to who might or might not teach my children diving (or any other activity), I have 56 years of life experience behind me. Additionally, I have a moral and a legal reaponsibility to them. I teach my children to continually expand their horizions, but first give them a solid grounding in the basics. After reading your second post, my opinion concerning your ability to teach my children is greatly reinforced. I believe that you would not meet my criteria.

And this is my final point; EVERYTHING on this - or any other - board is opinion.

 

[nereas]

I did not know Bismark claims to be an instructor. I keep him muted to save bandwidth. So I saw it in your quote.

The best solution to anything upsetting is the mute feature, besides saving bandwidth as well.

In logic, everything is either fact or opinion.

Fact: there is water all over the place;

Opinion: it rained.

 

[nereas]

Aviat Space Environ Med. 2006 May;77(5):526-32.Links
CNS toxicity in closed-circuit oxygen diving: symptoms reported from 2527 dives.

Arieli R, Shochat T, Adir Y.
Israel Naval Medical Institute, IDF Medical Corps, Haifa, Israel. rarieli@netvision.net.il
INTRODUCTION: Oxygen toxicity is a problem in diving and can have fatal consequences in the water. Various aspects of oxygen diving have been studied in dry hyperbaric chambers, but there is a lack of information on in-water diving using closed-circuit oxygen apparatus. METHOD: We collected 2527 dive reports from 473 closed-circuit oxygen divers (a mean of 5.2 reports per diver), and analyzed the relationships between various symptoms and their dependence on depth and diving time. RESULTS: No CNS oxygen toxicity-related symptoms were reported at a depth of 2 m seawater (msw), but their proportion increased at depths from 3 to 6 msw. We found that CNS oxygen toxicity-related symptoms appeared in 2.5% of dives conducted at a Po2 of 119 kPa. The main symptoms and signs reported were headache: 4.5%; nausea: 2.6%; hyperventilation: 2.6%; heavy breathing: 2.4%; dizziness: 1.6%; hiccups: 1.5%; bloody sputum: 1.4%; cold shivering: 1.1%; tinnitus: 0.9%; difficulty maintaining a steady depth: 0.9%; disorientation: 0.6%; tiredness: 0.5%; tingling in the limbs: 0.4%; hearing disturbances: 0.4%; a choking sensation: 0.4%; extreme effort: 0.4%; and loss of consciousness: 0.3%. DISCUSSION: Environmental factors, light vs. dark and temperature, had no effect on symptoms. The number of symptoms increased with diving time. Divers who experienced amnesia, facial twitching, hearing disturbances (p < 0.001), and disorientation (p < 0.014) were prone to suffer loss of consciousness. It was found that some divers are more sensitive to oxygen than others (p < 0.0001).

I would be useful if these units were ATAs rather than kPa, Thal.

As long as we are talking about CCRs, again. [Apples and oranges.]

 

[ucfdiver]

I choose to be conservitive - that is my choice.

I think I can hopefully shed some light on what he's talking about, maybe you're not fully understanding him, because what I'm reading is far from someone acting like a dare devil.

When I first dove nitrox, I chose to blindly follow agency standards. Now, I've chosen to do more research, and can honestly say that I'm conservative.

Example-
One of my pet peeves are people who dive nitrox to be conservative, yet push NDL limits. If you're at 99.99% of your m value, it doesn't matter how you got there, 40% or 21% in the breathing mix, you're riding the NDL REALLY hard. Also, I've noticed that several divers who dive nitrox on air tables or an air computer because it's "conservative" will turn around and dive air the very next weekend on a similar profile! Or people who dive Nitrox as Air for safety, yet don't bother staying in shape or hydrating themselves before a dive. This is a classic example of the downside that comes along with the diving industry pumping out as many students as they do today.

I did not know Bismark claims to be an instructor. I keep him muted to save bandwidth. So I saw it in your quote.

The best solution to anything upsetting is the mute feature, besides saving bandwidth as well.

In logic, everything is either fact or opinion.

Fact: there is water all over the place;

Opinion: it rained.

Actually, "it rained" would be an inference if you weren't there to witness it, or a fact if you were. An opinion would be "It's not safe to drive in these wet conditions".
http://www.google.com/search?hl=en&...l&hs=r0l&q=fact+opinion+inference&btnG=Search

 

[Bismark]

The one who is defensive is you, sir. Your profile states you are an instructor; therefore, you are a professional, not a recreational diver. I have learned the math involved concerning EAN; the physics involved with diving does not change. We do, hopefully, learn additional information concerning this activity, and others as well, with the passage of time. I choose to be conservitive - that is my choice.

The OP is, apparently, a new recreational diver. I maintain that the discussion should remain within the limits of the question asked. Someone who is new at a particular activity, like me with EAN, should take things slowly and carefully. Discussions involving tech diving with long multi-stage decompressions or suggestions to do other than what one was initialy taught may, in my opinion, cause someone serious issues.

It is all a matter of risk management. The risks that should be incurred by a new, recently trained diver (or anyone who has just acquired a new knowledge skillset) must be less than those incurred by a more experienced person. One must learn crawling before walking or running. This is mere prudent common sense.

As for my judgement as to who might or might not teach my children diving (or any other activity), I have 56 years of life experience behind me. Additionally, I have a moral and a legal reaponsibility to them. I teach my children to continually expand their horizions, but first give them a solid grounding in the basics. After reading your second post, my opinion concerning your ability to teach my children is greatly reinforced. I believe that you would not meet my criteria.

And this is my final point; EVERYTHING on this - or any other - board is opinion.

Diving knowledge is not the sole repository of diving instructors. Several divers I know are not instructors yet are a wealth of diving knowledge. The only thing that separates us is I have training in how to teach diving. The subject matter itself is available for anyone to learn. Recreational diver, technical diver, instructor, are all points on a curve and not end points in and of themselves. The fact that you draw a line between an instructor and a recreational diver does say something about your mindset in regards to diving knowledge though. Diving knowledge is available for all to learn and if you chose to include learning how to teach, that is something else but not necessarily linked to learning the knowledge itself.

You state that "We do, hopefully, learn additional information concerning this activity, and others as well, with the passage of time" in reference diving nitrox. What exactly do you think you are going to learn from your experience diving nitrox? I applaud your decision to be conservative in your diving but how does "Someone who is new at a particular activity, like me with EAN, should take things slowly and carefully" apply to diving nitrox? Both statements clearly demonstrate a misunderstanding of EAN and using it as a diving gas. This is further demonstrated by your mistaken analogy where you compare air and nitrox diving to crawling and walking. It simply does not work that way.

Finally, you state that "I teach my children to continually expand their horizions, but first give them a solid grounding in the basics", yet when I suggested that you learn more than what an agency dictates as being "enough" you accuse me of teaching people to dive "beyond their limits". It has nothing to do with diving beyond their limits and everything to do with providing all the information to divers so they can make informed decisions.

I am sorry that you seem to have taken this so personally. I mean no disrespect to you and do not challenge your position as your children's protector and guardian. I have also not asked to be considered to teach your children. You do not know me and I do not know you. I would urge you to seek out more information regarding nitrox diving so that you can approach this issue from a position of knowledge and make decisions from that vantage point. That would indeed be the prudent thing to do.

Some things like science and physics are not matters of opinion.