Maybe other people said it, but they got their posts removed by moderators?
OXTOX limits - MOD, PPO2 or CNS Clock?
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Only you, Howard.
How about turning the discussion to something worthwhile? If someone is diving 100fsw on EAN36, the PPO2 would be 1.44, but if he were at EAN40, his PPO2 woud be 1.6.
Given that the 1.6ATA has a single dive Oxygen Presure time limit of 45min, is it so impossible to believe a recreational diver could have been affected enough to go OOG and not have the wherewithal to recover?
The above is purely speculative, and I am sure you will immediately point out the slightest discrepancy, real or imagined.
Oldie but goodie:
Lambertsen CJ, Ewing JH, Kough RH, Gould R, Stroud MW. Oxygen toxicity. Arterial and internal jugular blood gas composition in man during inhalation of air, 100% O2 and 2% CO2 in O2 at 3.5 Atmospheres Ambient Pressure. J Appl Physiol 8: 255-263, 1955.
Describes higher doses of O2 due to cerebral vasodilation from increased CO2.
////////////////////////////////////////////////////////////////////////
And a modern summary found in Rubicon's archive:
Rubicon Research Repository: Item 123456789/21
...................just to throw in some more uncertainty.
Just say NO to skip breathing on Nitrox.
-matt
Lambertsen CJ, Ewing JH, Kough RH, Gould R, Stroud MW. Oxygen toxicity. Arterial and internal jugular blood gas composition in man during inhalation of air, 100% O2 and 2% CO2 in O2 at 3.5 Atmospheres Ambient Pressure. J Appl Physiol 8: 255-263, 1955.
Describes higher doses of O2 due to cerebral vasodilation from increased CO2.
////////////////////////////////////////////////////////////////////////
And a modern summary found in Rubicon's archive:
Rubicon Research Repository: Item 123456789/21
...................just to throw in some more uncertainty.
Just say NO to skip breathing on Nitrox.
-matt
drrich2
Contributor
Most of this thread is over my head. I have seen some themes that bear a question or two, though. Pulling a couple of statements out of their original posts to illustrate the idea:
I see the logic behind these observations, particularly when there's a concern a rescue attempt would be refused (though I question the likelihood of that, it could in theory happen). But otherwise, a key question is: What audience are you playing to?
An old teacher of mine years ago told me you can broadly divide people into splitters & lumpers. I take it splitters like to finely discriminate, really get into things, and lumpers like to 'get the gist.' Applying that philosophy to some Nitrox-related threads on this forum, I suspect Nitrox users might roughly (from a lumper's perspective) fall into 2 categories:
1.) 'License to dive EAN 32' types - recreational divers who need certification to get the EAN 32 tanks at Bonaire or on Live-aboards, never mix their own, don't mess with custom mixes, don't go over the MOD for a mix & don't really think much about it otherwise. Certainly don't do any calculating. Won't remember the more technical aspects of their course material well, or review the manual much. Mainly need to stay shallow enough to stay out of higher risk ox tox territory. Give them a strict depth not to exceed so they don't seize, & warn them that nitrox can still cause narcosis, much like air can.
2.) Technically inclined EAN users - may be recreational or tech., but either due to need due to type of diving, or simply an inherent 'need to get into it and know' personality type, these people want to learn and ideally retain the more technical aspects of the training, and to have presented to them the theoretical basis for the proposed limits. Some of these folks might decide to make their own decision & exceed an oxygen clock rating of 100%. Or briefly dive just over the 1.6 depth for something special. Or just plain want to know 'why?'
The problem is, you can bore the living crap out of category 1 people trying to teach to category 2 people, and if you bore them badly enough, they may not even retain the 'just keep them alive' stuff. It's like tell me 1 thing I remember it, tell me 5 things I remember 2 or 3, tell me 10 & I may remember none of it.
For 'entry level' nitrox courses like PADI's, the current system seems adequate to me, for what a lot of students actually go on to do with it. I would expect a technically oriented course, or one taught by an agency such as GUE that seems to have an advanced focus from the git-go, to be more oriented toward category 2 divers.
What about you guys? If we did a random sample of 100 nitrox-certified divers who actually dive at least once per year, what percentage do you estimate would be category 1? What percentage category 2?
Richard.
I see the logic behind these observations, particularly when there's a concern a rescue attempt would be refused (though I question the likelihood of that, it could in theory happen). But otherwise, a key question is: What audience are you playing to?
An old teacher of mine years ago told me you can broadly divide people into splitters & lumpers. I take it splitters like to finely discriminate, really get into things, and lumpers like to 'get the gist.' Applying that philosophy to some Nitrox-related threads on this forum, I suspect Nitrox users might roughly (from a lumper's perspective) fall into 2 categories:
1.) 'License to dive EAN 32' types - recreational divers who need certification to get the EAN 32 tanks at Bonaire or on Live-aboards, never mix their own, don't mess with custom mixes, don't go over the MOD for a mix & don't really think much about it otherwise. Certainly don't do any calculating. Won't remember the more technical aspects of their course material well, or review the manual much. Mainly need to stay shallow enough to stay out of higher risk ox tox territory. Give them a strict depth not to exceed so they don't seize, & warn them that nitrox can still cause narcosis, much like air can.
2.) Technically inclined EAN users - may be recreational or tech., but either due to need due to type of diving, or simply an inherent 'need to get into it and know' personality type, these people want to learn and ideally retain the more technical aspects of the training, and to have presented to them the theoretical basis for the proposed limits. Some of these folks might decide to make their own decision & exceed an oxygen clock rating of 100%. Or briefly dive just over the 1.6 depth for something special. Or just plain want to know 'why?'
The problem is, you can bore the living crap out of category 1 people trying to teach to category 2 people, and if you bore them badly enough, they may not even retain the 'just keep them alive' stuff. It's like tell me 1 thing I remember it, tell me 5 things I remember 2 or 3, tell me 10 & I may remember none of it.
For 'entry level' nitrox courses like PADI's, the current system seems adequate to me, for what a lot of students actually go on to do with it. I would expect a technically oriented course, or one taught by an agency such as GUE that seems to have an advanced focus from the git-go, to be more oriented toward category 2 divers.
What about you guys? If we did a random sample of 100 nitrox-certified divers who actually dive at least once per year, what percentage do you estimate would be category 1? What percentage category 2?
Richard.
OP
DevonDiver
N/A
I think there is some confusion about the teaching objectives of a course...
Some courses teach what you need to know. The OW course is a fine example of this. As courses get more technical, they go into more detail.... but (relative for their level) they still only teach you what you need to know.
i.e. 'Don't exceed this limit, as it is dangerous' OR 'Perform this skill, as instructed, as it is best'.
In general, most courses supplement the 'need to know' data with sufficient background to ensure validity and understanding.
This could be illustrated by:
Bare Minimum 'Need to Know' = Don't hold your breath when diving...
Basic Supplementation = ...because it can cause lung injury if you hold your breath...
Developed Supplementation = .... due to expanding air rupturing the lung...
More Supplementation = .... which can lead to several types of lung-overexpansion injuries...
Advanced Supplementation = ...such as pneumothorax, subcutaneous emphasema, arterial gas embolism or mediastinal emphsema....
More Advanced Supplementation = ...which consist of the following symptoms, as the following effects take place inside the body....
Very Advanced Supplementation = ...which are treated by administering O2 and immediate evacuation to professional medical care, as an emergency case.
At what point does supplementation develop into an entirely new subject?
At what point is the student 'overwhelmed' by data and 'lose' the initial goal of training?
In the respect of THIS debate..... is it really necessary for a Nitrox student (maybe fresh off their OW course...) to understand how PPO2 develops over time, in respect of CNS build-up...or the phsiological mechanisms that describe why and how this can happen??
The goal of the nitrox course if for divers to utilise nitrox in a safe way and enjoy the benefits that it can bring. In respect of that goal... they just need to know that they should never exceed PPO2 1.4 (1.6 in contingency) or their MOD...and to utilise the correct tables/computer and procedures for the planning and conduct of their dives...
Some courses teach what you need to know. The OW course is a fine example of this. As courses get more technical, they go into more detail.... but (relative for their level) they still only teach you what you need to know.
i.e. 'Don't exceed this limit, as it is dangerous' OR 'Perform this skill, as instructed, as it is best'.
In general, most courses supplement the 'need to know' data with sufficient background to ensure validity and understanding.
This could be illustrated by:
Bare Minimum 'Need to Know' = Don't hold your breath when diving...
Basic Supplementation = ...because it can cause lung injury if you hold your breath...
Developed Supplementation = .... due to expanding air rupturing the lung...
More Supplementation = .... which can lead to several types of lung-overexpansion injuries...
Advanced Supplementation = ...such as pneumothorax, subcutaneous emphasema, arterial gas embolism or mediastinal emphsema....
More Advanced Supplementation = ...which consist of the following symptoms, as the following effects take place inside the body....
Very Advanced Supplementation = ...which are treated by administering O2 and immediate evacuation to professional medical care, as an emergency case.
At what point does supplementation develop into an entirely new subject?
At what point is the student 'overwhelmed' by data and 'lose' the initial goal of training?
In the respect of THIS debate..... is it really necessary for a Nitrox student (maybe fresh off their OW course...) to understand how PPO2 develops over time, in respect of CNS build-up...or the phsiological mechanisms that describe why and how this can happen??
The goal of the nitrox course if for divers to utilise nitrox in a safe way and enjoy the benefits that it can bring. In respect of that goal... they just need to know that they should never exceed PPO2 1.4 (1.6 in contingency) or their MOD...and to utilise the correct tables/computer and procedures for the planning and conduct of their dives...
But it would seem that people aren't making use or understanding the CNS or OTU clock or tables.
The details with over-expansion injuries are not needed since you can take care of it easily by just breathing and there are not that many incidences.
There are tons of people and seemingly more every day using nitrox with few incidences on the CNS side. The guidelines of 1.4 and knowing your MOD take care of it certainly, but in the example someone put forth above or rescues and liveaboards would illustrate the need for a little more knowledge.
I have never been on a true 5x a day liveaboard. But diving banked 36% to 60-80 feet 3-5 times a day means you might have a bigger does cumulatively during 12hrs than many "tech" divers. The opposite being true for a rescue after a low dose exposure or not diving for 12hrs; there would be plenty of clock time for you. You don't hop in the water without understand your Residual Nitrogen time; same should go for CNS and OTU. Just a basic off the top of your head calculation would do.
Averaging 1.1 PO2 with 36% at 70 feet average gives you more bottom time than you'd probably use. But if you last 60min per dive and actually dive 5x a day then that is 300min at 1.1 ATA, past the 24hr dose of 270min. (is it possible that people do 5 dives a day like this on a liveaboard? If so I want to go!)
Really just dive planning, but you now have the sense that you should not be the guy diving down to 150' for an emergency if 36% (2.0 ATA PO2 @ 150') is the only thing in the tank rack. If I had not been diving in 6-12 hrs I would not hesitate to jump in, the CNS clock also clears fast.
As Howard was saying, time is a VERY key element to it. Essentially that's all you have to explain on top of MOD and PO2. That would make for pretty deep understand without much extra time teaching.
PO2 of 2 ATA is fine, just not for very long or if you've had a recent dose.
-matt
Good points Richard. The 32% vanilla system works really well for a variety of reasons even for the biggest lumper of the lumpers. I would imagine that category 1 and 2 self select and seek out what appeals to them. They are both well served well by PADI(etc.) and GUE respectively.
I just don't like douche-bags on boats spouting BS, getting people all wound up. It's fine to say you don't really know or it's a little uncertain.
The difference between the liar and and BS'er. The liar tells untruths to get something or to deceive; the BS'er actually believes their own lies and that is more dangerous in many instances.
-matt
There was a thread here on SB... not too long ago, where a poster posted essentially that he was in need of getting his buddies attention, but his buddy went a little too deep, and he didn't want to exceed his MOD, and as I recall he opted to separate from his buddy because he didn't know what else to do. If you ask me... The way it's being explained now, on the basic level is incomplete, and leads people to exercise TOO MUCH fear of MOD, instead of having a better understanding.
Basic nitrox classes don't even require diving anymore.
All it takes is the addition of the words "TIME" to the equation, that OX TOX is a function of EXPOSURE + TIME at exposure.
Andy - I understand your defense of instructors, but the aforementioned thread (wherever it is here on SB) is a real life situation, where prudence was opted out on because of the current instruction methods... that's all
Basic nitrox classes don't even require diving anymore.
All it takes is the addition of the words "TIME" to the equation, that OX TOX is a function of EXPOSURE + TIME at exposure.
Andy - I understand your defense of instructors, but the aforementioned thread (wherever it is here on SB) is a real life situation, where prudence was opted out on because of the current instruction methods... that's all
OP
DevonDiver
N/A
Andy - I understand your defense of instructors, but the aforementioned thread (wherever it is here on SB) is a real life situation, where prudence was opted out on because of the current instruction methods... that's all
I didn't read the thread, but I can think of several experiences that I've had which also illustrate that.
It's a fine balancing act to teach the concept of O2 Exposure vs Risk Avoidance.
I like to be strict on my courses. Getting students to plan and conduct their nitrox dives. I am firm that they are not to exceed the planned MOD on the training dives. I'll normally test that awareness, by seeing if they go into 'sheep' mode and follow me (slightly) below the MOD without noticing.
In that case, it is really awareness and discipline that I am teaching - rather than the need to fear going below PPO2 1.4 /1.6 if an emergency dictates it.
I know other instructors have simular approaches. I suppose, unless that point is clearly explained to the student, then they could easily have a false impression left at the end of the course?!
I also guess that many instructors don't wish to engage in too much detailed debate about the specifics of OXTOX risk.... as this could weaken the overall safety message they are trying to ingrain into their students.
The worst example of this that I can give is; an instructor I used to work with, who decided to chat with my nitrox class whilst on a dive boat. He proceeds to tell them that "95% of people are immune to oxygen toxicity". I nearly hit him....
Whilst his point was open to debate.... as his logic came from OXTOX stats from chamber dives... it was a terrible message to be sending to the students - who were not at a level of knowledge and experience to assess the merits of such a debate... and who may have exposed themselves to future risk because of that advice from an 'expert'.
IMHO, it is far safer for them to know that it is dangerous to exceed your MOD for PPO2 1.4.
Again... I guess the viewpoint in this discussion is determined by whether you see the primary focus of a nitrox course to increase knowledge or to permit safe nitrox diving..... as these are very different objectives.
Only you, Howard.
How about turning the discussion to something worthwhile? If someone is diving 100fsw on EAN36, the PPO2 would be 1.44, but if he were at EAN40, his PPO2 woud be 1.6.
Given that the 1.6ATA has a single dive Oxygen Presure time limit of 45min, is it so impossible to believe a recreational diver could have been affected enough to go OOG and not have the wherewithal to recover?
The above is purely speculative, and I am sure you will immediately point out the slightest discrepancy, real or imagined.
This is quite simply a poor dive plan.
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