EaNX and PPO2 of 1.6

[jim2386]

Hey guys,

I'm going to be diving the Oriskany in a few weeks with a dive group and we will be diving nitrox. I've been certified to use it for over 2 years but have never found the opportunity to use it (air has worked fine for all my ocean dives since we'd do a deep dive then a shallow dive, shallow cavern diving etc.) . My computer can handle nitrox and I'm familiar with the rules etc. but I think maybe during my classes I misunderstood my teacher and just would like some clarification.

My instructor said the limit for PPO2 is 1.6. Now is that limit tied to the same limit as your O2 clock? Let me see if I can explain what I thought he meant and then what my confusion is.

When I first took the class, my understanding was PP02 1.6 was THE limit. If you hit 1.65 you instantly black out from OxTox. This was seperate from your O2 clock where if you reached 100%+ of your O2 clock limit, you'd black out from OxTox. They were two seperate ways to croak....for lack of a better term lol.

Now that I'm thinking about it. What if it's your first dive of the day on nitrox and you go straight to the bottom and hit PPO2 1.65 for say 1 minute and come back to a level where your PP02 is 1.3 or so. Is what my instructor was trying to say was "If you go below PP02 1.6 your O2 clock is used up much much faster so you consider it "instantly" using up 100% of your O2 clock because it only takes maybe 10 minutes to use it up at PP02 1.6?"

The reason I ask is we will be diving 29% O2 and at the beginning of the dive we're planning on touching the deck at 137'. This puts me at a PP02 of 1.58. We would only stay for a minute or two and then go hang out around 110' and shallower. Now I can have my computer beep at me if I were to hit PP02 1.6, but if something goes wrong (heaven forbid) and I get distracted for a second or take a second to become neutrally bouyant and accidentlly go slightly over PP02 1.6 I'm not going to black out right?

Sorry if it's a stupid question, just like to be very prepared for things (taking my rescue diver classes this weekend, I guess it's rubbing off on me already :D ).

Thanks for your responses in advance!
Jim

[crpntr133]

Your probably not going to black out and die if your Po2 is 1.6. Everyones tolerance levels are a bit different. Figure it at 1.4 if you want.
Talk to some of those that have been around and you will find some that use to dive to PO2 of 2.0. Not really advised to do that now but.

[S&V]

Jim,
Just as a quick OBTW, reports from divers going to the Oriskany since the passage of Hurricane Gustav say that the previously known depth checkpoints are now about 10 ft deeper. The ship must have settled into the seabed. Anyway, the flight deck is now likely at 145 or so...
http://www.scubaboard.com/forums/deep-dixie-divers/251765-oriskany-post-gustav-report.html

[lamont]

When I first took the class, my understanding was PP02 1.6 was THE limit. If you hit 1.65 you instantly black out from OxTox. This was seperate from your O2 clock where if you reached 100%+ of your O2 clock limit, you'd black out from OxTox. They were two seperate ways to croak....for lack of a better term lol.


there is no "instant croak" limit.

you might be able to do a 30 minute dive on 2.3 and not have an issue. the next day at 2.1 you might tox after 5 minutes.

technical divers do 1.6 on decompression stops where they're trying to push higher ppO2s in order to decompress and they are (ideally) decompressing at rest. they also don't spend much time there.

for recreational divers the recommended limit is 1.4 since you may be at that limit for longer and may be under some exertion (swimming around, fighting current, chasing your buddy, whatever). planning for 1.4 on the bottom also gives some leeway where an accidental short excursion deeper to 1.6 isn't likely to cause you to tox.

for longer exposures and/or if you're decompressing afterwards with high ppO2 decompression gases, then you should think about backing off your ppO2 on the bottom to 1.3 or 1.2

[nereas]

Hey guys,

I'm going to be diving the Oriskany in a few weeks with a dive group and we will be diving nitrox. I've been certified to use it for over 2 years but have never found the opportunity to use it (air has worked fine for all my ocean dives since we'd do a deep dive then a shallow dive, shallow cavern diving etc.) . My computer can handle nitrox and I'm familiar with the rules etc. but I think maybe during my classes I misunderstood my teacher and just would like some clarification.

My instructor said the limit for PPO2 is 1.6. Now is that limit tied to the same limit as your O2 clock? Let me see if I can explain what I thought he meant and then what my confusion is.

When I first took the class, my understanding was PP02 1.6 was THE limit. If you hit 1.65 you instantly black out from OxTox. This was seperate from your O2 clock where if you reached 100%+ of your O2 clock limit, you'd black out from OxTox. They were two seperate ways to croak....for lack of a better term lol.

Now that I'm thinking about it. What if it's your first dive of the day on nitrox and you go straight to the bottom and hit PPO2 1.65 for say 1 minute and come back to a level where your PP02 is 1.3 or so. Is what my instructor was trying to say was "If you go below PP02 1.6 your O2 clock is used up much much faster so you consider it "instantly" using up 100% of your O2 clock because it only takes maybe 10 minutes to use it up at PP02 1.6?"

The reason I ask is we will be diving 29% O2 and at the beginning of the dive we're planning on touching the deck at 137'. This puts me at a PP02 of 1.58. We would only stay for a minute or two and then go hang out around 110' and shallower. Now I can have my computer beep at me if I were to hit PP02 1.6, but if something goes wrong (heaven forbid) and I get distracted for a second or take a second to become neutrally bouyant and accidentlly go slightly over PP02 1.6 I'm not going to black out right?

Sorry if it's a stupid question, just like to be very prepared for things (taking my rescue diver classes this weekend, I guess it's rubbing off on me already :D ).

Thanks for your responses in advance!
Jim

Thal (Thallassamania from Hawai'i) gave a great explanation of that in a thread recently here:

http://www.scubaboard.com/forums/3779348-post188.html

Ox Tox hits normally occur well beyond !.6 ATAs of ppO2. However, the retail scuba training agencies all agree on 1.4 ATAs as the limit to ensure that Ox Tox seizure never occurs. So that is what they teach to novices. Then you are on your own to figure out exactly what the limits mean.

At a ppO2 of 1.6 ATAs your maximum safe exposure time is 45 minutes. However your NDL limit with basic nitrox is going to be a lot less than this, therefore even at 1.6 you are going to be quite safe from Ox Tox seizures, simply because NDL limits are a lot less.

There are all sorts of inexperienced novices that think 1.4 is magic, and that anything more is UN-safe, and that at 1.4 you are absolutely safe.

In reality, at 1.4 ATAs ppO2 your maximum safe exposure time is 150 mins, which is just a larger safety margin for NDL scuba, that's all.

If you should ever progress beyond simple NDL diving, on to CCR, SCR, or deco diving, you will learn that 1.2 ATAs is the limit that you should consider, due to the long underwater times, sometimes which may also be at the 1.6 ATA limit point. However for your current NDL diving, this is not at issue.

[jim2386]

Thanks guys, makes me feel a lot better. Like I said, the dive leaders said the longest we'd stay is to touch the deck and head back up. Thanks for not flaming me, just trying to be safe and have a really good experience at the same time! :D I figured the dive instructors here who've dove it many many many times knew what they were talking about, but for my own knowledge it makes me feel much more comfortable!

[Charlie99]

NOAA's best guess at the relative risks can be found in the table at the very bottom of this article: DAN Divers Alert Network : OXTOX: If You Dive Nitrox You Should Know About OXTOX (http://diversalertnetwork.org/medical/articles/article.asp?articleid=35) That table implies that the CNS clock runs 4 times faster at 2.0ppO2 than at 1.6ppO2.


When I first took the class, my understanding was PP02 1.6 was THE limit. If you hit 1.65 you instantly black out from OxTox. This was seperate from your O2 clock where if you reached 100%+ of your O2 clock limit, you'd black out from OxTox. They were two seperate ways to croak....for lack of a better term lol.This seems to be a pretty common misconception, but with many instructors leaving their student thinking that they will black out as soon as they pass 1.4ppO2. It is definitely just a time-dose sort of thing. The clock runs faster at higher ppO2. CNS is a highly variable, not only person-to-person but also from day-to-day with the same person. So the limits have a pretty large margin of safety, very appropriately since CNS convulsions is likely to lead to drowning.

[CoralSeaMan]

If you are a recreational diver, you should not exceed your training even if an instructor is along. These things are not very predictable but if you are going to the 145 foot range your are exceeding every limit you have been trained for.

[Gene_Hobbs]

http://www.scubaboard.com/forums/3779348-post188.html


Dick's write up there is a great refresher... Some other resources worth checking out if you have the time are:
*wikipedia nitrox article (http://en.wikipedia.org/wiki/Enriched_Air_Nitrox) -needs some work but not bad, check out reference #3 (http://archive.rubicon-foundation.org/4855) as well.
*DAN Tech Conference talk on O2 tox (http://www.diversalertnetwork.org/FastAccess/2008TechnicalDiving.aspx)
and if you are really having fun (and still awake)...
*Rubicon Research Repository suggested reading list - oxygen toxicity (http://rubicon-foundation.org/RRR_reading.html#Oxygen)

Have fun on the trip!

[ucfdiver]

Isn't your partial pressure of nitrogen a bit too high at 140-150ft as well? I would be VERY concerned about my reaction time if a buddy needed me.

[Oside Jimc]

Just curious and wanting to learn, but why not just go to tri-mix for a dive like this? Seems like a safer mix all around for such a deep dive.

[String]

Just curious and wanting to learn, but why not just go to tri-mix for a dive like this? Seems like a safer mix all around for such a deep dive.

The huge increase in cost and skills needed. Trimix will cost roughly 8x per dive than nitrox here at least.
Also you need to be proficient in stage handling for decompression and various other things.

[jviehe]

Hey guys,

I'm going to be diving the Oriskany in a few weeks with a dive group and we will be diving nitrox. I've been certified to use it for over 2 years but have never found the opportunity to use it (air has worked fine for all my ocean dives since we'd do a deep dive then a shallow dive, shallow cavern diving etc.) . My computer can handle nitrox and I'm familiar with the rules etc. but I think maybe during my classes I misunderstood my teacher and just would like some clarification.

My instructor said the limit for PPO2 is 1.6. Now is that limit tied to the same limit as your O2 clock? Let me see if I can explain what I thought he meant and then what my confusion is.

When I first took the class, my understanding was PP02 1.6 was THE limit. If you hit 1.65 you instantly black out from OxTox. This was seperate from your O2 clock where if you reached 100%+ of your O2 clock limit, you'd black out from OxTox. They were two seperate ways to croak....for lack of a better term lol.

Now that I'm thinking about it. What if it's your first dive of the day on nitrox and you go straight to the bottom and hit PPO2 1.65 for say 1 minute and come back to a level where your PP02 is 1.3 or so. Is what my instructor was trying to say was "If you go below PP02 1.6 your O2 clock is used up much much faster so you consider it "instantly" using up 100% of your O2 clock because it only takes maybe 10 minutes to use it up at PP02 1.6?"

The reason I ask is we will be diving 29% O2 and at the beginning of the dive we're planning on touching the deck at 137'. This puts me at a PP02 of 1.58. We would only stay for a minute or two and then go hang out around 110' and shallower. Now I can have my computer beep at me if I were to hit PP02 1.6, but if something goes wrong (heaven forbid) and I get distracted for a second or take a second to become neutrally bouyant and accidentlly go slightly over PP02 1.6 I'm not going to black out right?

Sorry if it's a stupid question, just like to be very prepared for things (taking my rescue diver classes this weekend, I guess it's rubbing off on me already :D ).

Thanks for your responses in advance!
Jim
The 02 clock is to protect you from pulminary toxicity, damage to your lungs. But, I would recommend rereading your nitrox book.

[Charlie99]

The 02 clock is to protect you from pulminary toxicity, damage to your lungs. But, I would recommend rereading your nitrox book.I see that you are a scuba instructor.

Are you qualified to teach nitrox classes, and if so, is this what you teach ??

For which agency?

Do teach about CNS toxicity calculations in addition to pulmonary toxicity calculations? If the "O2 clock" is pulmonary-related, what do you call the CNS related calculations, if anything?

--------------------

[jviehe]

I see that you are a scuba instructor.

Are you qualified to teach nitrox classes, and if so, is this what you teach ??

For which agency?

Do teach about CNS toxicity calculations in addition to pulmonary toxicity calculations? If the "O2 clock" is pulmonary-related, what do you call the CNS related calculations, if anything?

--------------------

Yes, yes, PADI, and yes. CNS calculations are called maximum operating depths. This is all in the nitrox book. Are you disagreeing, testing my knowledge, or interested in learning about nitrox? I am simply trying to reinforce to ALL students that you have books for a reason. They are a reference if you forget something.

[Tomeck]

I often dive at 1.6. I find 1.6 is very reasonable, because we can stay at 1.6 during 45 minutes, it is enough long.

[Scubakevdm]

I think that Charlie is the cleverest guy I've ever met. For real.

[Bismark]

CNS calculations are called maximum operating depths. .


So are you saying that CNS is only a function of your MOD?? Are you then implying that staying within your MOD is sufficient to ward off CNS???

[Charlie99]

Yes, yes, PADI, and yes. CNS calculations are called maximum operating depths. This is all in the nitrox book. Are you disagreeing, testing my knowledge, or interested in learning about nitrox?A bit of all three. I can only disagree once I know for sure what you are saying. And when I am in disagreement with someone, I often find that figuring out why we disagrees leads to further enlightenment. :D

It does appear that what I consider to be a CNS O2 clock you say is controlled by lung/pulmonary considerations.

For example, I consider the 300 minutes max at 1.0ata ppO2, 210 minutes max at 1.2ata ppO2, and 150 minutes max at 1.4ata ppO2 to be CNS limits, not pulmonary. When I refer to CNS clock, I refer to using these sorts of limits, but expressed in %/minute terms to calculate the "% of CNS clock" that has been consumed. (For example 300 minute limit at 1.0ata turns into 0.33%/ minute, 150 minute limit at 1.4ata becoms 1/150 = 0.67%/minute).

Is the above sort of calculation what you are calling lung/pulmonary toxicity calculations? I call the above the O2 clock or CNS clock, and don't believe it has anything to do with pulmonary effects such as lung damage, edema and breathing difficulty. I've never had to calculate OTUs for any recreational dive.

-----------------------

The MOD of 1.4ata is indeed a CNS-related calculation, but it is simply a very quick and dirty way of keeping the CNS clock in limits, since it is unlikely that a non-technical open circuit diver will exceed the 150 minute per dive CNS limit for 1.4ata ppO2.

[jviehe]

So are you saying that CNS is only a function of your MOD?? Are you then implying that staying within your MOD is sufficient to ward off CNS???

THere are some other physical factors such as workload, drugs, and c02 levels, but yes, CNS is a result of depth, and not time for recreational divers. Staying below recomended partial pressure limits (1.4 for PADI) will ward off CNS in most cases. We dont need to get into disclaimers.

Pulminary toxicity however is a result of time at above normal pressures and is tracked using the 02 clock.

[jviehe]

A bit of all three. I can only disagree once I know for sure what you are saying. And when I am in disagreement with someone, I often find that figuring out why we disagrees leads to further enlightenment. :D

It does appear that what I consider to be a CNS O2 clock you say is controlled by lung/pulmonary considerations.

For example, I consider the 300 minutes max at 1.0ata ppO2, 210 minutes max at 1.2ata ppO2, and 150 minutes max at 1.4ata ppO2 to be CNS limits, not pulmonary. When I refer to CNS clock, I refer to using these sorts of limits, but expressed in %/minute terms to calculate the "% of CNS clock" that has been consumed. (For example 300 minute limit at 1.0ata turns into 0.33%/ minute, 150 minute limit at 1.4ata becoms 1/150 = 0.67%/minute).

Is the above sort of calculation what you are calling lung/pulmonary toxicity calculations? I call the above the O2 clock or CNS clock, and don't believe it has anything to do with pulmonary effects such as lung damage, edema and breathing difficulty. I've never had to calculate OTUs for any recreational dive.

-----------------------

The MOD of 1.4ata is indeed a CNS-related calculation, but it is simply a very quick and dirty way of keeping the CNS clock in limits, since it is unlikely that a non-technical open circuit diver will exceed the 150 minute per dive CNS limit for 1.4ata ppO2.

PADI calls it the oxygen exposure table, but in advanced nitrox its OTUs. Im speaking only of recreational nitrox, and im not formally trained in advanced nitrox. Using 100% of your 02 clock puts you at risk for pulminary toxicity and increases your risk of CNS toxicity. The exposure table and 1.4 limit is designed to keep rec divers withing conservative limits.

So basically, CNS is based on depth, pulminary based on time, though both are called oxtox.

[Charlie99]

We disagree on this.

I don't have a PADI nitrox book handy, so I googled for "PADI Oxygen Exposure Table" and found a table that, although it just says "Oxygen toxicity", is one that calculates the CNS clock. That table (the one with equivalent air depths on the backside) is NOT pulmonary calculations. That PADI/DSAT Oxygen Exposure Table is simply the NOAA CNS O2 exposure limits in a tabular form.

Erik Baker has an article "Oxygen Toxicity Calculations", which pretty clearly explains both CNS calculations and the pulmonary/OTU/UPTD calculations. Even a brief glance at that article would show you that the 150 minutes at 1.4ata ppO2 is a CNS limit, not a pulmonary limit. The pulmonary limit (for 4% loss of vital capacity) is somewhere around 5 hours at 2ata ppO2, and much longer at 1.4ata. See ftp://ftp.decompression.org/pub/Baker/Oxygen%20Toxicity%20Calculations.pdf

[Bismark]

Like Charlie Said.

Also, JeViehe, I make my share of typos, but you should probably start spelling pulmonary correctly (not pulminary) or one of your students is going to point that out to you......... ;-)

[Scubakevdm]

And when I am in disagreement with someone, I often find that figuring out why we disagrees leads to further enlightenment. :D



It has lead to my enlightenment! Thanks Charlie!

[jviehe]

We disagree on this.

I don't have a PADI nitrox book handy, so I googled for "PADI Oxygen Exposure Table" and found a table that, although it just says "Oxygen toxicity", is one that calculates the CNS clock. That table (the one with equivalent air depths on the backside) is NOT pulmonary calculations. That PADI/DSAT Oxygen Exposure Table is simply the NOAA CNS O2 exposure limits in a tabular form.

Erik Baker has an article "Oxygen Toxicity Calculations", which pretty clearly explains both CNS calculations and the pulmonary/OTU/UPTD calculations. Even a brief glance at that article would show you that the 150 minutes at 1.4ata ppO2 is a CNS limit, not a pulmonary limit. The pulmonary limit (for 4% loss of vital capacity) is somewhere around 5 hours at 2ata ppO2, and much longer at 1.4ata. See ftp://ftp.decompression.org/pub/Baker/Oxygen%20Toxicity%20Calculations.pdf

I think the only think we disagree on, or rather you disagree with PADI on, is that you can predict CNS tox or track it. PADI thinks not, and thats what I was taught and what it says in the manuals. Since they dont beleive you can track it, the oxygen exposure table (which is the NOAA math) is only used by PADI to track pulminary tox. CNS tox is simply avoided by staying below 1.4. Now, there may very well be more advanced and detailed info in other references and courses. I was simply answering the op, who is only recreationally trained, as am I.

TO quote:


Most physiologists consider attempts to predict CNS toxicity on a partial pressure/time basis unreliable. FOr this reason divers avoids CNStox by staying well within a max partial pressure.

-PADI Encylopedia

[jviehe]

Like Charlie Said.

Also, JeViehe, I make my share of typos, but you should probably start spelling pulmonary correctly (not pulminary) or one of your students is going to point that out to you......... ;-)
Ill see what I can do.

[nereas]

Like Charlie Said.

Also, JeViehe, I make my share of typos, but you should probably start spelling pulmonary correctly (not pulminary) or one of your students is going to point that out to you......... ;-)

Florida is not Canada.

In Florida they just spell stuff different!:eyebrow:

[nereas]

...So basically, CNS is based on depth, pulminary based on time, though both are called oxtox.

They are actually both based on "duration of exposure" which is like what you said about "time."

CNS = central nervous system (in other words, siezures).

Pulmonary = lung tissues (in other words, injury to the tissues).

With NDL scuba, when you limit your diving depth to correspond with 1.6 ATAs ppO2 or less, you have virtually no risk of either.

1.4 is a very popular limit to teach novice nitrox divers. Although for NDL scuba this is actually way "too" conservative to really be meaningful, as was explained earlier and in the referenced posting.

When you exceed 1.6 then you need to correctly calculate to avoid risk.

When you get really high, in the ranges of 2.0 or more, then the onset of CNS is very likely.

Pulmonary injury would be very difficult to achieve with NDL scuba. You just don't spend enough time underwater to do it. Maybe yes, if you tried to set a world endurance record. Otherwise not.

[nereas]

Just curious and wanting to learn, but why not just go to tri-mix for a dive like this? Seems like a safer mix all around for such a deep dive.

I have noticed that a lot of divers prefer nitrox instead of trimix for certain depths and use nitrox whenever possible.

For 130 to 150 ft, EAN 25 is quite popular, although it is barely better than air.

For 100 to 130 ft, EAN 32 is quite popular, and for some the ideal mix.

For 50 ft to 100 ft, EAN 36 is a very popular mix, expecially with expert divers, who are not paranoid about a limit of 1.4 ATAs.

Nitrox is easier to get, and easier to mix, and faster to decompress from when you have only one gas. And for strictly NDL diving, nitrox gives you longer NDL times than does trimix of the same O2 levels.

Also with trimix, you need to have splendid buoyancy control. If you happen to shoot to the surface with trimix, it would likely be a fatal error. Helium is unforgiving of novice divers.

[jviehe]

Ok, after reading some more, I think the problem here is that we are saying the same thing, but you are saying it in more detail. PADI simply eliminates unnecesary information. According to sources other than PADI, CNS tox can be time dependant if single exposures to ppo2 exceeds whatever time. However these times are impossible to do as a recreational diver, which is why PADI discards them. For example you could be exposed to 1.4 for 150mins, which you cant do without doing deco, even at 40% nitrox. So, in effect, we are both right, but you are more right.

[Bismark]

I have noticed that a lot of divers prefer nitrox instead of trimix for certain depths and use nitrox whenever possible.

For 130 to 150 ft, EAN 25 is quite popular, although it is barely better than air.

For 100 to 130 ft, EAN 32 is quite popular, and for some the ideal mix.

For 50 ft to 100 ft, EAN 36 is a very popular mix, expecially with expert divers, who are not paranoid about a limit of 1.4 ATAs.

Nitrox is easier to get, and easier to mix, and faster to decompress from when you have only one gas. And for strictly NDL diving, nitrox gives you longer NDL times than does trimix of the same O2 levels.

Also with trimix, you need to have splendid buoyancy control. If you happen to shoot to the surface with trimix, it would likely be a fatal error. Helium is unforgiving of novice divers.


Here we go again.........I don't have the time to waste on this again........

[nereas]

Ok, after reading some more, I think the problem here is that we are saying the same thing, but you are saying it in more detail. PADI simply eliminates unnecesary information. According to sources other than PADI, CNS tox can be time dependant if single exposures to ppo2 exceeds whatever time. However these times are impossible to do as a recreational diver, which is why PADI discards them. For example you could be exposed to 1.4 for 150mins, which you cant do without doing deco, even at 40% nitrox. So, in effect, we are both right, but you are more right.

Stop quoting PADI. That is a common mistake made by novice DMs.

Most people view PADI as the definitive word on incompetence.

Learn the laws of physics, and the research data, and then develop your own views.

[tboxcar]

As a nitrox diver, I found this thread quite informative and interesting, good work guys!

[nereas]

As a nitrox diver, I found this thread quite informative and interesting, good work guys!

You also have the additional issue of high altitude, like the Swiss lakes.

Nitrox is invaluable for high altitude diving.

But in addition, a diver must make sure that the computer is set for high altitude, and that you have checked the NOAA tables for equivalent high altitude adjustments.

That is not an CNS nor pulmonary tox issue, of course. Just a regular N2 DCS issue. Therefore diving with richer oxygen in the mix is a major benefit with the altitude difference and added sensitivity to DCS from depths normally easy at sea level.

I am sure that you know all this already, since high altitude is your back yard. I just wanted to mention it for anyone else.

High altitude lakes are usually crystal clear and fun to dive in, just really cold waters!

[Charlie99]

the oxygen exposure table (which is the NOAA math) is only used by PADI to track pulminary tox. CNS tox is simply avoided by staying below 1.4. Although this is apparently what you believe, and unfortunately what you are apparently teaching your students, the DSAT/PADI Oxygen Exposure Table has NOTHING to do with pulmonary toxicity. The PADI Oxygen Exposure Table is based upon CNS oxtox experimental data and is used to track CNS toxicity.

Look at the table and calculations of the references I linked to above. CNS oxtox limit at 1.6ata is about 45 minutes, while the 4% vital capacity (pulmonary oxtox) limit is around 360 minutes. Clearly, the PADI/DSAT table is CNS oxtox, not pulmonary.

CNS oxtox is a function of both time and ppO2. I have seen many posts on Scubaboard that show ignorance of that fact. It appears both you and many other instructors are incorrectly teaching their students.

Charlie Allen

[nereas]

...
CNS oxtox is a function of both time and ppO2. I have seen many posts on Scubaboard that show ignorance of that fact. ...

Charlie Allen

Exactly. It takes time to figure all this out, I think, and that is why there is so much bewilderment.

[jviehe]

Stop quoting PADI. That is a common mistake made by novice DMs.

Most people view PADI as the definitive word on incompetence.

Learn the laws of physics, and the research data, and then develop your own views.
Either they are right or wrong. Are you claiming that PADIs material is factualy incorrect?

[jviehe]

Although this is apparently what you believe, and unfortunately what you are apparently teaching your students, the DSAT/PADI Oxygen Exposure Table has NOTHING to do with pulmonary toxicity. The PADI Oxygen Exposure Table is based upon CNS oxtox experimental data and is used to track CNS toxicity.

Look at the table and calculations of the references I linked to above. CNS oxtox limit at 1.6ata is about 45 minutes, while the 4% vital capacity (pulmonary oxtox) limit is around 360 minutes. Clearly, the PADI/DSAT table is CNS oxtox, not pulmonary.

CNS oxtox is a function of both time and ppO2. I have seen many posts on Scubaboard that show ignorance of that fact. It appears both you and many other instructors are incorrectly teaching their students.

Charlie Allen

Then it appears that you think PADI is wrong. Is this your belief?

[HowardE]

The Table is called the "CNS Oxygen Exposure Table" and the times can be displayed in % CNS per minute.

OTU's are different.

CNS Oxygen Toxicity is a function of both exposure (time) and ATA's of O2 (ppo2).

A single breath at a PO2 of 2.0 ATA will (most likely) not cause a convulsion. However, prolonged exposure to high PO2's will (most likely) cause eventual convulsions.

From the TDI Advanced Nitrox Manual

Exen at the advanced nitrox level, pulmonary oxygen toxicity remains an unlikely condition to be suffered by the diver. Pulmonary oxygen toxicity is characterized by a long term, low dose rate of oxygen. Typical oxygen pressures must be at more than 0.5 ATA and less than 1.1-1.2 ATA. MANY HOURS of exposure to oxygen continuously are required before symptoms may manifest.

[rab]

Hey guys,

I'm going to be diving the Oriskany in a few weeks with a dive group and we will be diving nitrox. I've been certified to use it for over 2 years but have never found the opportunity to use it (air has worked fine for all my ocean dives since we'd do a deep dive then a shallow dive, shallow cavern diving etc.) . My computer can handle nitrox and I'm familiar with the rules etc. but I think maybe during my classes I misunderstood my teacher and just would like some clarification.

...

Now that I'm thinking about it. What if it's your first dive of the day on nitrox and you go straight to the bottom and hit PPO2 1.65 for say 1 minute and come back to a level where your PP02 is 1.3 or so. Is what my instructor was trying to say was "If you go below PP02 1.6 your O2 clock is used up much much faster so you consider it "instantly" using up 100% of your O2 clock because it only takes maybe 10 minutes to use it up at PP02 1.6?"

The reason I ask is we will be diving 29% O2 and at the beginning of the dive we're planning on touching the deck at 137'. This puts me at a PP02 of 1.58. We would only stay for a minute or two and then go hang out around 110' and shallower. Now I can have my computer beep at me if I were to hit PP02 1.6, but if something goes wrong (heaven forbid) and I get distracted for a second or take a second to become neutrally bouyant and accidentally go slightly over PP02 1.6 I'm not going to black out right?

Sorry if it's a stupid question, just like to be very prepared for things (taking my rescue diver classes this weekend, I guess it's rubbing off on me already :D ).

Thanks for your responses in advance!
Jim

FYI, I was one of the divers on the MBT/H2OBelow trip to the USS Oriskany on 6-Sep-2008. It was their first trip out in a week due to Gustav. The Flight deck just forward of the "Island" measured 45.1m (148ft) on my Nitek Duo set to "sea" and 44.8m (147ft) on my Suunto Mosquito (sitting a couple inches higher on my forearm).

It will be interesting to know how the dive briefings change with respect to the flight deck. Our briefing called it 135' and the materials at MBT (More Bottom Time) Divers listed 137' -- a quick touch on the flight deck to say you'd "been there" was tacitly approved, but PPO2 starts to be an issue for Nitrox above 25% with the new depths. (I noticed that Rich, the Dive Master for our trip, was using 24%)

IF you are planning to touch the deck, 29% has a 1.6 MOD of 149' -- not much of a safety margin. You're certainly not going to stay on the flight deck for "a minute or two" even if your profile is allowed by the time you make your trip.

Our viz was less than 25ft so you couldn't even see the flight deck before you were nearly on it, but that should improve by the time you're there. While I don't know if I'll ever make it back for another dive (it is rather expensive!), it would be great to have the 80ft viz that is more typical.

-Rob

[jviehe]

Ill admit Im wrong in that the table is tracking pulmonary toxicity. PADI seems to simply be ignoring pulmonary tox for recreational limits, and using the CNS table as a more conservative 24 hour clock to avoid any tox. There is no mention of time based CNS tox, only depth based. The eanx manual has much more limited info, but the encyclopedia expands on that and mentions OTUs and mentiones 850 as the limit for single days, and 300 per day if multiple. This is more inline with advanced nitrox material.

[HowardE]

The thing is - that to reach an OTU level high enough to be of concern... you'd have to exceed the CNS clock by more than 200% the daily limit.

Time based CNS tox is definitely a reality. My tech instructor (who was at one time commercial diver) told me that when he was in commercial diving academy.... They (at the time) put the would be divers in a chamber and exposed them to 2.0 ATA PPO2 for 30 minutes. If they convulsed... they couldn't be commercial divers. If not... they could be. The point is... CNS Ox Tox is a function of both PPO2 and TIME. It's not an instant hit if you go to 2.0 or beyond. CNS Ox Tox is the MAIN thing to worry about as both tech and rec divers.

[Charlie99]

Although this is apparently what you believe, and unfortunately what you are apparently teaching your students, the DSAT/PADI Oxygen Exposure Table has NOTHING to do with pulmonary toxicity. The PADI Oxygen Exposure Table is based upon CNS oxtox experimental data and is used to track CNS toxicity.<I assume that this is the section you are responding to>
Then it appears that you think PADI is wrong. Is this your belief?My belief is that PADI is correct, but that you have misunderstood what PADI is teaching. It appears that you are not alone in the misunderstanding, so it seems like PADI should alter or add to the training materials a bit.

[Charlie99]

For the next iteration of PADI training materials, I would also recommend PADI use an appropriate halftime calculation for oxtox decay. Right now, they use the NOAA tables where previous exposures are treated as if they have full effect for 24 hour hours and then instantaneously go to zero effect after 24 hours.

Many dive computers assume a 90 minute halftime for CNS oxtox clock decay calculations -- in other words, if a dive pushes you to 60 percent of the allowable O2 clock, then after 90 minutes the computer assumes that you are only at 30% of the clock. (For comparison, the NOAA/PADI table would keep you at 60% from that dive for 24 hours, and then drop instantly to 0 after 24 hours).

Strangely, one computer manufacturer that doesn't use an assumed 90 minute halftime for CNS O2 clock is Suunto. They use a more agressive 60 minute halftime -- not at all what one would expect considering their conservative decompression calculations.

[ianr33]

As an aside does anybody know of a case where a diver has suffered pulmonary oxygen issues diving open circuit? It would seem to be pretty much impossible so its not something I worry about.

[jviehe]

My belief is that PADI is correct, but that you have misunderstood what PADI is teaching. It appears that you are not alone in the misunderstanding, so it seems like PADI should alter or add to the training materials a bit.

I can agree with that, but after rereading the material a few times, I think its also that its not detail enough for advanced thinkers, and so I made the jump with connecting pulminary to the exposure table. The reason being that CNS tox is not mentioned in regards to time, only depth. Essentialy the how is correct, the why is not expanded upon. This works for recreational diving. Consider me corrected.

[nereas]

As an aside does anybody know of a case where a diver has suffered pulmonary oxygen issues diving open circuit? It would seem to be pretty much impossible so its not something I worry about.

Exactly!

I have no idea why the pulmonary chart is even taught.

CNS problems will catch up to and haunt you long before anything else, and even that is primarily a tech-deco issue.

Neither is a realistic issue for NDL as long as depth is controlled so as not to wander too far into forbidden territory.

[nereas]

The thing is - that to reach an OTU level high enough to be of concern... you'd have to exceed the CNS clock by more than 200% the daily limit.

Time based CNS tox is definitely a reality. My tech instructor (who was at one time commercial diver) told me that when he was in commercial diving academy.... They (at the time) put the would be divers in a chamber and exposed them to 2.0 ATA PPO2 for 30 minutes. If they convulsed... they couldn't be commercial divers. If not... they could be. The point is... CNS Ox Tox is a function of both PPO2 and TIME. It's not an instant hit if you go to 2.0 or beyond. CNS Ox Tox is the MAIN thing to worry about as both tech and rec divers.

I am sure you would agree that there is lots of beach (sand) in Colorado, just no ocean!:eyebrow:

[We joke about that whenever we are in Las Vegas, too!]

I have noticed that people who live on the seashore vacation in the mountains, and vice versa. I guess that is what a change of pace is all about.

I have friends in Key West Florida who run a dive boat business, and every year the whole extended family meets for a vacation at Lake Tahoe California!

[Tienuts]

Exactly!

I have no idea why the pulmonary chart is even taught.

CNS problems will catch up to and haunt you long before anything else, and even that is primarily a tech-deco issue.

Neither is a realistic issue for NDL as long as depth is controlled so as not to wander too far into forbidden territory.
I was taught OTU's come in to play over multiple days. 2 deco dives a day over 7 days kind of thing....

[Shawn@IReallyloveScub]

I am an ICU nurse, whole body tox or pulmonary oxygen tox is not ever going to happen to a tech diver in the real world. Now the WKPP divers who are in caves 24+hours do. But with the right gas mix's even then they dont have worries other than to be aware of it.
Pulmonary tox is possible in some pts on vents in ICU or babys in O2 tents for days at a time on high % of O2.

[Charlie99]

Here's a case of pulmonary oxtox. An unusual case, by an unusual guy, Richard Pyle, the guy that first popularized deep stops.

http://www.deepcaves.net/diving/confessions_II.html

The oxtox stuff is about 2/3rd in. 3 days of multiple rebreather dives at constant 1.4ata ppO2 setting, with lots of surface O2 in between. He got bent while in some remote NW Hawaiian islands and went onto a 2 hours on, 30 minutes off O2 treatment cycle while the boat headed back towards civilization. He started having some pretty severe symptoms after 8 hours on O2 (following many hours in the previous 3 days at 1.4ata and 1.0ata O2).

[jim2386]

Hey guys,

Sorry for causing all this craziness. It really wasn't my intention to get everyone worked up. Just wanted clarification is all. I apologize.

Btw, we talked to H20 Below and for those of you wondering, the new requirement is if you're going to touch the deck, you must show proof of an advanced technical diving card. This would be like advanced nitrox or tri mix. In the words of H20, if you don't have these and go below 137', you sit out the next dive. It doesn't really bother me either way. Trust me, I try my best to be very safe when I dive and don't push things. I just wanted to know what the ramifications of passing 1.6 for a minimal amount of time would be just for peace of mind.

Anyway, looks like my trip to the oriskany is on for next weekend (Sept 18th-21st) and I'll have a trip report when I get back and of course underwater pictures and movies as always :D

-Jim

[nereas]

Hey guys,

Sorry for causing all this craziness. It really wasn't my intention to get everyone worked up. Just wanted clarification is all. I apologize.

Btw, we talked to H20 Below and for those of you wondering, the new requirement is if you're going to touch the deck, you must show proof of an advanced technical diving card. This would be like advanced nitrox or tri mix. In the words of H20, if you don't have these and go below 137', you sit out the next dive. It doesn't really bother me either way. Trust me, I try my best to be very safe when I dive and don't push things. I just wanted to know what the ramifications of passing 1.6 for a minimal amount of time would be just for peace of mind.

Anyway, looks like my trip to the oriskany is on for next weekend (Sept 18th-21st) and I'll have a trip report when I get back and of course underwater pictures and movies as always :D

-Jim

Jim,

Advanced nitrox (EAN 50 thru 100% O2) is normally taught together with Decompresion Diving.

The other advanced tech courses are:

Deep Air (to 185 ft)

Basic Trimix (also to 185 ft)

Advanced Trimix (beyond 185 ft)

CCR

Anytime you dive deeper than 130 ft, your NDL time is so short (5 mins USN) that you are basically going into deco. And all of these advanced tech courses presume deco.

[HowardE]

Hey guys,

Sorry for causing all this craziness. It really wasn't my intention to get everyone worked up. Just wanted clarification is all. I apologize.



Jim...

Don't be sorry. It's a polite informative discussion here... That's what ScubaBoard is all about :D

[DA Aquamaster]

Pulmonary toxicity is the result of above normal PPO2's over time not just pressure. If you are in the hospital long enough on 100% O2 you run the risk of pulmonary issues even at 1 atm.

I agree that a PPo2 of 1.6 is not going to mean bad things for a particular diver on a particular dive, but statistically it does increase the risk and mileage varies from diver to diver. Being stressed, working hard, retaining CO2 could all increase the potential for ox tox. While it is not likely to be an issue in a brief exposre, I'd question the wisdom of an instructor diving to the deck on the oriskany and incurring a PPO2 of 1.6 just to say you went there.

If its important to go there, do it with a mix that stays under a PPO2 of 1.4 and accept the reduced NDL for the dive overall.

I'm middle of the road on Trimix. An END of 135-145' in good viz under good conditions with no penetration for a diver who has experience working down to that depth over several recent dives is not that big an issue, but if any one of the above is missing, it gets potentially much more serious if something goes wrong. I also tend to discourage anyone from going below 130' period on a single tank because the gas margin is tight and the NDL's are short and both severely limit the time you have to resolve a problem regardless fo the gas used.

[ianr33]

Jim,

The other advanced tech courses are:

Deep Air (to 185 ft)

Basic Trimix (also to 185 ft)

Advanced Trimix (beyond 185 ft)



"Deep Air" is actually called Extended Range and is good for 180 feet (not 185) This is rapidly falling out of favor as not many divers want to use air at that depth

Basic (Intro Trimix) goes to 200 feet

Advanced Trimix has a limit of 330 feet (At least for TDI)

[jviehe]

Hey guys,

Sorry for causing all this craziness. It really wasn't my intention to get everyone worked up. Just wanted clarification is all. I apologize.

Btw, we talked to H20 Below and for those of you wondering, the new requirement is if you're going to touch the deck, you must show proof of an advanced technical diving card. This would be like advanced nitrox or tri mix. In the words of H20, if you don't have these and go below 137', you sit out the next dive. It doesn't really bother me either way. Trust me, I try my best to be very safe when I dive and don't push things. I just wanted to know what the ramifications of passing 1.6 for a minimal amount of time would be just for peace of mind.

Anyway, looks like my trip to the oriskany is on for next weekend (Sept 18th-21st) and I'll have a trip report when I get back and of course underwater pictures and movies as always :D

-Jim

Well, your original question was whether youd instantly tox if you go below 1.6 pp02 and how does this relate to exposure over time. The answer, if i understand correctly now, is that, basically, we dont know. PADI reccomends that recreational divers stay below a pp02 of 1.4, and that the risk of tox above that is high, and above 1.6 is unnaceptable. The time, according to the single exposure table would be be 45mins at 1.6, iirc. Since on nitrogen limits you cant spend more than a few mins at that depth, its moot. So, the ramifications could be fatal if you are going to push the limits, or could be negigible. Unless you are properly trained, equiped, and experienced, you should not be diving dangerously, in any case. There is nothing on the deck worth dying for, nothing beyond your abilites worth dying for.

[ucfdiver]

The other advanced tech courses are:

Deep Air (to 185 ft)
This class is still being taught? :shakehead:

[HowardE]

This class is still being taught? :shakehead:

As a matter of fact... I just did that class under advisement from my instructor: John Chatterton.

Here's my trip report: http://www.scubaboard.com/forums/technical-diving-specialties/251288-trip-report-tech-training-pirates-cove-dive-center-samana.html

[bleeb]

Well, your original question was whether youd instantly tox if you go below 1.6 pp02 and how does this relate to exposure over time. The answer, if i understand correctly now, is that, basically, we dont know.

I'm not sure if you just phrased that poorly or you really meant exactly what you just said. Some militaries used to (still?) set their PO2 limits as high as 2.0 and IIRC some posters in this thread have alluded to regularly going above 1.6, even during 'working' portions of dives. So the literal answer to the literal question "do you (always) instantly tox if you go below 1.6 ppO2" is "no" and not "we dont know". Some people will tox fairly quickly, especially if the other factors mentioned previously are in play, but some will take longer.

If that's not exactly what you meant, maybe try restating it before the gasoline you dripped restarts the fire. :D

[jviehe]

I'm not sure if you just phrased that poorly or you really meant exactly what you just said. Some militaries used to (still?) set their PO2 limits as high as 2.0 and IIRC some posters in this thread have alluded to regularly going above 1.6, even during 'working' portions of dives. So the literal answer to the literal question "do you (always) instantly tox if you go below 1.6 ppO2" is "no" and not "we dont know". Some people will tox fairly quickly, especially if the other factors mentioned previously are in play, but some will take longer.

If that's not exactly what you meant, maybe try restating it before the gasoline you dripped restarts the fire. :D
You just repeated what I said, which is that we dont know how going above 1.6 would affect the OP. I didnt say always. I repeated the common recreational nitrox teaching which is that going above 1.4 is unnecesarily risky.

[bleeb]

You just repeated what I said, which is that we dont know how going above 1.6 would affect the OP. I didnt say always. I repeated the common recreational nitrox teaching which is that going above 1.4 is unnecesarily risky.

Ok. In what you said the first time, I interpreted it as "always", since we do know some things, just not everything. Thanks for clarifying.

[jviehe]

Ok. In what you said the first time, I interpreted it as "always", since we do know some things, just not everything. Thanks for clarifying.
Yes, all I was getting at is that its not ok to go even just a little bit beyond safety limits, because there is a lot of uncertainty in how each person in each situation is affected by pressure. What we do know is that if you stay below 1.4 pp02 in recreational limts, you have low risk of problems.

[ucfdiver]

As a matter of fact... I just did that class under advisement from my instructor: John Chatterton.

Here's my trip report: http://www.scubaboard.com/forums/technical-diving-specialties/251288-trip-report-tech-training-pirates-cove-dive-center-samana.html
Thanks for the post. I can honestly say that I'll never experience that course, so it's nice to read about it.

[Thalassamania]

PADI simply eliminates unnecesary information. :rofl3:

Remember, what you don't know can't hurt you.

[Bismark]

Thal, that last post was too funny...........made my day so far........

[Thalassamania]

Thal, that last post was too funny...........made my day so far........It never ceases to amaze me, but I guess Forrest Gump was right.