Oxygen Toxicity vs Narcosis

[Jim Lapenta]

Also while there are more or less established limits for O2 toxicity everyone is different. It would take a doc going over history and all other factors to truly determine what happened and even that would be subject to interpretation. However as was already said poor technique and bad judgement will hurt or kill you just as fast as an O2 tox hit. Breaking a plan and leaving a buddy is just plain reckless and would lead me to consider finding another person to dive with. Maybe it was just the one time. But one time is all it takes for the stuff to hit the fan big time.

 

[Chris66]

Taking EAN-32 to 123FSW is not a big deal. That said, breaking an agreed to depth limit on a dive is. Divers who can not control their depth should not be diving EAN.

Thal, Rick and Walter - if a 110 feet on EAN 32 give a pp02 of 1.39 then presumably anything deeper give a ppO2 of >1.4 so why do you feel that 123feet is not a big deal. And if indeed you feel that it was not a big deal how do you explain his nausea

Thanks for your input

Chris

 

[Crowley]

Wow, I'm glad everybody can dismiss the descent to 123ft on 32% as meaningless!

This is from the DAN website:

For open-circuit scuba diving, consider the "green light" region any oxygen partial pressure of 1.4 ata or less (this is about 82 feet / 25 meters on a 40-percent oxygen mix.) As long as this level is never exceeded, other limitations of open-circuit scuba diving will limit the exposure time to lengths where CNS oxygen toxicity is unlikely to be encountered, even for exposures approaching four hours.

Proceeding With Caution

Between 1.4 ata and 1.6 ata (this is 99 feet / 30 meters on a 40-percent mix) is the "yellow light" region. The possibility of oxygen toxicity at 1.6 ata is low, but the margin of error is very slim compared to 1.4 ata. Individual variation, the likelihood of an unplanned depth excursion causing an increase in oxygen partial pressure, and the possibility of having to perform heavy exercise in an emergency put the possibility of oxygen toxicity at levels where caution should be exercised. Thus, levels of 1.5 to 1.6 ata should be reserved for conditions where the diver is completely at rest, such as during decompression. Again, as noted previously, the dive team must still be prepared for the possibility of an oxygen convulsion at these levels.

Stop!

Above 1.6 ata is the "red light" area. Just don't do it. Yes, there is evidence that short exposures at higher levels of pO2 (oxygen partial pressure) are possible but so are convulsions. At these levels, oxygen exposure depth/time limits must be adhered to. Even mild exercise may put divers breathing high-density nitrox mixes at increased risk; and even open-circuit scuba divers can achieve durations likely to get them into trouble at these levels. Diving using these high partial pressures of oxygen should be left to the trained professionals who can weigh the risks and benefits and who have the necessary training and support structure in place, if an oxygen convulsion occurs.

The fact that most people can be exposed to up to 2.0 ata ppO2 without problems does not mean that ALL people can. Physical condition, overexertion, even common pharmaceuticals can increase the risk of O2 toxicity. This diver hit a ppO2 of 1.53 - a partial pressure where O2 toxicity is perfectly possible. Given the duration of exposure it's highly unlikely, yes - but it shouldn't be dismissed out of hand.

Otherwise, I concur - this diver was more likely to be narced than otoxed, and as others have stated, it is important that divers stick to planned depth and time limits - especially when diving with Enriched Air Nitrox....

Safe diving always,

C

 

[Charlie99]

Thal, Rick and Walter - if a 110 feet on EAN 32 give a pp02 of 1.39 then presumably anything deeper give a ppO2 of >1.4 so why do you feel that 123feet is not a big deal. And if indeed you feel that it was not a big deal how do you explain his nausea

Thanks for your input

Chris

Although most agencies teach "keep ppO2 below 1.4ata", the NOAA limits are 150 minutes at 1.4ata ppO2 and are 45 minutes at 1.6ata ppO2 (132' on EAN32). The exposure was both less than 1.6ata and much shorter than the 45 minute limit at 1.6.

CNS toxicity is a time-dose sort of thing ---- one doesn't magically cross some line and instantly get a CNS hit. It is a caused by both the exposure level (ppO2) and the exposure TIME.


In practice, if you stay shallower than a 1.4ata ppO2 MOD, then it is pretty hard to get to the CNS limit without going into decompression. So "keep ppO2 less than 1.4ata" is a pretty simple rule to teach divers that will keep them out of trouble. The flip side, is that without full knowledge, many of them assume that stepping 0.01ata beyond 1.4 is instant death.

==============================================

IF YOUR BUDDY HAD SOME SORT OF PROBLEM, HOW DEEP WOULD YOU HAVE GONE TO ASSIST HIM?

Having looked at this issue, I've come to the conclusion that running out of gas is the only problem I face when using an AL80 filled with EAN32. I'm willing to exceed even 2.0ata ppO2 for the short periods needed for a rescue. Something to think about and decide, before you need to make a split second decision.

Charlie Allen

 

[Rick Murchison]

Although most agencies teach "keep ppO2 below 1.4ata", the NOAA limits are 150 minutes at 1.4ata ppO2 and are 45 minutes at 1.6ata ppO2 (132' on EAN32). The exposure was both less than 1.6ata and much shorter than the 45 minute limit at 1.6.

CNS toxicity is a time-dose sort of thing ---- one doesn't magically cross some line and instantly get a CNS hit. It is a caused by both the exposure level (ppO2) and the exposure TIME.


In practice, if you stay shallower than a 1.4ata ppO2 MOD, then it is pretty hard to get to the CNS limit without going into decompression. So "keep ppO2 less than 1.4ata" is a pretty simple rule to teach divers that will keep them out of trouble. The flip side, is that without full knowledge, many of them assume that stepping 0.01ata beyond 1.4 is instant death.

==============================================

IF YOUR BUDDY HAD SOME SORT OF PROBLEM, HOW DEEP WOULD YOU HAVE GONE TO ASSIST HIM?

Having looked at this issue, I've come to the conclusion that running out of gas is the only problem I face when using an AL80 filled with EAN32. I'm willing to exceed even 2.0ata ppO2 for the short periods needed for a rescue. Something to think about and decide, before you need to make a split second decision.

Charlie Allen

Again, I agree with everything Charlie has to say on this.
--
However... let me say that any time you are diving a mix other than air and you have any symptom of oxygen toxicity - and nausea fits that - (or any other unexplained weirdness) the dive is over. Commence a normal ascent to the surface, including all stops, and end the dive. At the PO₂ levels we use, as in this case, there should never, ever be any real danger of an oxygen hit, so if you have symptoms something is wrong! It is time to get out of the water and think about it on the surface - re-analyze the gas, what you had to eat & drink, take your temperature, pulse & blood pressure... somethin' just ain't right. Perhaps it was just a little piece of underdone potato, but the time to figure that out is topside, not at 120'.
And another thing...
I'd never really given this much thought before... folks are now hitting new personal max depths using Nitrox to their planned MOD. That's probably not a very good idea, and if there's anything to be said in favor of a little deep air diving, it is that you should have a crystal clear picture of "your" narcosis at any given depth before you start exploring the edges of the oxygen envelope.
Rick

 

[Cacia]

folks are now hitting new personal max depths using Nitrox to their planned MOD. That's probably not a very good idea, and if there's anything to be said in favor of a little deep air diving, it is that you should have a crystal clear picture of "your" narcosis at any given depth before you start exploring the edges of the oxygen envelope.

hmmm

good point.

I almost think it might be better to experience a little narcosis before adding other gases. It can be very "muddy" down there, as I found out with the bad gas the other day.....I thought something was "off" but was not very decisive about it. Things are certainly more clear topside..

I have never experienced the "dark narc"...I associate that with CO2 from exertion, it gives me impending doom sensation, paranoia. It always happens if I am working too hard, and gradually lifts as I rest.

The flip side, is that without full knowledge, many of them assume that stepping 0.01ata beyond 1.4 is instant death.

yes, I know a Navy Salvage diver who is always emphasizing that to me.

Doesn't the Navy use 1.6? ...I use 1.2 because I don't know why...I feel like my seizure threshold might be lower than most.

 

[H2Andy]

my guess (and it is only a guess) is that the nausea was a result of narcosis and not oxtox ...

that said, it doesn't really matter, does it? this guy broke the dive plan and as everybody has said, should not be diving gas where max depth within recreational limits is critical and thus bouyancy/depth control is critical

 

[Charlie99]

Commence a normal ascent to the surface, including all stops, and end the dive. At the PO₂ levels we use, as in this case, there should never, ever be any real danger of an oxygen hit, so if you have symptoms something is wrong! It is time to get out of the water and think about it on the surface - re-analyze the gas, what you had to eat & drink, take your temperature, pulse & blood pressure... somethin' just ain't right.

Agreed. If you look at real life cases of oxtox, almost all are caused by some major mistake.

It's not pushing MODs a bit that causes problems, it's breathing something other than what you think your are breathing --- either using a deco mix at depth, or having a tank that has been misanalyzed (or not analzyed) and is much high FO2 than you think.

 

[Tigerman]

I do not dive nitrox, altho Im planning to get the training in not too distant future.
What I DO is stick strictly with the dive plan. If I have set a max depth of 110 feet, that is MAX and I will NOT go below that limit. Changing the plan during the dive is for most of my dives NOT an option as Im mostly diving solo and I wont have a 2nd opinion on the changes.

 

[DiverLaura]

Were you guys swimming? Nausea and odd feeling sounds more like CO2... Were you diving off a boat? If so were it's engines idling when you were floating around in the water breathing in nasty fumes? If so then I'd think about CO also. (it binds up and stays in system for a long time, and at "lower doses" just makes you feel ill)

ALWAYS analyze your gas and label it. period. the morning of dive or the night before if it's locked in your trunk. This is just a good practice to get into.

This really doesn't sound like O2 to me. Mostly cause it is a rather low PPO2 to be having those symptoms (not unheard of but...) and because the symptoms did not go away with ascent etc... Same with the Narcosis theory. You come up, it goes away, whatever kind of narc you experience.