Another (legit) nitrox ?

[Steve SDI/TDI HQ]

Sorry, I used the wrong words when I tried to explain something. I thought it would be clear from the context.



I dont believe someone have said that you shouldn't track it. Ofcourse I dont care about it if I dive one 1 hour dive per week. The question was when we are at a risk. You could also note that I have used NDL diving all the time.



Sure, everyone is getting killed.



You have showed a very nice up down attitude in this thread. You haven't really cared about other peoples questions, points or arguments at all. Nice attitude for an instructor.

edit: I found this link to SDI training
SDI-Training
Nitrox with a computer, ignore the tables and calculations. And you are the person in this thread that claim that is is extremely important to know the theory and be able to calculate the CNS loading. Why are you working in the head quarter of a agency that doesn't seem to follow your advice at all? What have I missed? Was your point something like this. Using a dive computer set on air for nitrox diving shouldn't been done because no one can do the CNS calculations without a computer and the risk to go over the limit by misstake is to large.

PM sent

 

[Chernish]

Many say that diving Nitrox on an air table or puter makes them safer as in less likely to get hit, because of the THEORETICAL less N2 loading. Which imho hasn't been proven or documented hence when I teach Nitrox I say the best reason to dive Nitrox is longer BT's and shorter SI's and that it isn't safer.

Do you believe the DCS risk for a 25 min air dive to 20 m is less compared to a 45 min air dive to 20 m (the NDL limit)? Do you believe this have been proven or documentet? If yes on both, why should it be a difference when we dive nitrox? Do you believe that the EAD makes sense (base your NDL times on the EAD table) and is it proved?

What he's saying is that even though Nitrox pushes the limits of safety, if you go and reach these new limits you won't be safer. And people tend to reach for the new limits, that's what human beings do.

I believe that if people are able to understand Nitrox, they are able to understand this, but other persons - typically teachers - prefer to err on the side of safety and to reinforce the point, sometimes very insistently. That can be understandable: they don't want anyone dying on them, especially on such a simple thing.

On the subject, there are 3 ways you can have an ox tox, two of them being related to the Central Nervous System, which doesn't help with the confusion. The third way is pulmonary toxicity.

CNS I - Simple exposure to very high PPO2
If you are exposed to a very high PPO2, no matter the length, you might have a CNS ox tox.
That one requires a minumum of planning before the dive and of discipline during the dive.
The limit is easy to calculate and to respect: do not expose yourself to a very high PPO2.

CNS II - Long exposure to high PPO2
That's what people are usually taking about when they talk about CNS.
It is not easy to calculate (at least not as easy as the CNS I).
Dive computers, however, do it very well.

OTU - Very long exposures to very high PPO2
For all practical purposes, only dive bells and hyperbaric chambers are concerned by this.
You will reach the CNS limits waaaaay before OTU becomes a concern.
If a recreational diver is subject to this type of toxicity, it will be because he is in the can. The CNS toxicity measures will go through the roof. Several times. Don't worry about it. Just let the hyperbaric personel handle this, they have forgotten more on the subject that you will ever know.



Cheers!

 

[Steve SDI/TDI HQ]

There are two type of oxygen toxicity: CNS Toxicity and pulmonary or whole body toxicity. The original question was related to enriched air exposure over multiple days.

Yes, there are two types of oxygen toxicity present as risks to nitrox divers.

No, the original question concerned multiple dives over multiple days

You combat the first type of toxicity by keeping the partial pressure of oxygen below a given number; say 1.4 atm, throughout every dive.

Not completely true. One manages CNS toxicity by keeping BOTH oxygen partial pressure and TIME within established NOAA limits.

You have made the classic error of completely ignoring TIME. Citing a partial pressure without associating it with time gives insufficient information to form an opinion or make a statement about "safety."

You combat the second type of toxicity by monitory your overall oxygen exposure over multiple dives. This is tracked as OTU's. If the maximum OTU exposure per day is 300 and you’ve been exposed to 150 OTU's then the CNS% is 50%.

The CNS% is a measure of pulmonary toxicity.

Absolutely NOT. One does monitor pulmonary toxicity by tracking OTUs, and the allowable daily exposure is NOT 300. It varies depending on the number of days one dives. The single day exposure for instance is in excess of 1400 units.

If a diver is exposed to 150 OTUs the CNS percentage is NOT 50%. CNS loading has nothing to do with OTUs. These are units used to gauge pulmonary toxicity levels.

Doopler: with all due respect I think this thread is about enriched air exposure over multiple days or pulmonary toxicity. The number PADI uses (and the number that programs like V-Planner use) is a maximum of 300 OTU's per day.

My nickname is Doppler and I appreciate your respect. A daily limit of 300 has been adopted by a number of divers as a "set" daily loading for OTUs. I have no idea what PADI uses. I was a beta tester for V-planner and have used it since its first iteration. None of this alters the fact that the daily limits for OTUs set out in the original work was in excess of 1400 and a daily limit of 850 is often quoted. The fact is that the most I have ever experienced on a dive is 600 and something and that was a long dive.

You are correct my post was confusing because 150 refers to minuets and not OTU's. However, using the PADI tables I still contend that you could dive up to 6 dives using EAN36 at 90 fsw for 24 minutes (NDL for air tables) per dive and NOT exceed the daily limit of 300 OTU's. You would exceed the 300 OTU limit on your 7th dive.

Please read my earlier posts. I am not trying to nit-pick here just trying to put out correct information. OTUs are not the issue. The 24-hour CNS limits are the issue I brought up. You have NOT displayed any understanding of this issue nor do you seem to have a basic understanding of the difference between pulmonary and CNS toxicity.

 

[raymond phule]

What he's saying is that even though Nitrox pushes the limits of safety, if you go and reach these new limits you won't be safer. And people tend to reach for the new limits, that's what human beings do.

We talked about diving nitrox on air tables. I dont see how that pushes the limits for nitrox. The NDL limit on an air table is shorter than the NDL limit for a nitrox table. Planned dives using the air table is thus safer compared to planned dive using the nitrox table (ofcourse only if the NDL limit is the limit for the dive) if we use nitrox.

I agree with the rest of the post and your explaination is very very similar to my own post above.

 

[jon m]

thanks for all the opinions! sheesh- didn't mean to cause such a stir....

 

[optimator]

I stand (or is it sit?) corrected. I mixed up CNS and pulmonary toxicity in my previous posts. Sorry for the confusion.