Another (legit) nitrox ?

[ianr33]

To answer the Ops question let’s create a dive plan. Let’s make the limiting factor in the dive plan OTU exposure. Let’s use some actual tables.

So the first question to answer is what is OTU exposure and what is the maximum daily OTU exposure.

An OTU is defined as 1 minute of breathing pure oxygen at 1 ATM.

The next question we must answer is how many OTU's can a person be exposed to in 1 day. In 1989 Dr. Bill Hamilton came out with the REPEX method specifying OTU's for multi-day exposure. However, since we’re recreationally diving let’s use the more conservative DSAT tables.

Using EAN36 the MOD is 90 fsw.

Using the DSAT Air tables the NDL for 90 fsw is 24 minutes

The maximum OTU exposure at 1.4 ATM is 150 minutes.

150 max OTU exposure per day / 24 minutes per dive = 6.25 dives. Or 6 dives on EAN36 at MOD using air tables to reach your daily oxygen toxicity limit.

If the OP wanted to dive the EAN36 table the NDL is 35 minutes at 90 fsw.

150 max OTU exposure per day / 35 minutes per dive = 4.28 dives. Or 4 dives on EAN36 at MOD using EAN36 tables to reach your daily oxygen toxicity limit.

You are totally mixed up between CNS oxygen toxicity (High pO2 causing seizures)
and OTU's (lower pO2 over days) causing respiration problems

OTU's are not a problem on open circuit scuba. may be a problem for rebreather divers doing a LOT of diving over several days.

CNS O2 toxicity is the subject of this thread.

 

[Doppler]

Well Raymond has edited his posting and done away with the toxicity #1 and #2 nonsense... but there's still confusion about the need for CNS tracking in sport dives. (Raymond: FYI technical diving is still recreational... not my definition but the industry's informed by a couple of court rulings... since it is not commercial, military, public safety or scientific, it's recreational... but I know what you mean because it is a common mistake). Disregarding CNS loading -- which is an issue in sport exposures as well as in technical diving -- will get a diver killed.

Apart from that... I give up... this is a waste of time


Optimator: you should resist posting anything you have not thoroughly proof read. In addition, you should not post pretending to know about something when you do not. Your information is garbled and more importantly incorrect. Last time I checked the single day pulmonary toxicity limits are not 150 OTUs but 1440! And in any case, this thread is NOT about pulmonary toxicity.

Later edit: It has become obvious that Optimator is confused about the differences between CNS and Pulmonary oxygen toxicity...

 

[ianr33]

And people say you should not learn to dive on the internet !

 

[1_T_Submariner]

I'm just going to tell you what I do I'm sure you have had more than enough in depth theory.

I dive with my computer set to the correct mix and come up with some time remaining. This way your computer keeps track of O2, Mod etc...and the time left adds some safety. I will say this is how my wife and I do it in Bonaire where we dive 32% on multiple dives (3-5 for a week).

 

[Michael Schlink]

Doppler, I thought that that's exactly what this thread was about. The OP asked about O2 build up after mulitple dives over multiple days. Did I miss something?
Nonetheless 1 T said what I said. With typical recreational diving using some common sense a diver shouldn't have to worry too much about O2 build up which I believe is better called OTU's, am I wrong here? 'cause if I am I missed something along the way

 

[optimator]

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.

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.

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.

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.

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.

 

[ianr33]

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.

NO NO NO NO NO

What you wrote is just plain wrong. CNS toxicity (CNS%) and pulmonary toxicity (OTU's) are COMPLETELY DIFFERENT. Please,get a clue or shut up.

I'm done here.

 

[raymond phule]

Optimator is incorrect and ianr33 is correct.

This misunderstanding was the reason for my post about the #1, #2, #3 problems. You could also find it explained here DIR-diver.com - Nitrox Class Part 2

 

[raymond phule]

Well Raymond has edited his posting and done away with the toxicity #1 and #2 nonsense...

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

but there's still confusion about the need for CNS tracking in sport dives.
(Raymond: FYI technical diving is still recreational... not my definition but the industries informed by a couple of court rulings... since it is not commercial, military, public safety or scientific, it's recreational... but I know what you mean because it is a common mistake).

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.

Disregarding CNS loading -- which is an issue in sport exposures as well as in technical diving -- will get a diver killed.

Sure, everyone is getting killed.

Apart from that... I give up... this is a waste of time

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.
edit:clarification for steve. I didn't mean that the course teaches you that you should ignore the calculations done by the computer. It is clear from the course though that you are not going to learn how to do the calculations. It is actually a selling point. end of edit.
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.

 

[raymond phule]

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?

Are there any other reason for a longer bottom time than less nitrogen loading at a given time and depth?

(you used proved but nothing about diving is actually proved)

Nonetheless 1 T said what I said. With typical recreational diving using some common sense a diver shouldn't have to worry too much about O2 build up which I believe is better called OTU's, am I wrong here? 'cause if I am I missed something along the way

OTU's are about pulmonary O2 toxity. The build up used mostly in this thread have been the buildup at ppO2<1.4 that might result in CNS toxity.