PADI Nitrox Course

[BCS]

DD. Please expand on "help with the off gassing."

 

[BCS]

Wreck Writer. Here's a little of what I have read about O2 and it's narcotic effect. The narcotic effect (or anaesthetic potency) of gases in humans closely parallels the lipid solubility of those gases. This was observed by Meyer and Overton in the early 1900's. The Meyer Overton rule states that the anaesthetic potency of a gas is inversely related to it's lipid solubility. This rule does predict "narcosis" in inert gases, but there seems to be more to it than just the lipid solubility. The bodies metabolism of these gases plays a role as well. For example, oxygen, although it should be twice as narcotic as nitrogen, is readily metabolized by the tissues. Thus the gas partial pressure in the tissue does not follow the inspired gas partial pressure. This causes some trouble in predicting it's narcotic effect, coupled with the fact that it is usually toxic at partial pressures above 2.0, makes it hard to test the actual "narcotic" effect of O2. Another problem seen with the Meyer Overton rule is that it does not seem to accurately predict the narcosis of many compounds. i.e CO2.
So your statement is about percieved equal impairment levels is probably right on. The differences would be hard to detect based on O2 or N2 at those depths and mixes.

 

[WreckWriter]

Good info.

WW

 

[detroit diver]

BCS once bubbled...
DD. Please expand on "help with the off gassing."

I havent' stayed at a Holiday Inn Express, but here's my take on it:

As you ascend, you are still taking on gasses, nitrogen being one of them. Your decompression is the need to release this nitrogen slowly so that is doesn't bubble and cause problems. If you have a higher concentration of O2 and less N2 as in EANx, you are uptaking less N2 and thus have to off gas less N2. The O2 is utilized by the cellular structure.

If I'm off based, please feel free to correct me.

 

[BCS]

Aaaahhh....the student has become the teacher...DD, I have stayed at the Holiday Inn Express so let me ask you to say what you mean. Do you believe that EANx increases the rate at which a diver offgasses? That is what I understood you to mean when you wrote;
"Wouldn't the fact that there is more O2 seem to imply that there is Less N2? That would make it less Nitrogen narcotic, woudn't it? It would also help with offgassing, yes?"
Please clarify. Does it increase the rate or the amount of N2 being eliminated? Once again, a change to a helium based gas on the ascent would increase the rate at which N2 is being eliminated from the body. Whereas an EANx mixture just decreases the amount of N2 absorbed hence the amount needed to be eliminated as well. This is not necessarily "helping" with the offgassing, this is actually helping to slow the ongassing by limiting uptake. Sure, they are just semantics to some, but we are on the Scubaboard and darn it, you must use the correct terminology and try to be more precise in your choice of words or you will confuse me, the new guy, and others who are new to scuba as well. Some of us are only at the 20 to 30 posts mark in our career. That reminds me, I heard talk of another thread where there is the possibilty of counting an "x" number of posts as an actual dive. Is this true?? Boy, I could be a dive jester...uh...I mean dive master soon.

 

[Drew Sailbum]

Walter once bubbled...
Take exception all you like. That's fairly common in our discussions, I believe. If we dive together with the same profile, you using a "standard" mix (I've yet to see a true standard mix) with a lower percentage of oxygen than the best mix, while I use a custom best mix, we may or may not be limited by our respective NDL's. If we are limited by gas supply and assuming we surface at the same time, I will have a shorter required surface interval (assuming we are using the same computer or same tables) prior to our next planned dive. If we remain buddies on the next dive and go down together again diving the same profile you will be closer to your NDL. Perhaps it's not significant, but I like every edge I can get. So yes, you wasted some of the benefit of diving nitrox by being unaware of the usefulness of best mix. You certainly have not wasted all the benefits of diving nitrox.

The diver clearly has a choice. You can choose to max out the O2 exposure, the NDL, or neither. I'll choose my "standard" mix and stay away from max O2 exposure. I see an ox tox hit as being the primary danger and I give it a wide margin. While exceeding my NDL by a minute or two is not good, it is a mistake that I can take concious action to remedy. Exceeding my safe O2 exposure is not something that I would have any concious control over.

If we are diving together, rest assured that I won't have to wonder if I'm putting myself at undue risk if I need to descend to rescue you from an ox tox hit.

Walter once bubbled...
Diving the walls of Cayman, I'll pass on all the benefits of nitrox. When possible, I plan my best mix for the hard bottom. Walls prevent planing for the bottom, so I stay with air.

Wall diving too dangerous on nitrox? Better not use air. The hard bottom along some sections of those walls is way deeper than the MOD for air at either 1.4 or 1.6 ppO2. Or you could be realistic and use a mix at a depth where you aren't maxing out your O2.

Walter once bubbled...
True, but many of the students I see are not comfortable with math. I find it simple to manipulate some equations to come up with others. Many people do not find such proceedures simple. Unless we actually teach the concept, it is misleading to say it is covered because some people can figure it out for themselves from the equations in the text by manipulating them. If it were an algebra class, you'd have some justification for letting the students solve that one on their own. Since it is not an algebra class, you are either misleading people by saying the material is covered or you should simply fess up that best mix is not part of the course, the other option is, of course, to actually cover it.

I do not assume the lowest common denominator of my students. Enriched Air is a course in which the student must understand the relationship between the FN2 and NDLs for a given mix. The relationship of FO2, ppO2 and depth is another crucial concept.

The goal of the PADI Enriched Air course is not solely to have someone be able to answer the questions on the test. If you have students that can't understand the relationship between these factors well enough to compute one given values for the other two, then what have they learned? Or do they just need to learn to plug numbers into a formula? I prefer to focus on building an understanding of the underlying concepts.

We do teach these concepts in PADI. Do you with YMCA? I don't know what the requirements for YMCA courses are because I do not teach them. You seem to frequently posit on the requirements for courses through other agencies.

Do you even know what the required materials are for a PADI Enriched Air course are? Do you have the student text? The instructor's outline? The video? Anything to back up what you are saying?

 

[detroit diver]

BCS once bubbled...
Aaaahhh....the student has become the teacher...DD, I have stayed at the Holiday Inn Express so let me ask you to say what you mean. Do you believe that EANx increases the rate at which a diver offgasses? That is what I understood you to mean when you wrote;
"Wouldn't the fact that there is more O2 seem to imply that there is Less N2? That would make it less Nitrogen narcotic, woudn't it? It would also help with offgassing, yes?"
Please clarify. Does it increase the rate or the amount of N2 being eliminated? Once again, a change to a helium based gas on the ascent would increase the rate at which N2 is being eliminated from the body. Whereas an EANx mixture just decreases the amount of N2 absorbed hence the amount needed to be eliminated as well. This is not necessarily "helping" with the offgassing, this is actually helping to slow the ongassing by limiting uptake. Sure, they are just semantics to some, but we are on the Scubaboard and darn it, you must use the correct terminology and try to be more precise in your choice of words or you will confuse me, the new guy, and others who are new to scuba as well. Some of us are only at the 20 to 30 posts mark in our career. That reminds me, I heard talk of another thread where there is the possibilty of counting an "x" number of posts as an actual dive. Is this true?? Boy, I could be a dive jester...uh...I mean dive master soon.

If this wasn't a scuba board, I would say it was really getting deep in here...but to answer your first question:

The uptake would be diminshed, so the amount to be off gassed would be lower. The N2 would not come out of your system any faster (rate), there just would be less of it to come out.

This thread wasn't about helium, but yes, it would be a better alternative to simple EANx. The helium would replace the N2 and be absorbed fast, but also offgassed quickly. Bouyancy control would be important here due to the quick offgassing on ascent.

You seem very confused for a new guy....:dazzle: You need to stay at that place that they leave the light on for ya!

 

[raxafarian]

BCS once bubbled...
... Whereas an EANx mixture just decreases the amount of N2 absorbed hence the amount needed to be eliminated as well. This is not necessarily "helping" with the offgassing, this is actually helping to slow the ongassing by limiting uptake. Sure, they are just semantics to some, but we are on the Scubaboard and darn it, you must use the correct terminology and try to be more precise in your choice of words or you will confuse me, the new guy, and others who are new to scuba as well.

Using EAN certainly does help with offgassing.

I'm gonna use the following 2 dives and compare the deco.
1. 110 ft EAN32 for 60 min.
Stops = 1min. @50ft, 2min. @40ft, 5min. @30ft., and 38min. @20ft.

total deco = 46minutes

2. 90 ft on AIR for 60 min. (same dive as the first... EAD)
stops = 1 min @50ft., 2 min. @ 40ft, 6min @30ft, and 54 min. @ 20ft.

total deco = 63 minutes

Both dives stop ongassing / start offgassing around 60Ft during ascent.

and if you switch to a higher EAN during deco, offgassing occurs faster.

 

[detroit diver]

raxafarian once bubbled...



Using EAN certainly does help with offgassing.

I'm gonna use the following 2 dives and compare the deco.
1. 110 ft EAN32 for 60 min.
Stops = 1min. @50ft, 2min. @40ft, 5min. @30ft., and 38min. @20ft.

total deco = 46minutes

2. 90 ft on AIR for 60 min. (same dive as the first... EAD)
stops = 1 min @50ft., 2 min. @ 40ft, 6min @30ft, and 54 min. @ 20ft.

total deco = 63 minutes

Both dives stop ongassing / start offgassing around 60Ft during ascent.

and if you switch to a higher EAN during deco, offgassing occurs faster.

I think BCS is making the distinction between less N2 aborbed (and therefor better) and the RATE of offgassing. The EANx doesn't push N2 out faster, there's just less of it to come out.

But I dont' want to put words in his mouth. Oh gosh, no.

 

[raxafarian]

detroit diver once bubbled...


I think BCS is making the distinction between less N2 aborbed (and therefor better) and the RATE of offgassing. The EANx doesn't push N2 out faster, there's just less of it to come out.

But I dont' want to put words in his mouth. Oh gosh, no.

There is the same amount of nitrogen uptake in both dives I gave. 110 ft on EAN32 IS THE SAME as 90 ft. on air. So same amount of N2 absorbed. It definitely offgasses faster when using EAN.