PADI Nitrox Course

[Walter]

BCS,

Actually, a higher percentage of oxygen also speeds up the off gassing.

Drew,

You quote me, but you obviously didn't comprehend what you quoted. "Walls prevent planing for the bottom, so I stay with air." We aren't going to the bottom of those walls on any mix and live.

"Wall diving too dangerous on nitrox?"

I never made that statement. It is easy to dive walls safely on nitrox. It is not safe to go after someone who's narced and heading deeper. When that happens, I'll be on air instead of nitrox, so that I will be able to make a deeper rescue.

"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 certainly agree we have choices. Fromn your statement, it seems you believe a PPO2 of 1.4 atm is too high an exposure? Am I incorrect in my belief that PADI also teaches 1.4 as the working limit with 1.6 as a contingency? Do you think they should lower the recommended limit? Best mix can be planned at 1.3, 1.2, 1.0 or any other limit you feel is best. Best mix allows you to make your choice of what oxygen exposure you are comfortable.

"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."

Drew, don't worry, I'm under no illusions about actions you'd take on my behalf.

"I do not assume the lowest common denominator of my students."

Apparently not, you expect them to understand a concept you don't teach. Not to worry, you don't test them on that concept either.

"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?"

How would you know?

"Do you even know what the required materials are for a PADI Enriched Air course are?"

I know what students of this course have and have not received. I freely admit, this may be short of, right on or in excess of standards. I have talked with several PADI nitrox students, none of them understood the concept, nor could any of them plan a best mix at the completion of their course.

"Do you have the student text?"

I have read the student text, but I do not have a copy. I discussed this topic with a PADI nitrox instructor while I had the text in my possession. We agreed this concept is not covered.

"The instructor's outline?"

I do not.

"The video?"

No.

"Anything to back up what you are saying?"

What exactly am I saying? "that particular course doesn't include the concept of best mix." You've as much as admitted that it is not part of the course because your students can figure it out themselves and because it's not a good idea to use best mix. I'm confused when you try to claim credit for PADI including various skills and topics while explaining why it is not included.

All I did was suggest that someone taking a course ask to have a concept covered. I did not suggest he take a "better" course. From what I can see PADI offers a nitrox course that covers everything except one concept that can easily be added in a few minutes.

 

[MikeFerrara]

Walter
I know the answer to this...

"I never made that statement. It is easy to dive walls safely on nitrox. It is not safe to go after someone who's narced and heading deeper. When that happens, I'll be on air instead of nitrox, so that I will be able to make a deeper rescue."

...and it isn't in the choice of gasses is it?

 

[Scot]

raxafarian,

What ya doing going into any kind of real deco on air. Air is a terrible gas to deco on and shouldn't even be considered. Trim that dive down to something more reasonable (a non deco dive so no penalties for air). At an END of 90' that would be a 30 minute dive (120 rule). I run those numbers on GUE's deco planner and I get a 42 minute dive either way (32% @110 vs 21% @ 90').

 

[Scot]

make that a EAD not END..... It's almost 2:00 am.... I'm out:snore:

 

[raxafarian]

Scot once bubbled...
raxafarian,

What ya doing going into any kind of real deco on air. Air is a terrible gas to deco on and shouldn't even be considered. Trim that dive down to something more reasonable (a non deco dive so no penalties for air). At an END of 90' that would be a 30 minute dive (120 rule). I run those numbers on GUE's deco planner and I get a 42 minute dive either way (32% @110 vs 21% @ 90').

I'm not doing those dives. The statement that BCS made (kinda sarcastic, especially since he was wrong ) was that EAN does NOT increase the rate of offgassing of N2. Well, that is wrong. So I was just showing the numbers for 2 different dives that would have absorbed the same amount of N2, with offgassing shown being faster using the EAN gas. I used the longer time to better demonstrate the difference in offgassing rates. Sorry to confuse you.


Ok...without the numbers. While breathing EAN your inspired nitrogen is less (and the higher the O2 in your gas, the less your inspired N2). The less that your inspired N2 is, the greater the difference between the nitrogen absorbed and the N2 in your lungs, the faster the rate of offgassing.

why else would deco divers switch to a higher % O2 gas during ascent / deco ? To speed up offgassing.

 

[BCS]

Rax,
Please explain how when using the EAD tables you can get two different dive profiles for the same schedule. Using the EAD concept, a diver would use the same schedule for a 110'/:60 on 32% profile as they would for a 90'/:60 on air (21%) profile, IOW, 110'/:60 on 32% uses the 90'/:60 air schedule AND 90'/:60 on air uses the 90'/:60 on air schedule, hence EAD. Yet, you show two completely different schedules for these dives. Are you plugging these into a deco program? If so look at the M-values at the different stop depths. The equivalent stop depths on air are not the equivalent stop depths on 32%, they yeild different M-values. This causes minor variances in stop times at those depths and this gives two different profiles for supposed "equivalent" dive schedules.
And yes, of course, EANx does increase the rate at which inert gas is off gassed on an ascent when switched to higher O2 %. this is due to a gradient increase brought about from the change in inert gas %. I do not argue that.
But, please point me to your source that says that EANx increases the RATE at which N2 is eliminated. Key word here is "RATE". Not amount. Also, I am not speaking about a gas switch either. Same gas on bottom as during ascent. The changes in amount (%) of N2 result in changes in the amount absorbed and the amount to be eliminated, but I do not believe the rate. I am in no way an expert on decompression mechanics, I doubt anyone here is, but there may be something new here that I am completely unaware of, and if that is the case, I stand corrected...Oh...and I am writing all of this most non-sarcastically.

Oh and my apologies to the thread starter for getting so off the topic. Though it is nice to get some good discussion going, I hope your question about your EANx course was answered. Make sure you ask your instructor what to do with a toxing diver and to please explain how EANx changes the RATE of N2 elimination, but make sure you specify rate, that means speed, not amount.

 

[BCS]

Rax wrote:
"The less that your inspired N2 is, the greater the difference between the nitrogen absorbed and the N2 in your lungs, the faster the rate of offgassing."
Rax,
Actually, when you inspire less N2 (as in the case with EANx) you ABSORB less N2. Thus, the ratio (or difference, as you say) between absorbed N2 and the N2 one is breathing does not change (unless you change it with a gas switch, that would increase the off gassing rate-BUT we are not talking about gas switches here). Let me see if I can put it another way. If I am breathing a 4x amount of N2. My body will absorb, say for argument's sake, 6x (the no.'s are arbitrary but the body will absorb greater amounts of N2 due to increased pp from the depth) in a set amount of time. The ratio of absorbed gas to breathing gas will be 6:4 or reduced, 3:2 (tissue:lung gas pN2--this is how gas is pushed from the tissues...a greater tissue pp than lung gas pp) . NOW, lets try an EANx mix of 2x (more O2 hence less N2), the body will still absorb N2 based on ambient pressure (depth) for the same amount of time, so I will absorb 3x (half the N2 as compared to the prior mix equals half the N2 absorbed compared to the prior dive). This still yeilds the same 3:2 tissue to lung gas pN2 ratio.
The only way to change this ratio is to change the gas during the ascent. THAT is how EANx can, in fact increase off gassing rates.
Once again, this is all non-sarcastically written.

 

[raxafarian]

BCS once bubbled...
And yes, of course, EANx does increase the rate at which inert gas is off gassed on an ascent when switched to higher O2 %. this is due to a gradient increase brought about from the change in inert gas %. I do not argue that.

Ok... no gas switch.

Using EAN increases the RATE of offgassing because the pressure of nitrogen inspired is LESS than the inspired pressure of nitrogen if breathing air. Same as if you had switched to a higher O2 %, because you HAVE switched (air vs. EAN). So there is a gradient increase due to less inert gas inspired than if you were breathing air. Breathing .68%N2 vs .79%N2 will create a greater difference between the pressure of N2 in your lungs and the pressure of the aborbed N2 in your tissues (using the extra time avail. with the EAN to have absorbed the same amt. of N2 as an air dive), therefore the N2 will offgas faster using EAN.

You absorb nitrogen slower during descent and bottom time. You get rid of it faster during ascent.

 

[raxafarian]

yes... I'll agree you can absorb less nitrogen using EAN. But most people use EAN to extend bottom time, and therefore end up with close to the same amount of N2 absorbed as on an air dive.

 

[BCS]

Rax,
You were doing pretty good before the last posts.
Off gassing rate is based on ratios (or gradients). If you absorb less N2, as in the case with EANx, the ratio of absorbed gas is contrasted to the lower amount (%) of N2 in the EANx. Lower absorbed pN2:lower breathing pN2 (EANx). Both values are lower, this is simple math, the ratio does not change, just the values. The ratio is what governs off gassing rate. Same ratio = same off gassing rate.
I did not just receive my nitrox card.
ps. that is sarcastic.