Nitrox question.

[Scuba_Steve]

Hey CD, yes it's just numbers, you're correct. None of it is compicated, what a lot of it is from a field useability stand-point is nonsensically and needlessly overly complicated, because you've now made it that way because of the choices being employed.

What Ross hasn't yet designed into his V-planner program is an arm that'll come out of the computer and smack someone for running such a profile.

Next time I see him I'm going to ask him why.

What the program is whispering to you, which is probably why you don't see (hear) it, is that diving a simple 32 over that sweet 39 mix on that 80ft dive is that by somehow believing you've gain some huge NDL benefit, which you haven't, as it's pretty obvious that how myself and I would assume most of us dive is that you're doing a 3min S/Stop anyway, so the reality is you've theoretically gain what, 2-3mins?......well OK if you think that means much, fill your boots because click that ascent speed or Conservatism button one notch and you'll see that either way you play it, getting on the boat after a 3 min S/S on either gas certainly is no violation of anything.

OK that's nonsense is cleared up, you've gained "hypothetical nothing" for NDL.

What you've probably never had happen to you, which IS a real concern, is 02 stress loading on your body, because believe it or not, as much as 02 is your friend, he ain't given anything away for free.

If you think an hour straight of 1.3+ vs. 1.0+ means nothing, you'd be seriously wrong. If you think you can't get a fair amount of 02 burn within the table limits, you'd be wrong again. I've seen it happen first hand, and WELL within the 02 exposure limits.

So basically you're seriously abusing your body with 02 for nothing gained in return.

You've basically added far more 02 loading than you ever needed to abuse yourself with.

Heck, you may as well have done a deep trimix dive and then run your last stops for 20mins on pure 02 plus previous deco gases "abuse" since you've done such a fine job of ramping the loading up so much. What's worse is you did it on a rec dive where in 1 hr you'll be doing it yet again!

Not to mention you have to use V-planner to figure out all your NDL's for all the best mix gases you choose to run anyway, so in the end it's a Cluster F* of various NDL calcs, PPO2's, MOD's, all needlessly complicating, however small (OR NOT as you've seen) what should be a fun and easy day of diving. Where's my table, which table, what's my this, what's my that.........horse-feathers!

It's really tough to not to have to lug all the software, tables etc around, and to not worry about going to site "B" vs. "A" because my mix is too hot, but we must endure

There's lots more to add here.......but not today, as that should be enough to make one think for a while.

Don't sweat it Dave, agreeance is not mandatory.

Regards

 

[wedivebc]

What you've probably never had happen to you, which IS a real concern, is 02 stress loading on your body, because believe it or not, as much as 02 is your friend, he ain't given anything away for free.

If you think a hour straight of 1.3+ vs. 1.0+ means nothing, you'd be seriously wrong. If you think you can't get a fair amount of 02 burn within the table limits, you'd be wrong again.I've seen it happen first hand, and WELL within the 02 exposure limits.

That is real nonsense since it seems OK to deco for an hour on O2 to get the "oxygen window" effect but 1.3 as a bottom gas will burn your lungs? As a rebreather diver I do 1.3 all the time with no ill effects. I will admit each diver has different suseptability but the argument you make against proper mix selection falls apart when you look at your agency's accepted deco strategy.

 

[H2Andy]

So basically you're seriously abusing your body with 02 for nothing gained in return.

do you have some links where i can learn more about this O2 abuse issue?

i must admit than other than CNS and pulmonary toxicity issues, i've never
heard of O2 "abusing" the body.

 

[PerroneFord]

I did IANTD Nitrox/Adv Nitrox. My instructor used the IANTD materials, TDI materials, and the NOAA diving book. IANTD does not provide tables for the course. So you dive air tables and all calcs require transfer to EAD, and we were asked to do END as well. Seemed ok to me.

As for getting a mix that is "too hot" for the depth, well, no one says you have to violate MOD just to get in the water. And while it may be dubious to have a hot mix in water deep enough to get you into trouble, that point can be argued.

Dive safe.

 

[Charlie99]

Since you always round up and the EAD method is more steps, you get a more conservative answer using EAD with air tables than the dedicated Nitrox tables.

http://www.gooddiving.com/nitroxx4.pdf is a table of Equivalent NITROX depths that eliminates that problem. In other words, rather than taking 10' increments of depth on nitrox and giving the equivalent random depths on air, it take 10' steps of air depth and gives the equivalent nitrox depth for the different mixtures.

The attached excel file has the same info, plus MODs for various ppO2 such as 1.0, 1.4, 1.6 and 2.0ata.

 

[CD_in_Chitown]

What the program is whispering to you, which is probably why you don't see (hear) it, is that diving a simple 32 over that sweet 39 mix on that 80ft dive is that by somehow believing you've gain some huge NDL benefit, which you haven't, as it's pretty obvious that how myself and I would assume most of us dive is that you're doing a 3min S/Stop anyway, so the reality is you've theoretically gain what, 2-3mins?......well OK if you think that means much, fill your boots because click that ascent speed or Conservatism button one notch and you'll see that either way you play it, getting on the boat after a 3 min S/S on either gas certainly is no violation of anything.

Of course I used Vplanner to do the math, it doesn't mean I'm incapable, it means this exercise is not worth my effort.

Its 9 minutes and several OTUs difference, if you've only got one dive and want to stay within NDLs you can do it as illustrated.

If you're deadset on 32% have fun, I'm sure it helps focus on the fun if you don't have to do the math.

 

[espenskogen]

Of course I used Vplanner to do the math, it doesn't mean I'm incapable, it means this exercise is not worth my effort.

Its 9 minutes and several OTUs difference, if you've only got one dive and want to stay within NDLs you can do it as illustrated.

If you're deadset on 32% have fun, I'm sure it helps focus on the fun if you don't have to do the math.

I'm with you and Dave on this one. If for no other reason, reducing the n2f by 7-8% will benefit by just reducing the gradient. Realistically, if the argument for diving 32% is that you can go deeper than on a hot mix, then it simply won't hold up.

I thought the whole DIR mantra involved plan your dive, dive your plan?

You should know your max depth before you get in the water, and if you find it's deeper than you planned, you hold your planned depth, and end the dive. Period.

I think it's beyond discussion that a high N2 fraction does more damage than a high o2 fraction, assuming the PP is within range for both gasses. (That would mean an END of 30 m and PP02 of 1.4 for the working portion of the dive)

 

[espenskogen]

What you've probably never had happen to you, which IS a real concern, is 02 stress loading on your body, because believe it or not, as much as 02 is your friend, he ain't given anything away for free.

If you think an hour straight of 1.3+ vs. 1.0+ means nothing, you'd be seriously wrong. If you think you can't get a fair amount of 02 burn within the table limits, you'd be wrong again. I've seen it happen first hand, and WELL within the 02 exposure limits.

So basically you're seriously abusing your body with 02 for nothing gained in return.

You've basically added far more 02 loading than you ever needed to abuse yourself with.

This whole thing here has no root in reality, and I suspect you know it.
Pulmonary tox would not be any worse with 1 hour exposure of 1.3 vs an hour of 1.0 - As you should know, pulmonary tox is an issue when you're exposed multiple hours of PPo2 in excess of 0.5. Increasing the PPo2 would make little difference on such short exposure. And before the exposure gets high enough to actually make a difference on pulmonary tox, you'd be convulsing.

Now, we all know that the chances of convulsing on a setpoint of 1.3 is almost non-existent as long as you stay within the daily exposure limits, so quite frankly I'd be quite curious how this O2 abuse would manifest itself.