Nitrox question.

[CD_in_Chitown]

What I am surprised at is that so many nitrox divers are reliant on nitrox tables. Don't they teach EAD calculations any more. And what if you want a different gas? I like 30% on many dives. I haven't seen any tables for that.

I went TDI and learned the nitrox tables as well as how to use EAD for air tables, but the recommended safety margin was achieved diving air tables as if diving air. We didn't get into planning dives using EAD until adv nitrox.

 

[Scuba_Steve]

What are 32 and 36% if not standard gasses?

Well that's a start at least.

What would be kinda nice to have as an add-on to that is to see just how rediculous it is to attempt to dive 36 over 32 or many other best mix calcs for your basic recreational dive, given the percieved advantage, which is nil. Add to that, other needlessly complicated, however small, situations that can develop and need to be addressed, and I can start to see why everyone is trying to run amuck with excel spreadsheets, expensive and needless slates up the hoop, formulae for this and that etc, when I think what is needed most, which is a diver that should just be aiming to simplify their gas planning and make it bare-bones simple and effective, and make it workable while bouncing around on a boat with nothing but your noggin' on.

 

[CD_in_Chitown]

Well that's a start at least.

What would be kinda nice to have as an add-on to that is to see just how rediculous it is to attempt to dive 36 over 32 or many other best mix calcs for your basic recreational dive, given the percieved advantage, which is nil.

Are you saying that diving the highest operating PO2 possible (to diver's threshhold ie 1.4, 1.5, etc) is less desirable than diving 32% for all rec dives? IE Diving 39% on a dive to 80 fsw is nil benefit vs 32%?

 

[wedivebc]

Well that's a start at least.

What would be kinda nice to have as an add-on to that is to see just how rediculous it is to attempt to dive 36 over 32 or many other best mix calcs for your basic recreational dive, given the percieved advantage, which is nil. Add to that, other needlessly complicated, however small, situations that can develop and need to be addressed, and I can start to see why everyone is trying to run amuck with excel spreadsheets, expensive and needless slates up the hoop, formulae for this and that etc, when I think what is needed most, which is a diver that should just be aiming to simplify their gas planning and make it bare-bones simple and effective, and make it workable while bouncing around on a boat with nothing but your noggin' on.

Those of us who can handle simple arithmetic find best mix beneficial and far from complicated. The only thing missing from your post is a link to Georges "bakers dozen" rant.

 

[Scuba_Steve]

Are you saying that diving the highest operating PO2 possible (to diver's threshhold ie 1.4, 1.5, etc) is less desirable than diving 32% for all rec dives? IE Diving 39% on a dive to 80 fsw is nil benefit vs 32%?

I'm saying it's bascially pointless given the other considerations you have to deal with, when you're attempting to maximize the so called "best mix" scenario, which include a host of issues on top of just your basic PP02 calcs which it seems to me occupy a large portion of everyone's worry.

 

[CD_in_Chitown]

Those of us who can handle simple arithmetic find best mix beneficial and far from complicated.

Its just numbers after all

Decompression model: VPM - B

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 80ft (1) Nitrox 32 50ft/min descent.
Level 80ft 58:24 (60) Nitrox 32 1.07 ppO2, 64ft ead
Asc to 20ft (62) Nitrox 32 -30ft/min ascent.
Stop at 20ft 9:00 (71) Nitrox 32 0.51 ppO2, 12ft ead
Surface (71) Nitrox 32 -30ft/min ascent.

Off gassing starts at 45.6ft

OTU's this dive: 68
CNS Total: 24.5%

131.8 cu ft Nitrox 32
131.8 cu ft TOTAL



Decompression model: VPM - B

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 80ft (1) Nitrox 36 50ft/min descent.
Level 80ft 58:24 (60) Nitrox 36 1.21 ppO2, 58ft ead
Asc to 20ft (62) Nitrox 36 -30ft/min ascent.
Stop at 20ft 1:00 (63) Nitrox 36 0.57 ppO2, 10ft ead
Surface (63) Nitrox 36 -30ft/min ascent.

Off gassing starts at 40.9ft

OTU's this dive: 81
CNS Total: 28.7%

124.1 cu ft Nitrox 36
124.1 cu ft TOTAL


Decompression model: VPM - B

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 80ft (1) Nitrox 39 50ft/min descent.
Level 80ft 58:24 (60) Nitrox 39 1.31 ppO2, 54ft ead
Asc to 20ft (62) Nitrox 39 -30ft/min ascent.
Surface (62) Nitrox 39 -30ft/min ascent.

OTU's this dive: 91
CNS Total: 33.9%

123.3 cu ft Nitrox 39
123.3 cu ft TOTAL


DIVE PLAN COMPLETE

********* WARNING & DISCLAIMER *********
This V-Planner generated dive schedule could indirectly kill you.
The author does not warrant that it accurately reflects the Varying
Permeability Model algorithms, that it won't get you bent or dead, or that it
will produce safe, reliable results. This dive schedule is experimental
and you use it at your own risk. Diving in general is fraught with
risk, and decompression diving adds significantly more risk.
Deep diving utilizing multiple gasses, including Helium, is about
as risky as it gets.

This schedule is not intended for uneducated users. V-Planner and the
decompression schedules it produces are tools for experienced mixed-gas
decompression divers ONLY. If you have not been properly trained in
mixed-gas decompression diving by an internationally recognized technical
certification agency and/or don't have a firm handle on decompression
planning and mixed-gas diving, then DO NOT USE THIS DIVE SCHEDULE.

1.07 PO2 on 32%

1.31 PO2 on 39%

So it isn’t that much when converted to residual nitrogen….It’s only the difference between an NDL dive and a deco obligation.

 

[Scuba_Steve]

Those of us who can handle simple arithmetic find best mix beneficial and far from complicated. The only thing missing from your post is a link to Georges "bakers dozen" rant.

Too bad you never figured out what it is they were talking about Dave.

It doesn't get much more simple than how they do it, and the reason are sound as can be.

Tell me Dave, what do you really gain with 36 over 32 that has any meaning given how you've now needlessly comlicated, however marginal the entire EAD, NDL calcs.

The simple answer is it's a pointless exercise, but hurrah, you've worked it out to 3 decimal places!

One day because you've best-mixed your butt into blowing a dive because the site was changed and now you're too hot for the site that's now on tap should be interesting.

It may not be that way where you dive, but I can tell you I've seen a whole pile of divers doing just that around our parts.

It's right about then they figure out why we do what we do.

I'm sure the $60.00 charter to sit on a boat stung a bit, but it was a lesson well learned.

I figure I'll just save my students the dough and tell them up front how they should be doing it, and exactly why.

 

[wedivebc]

Too bad you never figured out what it is they were talking about Dave.

It doesn't get much more simple than how they do it, and the reason are sound as can be.

Tell me Dave, what do you really gain with 36 over 32 that has any meaning given how you've now needlessly comlicated, however marginal the entire EAD, NDL calcs.

The simple answer is it's a pointless exercise, but hurrah, you've worked it out to 3 decimal places!

One day because you've best-mixed your butt into blowing a dive because the site was changed and now you're too hot for the site that's now on tap should be interesting.

It may not be that way where you dive, but I can tell you I've seen a whole pile of divers doing just that around our parts.

It's right about then they figure out why we do what we do.

I'm sure the $60.00 charter to sit on a boat stung a bit, but it was a lesson well learned.

I figure I'll just save my students the dough and tell them up front how they should be doing it, and exactly why.

You may be surprised to find out I have done lots of investigation on the merits of standard mix vs best mix. Just because I don't agree with your point don't think I don't know where DIR stands on standard mix. I personally find I prefer to reduce the amount of N2 I absorb during a dive and to that end don't find a couple of simple calculations, which most people with high school education can do in their head. I think CD's post above shows far from marginal results, if anything they are quite significant. And that is on a non-mandatory deco dive. The difference is even more pronounced on a long deco dive. Here in the great white north water temp limits my comfort zone to about 1 hr of in water time before I am ready to get out. For the kind of diving I do the difference between standard mix and best mix can mean 15-20 minutes of deco on a single dive.
This is yet another example of DIR trying to make a set of rules fit to all circumstances. Life is full of diversity and so is diving.

 

[fire_diver]

What are 32 and 36% if not standard gasses?

What I am surprised at is that so many nitrox divers are reliant on nitrox tables. Don't they teach EAD calculations any more. And what if you want a different gas? I like 30% on many dives. I haven't seen any tables for that.

I took the PADI EANx course and the calcs are part of the book. And while the math is simple and straight forward, a preprinted page with every step from 22 to 40 makes life easier. And yes, there are tables with more than just 32 and 36.

FD

 

[Mothball]

By BC: "Hey, wasn't I just looking something up for you on RBW?"

Yes sir, I would the same Mothball. I got your PM. Thanx I appreciate the help. i just got on this site this week. Nice place. Blue water wishes and Semper Fi Dave