Nitrox safer than air

[Scubaroo]

I still had some moron yell out "Devil's Gas!" at the LDS as I carried my tank in for a fill this weekend. Looks like I'll be diving mostly EAN36 because that's what they bank. Mixing EAN32 is a process of filling with EAN36, blowing clean air on top, analyzing, adjusting with more air, etc etc. Most of my diving is in less than 60' anyway, so EAN36 fits the bill. :shhhh:

 

[Uncle Pug]

bengiddins once bubbled...
Looks like I'll be diving mostly EAN36 because that's what they bank.

my diving is in less than 60' anyway, so EAN36 fits the bill.

The point isn't 32 or 36... more like pick a standard and stick with it... none of this, "Well my calculations show that the best mix for this dive is 33.7%.... oh, dang... it analyzed out to 33.4%... dump it and start over Mr. Mixer!"

It is even possible that 36% would be a better fit in the scheme of things if one were to use 30/30 for all dives 80~120.

BTW.. you probably already know this already Ben so let someone else take a stab at it... what is the safety factor of 36%?

 

[Stone]

Diver A makes a dive to 100 fsw on air (his NDL is 20 minutes).
He begins his ascent at 20 minutes because he has no more “safety margin”.

Diver B makes a dive to 100 fsw on EAN32 (his NDL is 30 minutes).
He begins his ascent at 20 minutes (he is using his air table).

How much “safety margin” did Diver B gain over Diver A by diving EAN32 on an Air Table?

--------------------------

I would propose that Diver B would have run out of “safety margin” at 30 minutes, so by beginning his ascent at 20 minutes, he had a “safety margin” of 10 minutes

Expressed as a percentage (a percent difference) the calculation is 100 *(30-20)/30 = 33 %

Is there a flaw in this reasoning?

 

[Uncle Pug]

Northeastwrecks once bubbled...
I'm not taking my DIR-F course until this October, when I'm told that I will learn such things.

I don't know if they will be getting into that with you in the DIRF...
But maybe you could ask the question if they don't.

btw... I just stumbled onto the thread that talks about youse guys going on a u-boat dive......
Bwaaaaa... sniff...whaaaaaaa.. ;-0

I wanna go.....

 

[O-ring]

BTW.. you probably already know this already Ben so let someone else take a stab at it... what is the safety factor of 36%?

33%?

Depth	EAD	%
20	10	50%
30	18	40%
40	26	35%
50	34	32%
60	42	30%
70	50	29%
80	59	26%
90	67	26%

Average		33%

 

[Uncle Pug]

Stone once bubbled...
Is there a flaw in this reasoning?

I was referring to a safety factor in relation to Equivalent Air Depth.... not NDL.

EAD safety factor works for all depths.
NDL safety factor changes for different depths.

Or at least I think it does... remember... I hates math...
Check me out on this one.

 

[Stone]

If O-Ring's tables above calculate the "Safety Factor" you are talking about, then the safety factor changes with depth (and the 20% is a rule of thumb). ?

 

[Uncle Pug]

O-ring once bubbled...
33%?

That wouldn't work for 90' would it.
Take the deepest depth and figure for that.
The increased SF at shallower depths isn't a problem.
Averaging the SF will get you into trouble deeper.

And while your at it remember to keep things simple.

I hates math... I don't want to figure no stinking 27.5% of anything... even with a calculator...

I know that 20% is 1/5th and I can work with that as well as .20
I know that 25% is 1/4th and I can work with that as well as. 25

So I use 20% for EAN32 and 25% for EAN36 to figure EAD.
And I only carry air tables. And the safety factor increases as I get shallower.

 

[Northeastwrecks]

Uncle Pug once bubbled...

I don't know if they will be getting into that with you in the DIRF...
But maybe you could ask the question if they don't.

btw... I just stumbled onto the thread that talks about youse guys going on a u-boat dive......
Bwaaaaa... sniff...whaaaaaaa.. ;-0

I wanna go.....

Thanks for the information. Your point is well taken. FWIW, I did my 35 fsw dives this weekend on Nitrox 32 just to save the shop's O2 supply.

I plan to take DIR Tech 1 next year. I'm taking TDI's advanced Nitrox and Deco Theory later this year (thereby avoiding any of the problems I've heard about boats not accepting GUE cards). So you're probably right, I will look at trimix for intermediate depth dives after we finish installing the helium system in my buddy's garage.

As for the sub, we would welcome the opportunity to have you out. You could ship your tanks out via carrier. I know a place about an hour away that does trimix fills, so you'd be all set.

The sub is great. There is another (USS Bass) that is split in two pieces in about 150 feet. You can penetrate both portions.

I can't dive the Bass until I get my doubles rigged. Obviously, mix would be nice as well. However, just for giggles, I calced the dive today as 30 minutes at 150 with a sling bottles of Nitrox 50 and 100. Looks pretty cool.

 

[Uncle Pug]

Stone once bubbled...
If O-Ring's tables above calculate the "Safety Factor" you are talking about, then the safety factor changes with depth (and the 20% is a rule of thumb). ?

yes... it's a rule of thumb.
And an easy one to remember.
So we don't carry nitrox tables...
We just remember the air tables and figure our EAD as 20% less than actual.
Or not.