why a 32 mix standard?

[scubajohn921]

any reason why for dives of 100ft and below DIR uses the 32 EANx mix? i was just wondering,

 

[cudachaser]

At 1.6 pp O2 132 is the max 32%

 

[mwhities]

At 1.6 pp O2 132 is the max 32%

and I love the fact that I understand what you are saying here. I just finished my Nitrox class. I love knowledge.

Michael

 

[DIR-Atlanta]

any reason why for dives of 100ft and below DIR uses the 32 EANx mix? i was just wondering,

Anything leaner is not going to give you much benefit over diving air, and anything richer has the potential to create concerns with oxygen toxicity at depths approaching 100 FSW. With 36%, for example, the MOD is 95 FSW at a max PO2 of 1.4 ATA, so that limits what you can do depth-wise. There's not that much benefit to be gained with the hotter mixes in terms of increased bottom time, so 32% is considered a pretty good compromise between maximizing dive time and minimizing risk of O2 Tox, throughout the accepted range of recreational depths.

Also, 32% is a key component for creating so-called "standard gases". All the standard GUE mixes except 30/30 can be created by topping pure helium with 32%, so if you are operating a fill station you can set things up to do a continuous blend of 32%, and then make everything else from that (including "plain old Nitrox"). This is a very cost effective way to run a fill station (allows you to drain your oxygen and helium bottles close to empty before refilling them). In particular, it allows maximum utilization of your helium, which helps keep costs down.

Making 30/30 is a little trickier, but not too bad. And at rec depths, you get pretty much the same bottom time with 30/30 as you do with 32%, so you basically already "know" what your profiles and bottom times are going to be if you have been standardizing on 32% to begin with.

 

[spectrum]

I'm trying to figure out why the OP has the question if he is EAN certified.

I assume by "100ft and below" he means 100 feet and shallower.

PPo2, 1.4 at 111, a nice margin for 100 foot dives while still getting a good break in the nitrogen.

Is the application of EAN different for DIR?

Pete

 

[DIR-Atlanta]

Is the application of EAN different for DIR?

A little bit - with DIR, we typically don't think in terms of "best mix". Rather, we concentrate on standard mixes, which are optimized for a particular depth range. Using the same mix for all your dives in a particular depth range gives you a pretty good feel for what the profiles and deco schedules will look like, so you can build a sort of "database" of common profiles for dives that you frequently do.

For dives shallower than 100 FSW, we recommend 32%, unless you prefer a helium-based mix for the deeper dives (in which case you would use 30/30). For dives deeper than 100 FSW, we would typically use a normoxic or a slightly hypoxic trimix (for example, 21/35 or 18/45).

 

[divad]

Not DIR, but it just makes sense as a next-to-the-door, commonly banked, mix when you don't know how deep your first dive is the next day.

 

[Jason B]

delete

 

[texdiveguy]

For dives deeper than 100 FSW, we would typically use a normoxic or a slightly hypoxic trimix (for example, 21/35 or 18/45).

?? Since when did 18/45 TMx become hypoxic?

 

[LG Diver]

?? Since when did 18/45 TMx become hypoxic?

Why wouldn't it be?