Standard gasses?

[rjack321]

Been real quite around here lately.... tooo quiet

I have no idea how other people here treat the 32, 30/30 and 25/25 debate. Personally I chose gases based on my objectives and team more than what any particular agency/instructor says. And other than not having anything between 50% and 100% O2 (as in I'm not using anything in that range) I can continuous blend most anything I'm likely to use. So "ease of mixing" is a bit of a red herring IMO.

Anyway, here are my backgas selection criteria:
0' - 100' : Nitrox 32
80 - 110 : Triox 30/30
90 - 120 : Triox 25/25
121 - 150: 21/35
151 - 200: 18/45

In the fuzzy 80-120ft range my choice depends on currents, vis, overhead (or not), and whether I might need or want to push a little deeper than planned (e.g. on a wall where you're hovering just over the cool stuff), or at a new site that I'm not positive of the depths to be encountered.

I'm curious about other thoughts and discussion...
RJ

 

[KMD]

Been real quite around here lately.... tooo quiet

I have no idea how other people here treat the 32, 30/30 and 25/25 debate. Personally I chose gases based on my objectives and team more than what any particular agency/instructor says. And other than not having anything between 50% and 100% O2 (as in I'm not using anything in that range) I can continuous blend most anything I'm likely to use. So "ease of mixing" is a bit of a red herring IMO.

Perhaps more accurate to say that "ease of mixing" is a bit of a red herring to you. Others use different systems and thus have different needs.

For example we have one gentleman who has several T and K bottles of He and O2 in his garage. He partial pressure blends all the time.

 

[rjack321]

Perhaps more accurate to say that "ease of mixing" is a bit of a red herring to you. Others use different systems and thus have different needs.

For example we have one gentleman who has several T and K bottles of He and O2 in his garage. He partial pressure blends all the time.

That's true its not applicable to me. Nor any of the shops I know since they all have boosters. In WA, its rare for a shop to allow you to bring in anything and ask for an air or 32% top-off. I don't know how easy it is in other places to PP at home and get topoffs at a shop.

 

[Adobo]

That's true its not applicable to me. Nor any of the shops I know since they all have boosters. In WA, its rare for a shop to allow you to bring in anything and ask for an air or 32% top-off. I don't know how easy it is in other places to PP at home and get topoffs at a shop.

Really? Do they analyze your tanks before they will top off or do the completely drain them first?

 

[Rainer]

I'll play. Certainly *not* GUE DIR.

Shore dives (0-40'): Air
Here in MA (Cape Ann and Cape Cod) almost ALL of the shore dives are 15-30' (max). Nitrox isn't convenient to get, and O2-clean air is free and convenient. Not DIR, but all of MA DIR guys I know dive air on shore dives. DIR divers closer to CT and Ed Hayes seem to always dive 32%.

40-100': 32%
Actually most of the DIR guys I know in MA have standardized on 28% (allows a broader range of dives off the boats). My team dives 32% in this range.

100-120': 28%
Haven't actually done any dives past 100' since GUE-F, but I will, and we'll be standardizing on 28%, which we used before GUE training (PPO2 of 1.3, gives a 0.9 EAD multiplier). I'd prefer some He for dives in this range, and will seek the training to do so in the near future. In the meantime, I *will* continue to do these dives on 28%.

 

[rjack321]

Really? Do they analyze your tanks before they will top off or do the completely drain them first?

Either. My local recreational shop would flip out if I recorded 25% in their log when they thought they pumped 32%. And since it takes them 2 days to pump 32% they may very well check the contents if you leave them and I don't know what they'd do if you snuck in some He - probably dump it.

I do know if you ask, they will not top with either air nor 32% to provide any kind of trimix. Since they don't pump He themslves they won't let you walk out with any kind of trimix. That was 2 years ago when I inquired. Maybe they changed their policy since then.

 

[rjack321]

Shore dives (0-40'): Air
Here in MA (Cape Ann and Cape Cod) almost ALL of the shore dives are 15-30' (max). Nitrox isn't convenient to get, and O2-clean air is free and convenient. Not DIR, but all of MA DIR guys I know dive air on shore dives. DIR divers closer to CT and Ed Hayes seem to always dive 32%..

How many shops have just air vs. how many can provide 32%? When you say "inconvenient" what are we talking here, 4 hour drive drive vs. 20mins or what?? Just trying to put some boundaries on your criteria/justifications.

<40ft is danged shallow for 32% if its a burden. Personally I don't want an even bigger mishmash of gases in various tanks. Its hard enough to plan dives so I use the tank(s) I want, with the gas I want, for a given dive.

 

[SparticleBrane]

I'll use air for most of my diving, since it's all relatively shallow -- mostly quarry stuff these days due to geographic limitations. I can get it free at school if I give enough advanced notice since I work with the scuba program, so that's a nice economic benefit.

If I head off the coast I'm using 32%. It can definitely be a pain to get 32% in my tanks without the ugly nitrox wraps.

 

[Rainer]

How many shops have just air vs. how many can provide 32%? When you say "inconvenient" what are we talking here, 4 hour drive drive vs. 20mins or what?? Just trying to put some boundaries on your criteria/justifications.

<40ft is danged shallow for 32% if its a burden. Personally I don't want an even bigger mishmash of gases in various tanks. Its hard enough to plan dives so I use the tank(s) I want, with the gas I want, for a given dive.

For $20 fills it's a two-hour drive (total), and those are for crappy fills (mix off 1% and under-filled), or $30 for ok fills and an hour commute. Non-O2-clean nitrox can be had closer, but I keep my cylinders clean (certain shops I frequent in CT and NH only PP blend). Nitrox requires I leave the cylinders overnight. O2-clean air is free at the local dive shop (20 minutes away; they'll fill while I wait and I get "good" fills on LPs). The average shore dive on Cape Ann (where the vast majority of MA divers are diving) is 15-25' (max). I rarely see 30' from shore. It's really hard to justify the pain for 32% in these cases. I didn't get much complaint from my GUE instructor.

 

[rjack321]

Yeah, probably just use air too for all that rigamarol. There's DIR and then there's reality.