Why not air?

[Rainer]

Jeff, let me assure you that all of the local DIR/GUE guys here are diving air for the shallow shore dives (probably everything except Cat Rocks and Ft Wetherill, sometimes Folly). With free O2-clean air at PG, it just doesn't make a lot of sense to do otherwise. If nitrox were easier to get here, that'd also make a difference. It's often a hassle. We started mixing our own nitrox for this very reason.

For those not local to the area, the usual Cape Ann shore sites (i.e. where most of us in eastern MA shore dive) level out at around 40'. Many of the more popular sites rarely see 30'. We don't get MDL limited. We don't get gas limited. Sometimes we get cold limited. But usually it's stamina limited. After 90 minutes, I'm done. If I want to keep diving, I'll do so on dive 2. 32% adds no safety benefit for these particular shore dives. It adds no MDL benefits either. IMO it's a silly choice.

When I talked with Ed Hayes (local GUE instructor) about why we tend to dive air here (for easy/shallow shore dives only), he made it clear he would dive nitrox, but understood and accepted our choice not to.

I've never taken air out on any of my local boat trips, however. For boat dives, we dive standard gases. Usually, those are GUE standard gases.

 

[MXGratefulDiver]

For those not local to the area, the usual Cape Ann shore sites (i.e. where most of us in eastern MA shore dive) level out at around 40'. Many of the more popular sites rarely see 30'. We don't get MDL limited. We don't get gas limited. Sometimes we get cold limited. But usually it's stamina limited. After 90 minutes, I'm done. If I want to keep diving, I'll do so on dive 2. 32% adds no safety benefit for these particular shore dives. It adds no MDL benefits either. IMO it's a silly choice.

Oh man ... I GOTTA get back out there and check out the diving ... when I lived and worked on Cape Ann (Rockport and Gloucester, respectively), I wasn't a diver.

When I talked with Ed Hayes (local GUE instructor) about why we tend to dive air here (for easy/shallow shore dives only), he made it clear he would dive nitrox, but understood and accepted our choice not to.

Availability sometimes makes it an issue ... for some reason, nitrox doesn't seem to be readily available in some areas, like ... surprisingly ... So Cal. When I was on Catalina Island, it was either dive air or don't dive ...

... Bob (Grateful Diver)

 

[Peter Guy]

PPO2 wrote that one of the reasons is that it makes it easy to mix "standard mixes." Is not 30/30 a standard mix -- and if I recall correctly, it is NOT just "put in 30% He and top off with 32%." Or do I recall incorrectly?

I was just in Mexico diving in the Cenotes (18 dives) -- max depth was 67 feet -- the average depth tended to be 35 feet or less. I couldn't think of any reason not to dive 21% EAN -- and that is pretty much what I did -- AND I SURVIVED. (Each fill of 21% instead of 32% paid for a Margarita -- I think a good tradeoff.)

 

[JeffG]

PPO2 wrote that one of the reasons is that it makes it easy to mix "standard mixes." Is not 30/30 a standard mix -- and if I recall correctly, it is NOT just "put in 30% He and top off with 32%." Or do I recall incorrectly?

You got it right. 30/30 is the "odd" mix. The Heretic uses 25/25 LOL

 

[crlavoie]

With free O2-clean air at PG, it just doesn't make a lot of sense to do otherwise. If nitrox were easier to get here, that'd also make a difference. It's often a hassle. We started mixing our own nitrox for this very reason.

The only place less than an hour from me also charges $17 / tank. Ouch! So a day of diving is $34 before charters and post-dive beer.

We talked with Ed and George about setting up our own nitrox system and they offered some good advice. I'm VERY interested to see what you've done.

 

[SparticleBrane]

If I were in a situation where I had to drive an extra hour to get Nitrox, or pay double for it every time I topped off a half-full tank, I might exercise some discretion in when and where I used it, despite the recommendation to be on 32% all the time.

Bingo, that's the situation a few of my buddies and I are in. Since we all volunteer with the scuba classes at school we can generally fill our cylinders there for free (involves a bit of planning ahead and a few phone calls, but in the end it's worth it).


As an example, yesterday morning we drove to the fill station at school with 15 cylinders that needed fills. Most of our diving this summer is going to be shallow stuff so I really don't see any decompression/physiological reason to dive nitrox unless we go offshore -- at which point we'd all shell out the $$ for voodoo gas. For me, this is a purely economic decision.

Here's the breakdown for how much this would have cost us at an average LDS in my area:
(note that no LDS locally charges by the cubic foot -- you pay for a full tank no matter how much is left over from your previous dive, which is a rant for another time :11

---------------------
(3) sets of double 130s: $30/set -- $90
(1) set of double Al80s: $20
(1) set of double 72s: $20
(2) 119s: $30
(2) LP80s: $20
(1) 130: $15
---------------------
Total: $195


At school, filling with air: Free, besides the time it takes out of my schedule to fill tanks -- meaning I just have to get to school a bit earlier the morning we do fills. We all fill our own cylinders, which I see as a major advantage; we can control how much each gets, how fast they're filled, and we don't have to worry about someone getting water or whatever else inside our cylinders.

 

[amascuba]

I dive Nitrox almost exclusively. I also get my gas for free, besides the time it takes to fill my tanks. Out of 78 dives last year, 4 of them were done on air. All 4 of the dives were in a spring that maxes out at 22 feet.

Personally, I don't see the benefit of diving Nitrox on dives <40ft. From the 40>100ft. range there are definitely advangates.

I know that if I were personally paying for my fills then I would most likely opt for air for my dives in the <40 range.

 

[AndyNZ]

Are there not advantages in terms of simplified dive planning? I've have to go back and look at my fundies stuff, but all the deco-on-the-fly, minimum deco, CNS "guesstimates" etc are based on a 32% mix. I'm sure you could re-work out those guesstimate rules for air, but whether they be easy to remember I'm not sure.

 

[Rainer]

Are there not advantages in terms of simplified dive planning? I've have to go back and look at my fundies stuff, but all the deco-on-the-fly, minimum deco, CNS "guesstimates" etc are based on a 32% mix. I'm sure you could re-work out those guesstimate rules for air, but whether they be easy to remember I'm not sure.

Sure, and that's why we dive 32% off the boats for rec dives (in the 60-100' range). But out here at Back Beach (max 25'), we aren't calculating deco-on-the-fly, min deco, CNS "guesstimates", etc. You dive around till you get bored. Then you get out. Sometimes with lobsters. That's just the reality of the dive sites. I assure you, at 25', I don't need that 20% credit.

 

[BarryNL]

You can always use the reverse EAD calculations. If you make a dive to 8m with air just write 10m on EAN32 in your logbook. Fully DIR compliant