Recreational dive poll - Nitrox

[billt4sf]

Hey OP here. Sorry I have not been back to this until now.

What motivated me to do the poll is that I think there is a YUUUUUUGE gap between what RECREATIONAL divers ACTUALLY do and what those of us on scubaboard (or other scuba social media) do. It really annoys me.

Maybe for nitrox checking, it's not as bad as I have been thinking. We're getting ready to go on a LOB, I'll look more carefully to see what the other divers do.

To be honest I think the whole nitrox thing is highly over-rated for most recreational divers. Most of us use 32% (if anything) so all we need to know is that the MOD is 110 feet and the dives themselves are structured to go no deeper than that anyway. To see a gauge indicate 32.5 ... 32.4 ... etc. isn't that meaningful. Who knows how carefully it was calibrated? Almost no one without their own gauge looks for that. And isn't it true that the nitrox may have been mixed by the .. I think it's called the "partial fill"` method? Which recreational divers understand what's going on?

And how do we know the "air" we supposedy have is not nitrox? Who checks that?

Beyond that, how do we know the gas is uncontaminated in other respects? CO is one risk, we never check for that. I bet there are others.

We can check all the gauges we want, but I have the feeling that we're diving more on hope (and trust in the operator) than on facts that we have independently verified.

- Bill

 

[kelemvor]

What motivated me to do the poll is that I think there is a YUUUUUUGE gap between what RECREATIONAL divers ACTUALLY do and what those of us on scubaboard (or other scuba social media) do.

I have no doubt you are 100% correct.

 

[Lorenzoid]

Thanks for the clarification, Bill. As others said upthread, I think it depends on what kind of recreational diving we're talking about. I suspect you're 100% correct about the gap between what we hear from SB members and what we are likely to observe with the liveaboard and dive resort crowd. But SB reflects the larger dive community. I believe some of the more vocal SB members do a lot of their diving outside the realm of liveaboards and resorts, where analyzing is indeed taken seriously.

I believe the point of us recreational divers analyzing our tanks is primarily to check that dive ops that don't bank their nitrox (e.g., they partial pressure blend each tank) don't inadvertently fill a tank with a mix having a MOD significantly less than the maximum depth of the dive. The likelihood of this happening has been debated in many threads. What's the likelihood of me finding 40%, or for that matter, 100% O2 in my tank that's purported to be 32%? I don't know, but I would use the word "low"--at least in relation to other risks we rec divers face and routinely tolerate as acceptable.

If I were forced to choose between analyzing for O2 and analyzing for CO with a dive op that fills with banked nitrox, or on a liveaboard or similar trip, I might actually choose analyzing for CO as being more likely of benefit.

Please do report back on what you observe on your upcoming liveaboard. I'll do the same!

 

[drrich2]

And isn't it true that the nitrox may have been mixed by the .. I think it's called the "partial fill"` method?

I minor pertinent tangent from the main topic may be interesting for this thread.

Just how common is the practice of partial pressure blending individual tanks vs. generating 'banked' nitrox and filling multiple tanks? Especially on live-aboards?

I ask because if 10 tanks are filled off a bank, odds of 9 being 32% & 1 being 50% sound low. With partial pressure blending, I suspect it's a higher risk.

We can check all the gauges we want, but I have the feeling that we're diving more on hope (and trust in the operator) than on facts that we have independently verified.

Yes, we generally take compressed air quality on faith.

Richard.

 

[boulderjohn]

I minor pertinent tangent from the main topic may be interesting for this thread.

Just how common is the practice of partial pressure blending individual tanks vs. generating 'banked' nitrox and filling multiple tanks? Especially on live-aboards?

I ask because if 10 tanks are filled off a bank, odds of 9 being 32% & 1 being 50% sound low. With partial pressure blending for nitrox, I suspect it's a higher risk.

If you are filling a fair number of tanks, partial pressure blending is the most expensive, the most labor-intensive, the most dangerous, and the most error-prone way to do it. If you are filling a fair number of tanks regularly, you will use a different method.

Partial pressure blending is the only way I do it, though. The only shop in my area that can regularly provide nitrox is the same way. That is because we don't do it often enough or fill enough tanks to justify the initial cost of a better system. In addition, we do most of our filling in the field, at the dive site, so we can't take the system with us.

 

[Landau]

My last time diving nitrox, with rented tanks on a day trip organized by my local LDS. This was shortly after getting my nitrox cert from them.

DM - "Your tank is the yellow one in the van. I've tested and labelled it for you"

Me - "Can I retest it myself?"

DM (smiling) - "Good answer, I wasn't going to let you go with out that. The analyzer is over there"

The DM was an instructor, but not the one who certified me.

 

[blue steal]

It depends, I have seen most divers analyze their own tanks and I have seen DM's analyze tanks with divers observing.
What I would like to know is how many have analyzed their tanks and either found them labeled incorrectly, say 32% when it was 36% or even air. In all the years I've used Nitrox I've always had it analyzed close to the labeled %.

 

[robertalmario]

You must test personally.

 

[yle]

Yes, I've experienced that. I was with an OP this fall with my new nitrox cert ready to try nitrox on my own. I had been on nitrox previously on AOW course under guidance of the instructor. Different OP and island. They were very thorough. Well there was no onboard analyzer for customers to use, just go by the label they said. They didn't even want to see my Nitrox cert. This is all pretty new to me, how often do you see lax safety standards?

Where was this?

Last January in Cozumel I asked the dive op, in advance, for eight nitrox tanks for my group of four divers. When we arrived, the dive op told me they had been analyzed and were ready to go. They were all labeled 32%. I thanked him, pulled out my analyzer and started to check the first tank. He asked me to stop and seemed genuinely offended that I didn't trust him.

Many dive ops in locations like Cozumel pride themselves on providing the full "we do everything for you because you're on vacation" experience. They want to haul your gear, set up your gear, rinse it at the end of the day. Analyzing your nitrox for you is just another thing on that list, and if you want to analyze your own gas they seem to take it personally that you are rejecting their hospitality.

I made it clear to the guy (not in so many words, of course... I was as polite as possible) that I didn't give a rat's ass about hospitality and that I was going to analyze, with my analyzer, all eight tanks.

I found two of them had been filled with air. The other six were labeled accurately. I'll take safety over hospitality any day.

 

[yle]

Worth mentioning that the shop in Key Largo that I dive with most often offers nitrox. When they provide nirtox to guests, the analyzer and logbook is passed around to the divers on the boat before leaving the dock. The divers are responsible for analyzing their own tanks and filling out the logbook... while the crew watches them. Seems like the way it should be done.