Question NITROX (in less than 40 foot of water)

[myrddin]

Hey folks QQ for you. I just moved to a quarry where I plan to dive more often (just for training) and I have a question that I want to ask. I am not nitrox certified, nor have I had the need to dive with nitrox yet (one day I will expand to deeper dives). But I have two tanks I purchased where they filled with nitrox instead of air. If I were to dive in the quarry in 20-40 foot of water, would it be OK? Or should I dump the air, and get them refilled with air instead? I know I need the cert for proper use... I just have two tanks with 32% sitting here and thought it would be nice if I didn't need to go into town for a fill is all. If I do, then I do... not the worst thing in the world. If it doesn't matter, then I can select 32% Nitrox on my dive computer and use what's in the tanks.

 

[Marie13]

Don’t dive it if you’re not nitrox certified.

 

[Cthippo]

I think the answer here is dive them like they were just air. From a DCS standpoint that is a more conservative profile and you can't get into oxygen toxicity without drilling down through another 60 feet of rock.

Others who know better will be along shortly.

Alternatively, you could take the class online and use the two tanks for your Nitrox cert dives.

 

[SATurner]

I'll play a bit of Devil's advocate. Are the tanks marked as nitrox? Are they labeled by who filled them? How will you analyze them?

I'll stop there and let others weigh in.

 

[Cthippo]

I'll play a bit of Devil's advocate. Are the tanks marked as nitrox? Are they labeled by who filled them? How will you analyze them?

I'll stop there and let others weigh in.

Strictly for the sake of arguing, what could be in them that would be actually dangerous at those depths? 100% oxygen? Some sort of hypoxic mix?

 

[Brett Hatch]

Well, the on-paper answer is that you shouldn't dive with gas that you're not trained on. And, one thing they teach you in that nitrox class is to do a never dive if you are not confident in what's in the tank. You'll be taught to always analyze the tank's contents, and verify that it is safe for the dive you plan to do, which depends primarily on the max depth and the expected dive time.

Personally, if I were diving with my tanks that I had analyzed, I would feel OK lending one to a buddy who isn't trained on the gas, for a dive above a hard bottom of 40 feet. 40 feet is well within the range where 32% is safe to dive. But, that's a little different than what you're saying, which is diving potentially un-analyzed tanks, while not knowing much about the risks and rewards. In your shoes, if getting an air fill is no big deal, you might be best off asking the dive shop to fill them up with air. But, if you're confident that the tanks contain 32%, then there is little risk diving them to 40 feet.

The main risk factor here is not whether 32% is safe at 40 feet (it is perfectly safe, I've done it many times), it's the confidence in the contents of the tank. If something got miscommunicated or misunderstood or mislabelled, maybe the tank actually contains 100%, and 40 foot dive on 100% is extremely dangerous.

Edit to add: by the way, you might want to just take a nitrox class. They only cost around $100, take an hour or two, and don't require you to do any dives. You just do classroom and bookwork, learn how to do the gas analysis and paperwork, and learn about risks and rewards. It's one of the best scuba classes, and a lot of times you can just walk into your local dive shop and say "hi, I'd like to do the nitrox class," and they will say "OK, cool, how's right now sound?"

 

[SATurner]

@Cthippo if the source is unknown, what indeed. . Not sure I would want to splash on tanks of unknown fill source.

Edited to direct since I hosed up quoting...

 

[boulderjohn]

The concern would be that the tanks were mismarked at 32% and actually had a percentage too high for you maximum depth. In the case you are talking about, you would have to have a mix over 60% to have to worry.

 

[scubadada]

Analyse the cylinders to make sure what is in them. Go dive the cylinders as air, who cares?

 

[Jcp2]

Or they could be a mix with too little oxygen.