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Thread: Free dive to 12 feet and THEN breathe compressed air?

 


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    Free dive to 12 feet and THEN breathe compressed air?

    I just picked up a Spare Air and want to practice with it in a pool to get familiar with it. The dive-shop owner cautioned me and said, "Breathe from it going down. It's not safe to dive down 10 to 12 feet (feet, not meters) and then start breathing it."

    Said a different way, the owner was saying if you free dive down, you can't then start breathing compressed air.

    Q1. Is that really true? Obviously, once I breathe from it, all normal scuba rules about safe ascents apply.

    Q2. If it really is true, why when I am scuba diving is it safe to breate *out* all the compressed air, at depth, so that my lungs are empty, and then take a breath of compressed air? Because once my lungs are empty, how is that different then a free diver who dived down, and then breathed out? (Assume I only just got in the water, so I've had no significant time to run up on a nitrogen load.)

    ---------------------------
    Possibilities: It's known that offering compressed air to a free diver is dangerous because they might not know the rules for safe scuba ascents. Could this be why the owner said "free diving and then breathing compressed air is dangerous."

    Thanks. (And whatever your views on Spare Air are, that's not the topic du jour. )

  2. #2
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    captndale's Avatar
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    I know of no reason that would make it dangerous to to a breath hold dive and then switch to scuba for an ascent. It might, in fact, be more problematic to dive down breathing such a small cylinder of gas and expecting to have enough to then make a safe ascent.

    One wonders how much one can rely on the advice of a salesman who promotes Spare Air.
    Safe diving,
    Capt. Dale Bennett

    Instructor Trainer / Boat Captain

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    Instruction - Open water to Tri-mix Instructor

    "Breath out; breath in; repeat as necessary."

  3. #3
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    I can only assume he's cautioning you not to take a breath off the thing at the bottom of the pool and then hold it as you surface. If that's his intent, then he has a point ... as soon as you breathe off a compressed gas cylinder, you're scuba diving, and the physics of breathing compressed gas apply.

    As long as you breathe continually, you'll be fine ... just like you would on any other scuba cylinder. But don't take pool depths lightly ... holding a breath of compressed air from 12 feet to the surface can cause a serious lung overexpansion injury ... it doesn't really matter what size cylinder you took that breath from ...

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    elmer fudd's Avatar
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    I think you really need to think of the SpareAir solely as an emergency ascent device. Sure, you can practice with it in a pool, with the same rules as scuba, but using it as an adjunct to freediving would be a very bad idea since free diving involves many rapid and significant ascents and descents.

    I can see the appeal to free divers. Here's this tiny little bottle with none of the usual scuba paraphernalia that can multiply the length of your dives, but the downside of it is that with that bottle come all the hazards attached to breathing compressed air at depth.

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    It was either poor advice, or misunderstood. Breathing off it on the way down is OK, breathing off it on the way up is OK, the only real problem is taking a breath at depth, then holding your breath on the way up... you either need to breath off it ascending in a normal scuba rate, or do a CESA on the way up. It's that breath at the bottom that wants to expand on the way up that'll mess you up.

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    Paladin's Avatar
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    The only possible danger to what you are talking about (other than running out of air at depth) is if you hold your breath during ascent.

    When I was learning to dive back in the 1960s, my teacher would have me swim 30 or 40 feet down to the bottom, remove my SCUBA gear, do a "blow and go" back to the surface, take a couple of breaths, then dive back down to put my gear back on. The second half of the exercise is the same thing you're talking about.

    Just remember that Spare Air only holds about thirty breaths or so and if you stay down too long, you're going to have to do a "blow and go," what the fancy people now call a CESA.


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    Just to be clear: my intended use of the Spare Air is *not* for free-diving. I simply want to practice with it in a pool. And the person I was talking to said that swimming down (which she termed "free diving down"), and then taking a breath at depth was dangerous. She wasn't talking about the danger from the ascent -- i made it clear I would exhale properly. But she said even so, breathing in at depth when you didn't breath compressed air on the way down was risky, even if you exhale properly going back up. (To which i thought, "WTF?" Hence this post.)

    But Paladin954: thank you. I am an idiot: and you just convinced me.

    Because during my O/W pool training, indeed, we ditched our gear, did a gentle ascent to the surface. Then from the surface, we free dove down to the bottom, turned on our tank and started breathing from it. This is absolute standard practice for my instructor. He does this with every class. I did it myself twice, on two different weeks.

    So no freakin' way is what the salesperson saying correct. Diving down free, and then taking a breath is certainly fine.

    I am puzzled that an experienced diver (as this sales person is) would make this mistake. It sounded incorrect to me right away, and sure enough it is.

    Case closed.

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    Just a theory...

    The only "problem" I can think of is what if you swim down on a held breath, get to the bottom of the pool, go to take a refreshing gulp of air from your spare air and for some obscure reason it doesn't work. If you had been breathing from it on the way down, maybe you would have noticed the problem in time to surface without any problems?????????

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    elmer fudd's Avatar
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    I can't see where that would matter in a pool. I'm a big fan of having a redundant air supply as I suspect that most CESA's are done by panicked divers with empty lungs only after they've first tried their octopus and examined their SPG's, but then again, a pool is only 12' deep. Even I can ascend from that depth without worry.

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    How deep is the pool?

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