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Thread: Two C02 hits - time to get fit?

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    RBW Member delta-v is an unknown quantity at this point delta-v's Avatar
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    Two C02 hits - time to get fit?

    Twice now I've managed to overwhelm the scrubber through over-exertion until the onset of hypercapnia. I've been fortunate both times to have felt it coming (although today was much more stressful) and averted disaster, but that's not a game plan.

    Both incidents detailed below if anyone's interested. I'm asking myself if it's time to lose some weight and get into better shape. It's worrying because I'm not totally out of shape to begin with - else I wouldn't be diving. But it's obvious the scrubber can't handle a heavy breathing rate. What do you all think?

    First time (some months ago): Got blown off a deep reef (50m+) and dive leader attempted to go against the current to get back on track. Felt the hit coming and slowed down. Grabbed a bit of rock on the seabed to hang on to, and got things under control. Had the B/O DV in my hand but was alright after a few minutes. I wasn't the only one winded in our group, but the only one who had to stop.

    Yesterday: Very shallow wall dive (15m+). Dive leader on OC and chugging away against a pretty stiff current. I kept pace but felt the hit coming and slowed down, but it wasn't enough. Had to bailout (EANx29). Strangely, that kind of made it worse - the feeling I mean. On the loop I wasn't gasping for air. As soon as I ditched the loop and grabbed the DV, it felt like I couldn't get enough air in. Weird huh? In more than a decade of diving, I've never felt like that underwater (or even on land for that matter). Didn't panic per se, but only just managed to keep BCY under control - could've done better I suppose. Anyway, with the dive just started and it being the first dive of the day, surfacing seemed the best option anyway. Did a second dive later, and two more dives today - no issues at all.

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    RBW Member catalina_mike is an unknown quantity at this point catalina_mike's Avatar
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    Re: Two C02 hits - time to get fit?

    Get a stress test and see whats going on. It might not be diving...

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    Re: Two C02 hits - time to get fit?

    I don't have all the facts of your story, but you do paint a clear picture. There is a common misperception that you can over-breathe a scrubber. On some units that is possible, but on your unit that is unlikely. While its true that many have received CO2 hits from working hard on a rebreather, they did not all come from over breathing the unit...it comes from retaining CO2 internally. I'm sure many people will argue this point and they are welcome to, but the simple fact is...many times it comes down to simply retaining CO2 due to poor breathing. Of course, you have to rule out anything being wrong with your unit, the sorb you are breathing and even potentially the gas you are breathing. There are many variables to consider. But if you are able to rule out these issues, you might consider it came from over exertion, while under additional ambient pressure. Certainly the more fit you are the more likely you will avoid the problem or at least recover faster from such an event.

    Feel free to PM me for information on CO2 and how to manage yourself while diving to avoid the onset of issues.

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    Re: Two C02 hits - time to get fit?

    Sounds interesting:
    "Feel free to PM me for information on CO2 and how to manage yourself while diving to avoid the onset of issues."

    Would you consider posting this information....

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    Re: Two C02 hits - time to get fit?

    Would you consider posting this information....[/QUOTE]

    Please do..

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    Re: Two C02 hits - time to get fit?

    Quote Originally Posted by PSotis  View Original Post

    Feel free to PM me for information on CO2 and how to manage yourself while diving to avoid the onset of issues.
    Yes would be nice and really interesting.
    Best Ossi Italy

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    Re: Two C02 hits - time to get fit?

    I would be happy to give my opinion based on the information presented and my personal experience. Please don't take this the wrong way, but I won't get into a debate over my opinions which is so often the goal of so many participants on this board. I will be happy to participate in any thread that is positive in its nature, so as long as its a positive discussion I will do my best to give my input.

    As I stated before, it is a common misperception that comes from old training myths before we had real facts to substantiate the potential of over-breathing. There are some rebreathers that are capable of over-breathing, but they are few and far between. In most cases, any independently tested, CE rated rebreather will manage high workloads. The facts can be substantiated in part from their CE test data. This, of course, requires that the machine be in perfect working order and all consumables are within requirements.

    Generally speaking, but not always, CO2 events are brought about by the divers inability to release the increased amount of CO2 being produced, thus leading to a change in chemistry. Small amounts of CO2 can be recovered from easily. High amounts of loading can produce a sort of "run away train" that continues to worsen even when the diver stops working hard.

    Divers need to understand that when they start to feel the effects of exertion that they need to stop immediately before the event spirals out of control. They also need to understand that bailing out in most cases will not help them because the problem comes from within their own body and not from the machine. Please keep in mind, I am saying "in most cases"...none of this is absolute.

    Elevated fitness levels help in the efficiency of the bodies ability to manage work loads. Simply put, the body is more efficient. For normal diving ranges, being fit is not implying the fitness level of an athlete. Minimal fitness produces enormous advantages.

    Improved fitness, zero modifications to manufacturers equipment and gas density values all play a part in this equation. Simply put, you might want to consider getting in a little better shape, stop messing with your rebreather and do the math on your gas density values...this will go a long way to help prevent this problem. If you are all ready doing these things, then give yourself a pat on the back. Most of all, when you start to feel fatigue from exertion, stop where you are and wait to recover, if possible.

    If you really want to know more, I would suggest attending one of Dr. Claudia Roussos lectures on CO2. I personally learned a lot from that lecture and many people feel the same way. She offers this lecture in many locations annually along with the rest of the Add Helium team.

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    RBW Member Larry0428 is on a distinguished road Larry0428 is on a distinguished road Larry0428's Avatar
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    Two C02 hits - time to get fit?

    Hi, I'm only a noob on Rebreathers myself (so take what I say with the appropriately large grain of salt) and have the same unit as you. Can I ask have you made sure the scrubber O ring is properly lubricated (with silicone grease per Martin Parker's advice) and performed the bounce back test? Only reason I ask is I had a couple of similar situations (esp in strong current) and what I thought was false CO2 monitor alarms but in reality I hadn't sufficiently lubed the O ring (was using O2 grease and it was a bit to sticky). As a consequence some dives were OK and other not and I couldn't workout why. Never had an issue since I started lubing the O ring with silicone grease (40 odd hours later to 45m+ and some pretty stiff currents).

    Cheers
    Larry


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    RBW Member delta-v is an unknown quantity at this point delta-v's Avatar
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    Re: Two C02 hits - time to get fit?

    Thank you to catalina_mike for the reminder to get a stress test. Last one was on my 30th - and that was a very long time ago! Best to rule out any bodily ailments.

    Thanks to Psotis for his advice. I haven't modded the unit in anyway that impacts the loop.

    I believe it's currently impossible to design a scrubber that remains efficient at all breathing rates. The manufacturers/designers have aimed for specific min/max flow rates. As we all know, shallow breathing also leads to CO2 retention as Psotis points out.

    Next, ruling out other aspects such as gas purity, scrubber integrity etc., I'm left with two things to try:

    1. See if I can improve breathing technique as Psotis suggests - but I've worked hard underwater many times but this has only happened twice, so perhaps my technique won't have too much room for improvement.

    2. Get a stress test and start a diet. Lose that spare tyre around my middle at least!

    If what happened at 15m had happened at 50m, I'm quite sure I would've hurt myself pretty bad.

    As always I'm grateful for the training my instructors have given me, and the good sense to always dive with ample offboard bailout.

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    RBW Member delta-v is an unknown quantity at this point delta-v's Avatar
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    Re: Two C02 hits - time to get fit?

    Quote Originally Posted by Larry0428  View Original Post
    Hi, I'm only a noob on Rebreathers myself (so take what I say with the appropriately large grain of salt) and have the same unit as you. Can I ask have you made sure the scrubber O ring is properly lubricated (with silicone grease per Martin Parker's advice) and performed the bounce back test? Only reason I ask is I had a couple of similar situations (esp in strong current) and what I thought was false CO2 monitor alarms but in reality I hadn't sufficiently lubed the O ring (was using O2 grease and it was a bit to sticky). As a consequence some dives were OK and other not and I couldn't workout why. Never had an issue since I started lubing the O ring with silicone grease (40 odd hours later to 45m+ and some pretty stiff currents).

    Cheers
    Larry
    Hi Larry, thanks for the suggestion. Yes, I made the switch to silicone grease when MP sent out that advisory. And I always do the bounce test.

    I used the unit AS-IS for a dive an hour later with no issues, but much less current : )

    CO2 pass-thru can't be ruled out - there's a lot that can't be ruled out! - but if my assembly was poor then I'd be getting hit more frequently.
    Last edited by delta-v; 21st December 2014 at 10:41. Reason: typo

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