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Thread: Hypoxia and Convulsions

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    New Member robbcayman is an unknown quantity at this point robbcayman's Avatar
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    Hypoxia and Convulsions

    Let me see if I have this right, and feel free to correct me if I'm wrong. Basically, the 2 main causes of death on a rebreather are hypoxia (blackout) which results from too low of oxygen and convulsions from too much oxygen.

    Assuming that is the correct information are there not reliable methods to keep these levels in line? I read something about injecting certain amounts of gasses at certain times for the scrubber to maintain pp02 (partial pressure of oxygen) Our brains won't alert us to the overload or underload of oxygen which could cause initial blackout (drowning) or convulsions which could essentially cause a drowning as well. My question is how often does the equipment fail? How much is actual diver error? Why not create multipe oxygen checking systems, so if one system failed to detect an oxygen problem another would pick it up? Sorry for all the dumb questions just trying to determine the acutal risk for diving rebreathers. Thanks :)

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    Re: Hypoxia and Convulsions

    The biggest problem is the O2 cells themselves. They are a necessary (in current designs) but ugly device that when working properly are great, but their failure modes are somewhat unpredictable and very difficult to accurately detect while in use.

    Thus the use of three, but even then, common failures can still bite you.

    Of course there is also scrubber trouble (e.g. excessive CO2)
    Last edited by Genesis; 16th November 2006 at 17:37.

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    Re: Hypoxia and Convulsions

    Quote Originally Posted by robbcayman  View Original Post
    Let me see if I have this right, and feel free to correct me if I'm wrong. Basically, the 2 main causes of death on a rebreather are hypoxia (blackout) which results from too low of oxygen and convulsions from too much oxygen.

    Assuming that is the correct information are there not reliable methods to keep these levels in line? I read something about injecting certain amounts of gasses at certain times for the scrubber to maintain pp02 (partial pressure of oxygen) Our brains won't alert us to the overload or underload of oxygen which could cause initial blackout (drowning) or convulsions which could essentially cause a drowning as well. My question is how often does the equipment fail? How much is actual diver error? Why not create multipe oxygen checking systems, so if one system failed to detect an oxygen problem another would pick it up? Sorry for all the dumb questions just trying to determine the acutal risk for diving rebreathers. Thanks :)
    Well you forgot about hypercapnia (I think it is spelled incorrectly, not enough coffee yet) which is the build up of CO2 in the loop. This can cause many problems for the diver such as blacking out, confussion, etc. The Problems with O2 can easily be monitored via the 3 O2 cells we use to validate the breathing loop, but tracking the build up of CO2 is still a problem.

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    Re: Hypoxia and Convulsions

    Quote Originally Posted by robbcayman  View Original Post
    Let me see if I have this right, and feel free to correct me if I'm wrong. Basically, the 2 main causes of death on a rebreather are hypoxia (blackout) which results from too low of oxygen and convulsions from too much oxygen.

    Assuming that is the correct information are there not reliable methods to keep these levels in line? I read something about injecting certain amounts of gasses at certain times for the scrubber to maintain pp02 (partial pressure of oxygen) Our brains won't alert us to the overload or underload of oxygen which could cause initial blackout (drowning) or convulsions which could essentially cause a drowning as well. My question is how often does the equipment fail? How much is actual diver error? Why not create multipe oxygen checking systems, so if one system failed to detect an oxygen problem another would pick it up? Sorry for all the dumb questions just trying to determine the acutal risk for diving rebreathers. Thanks :)

    Sorry but I'm just curious. So you already have and dive an Evolution?

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    Re: Hypoxia and Convulsions

    Quote Originally Posted by Lake_Tahoe_Diver  View Original Post
    Well you forgot about hypercapnia (I think it is spelled incorrectly, not enough coffee yet) which is the build up of CO2 in the loop. This can cause many problems for the diver such as blacking out, confussion, etc. The Problems with O2 can easily be monitored via the 3 O2 cells we use to validate the breathing loop, but tracking the build up of CO2 is still a problem.

    Hmmm.. interesting I thought you can use a diluent flush to restore the balance in the loop? Is this even close to being right? Sorry I'm new here.

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    Re: Hypoxia and Convulsions

    Quote Originally Posted by jaap  View Original Post
    Sorry but I'm just curious. So you already have and dive an Evolution?
    No, when I signed up it was a default in the registration. I'm interested in getting one if the risk isn't too absurd.

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    Re: Hypoxia and Convulsions

    Well sure, you could flush to get rid of what's in there and replace it, but if the scrubber isn't working, that doesn't help for very long! :)

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    Re: Hypoxia and Convulsions

    Quote Originally Posted by Genesis  View Original Post
    Well sure, you could flush to get rid of what's in there and replace it, but if the scrubber isn't working, that doesn't help for very long! :)
    Doh!! That makes sense, but wouldn't be uncommon for all these things to be down and the same time? I'm sure I'm going to get a biased response, but what brand of rebreather is known for being the most reliable (i.e. few failures)?

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    Re: Hypoxia and Convulsions

    Quote Originally Posted by robbcayman  View Original Post
    Doh!! That makes sense, but wouldn't be uncommon for all these things to be down and the same time? I'm sure I'm going to get a biased response, but what brand of rebreather is known for being the most reliable (i.e. few failures)?
    Sure, but you only need one failure to "get" you.

    You will stay alive considerably longer if you look at all rebreathers as ugly, hairy red-chested beasts that are hellbent on killing you. That may be a bit of an overstatement, but not by much... :)

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    Re: Hypoxia and Convulsions

    Welcome to RBW robbcayman! Your line of questions is quite understandable. I was only a year ago that i started asking a lot of the same questions...newly married, i too did not want to have a sad ending. spend some time looking over the threads and looking through the archive, it will help a lot.

    I did a pretty thorough search and found that the evolution was the right rebreather for my needs. comming up with an objective analysis of which rebreather is the "best" is pretty much impossible. All of them can kill you. Getting solid training, and continuiously sharpening your skills is the way to make it both rewarding and safe. I would recommend seriously considering weather or not you really need a rebreather. If you are pretty happy with the limits of the diving you are doing then don't bother, a pony bottle may just be enough...rebreathers are expensive and time consuming and i believe it carries greater risk factors. If you want to go deeper for longer, go to more remote locations with fewer bottles, take up close and personal macro photography, stay warmer, get less fatigued then perhaps it's for you.

    I am quite happy with my choice to go with a rebreather, even though my longest dives at this point are around 90 minutes and not deeper than 130fsw. i love being able to relax and enjoy being able to hang out in the 70 to 90 foot range for practically the whole dive and receive an optimal nitrox mix at every depth. I am happy i chose the evolution, i think the oxygen controlling system and the temp stick have the edge as far as electronics, but i have also come respect each brand for it's pros and cons. Even the vision electronics that comes with the inspiration or evolution rebreathers has had it's share of electronics issues. No matter what rebreather you can go with, you will need to cary an entire redundant traditional Open circuit system with you and i have to say that that is the single biggest draw back for me, a guy who did exclusively no deco one tank excrusions into the wattery world using a sunto cobra (which never got me bent, never had a single glitch over hundreds of dives and was super easy to use).
    And having to monitor the balance of 02, Nitrogen and potential for CO2 build up is many degrees more complex than diving open circuit.

    Is it more risky than OC? well, i would say yes, but it also depends on how vigalent and disciplined you are or can learn to be. Is it worth it? that depends on what you need from it...a personal question for which you must gain experience and answere yourself. the feild has come a long way and yet has a ways to go before it's truly ready for the recreational market, IMHO. hope that helps.

    Gill Envy

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