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Thread: Evidence based guidelines on gas density planning

  1. #21
    RBW Member jneves is on a distinguished road jneves is on a distinguished road jneves's Avatar
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    Re: Evidence based guidelines on gas density planning

    [HTML]Perhaps I am a ludite but I take my own life prety seriously if only for my familys sake so I need to feel I have done all I can to minimise the risks /HTML]

    Exactly the reason why I dive the MkVI and the Se7en.
    I lernt to not trust my judgement when I was using other breathers after too many near miss events, either because of bad design, or because I got convinced I was so good at figuring out what was going on, or simply because I got distracted. But most important because of poor decision taking under stress. We as human are not to be trusted when we have to deal with several life threatening issues simultaneously.
    I love to dive. I want to live to dive another day. Since I started diving the Poseidon units the issues stopped. These breathers will not let you dive if something is wrong with your O2 sensors, or other type of issues. Period. So you only have to correct the problem to the system satisfaction, if the problem can be corrected in the field. If not, you donít dive.
    So, OK, I have missed a few divesÖ But the many ones I didnít miss, man, were they mind relaxed dives!!!

    Anyway, Mark, there is only one way of finding out weather you may trust an automated machine or not: get a deep understanding of the logics of what it does and why, and then dive it a lot.

    The Se7en is an amazing machine. Not to be discarded lightly. To me it is simply put the safest breather out there.
    Why donít you give it try?

    JNeves

  2. #22
    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by jneves  View Original Post
    [HTML]Perhaps I am a ludite but I take my own life prety seriously if only for my familys sake so I need to feel I have done all I can to minimise the risks /HTML]

    Exactly the reason why I dive the MkVI and the Se7en.
    I lernt to not trust my judgement when I was using other breathers after too many near miss events, either because of bad design, or because I got convinced I was so good at figuring out what was going on, or simply because I got distracted. But most important because of poor decision taking under stress. We as human are not to be trusted when we have to deal with several life threatening issues simultaneously.
    I love to dive. I want to live to dive another day. Since I started diving the Poseidon units the issues stopped. These breathers will not let you dive if something is wrong with your O2 sensors, or other type of issues. Period. So you only have to correct the problem to the system satisfaction, if the problem can be corrected in the field. If not, you donít dive.
    So, OK, I have missed a few divesÖ But the many ones I didnít miss, man, were they mind relaxed dives!!!

    Anyway, Mark, there is only one way of finding out weather you may trust an automated machine or not: get a deep understanding of the logics of what it does and why, and then dive it a lot.

    The Se7en is an amazing machine. Not to be discarded lightly. To me it is simply put the safest breather out there.
    Why donít you give it try?

    JNeves

    Thers two parts to the answer to this

    1: I dont beleive in the Posidens cell checking system. I have looked at how its suposed to work and i simply dont beleive it does its job properly.

    2: I have little faith in electronics and diveing

    I started on an inspo classic in 2004

    The inspo classic was sold as super safe because if one hand set failed the second hand set automaticly took control and there was a buzzer that sounded to let you know something was wrong.

    It was fantastic

    I did few hundred hours on it and it was faultless

    I was mad keen for the first hundred and fifty hours or so checking my handsets regularly but the damed things just said 1.3 1.3 1.3

    SO after a while I started cheking them once or twice a dive just like every one else

    Then one day I looked at my hand set and it was dead and I looked at my second hand set and it said slave waiting for data.

    The Posiden works on electronics that IMHO can and will eventualy fail


    Often the most dangerous CCR is the one that virtualy never breaks down because the day it does break down is the day it will kill you


    CCR diveing is very very simple

    The trick is to always know your PP02 and have working cells

    It is easy to acheive this with a hard dill to PP02 output test and a few spikes of 02 along the way to see if the cells can read higher than set point

    Building these checks into your dive plan will make you a much better CCR diver and it will keep you alive

    Trusting electronics designed and built in someones shed with a R&D budget usuely resereved for a food blender and then using them is a high humidity, high temp, salt water surounded environment just after they have been smashed about in a F4 on a dive boat for two hours is IMHO russian roulett


    My JJ is currently set up to be run manualy via a needle valve rig and I dont use the electronics. I have dived it like this for a few years now and it keeps me honest.

    Electronics are something I feel will either kill me or cost me dives.

  3. #23
    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Mark Chase  View Original Post
    Simon

    Isn't testing the cells at the end of the dive closing the door after the horse has bolted?

    Finding out my cells are limited at the end of the dive seems prety pointless to me

    I needed to know this 2 hours ago when I was on the bottom showing 1.3 across the board.

    ATB

    Mark

    Hello Mark,


    Not really the topic of the thread, and nor is it my area of expertise. However, the point seems to be that the spike test has poor validity at the start of a dive because it may suggest your cells are fine when they are not. The fact that a cell is failing may not be revealed until it has been under stress for a while.


    There is, of course, nothing to stop you doing the test at both ends of a dive, but I guess the message is that you should be cautious in your interpretation of a normal test at the start of a dive, and that a normal test at the end of a dive is more reassuring (for the next dive)!


    Simon M

  4. #24
    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Simon Mitchell  View Original Post
    Hello Mark,


    Not really the topic of the thread, and nor is it my area of expertise. However, the point seems to be that the spike test has poor validity at the start of a dive because it may suggest your cells are fine when they are not. The fact that a cell is failing may not be revealed until it has been under stress for a while.


    There is, of course, nothing to stop you doing the test at both ends of a dive, but I guess the message is that you should be cautious in your interpretation of a normal test at the start of a dive, and that a normal test at the end of a dive is more reassuring (for the next dive)!


    Simon M
    Simon sorry the threads gone off at a rather large tangent.

    In respect of the origional topic is there a safe END that would ensure gas density is not an issue? IE if I plan 25m max END for every dive can I feel confident I dont need to do gas density calculations?



    In answer to the cell issue thing:

    If the next dive is tomorow then the "end of dive test" is very useful, but id have thought no so much when the next dive is three weeks away

    I base this on experiance of cells passing said test, then failing in pre dive testing before the next one.

    Cell testing is something I do pre dive, start of dive, during the dive (multiple) & end of dive

    Personaly I dont think pre dive only, start of dive only or end of dive only are adiquate in them selves.


    ATB

    Mark

  5. #25
    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Mark Chase  View Original Post
    Simon sorry the threads gone off at a rather large tangent.

    In respect of the origional topic is there a safe END that would ensure gas density is not an issue? IE if I plan 25m max END for every dive can I feel confident I dont need to do gas density calculations?

    Hi Mark,


    I imagine that it would keep you fairly safe unless diving very deep, but I have not gone through the exercise of calculating out a range of scenarios. It would be fairly easy to do.

    Quote Originally Posted by Mark Chase  View Original Post
    In answer to the cell issue thing:

    If the next dive is tomorow then the "end of dive test" is very useful, but id have thought no so much when the next dive is three weeks away

    I base this on experiance of cells passing said test, then failing in pre dive testing before the next one.

    Cell testing is something I do pre dive, start of dive, during the dive (multiple) & end of dive

    Personaly I dont think pre dive only, start of dive only or end of dive only are adiquate in them selves

    All fair comments.


    Simon

  6. #26
    RBW Member matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Mark Chase  View Original Post
    Simon

    Isn't testing the cells at the end of the dive closing the door after the horse has bolted?
    Not if you consider multiple dives. The test at the end of the last dive, if recent, will be more useful knowledge to you than the test at the start of the current-dive.

    You may find the horse bolted, yesterday.

    Matt.

  7. #27
    RBW Member matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by dreamdive  View Original Post
    Looked at the calculation which works great for OC density calculation. For rebreathers, divers have to account for their [PO2] in their loop if they want to be even more accurate. :)

    Claudia
    I added the limits to a chart I drew sometime ago when looking into my own gas planning, might be useful to others. The chart takes the gas at depth with SP=1.3, then works out density, as you suggest.

    Some of the lower limits of common gas choices give food for thought.

    Matt.


  8. #28
    RBW Member deepdave is an unknown quantity at this point deepdave's Avatar
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    Re: Evidence based guidelines on gas density planning

    Hey Simon, may I ask a question semi-related to one of the sections in the paoer.

    I'm looking at ways to 'up the anti' in the gym to improve my diving related fitness, particularly around gaining further efficiencies in breathing and the bodies use of O2. With that in mind, the fitness instructor has recommended one of those elevation training masks which, as far as I can see, increases the WOB while working out. Now I'm no physician but surely the mask serves to increase the dead air space and restrict the bodies ability to ventilate CO2. But I'd be keen to hear your thoughts on this latest fad.

    Dave
    Last edited by deepdave; 3rd September 2016 at 21:19.

  9. #29
    RBW Member oya has a spectacular aura about oya has a spectacular aura about oya has a spectacular aura about oya has a spectacular aura about oya has a spectacular aura about oya's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by exposure  View Original Post
    oya, on the petrel or perdix you can show the PPO2 from your diluent at current depth, so no math here :)
    Do you have any idea how bloody stupid I feel right now?

  10. #30
    RBW Member exposure is an unknown quantity at this point exposure's Avatar
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    Re: Evidence based guidelines on gas density planning

    Nope, no idea. Ah ah

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