USING HELIOX WITH A TRIMIX (LOWER FHe) DECO ALGORYTHM

[JohnnyC]

The risk would be not knowing whether the 10/90 profile is the one that dictates the required amount of decompression, or the 10/65 profile dictates enough decompression, or somewhere in-between. If 10/90 is producing the right amount of deco, albeit using faulty reasoning, it would serve to be wary of the 10/65 profile dictating enough deco.

The end goal is doing enough decompression to remain unbent. Tricking an algorithm to dictate a more conservative profile (the current helium penalty) doesn't have nearly the same repercussions that tricking an algorithm to dictate a less conservative profile may have (no helium penalty but potentially shorter than necessary decompression).

If the ultimate determination of these studies is that FHe doesn't matter for overall decompression, maybe we need to be reevaluating the overall length of decompression to provide safer profiles when dives start to get deeper and longer.

 

[Seameadow]

The risk would be not knowing whether the 10/90 profile is the one that dictates the required amount of decompression, or the 10/65 profile dictates enough decompression, or somewhere in-between. If 10/90 is producing the right amount of deco, albeit using faulty reasoning, it would serve to be wary of the 10/65 profile dictating enough deco.

The end goal is doing enough decompression to remain unbent. Tricking an algorithm to dictate a more conservative profile (the current helium penalty) doesn't have nearly the same repercussions that tricking an algorithm to dictate a less conservative profile may have (no helium penalty but potentially shorter than necessary decompression).

If the ultimate determination of these studies is that FHe doesn't matter for overall decompression, maybe we need to be reevaluating the overall length of decompression to provide safer profiles when dives start to get deeper and longer.

Thanks Johnny, now you are getting where I am going with this, as per the NEDU study Shearwater article, the algorithm shouldn't' actually "say" 10/65 or 10/90 but rather 10/XX plus depth and time factor X and Y. I believe the clever people are currently working on correcting that but of course the exact science will take some time.

So my baseline argument (not literally argument bust discussion point ) is that where should we draw that x/y line?. So since the XX in 10/XX doesn't really matter, but the X and Y in depth and time does, why cant a safe profile be one we have been using all along, using the "XX" that comes from a END of 30m to give us the X/Y line. By adding a higher percentage of Helium we reduce the gas density, corresponding WoB, Narcotic effect and so on, and we dont necessarily need the additional hang time. So in the absence of current exact science, and the argument "because we have always done it this way", what reason is there for not doing this? (Not being facetious, I actually do want to know?! IBCD maybe?!?)

Thanks again!

 

[KenGordon]

doing the right deco for the wrong reason is about doing longer deco for helium leading to doing the correct deco for either helium or nitrogen, so assuming less is required for nitrogen is an error.

On the other hand, little research has been done for 100m bounce dives so the difference between the two might be small compared to the total error. Thus doing the same deco as Fred did last week might be as a good a plan as you can find - assuming Fred is still walking.

 

[JohnnyC]

I got the point you're making. I just think it's very easy to start going the other way with it, and wouldn't advocate for it at all.

Putting in 10/90 for a dive that requires 10/65 might be fine, however putting in 10/65 for a dive that requires the "corrected" deco obligation that comes with 10/90 in an effort to game the system might lead to issues.

Until the algorithms are adjusted to output satisfactory decompression obligations without FHe adjustments, it would be prudent to dive the mix you're telling your computer.

ETA: Tangential but it seems as if Rob Stewart's gas and his computer were two different values. Whether or not that contributed in any way to his incident remains to be seen.

 

[211ratsbud]

Thanks Johnny, now you are getting where I am going with this, as per the NEDU study Shearwater article, the algorithm shouldn't' actually "say" 10/65 or 10/90 but rather 10/XX plus depth and time factor X and Y. I believe the clever people are currently working on correcting that but of course the exact science will take some time.

So my baseline argument (not literally argument bust discussion point ) is that where should we draw that x/y line?. So since the XX in 10/XX doesn't really matter, but the X and Y in depth and time does, why cant a safe profile be one we have been using all along, using the "XX" that comes from a END of 30m to give us the X/Y line. By adding a higher percentage of Helium we reduce the gas density, corresponding WoB, Narcotic effect and so on, and we dont necessarily need the additional hang time. So in the absence of current exact science, and the argument "because we have always done it this way", what reason is there for not doing this? (Not being facetious, I actually do want to know?! IBCD maybe?!?)

Thanks again!

Try matching gas density and compare deco. Seems like that is critical especially hearing Dr s Mitchell discuss in the respiratory failures lecture. Ie bottom gas content match the arbitrary 30m density of either air or 32% {while keeping similar po2 also ?} Just some thoughts.