RD lost deco gas planning

[StreetDoctor]

hahahahahahaahahahahahaha I don't know how I got involved but I have learned a lot in these two threads

 

[StreetDoctor]

Man, I thought I had a firm toehold on this stuff, and you guys are confusing the dickens out of me.



Don't you stay on 50% all the way to the surface if you're doing a 21/35 Tech 1 dive? Or am I misunderstanding this statement?

yes, I believe he was talking about dives outside of the T1 realm.

I thought the idea was to add enough time to the gas switch depth to allow one complete circulation time (which is said to be 2 minutes, although what I know about circulatory mechanics would suggest that is probably longer than necessary). We didn't talk about adding any more than that, either in the Rec Triox classroom work or in my UTD T1 class.

Yep but also to take advantage of the ppO2 of 50% at 70'.

As far as lost deco gas goes, it puzzled me that we could do the time deep on the 50% and then go back to a normal schedule on backgas. Maybe it's because the deco we're doing is already pretty well padded? It's been interesting to me, running V-planner on +3 on my Liquivision for kicks and giggles, to see that even when I fail to remember to gas switch the computer, I clear the deco obligation before the end of the dive. So V-planner thinks we could lose our deco gas and just do pretty much our schedule on backgas and be okay . . .

Can't comment, wasn't taught that method.

 

[rjack321]

Don't you stay on 50% all the way to the surface if you're doing a 21/35 Tech 1 dive? Or am I misunderstanding this statement?

Yes stay on the EAN50 all the way to the surface, you might as well. But this is exactly why a GUE Tech1 dive is actually an exception to the rule which applies to 2,3,4+ deco gas dives where you will always have O2 along for the shallow segment. On a GUE Tech1 dive (20-25mins @ 150') you are assumed to not have enough slow tissue loading to need any slow tissue (aka shallow gradient driven) offgassing advantage.

Because:
On these deeper dives, EAN50's 50% time advantage over backgas is assumed for the 70-30ft segment only (actually its even less than that, its the 70-40ft segment with 30ft stops done as a backgas break but we can ignore the difference between 40 and 30ft here).

So EAN50 is 50% more efficient than air/backgas in the 70-30ft range. On a 200ft+ dive, EAN50 is not assumed to have any deco efficiency over backgas in the 20ft & up segment.

So to make it practical:
Assume you have 50% but now lose O2 on a deeper (200ft) dive. (ignore switching regs here, pretend the bottle is empty). Yes you stay on 50% at 20ft when you can, might as well if you got it. But this time might as well be "backgas deco" time. You only have 2 options, double the 20ft time (doing it on backgas or 50% doesn't matter) or share the O2 and do net 1.5x the time.

Sharing:
10mins on O2 for me while you do 10mins on backgas
10 on backgas for me while you do 10 on O2

One cycle for each of us = 15mins shallow time "done" for each of us. If we were to both do the 10mins of non-O2 time on EAN50 we wouldn't count that as more than 5 mins "done". E.g. 10mins on EAN50 would not be not 7.5mins "done". 10mins on anything other than O2 counts for only 5 mins.

This illustrates why EAN50 has no time advantage "shallow" in the T1 range, might as well do the time on backgas. Its the "exception" to every other (deeper or longer) dive where you actually need a deco advantage shallow. Feel free to pad tho, more time ain't gonna make you feel worse unless you have other issues like hypothermia going on.

 

[limeyx]

This illustrates why EAN50 has no time advantage "shallow" in the T1 range, might as well do the time on backgas. Its the "exception" to every other (deeper or longer) dive where you actually need a deco advantage shallow. Feel free to pad tho, more time ain't gonna make you feel worse unless you have other issues like hypothermia going on.

Right and so UTD's justification for lost gas scenario

 

[Rainer]

Next 150' dive we do, want to switch to back gas when leaving 60' and not modify the deco?

Right and so UTD's justification for lost gas scenario

 

[limeyx]

Next 150' dive we do, want to switch to back gas when leaving 60' and not modify the deco?

If we both double the 70 and 60 foot stops sharing the 50% bottle, sure

EDIT:
it's actually something that I think SHOULD be tried no matter what "scheme" we plan to use. If no one tries it, then how do we really know ?

I do know some pretty outrageous things have been anecdotally tried
- people staying at 120 on 30/30 until they basically bend themselves to see what the limits are (turns out the MDL of 20-25 mins is about 1/2 what you can do)
- people cutting deco to 15 mins on a 30 min deco dive to "see what happens"
- claims that it seems that doing all the 70-30 deco at 20 then normal deco from 20 on up seems to work as well as anything else (but does use more gas)


having seen what AG and Nick pulled off in the Pit, I am definitely having my own eyes opened to deco options. having 100 mins of stops (excluding the 45 min BG break) for just the 70-30 segment definitely causes you to need to be pretty confident in what you are doing...

 

[Rainer]

Jamie's going to kill me (us) if you end up bent!

LOL, I assume many schedules would get us out just fine. As rjack noted, it's more a case of wanting to walk away than walk away perfectly clean.

Still think extra time shallow, though, is the way to go (assuming you aren't cold).

If we both double the 70 and 60 foot stops sharing the 50% bottle, sure

 

[limeyx]

Jamie's going to kill me (us) if you end up bent!

LOL, I assume many schedules would get us out just fine. As rjack noted, it's more a case of wanting to walk away than walk away perfectly clean.

Still think extra time shallow, though, is the way to go (assuming you aren't cold).

She would definitely kill you. Then spend a month kicking me in the shins

 

[lobstah]

EDIT:
it's actually something that I think SHOULD be tried no matter what "scheme" we plan to use. If no one tries it, then how do we really know ?

Getting away with it once, hardly proves anything, but we are on. After doing a tad aggressive schedule with most of deco done at 70/60 stops we pretty much walked away with limeyx without feeling any negative effects. We shall arrange for a tryout.

 

[ScubaInChicago]

The Chicago Street, that's it yeah

No problem, I have respect for my elders...It kinda reminds me of my grandmother calling me by a different name shortly after being diagnosed Alzheimer's.