Scenario Ascending fromDepth

[H2OHead]

zeN|| once bubbled...
I'll take a diver who is independent and smart enough to forgo this petty preaching and has worked thru potential problems and is not ignorant enough to think that if he keeps on diving according to his 'plan' he is going to outsmart Mr. Murphy zeN||:mean:

If it’s “Murphy’s Law” you’re trying to cheat, try starting with a solid plan. My planning starts in my house (flight planning, dive planning, fishing trip, etc). If there’s anything suspect about the condition of a piece of equipment, it gets replaced, serviced, whatever. Some say that “god is in the details “. I’m not a religious person so I submit that your personal “Murphy” is in the details. I’ve logged a few hours in the air and under water and haven’t needed to discuss anything with Mr. Murphy yet. I’ve practiced what I’m going to do if we ever meet to the point that most emergency procedures are automatic, but magically being alone, too deep, and with no air isn’t a realistic event for me and it approaches absurd. Persistent and unwanted thoughts of events that will most likely never occur is a fairly accurate depiction of an obsession. Having a long history in military aviation, I’m perhaps the exception and I find the level of dedication (to anything) of others usually falls short of my own. My planning and gear checks are probably more thorough than most and have kept me and whomever is with me out of trouble so far, but I do not obsess about events that will never occur. Just as I don’t watch my kid sleep at night worried that he may stop breathing, I don’t run over what ifs that have me in similarly unrealistic situations. As I previously said, perhaps I may just be incredibly lucky. Maybe buying a couple of those spare air contraptions would be a wise investment for the folks prone to the events in the scenario.

 

[ppilot]

Cavediver, I'm just curious. Why would you run your air out at 20' rather than splitting it between 20 and 10?

 

[Dryglove]

Cavediver described it the best which is what i would do or something very similar.The good thing is as you get closer to the surface more air will become available to you.It may not be much but is better than sucking water.

If all else fails there is a very interresting thread about breathing your wing

 

[Tavi]

H2OHead once bubbled...
I’m a little brighter than I look .............

People who say things like this,
usually don't have a profile pic!!

 

[Charlie99]

ppilot once bubbled...
Cavediver, I'm just curious. Why would you run your air out at 20' rather than splitting it between 20 and 10?

If you are breathing 100% O2, then hanging at 20' offgases just as good as hanging at 10' (ignoring O2 CNS tox issues).

If you are coming up from a short, deep dive, then 10' vs 20' doesn't matter much even when using air.

Where is 10' vs 20' makes about a 50% difference is once you have loaded up the middle halftime compartments, like the 40 and 60 minute halftime compartments. You can easily do this with a 100' dive to NDL, then "riding the NDLs" back up with an ultra slow ascent. This also happens to be the sort of dive profile where people may inadvertantly find themselves near or slightly beyond NDL without sufficient gas. A real life example of this was the rather long thread started by SeaJay telling about one of his dives.

In this sort of case, you want to use most of your gas at 10', with just a minute or two at 20'. In a situation like this, 10' will offgass you 50% faster than 20'. (PM me if you want the math and assumptions that support this statement).

 

[Cave Diver]

ppilot once bubbled...
Cavediver, I'm just curious. Why would you run your air out at 20' rather than splitting it between 20 and 10?

Two reasons.

One, I've noticed that a lot of the "vacation divers" who are most likely to find themselves in this scenario have problems controlling their bouyancy. At 10' this is going to be significantly more difficult than at 20'. Making an unplanned ascent to the surface would really screw up your attempt to offgas.

Secondly, I chose that route because 20' is where you normally incur your longest deco obligation. If you extended your time at 20' past what was required of your deco stop, it's not likely to hurt you as you are still offgassing.

However, if you failed to meet all of your 20' deco obligation in order to get to a 10' stop you might be putting yourself at greater risk of DCS.

That's just my opinion, for whatever it's worth.

In actuality, once my gauge started reading 0 psi remaining, I would probably start easing up to about the 5' mark and stay there until the air completely ran out. Me and most of the people I dive with regularly could hold a 5' stop with no problems. I'm not so confident a lot of other divers can. IMO, someone who lacks the skills to properly plan the dive and monitor air usage is likely to be lacking in other fundamental skills as well. This is a bad situation and I felt this was the best approach to it.

 

[Cave Diver]

lal7176 once bubbled...
If all else fails there is a very interresting thread about breathing your wing

You need an oar to stir that with?

And aside from all the other fundamental problems with breathing off of a wing, with 0 psi if air left in the tank and hanging at a 15' stop, you *should* be neutral with an empty wing. Hard to breathe off of an empty wing I would think...

Not to mention, if you DID manage to have enough air in the wing to breathe off of, then you obviously need it for bouyancy. What's going to keep you from becoming negative when you suck all the air out of your wing?

 

[zeN||]

OK there are a few posts on target (rest of you scuba preachers gone-git!), offgassing at 10' that's a suprise, I can see the scenario bears some closer scrutiny, looks like as to the original query making a quick ascent to shallow depths and offgassing as much as possible, and then making an ooa emergency ascent are the best choices. The question in my mind is what is the best target depth, one that will still limit the rate of offgassing to prevent a dcs event, while providing the maximum safe (relatively) outgassing rate, and still be able to reach the surface (after depleting your tank).
Thanx to those who tried to work the scenario (the rest are sentenced to the twighlight zone diving hell, where you find yourself in an unscripted diving emergency, only to be repeated the next day-bwhahaha!) I'm outta here zeN||

 

[Charlie99]

Those programs aren't just for tech divers planning intentional deco dives.

It's real easy to play around with different scenarios, and a lot easier on your body!

The only drawback to GAP in this sort of simulation is that it won't let you enter conservatism values >100% ---- in other words, it won't let you intentionally violate the Buhlmann model.

CAVEDIVER: Could you give an example where using just backgas that the 20' stop is longer than the 10'? What decoprogram and profile?

 

[scubatexastony]

About 60/40 or so.... so on that 140/20 you'd do 9@20, 15@10.

tony