'Out Of Air Scenarios' - The Debate.

[Darren A]

Not sure where to put this question, so feel free to move it somewhere you may feel more appropriate.

All this talk of OOA scenarios got me thinking. In the following scenario, which is the best course of action.

A buddy pair, on single cylinders (no pony).

Having pushed the no deco limit to the max (say at 30m), they send up blob and start ascent. Diver 1 then has a freeflow, which emptys his cylinder, diver 2 is now low on gas. Sharing gas, they manage to get back to 6m safely.

They've talked about this scenario before, and decided that if it happens they will stay at 6m for as long as possible.

Which of the following should they do:

1) One breath off primary, the other off octo for as long as the gas allows, then ascend

2) or both alternatly breathe off the primary, therefore doubling (or at least increasing) the amount of time they can stay at 6m.

(Please ignore the fact that neither is carrying a pony - that would have made the answer too easy!)

[Janos]

Breathe off the octopus. It's what it's there for and it's a lot easier to do than to buddy breathe. I don't think it would use that much more air, and if it does surely that's because you need that much more air?

Also this is no-stop diving we're talking about isn't it. So why not surface?

Janos

[nigelH]

Which of the following should they do:
1) One breath off primary, the other off octo for as long as the gas allows, then ascend
2) or both alternatly both breathe off the primary, therefore doubling (or at least increasing) the amount of time they can stay at 6m.

I would say buddy breathing would decrease the time the air would last as gas consumption goes down when you relax and doing a repetative drill that involves giving up your ability to breath is anything but relaxing. Plus some gas will be lost clearing the regulator.

I bet they would wish they had a yellow blob to run up the line.....

[ratcliffe]

Given that a pony would be the obvious answer, but is assumed that neither diver has one, then I would go with the use both regs, and stay at 6m as long as possible. Buddy breathing probably wouldn't make the tank last longer as you will lose some air when you purge and you would also take big breaths and be slightly more anxious, probably using more air.
The diver with the empty tank, may need to exhale his used air into his BCD, so if the other diver has an uninterrupted supply it would make it easier for the diver in trouble to move between his reg and BCD inflator.

[Gavin Smith]

Surely they planned and therefore knew the minimum amount of gas they would need to safely complete the ascent and therefore left the bottom at an appropriate time thus ensuring that an ascent on the Octopus wouldn't be a problem.

Gavin

[Darren A]

Thanks for the replies so far. The point of the question wasn't intended to be about should they have AAS (of course they should) or shouldn't they have gas planned better (again of course they should). It was really which is safest from a "fizzing off" perspective. Breathing off primarly and octo for 10 min, or breathing alternatly off the primary for maybe 18 min.

I guess the question is more relevent when mandatory stops are concerned, si lets assume they've got 8 mins of stops at 6m, the rest of the time spent there is "padding".

Cheers

Darren

(PS the point about lost gas through purging is a really good one, I hadn't thought of that)

[colinicky]

i personally clean my wing regularly with buddy clean this means if the s**t hits the spinny thing i could take one breath of air then rebreath through wing for 4 breaths ,exhale completly then take a fresh breath .
just my 2 cents

[Ainsleyberryman]

Buddy breathing will raise the anxiety, loose gas when purging etc.

Use the Octopus - otherwise its an unnecessary bit of kit.

Off gassing requires time for the gas to come out of your tissues and be transported via the blood to the lungs. This will happen if you hold your breath or not. The blood still flows round, and takes several mins to do one complete circut. Obviously moveing gas in and out of the lungs takes it from the lungs to the outside world and brings in less compressed gas to help maintain the pressure differential to off gas.

I would reckon buddy breathing will not make much difference at all to off gassing compared to using the octopus. Using the less stressfull mode will lower the rate of consumption and allow for extra time to off gas which is preferable.

The difference between good slow controlled breaths vs. good slow controlled buddy breathing is too slight to make a difference. Calmness is going to be a bigger factor.

[Ainsleyberryman]

Or alternatively you could do your safety stop before the dive so this wouldent have to be done at the end when your low on gas

[wreckweasel]

i personally clean my wing regularly with buddy clean this means if the s**t hits the spinny thing i could take one breath of air then rebreath through wing for 4 breaths ,exhale completly then take a fresh breath .
just my 2 cents

No Scrubber = Co2 buildup, hard to quantify. Co2 is a stimulator for breathing.
Doing this will also "wobble" your bouyancy.

KISS is always good. Use the octopus, breathe normally, which supports optimal off-gassing. When things are just too low, surface and alert surface cover to your ommitted deco. Monitor for symptoms/admin o2/call coastguard as appropriate.

Complex solutions always goto ratshit when the brown stuff hits the spinny thing.