75 ft out of air, What do YOU do?

[The Iceni]

sheck33 once bubbled...
I have seen this posted before, how do you figure an ascent from 75' frees up .9 CF if an 80 has an interior volume of .4 CF?
you cant apply Boyle's law to a rigid container that way.
the volume of a -flexible- container would go from .4 to 1.3 CF, increasing by .9
The volume of the tank is not affected by depth.

To reinforce what Mike F posted, using ood old metric units.

It is all down to Boyle's Law which states;

Pressure x volume is constant,

At 20metres (70 -odd feet) the ambient pressure is 3 bar absolute so when the tank has become empty it will give you no more gas because the pressure of the fixed quantity of gas left inside - in that fixed volume - has dropped to ambient pressure of 3 bar. It cannot drop any further.

When you ascend the volume of the cylinder does not change, nor does that fixed mass of gas that was left in it when it ran out. Therefore the pressure within the tank remains constant at 3 bar, obeying Boyle's Law.

On the surface ambient pressure is 1 bar, and the cylinder contains 3 bar, therefore there the content's guage will read 2 bar and the cylinder will be able to deliver twice its water capacity as surface air.

From 20 metres a 12 litre cylinder will give 24 litres or 12 breaths of 2 litrs each - on the surface. In imperial units, if an an 80 cu ft tank has an internal volume of 0.4 cu ft this gives 0.8 cu ft of useable air.

On the other hand, of course, the BC is not held at a constant volume so as the diver ascends the volume of gas in it at the start of the ascent will expand by Boyle's Law and its buoyancy increase. - unless of course you breath it out or dump it. Probably a bit of task loading here?:boom:

 

[Genesis]

and need to "dump" from the BC I think I'd choose to dump it into my lungs, where it will do me some good!

 

[Popeye]

Dr Paul Thomas once bubbled...
On the other hasn, of course. the BC is not held at a constant volume so as the diver ascends the volume of gas in it at the start of the ascent will expand and its buoyancy increase. - unless of course you breathe it out or dump it. Probably a bit of task loading here?
__________________
Paul

(Not yet too old to learn something new)

Depends on whether you're not too old yet to learn something new. ;-)

 

[Laser]

Popeye once bubbled...


Depends on whether you're not too old yet to learn something new. ;-)

And that would be great time to learn!

 

[The Iceni]

Hi Guys,

I keep an open mind about most things. One thing for sure I make sure I never run out of gas/air. However I thought I had covered this in an ealier post.

I believe we are discussing an ascent when out of air in the open water situation, not what to do if you have deco obligations. If the diver is qualified to undertake deco, without equipment failure he is unlikely to run out of gas, will have a buddy and so will never need to perform an ESA or brath from his BC.

Such a diver could use his BC as a counterlung during the ascent with a lot of practice but without a need for deco stops why should he practice (or perform) a drill that carries an added risk of uncontrolled bouyant ascent or worse;- losing any residual buoyancy in the BC by exhaling it into the water.

In fact I have practiced using the BC to breath from as an additional alternative air source, (also as a rebreather in the pool alone), and it works with practice but is it really necessary?

The point I made, and it has been reinforced by others, is the sort of divers who run out of air are not likely to be the most highly skilled, it is therefore highly unlikely that they would be able to control their ascent if they added variable buoyancy to their problems.

Boyle will give the ascending diver enough gas for a few breaths from his cylinder but Dalton has already ensured that even by diluting the gas in his lungs by the ascent the diver will not become hypoxic even if he does not take another breath as long as he continues to ascend at a reasonable speed exhaling all the way. The SETT instructors prove this on a daily basis.

I doubt that the BC would be a cause of a nasty chest infection or rebreather divers would not be free of infection, but there is no need to complicate what is already a very stressful incident.

When I first learned to dive in the 1970's it was still routine to finish the dive when one ran out of air and perform a "free ascent". We know better now! =-)

 

[zeN||]

I'm often suprised when I see how people scoff at emergency procedures, and emergency aids like pony bottles, you can talk all you want about being prepared and avoiding a pitfall but the point is Murphy's Laws pre-empt dive planning, it's one of natures constants, the next time you do happen to find yourself out of air with the prospect of an emergency ascent at depth your philosophy on spare air will suddenly change zeN||

 

[The Chairman]

But practicing is better than planning on it not happening.

It is planning that will make it never happen. I used to run out in the 70s before SPGs. You hoped that you hadn't accidentally pulled the rod down! We thought Boyle was what you did to water to cook. I am glad I never suffered any trauma, but it was a kick till you got there scenario (no BCs either).

And even though Rick is still causing controversy with his cutting edge methodology, I will agree with him %100. You rebel rouser! :tease:

BTW, with the advent of the SPG, I have yet to run out. I have yet to have a buddy or student run out. We call it situational awareness. We call it planning your dive and diving your plan. There is no need to run out... and there is DEFINITELY no need for spare air or a pony IF YOU PLAN YOUR DIVE CORRECTLY AND CONSERVATIVELY AND THEN FOLLOW YOUR PLAN!

 

[Charlie99]

Rick Murchison once bubbled...
Miscalculatiing on the "exhale" side will simply cause one to run out of breath, which, while uncomfortable, ain't gonna kill you while miscalculation in the other direction can be disastrous. For those who practice the CESA on a regular basis - and everyone should - the transition from "slowly exhale" to "just keeping the airway open" procedure can be fine-tuned and perfected, but if you haven't practiced it, "slowly exhale" on ascent - that's the safe thing to do.

Keeping your airway open and letting the excess air bubble out isn't something that has to be fine-tuned. You simply keep your airway open, and your lung expansion at any normal spot in your breathing cycle. The expanding air does the rest automatically.

You have either closed your glottis or you haven't --- no fine tuning there either. If you need to practice that, just cough a few times and notice the closure before the cough, then learn how to control that closing action.

 

[zeN||]

OK This story was related to me by a fellow spearfisherman. He finds himself pursuing a fish at the end of his dive, he shoots-bam, the fish takes him on a little chase, with the line getting caught up in rocks, kelp, etc. Suddenly and unexpectantly the diver finds himself snagged (whether this was the line or kelp I don't recall), this diver is a large powerful guy but he is really having trouble getting untangled, he struggled till he was out of air, luckily he had enough 'preparation' to have spare air with him, finally he got loose, if it hadn't been for his spare air he assures me he would have been fishfood. There are countless stories like this of good divers that find chaos in the most unexpected places zeN||

 

[Popeye]

Dr Paul Thomas once bubbled...
Hi Guys,

I keep an open mind about most things. One thing for sure I make sure I never run out of gas/air. However I thought I had covered this in an ealier post.

Dr. Paul, I don't think anyone -plans- to run out of air, but if guys like Steve Berman can do it, I guess we're all pretty susceptible.

I believe we are discussing an ascent when out of air in the open water situation, not what to do if you have deco obligations. If the diver is qualified to undertake deco, without equipment failure he is unlikely to run out of gas, will have a buddy and so will never need to perform an ESA or breath from his BC.

-Assuming- he has a buddy.

A pole on this board last year showed a very high percentage of solo divers.

Even same-ocean-buddies is a reality.

You can focus your training on what -should- happen according to text books and rules, or focus it on real world scenarios.

If your buddy can help, hunky dory.

But what if he can't...?

Such a diver could use his BC as a counterlung during the ascent with a lot of practice but without a need for deco stops why should he practice (or perform) a drill that carries an added risk of uncontrolled bouyant ascent or worse;- losing any residual buoyancy in the BC by exhaling it into the water.

I disagree.

Firstly, I can't see how this could possibly be more dangerous pertaining to ascent than practicing ESA, and no recreational diver should dive deeper than they -know- they can ESA.

So I'm sure they all practice, like you and I.

Secondly, if taking a few breaths out of one's BC is a life threatening event, it's time to hit the links or collect butterflies.

In fact I have practiced using the BC to breath from as an additional alternative air source, (also as a rebreather in the pool alone), and it works with practice but is it really necessary?

I have your preferred method as my primary plan. I have my method, as an alternative plan. You don't, and don't advocate that others experiment with it.

If you get hung up in a tree, or on fishing line, or in a tourist wreck, net, ice, kelp, whatever, your plan has just failed to work.

And that's not all that failed.

Your plan may not work with some primary regulator failures, either.

I can now go to Plan B., free myself, continue to the surface.

Even if I'm re-breathing the one. single. breath. keeping me from asphyxiation.

Others will be concentrating on their struggling lungs, panic, die.

BTW, I just hold the discharge button down and breath in and out.

I don't cycle the button, exhale, use it like a secondary reg.

That can't be hard to learn.

The point I made, and it has been reinforced by others, is the sort of divers who run out of air are not likely to be the most highly skilled, it is therefore highly unlikely that they would be able to control their ascent if they added variable buoyancy to their problems.

So due to inexperience or lack of skill, you would encourage them not to learn new alternatives, and practice them?

Very odd.

Besides, if they're 30 seconds from drowning, I don't think that ascent rate is a big issue.

At least you can die looking at the sun.

Two divers that I can name off the top of my head that OOA fataly are Andre Smith and Steve Berman, each with thousands of dives. Also a female photog in California in 01, whos name escapes me. Thousands of dives.

I find your point above, reinforced by others, rather tinged with arrogance, no disrespect intended.

Boyle will give the ascending diver enough gas for a few breaths from his cylinder but Dalton has already ensured that even by diluting the gas in his lungs by the ascent the diver will not become hypoxic even if he does not take another breath as long as he continues to ascend at a reasonable speed exhaling all the way. The SETT instructors prove this on a daily basis.

Here again, you plan on the perfect ESA scenario, which, in all honesty, will probably be correct.

85%? 95%?

Me, I'm a Murphy advocate.

Seems I'm always in that last 5-15%.

You're planning on a best case scenario, which doesn't seem philosophically wise to me, concerning diving.

I'm planning on a worst case scenario.

Then, I'm already in the groove for best case.

I doubt that the BC would be a cause of a nasty chest infection or rebreather divers would not be free of infection, but there is no need to complicate what is already a very stressful incident.

Actually, the reference was to practice, I believe, and I have seen some -nasty- crap come out of rental gear.

This is from leaving a bladder wet, or with seawater inside, and sticking it in the closet for a month to, er, ferment.

Hopefully, the re-breather guys are more maintenance oriented, especially at the rate their ranks are thinning.

But I clean my wing bladder with warm, soapy water, and spit two mouthfuls of Listerene in it.

I suck my LPI/wing empty whenever I enter the water, and never get sick.

That's proper gear maintenance.

Anyone afraid of what's in their BC should learn to take care of their gear.

When I first learned to dive in the 1970's it was still routine to finish the dive when one ran out of air and perform a "free ascent". We know better now! =-)

Think of the guys that dove the Andrea Doria two days after she sank.

No wing, no octo, no SPG, no helium...!

Now people dive her with $10,000 of gear and trimix, and still die at a prestigious rate.

Makes you wonder.


But it all boils down to options.

I have two.

You have one.

Hope one will do it.