How does "real life" OOA looks like?

svidlano · Mar 10, 2003

In one of my pool sessions I took a chance to empty a tank just to see how it looks like. Breathing becomes harder, and with some self-control I managed to get few extra minutes of air (don't panic, just breath real slow).
So my question is "How real-life OOA looks like"? You can notice it coming a few minutes ahead so there is more than enough time to do what ever is necessary.

Any one can describe how was it for him/her?

Thx.

Sanjin

Amanda · Mar 10, 2003

I've been involved once in an OOA situation. It wasn't my buddy or me, it was our instructor !! He's gotten so much concentrated in ooking for that huge murray eel that he forgot to check air supply.

The onlyn thing I can tell you is that when he realized it, he really wasout of air ! He couldn't use that tiny bit of air he probably had left anyway.

:rolleyes:

Diver0001 · Mar 10, 2003

svidlano once bubbled...
In one of my pool sessions I took a chance to empty a tank just to see how it looks like. Breathing becomes harder, and with some self-control I managed to get few extra minutes of air (don't panic, just breath real slow).
So my question is "How real-life OOA looks like"? You can notice it coming a few minutes ahead so there is more than enough time to do what ever is necessary.

Any one can describe how was it for him/her?

Thx.

Sanjin

Modern regs breathe more or less effortlessly until almost the last breath. When you're almost out of air your reg will start to breathe very stiff. With a modern reg you'll probably get a few more "long-slow" breaths from it before you're really OOA but it takes a lot of self control to do this. Older "unbalanced" regs gave you a few more breaths before you were really OOA but they started getting stiff a lot sooner too.

Is this your question?

R..

svidlano · Mar 10, 2003

Thx. I didn't know that modern regs don't give you that warning. I was able to get some 10-12 really slow breaths and therefore concluded that in case of OOA I will have more than enough time to signal for help and take someone's reg.
That has eased my mind regarding OOA (you get a warning, you have enough time). I wonder now if it is false.

raxafarian · Mar 10, 2003

svidlano once bubbled...
Thx. I didn't know that modern regs don't give you that warning. I was able to get some 10-12 really slow breaths and therefore concluded that in case of OOA I will have more than enough time to signal for help and take someone's reg.
That has eased my mind regarding OOA (you get a warning, you have enough time). I wander now if it is false.

you were in a pool.... very shallow.

At depth, you'll be trying to get a whole lot more air with each breath, so you won't have "minutes". You'll probably only have a breath or 3 after you notice the sudden "difficulty" or "resistance".

Remember, though, even if you just exhaled and then tried to inhale and get nothing.... you still have time to swim to your buddy as long as you stay relaxed. It's not the lack of air that makes you want to inhale, it's the buildup of CO2. Give it a try... blow out all your air and then "hold your breath". You have plenty of time.

Edit: I meant to try this above water. Never hold your breath underwater.

Diver0001 · Mar 10, 2003

svidlano once bubbled...
Thx. I didn't know that modern regs don't give you that warning. I was able to get some 10-12 really slow breaths and therefore concluded that in case of OOA I will have more than enough time to signal for help and take someone's reg.
That has eased my mind regarding OOA (you get a warning, you have enough time). I wander now if it is false.

I did an experiment (above water) on this subject a while ago. Here's what I wrote about it at the time:

I took a 15 litre tank (104 cf in 'mercun) with a Y valve on it.

On one side a 3 year old Sherwood Maximus (balanced piston) with a tuned and adjustable 2nd.

On the other side a 28 year old AuqaLung Aquarius (unbalanced piston) with a detuned sherwood octopus.

These represent the two extremes of performance you're likely to see in the real world these days.

Started breathing at 30 bar (435psi). Pressure measured with AI computer with resolution of 0.5bar (7 psi)

At 20bar (290psi) no change

At 10 (145psi) bar no change

At 8 bar (116psi) the unbalanced reg starts to get heavy. The balanced reg is still breathing like it does with the tank full.

At 5 (72psi) bar the unbalanced reg is getting progressively heavier. The balanced reg is showing no decrease in performance.

At 2 (29psi) bar. No change as compared to 5 bar

At 1 bar (15psi). No change

At 0.5 bar (7.something psi). the unbalanced reg is heavy but it is still possible to breathe more or less normally. The balanced reg is *still* showing no decrease in performance.

Gauges jump to 0.0. Both regulators are still breathing. The unbalanced reg is heavy but possible. The balanced reg is still showing no deterioration in performance as compared to a full bottle.

Rob now turns on the stop watch.

10 breaths. Even the balanced reg is starting to show signs of protest.

20 breaths. The unbalanced reg becomes unusable.

30 breaths. The balanced reg is getting heavy

40 breaths. The tanks is completely empty. The balanced reg gives air until the last. Pressure in the tank is now so low that you can blow air back into the tank via the open valve.

Time 4 minutes 40 seconds from the moment the gauge turned to 0.0.

You can draw your own conclusions but I concluded:

- a balanced reg won't seriously deteriorate in performance until your gauges show more or less zero.
- An unbalanced reg will give you a bit of warning, showing significant performance degradation from 8 bar,
- but even an unbalanced reg will continue to function until the gauges read zero.
- A balanced reg gives you a couple more breaths as the tank pressure reaches zero.
- Neither reg cut out suddenly. They both showed performance decreases as the end drew near.
- Zero doesn't really mean zero on my computer. Probably everything needs to be padded up a bit

That's how it worked above water. What I don't know is how your depth will influence these results. I would expect that if you were deep enough that the reg would become heavy and then give a small amount of air again as you ascended. However, I've never tried this so I don't know for sure.

One more conclusion you might be able to draw is that once you notice your reg getting heavy that you should have enough time to secure your buddy's alternate before you're really in trouble. In pactice, however, people often (usually?) panic before they're well and truly out of air.

Related to this, of course, is the question of whether or not most divers would recognise the feeling of their reg getting a fraction heavier with each breath.....In an experiment it's easy to recognise the thing you're expecting to happen but if you're distracted enough to forget about checking your air then you're probably not going to notice your reg getting heavy either. I'd say (as I said before) that you shouldn't count on being able to get any more than a few more slow breaths once you notice your reg getting stiff.

R..

Groundhog246 · Mar 10, 2003

Not sure how it compares with a real OOA (empty tank), but part of our OW training was the instructor turning off your air at the bottom of the pool, so that (hopefully) if you should ever do it in real life you will recognize the extra resistance before you've drawn that last breath. Whether or not you will several years later is debateable, but it was certainly odd enough a feeling that at this stage, I'm pretty sure I'd recognize it again. Maybe it's a "task" I should add to my next pool dive. BTW, while the instructor was turning off your air, he held his octo ready in the other hand. As soon as you gave the OOA sign, he opened the valve again.

Uncle Pug · Mar 10, 2003

svidlano once bubbled...
...real-life OOA looks like"? You can notice it coming a few minutes ahead

Probably best to have a J-valve if this is the kind of diving you are going to do... reg. breaths hard... ooops... must be OOA... pull the reserve lever.

However I would suggest that you invest in an SPG (submersible pressure gauge.)

That way you will be able to *notice it* more than a few minutes ahead.

Actually with an SPG you can pre-plan the gas required for the dive and monitor your gas usage during the dive.

Works great!

Conor · Mar 10, 2003

just before we began our ascent I noticed my reg starting to breath heavy, I looked at the guage again and it still read 60bar. Assuming the guage was dodgy I signalled my buddy to stay close as my air was low and started my ascent and safety stop. By the time the safety stop ended I was really beginning to struggle to get any air out, but made it to the surface without needing any assistance.

When I got back on the boat I discover that the guage was fine, the cylinder was nearly closed. Rather than opening the cylinder fully and turning it back a bit, my buddy had closed it and reopened it, which should not have been a problem, except there must have been a notch or something in the thread because it stuck between one and two turns from closed, giving the impression of being fully open.

What it did mean was that I spent a few minutes in the water thinking about out of air scenarios and will pay a lot more attention to my guage and the location of my buddy as a result. I think I'll also pay more attention to the location of the valve on my BC, and practising turning on my own air in the water, a skill that I believe will be necessary if I ever use doubles anyway.

frogxman · Mar 10, 2003

Uncle Pug once bubbled...

Probably best to have a J-valve if this is the kind of diving you are going to do... reg. breaths hard... ooops... must be OOA... pull the reserve lever.

However I would suggest that you invest in an SPG (submersible pressure gauge.)

That way you will be able to *notice it* more than a few minutes ahead.

Actually with an SPG you can pre-plan the gas required for the dive and monitor your gas usage during the dive.

Works great!

Uncle Pug, can you explain how this device works?

How does "real life" OOA looks like?

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