Breathing 100% O2 at depth...

If I had no option other than a deco bottle full of 100%, I'd take a hit (or more) off it. However, I'd expect to die anyway, and for it to be less painful in my last seconds/minutes due to the seizure which would "mask" my consciousness of the final event.

Problem is, you won't have it with you in a cave. Protocol is to drop deco gas just below its safe breathing limit, so it does not encumber you with a gas you can't safely breathe anyway.

In the ocean this situation can arise however, since in the ocean protocol is NOT to drop deco gas, since you may get blown off the wreck, away from the ascent line, etc - and if you don't have it and need it, you're screwed.

With a cave TYPICALLY you come out the way you went in (intentional traverses excepted), so most times you would not carry it with you.

I hesitate to wade into this conversation, but since I saw a particular point repeated that is in extreme error I have to....

The air in your tank does NOT "expand" as you ascend. It does not change pressure by itself either. It is a FIXED volume.

What -does- happen is the pressure differential as you ascend between whats on one side of the regulator (inside the tank), and what's the ambient pressure on the other side of the piston or diapraghm, allows the regulator to release a little more of what's left in the tank. It's why you leave the regulator in your mouth on an emergency ascent, among a few other reasons.

This is real basic OW-I stuff I thought. If you don't grasp this, you sure shouldn't be dishing out potentially life-ending advice on the internet.

Be safe, Drew

IMHO:
You're in deep open water, catastrophic gas loss, all you have is an O2 bottle:

I'm thinking you need to get to the surface (or 20ft deco depth) quick!

Why aren't you swimming like heck for the surface- instead of locating and deploying the reg, turning on the bottle, switching regulators, etc.

You are wasting precious time! SWIM YOU FOOL!!!!!! ;-)

Given the choice of breathing O2 at depth, I'd take my chances on the back gas remaining in my wing, if I absolutely HAD to breathe.

(Obviously, if you're in an overhead environment, you're toast.)

Quote:

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Originally Posted by Gary

As 33' = 14.7 psi - 100' to 0' would provide less then 50 psi of availiable pressure in your tanks. Possiably less then the volume of a spare air canister.

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assuming a fixed tank pressure vs ambient point where your regs will deliver...

44.1/2640 = x/208 (double 104s)

cross multiply

44.1 * 208 = x * 2640

x= 9172.8/2640

x equals roughly 3.5 cubic feet...not a huge amount but several breaths at least

Drew

Depends at "what depth". If you're seriously deep then you're almost certainly ###### - if you explosively decompress you're dead (and that's gonna HURT) if you don't hit the O2 you're dead (and you ain't gonna like it) you may as well hit the O2 and go without knowing what happened.....

May be morbid to see it this way, but what are your alternatives? Go for it? Depends. If you have the O2 its probably because you also have a nice obligation at that point in time (since you just ran out of gas, right?) which means explosive "blow and go" is not gonna be a fun way to buy it....

BTW if you're tempted to practice an emergency ascent please do it with NO inert gas load. Instructors have been known to get bent this way doing them with OW students from 20'! This is definitely a "last ditch" thing.

This is one - of many - problems I have with the "party line" when it comes to diving...... IMHO if you're going to dive in open water more than 60' deep you should have a real pony (at least a 13 and a 19 is better) - and in any overhead (real or deco-induced virtual) you need DOUBLES (or independants)

Quote:

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Originally Posted by Genesis

This is one - of many - problems I have with the "party line" when it comes to diving...... IMHO if you're going to dive in open water more than 60' deep you should have a real pony (at least a 13 and a 19 is better) - and in any overhead (real or deco-induced virtual) you need DOUBLES (or independants)

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Ding! Ding! Ding! We have a winner.

Quote:

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Originally Posted by Limestone Cowboy

I hesitate to wade into this conversation, but since I saw a particular point repeated that is in extreme error I have to....

The air in your tank does NOT "expand" as you ascend. It does not change pressure by itself either. It is a FIXED volume.

What -does- happen is the pressure differential as you ascend between whats on one side of the regulator (inside the tank), and what's the ambient pressure on the other side of the piston or diapraghm, allows the regulator to release a little more of what's left in the tank. It's why you leave the regulator in your mouth on an emergency ascent, among a few other reasons.

This is real basic OW-I stuff I thought. If you don't grasp this, you sure shouldn't be dishing out potentially life-ending advice on the internet.

Be safe, Drew

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theirs always somebody to split hairs with on the net.

leaving the reg in and waiting for another breath on ascent is the way it's done. No need to bring the science of piston VS. diaphragm regs out, it will just muddy the water

And Like some of the other members of this board have stated. You should train for gas failure (so you know how to survive) and you should use a gas management plan that will insure your (and your buddies ) survival.

Training and proper gear is the key to not getting in this situation .

It's not splitting hairs. The gas in your tank does not expand, period. It has little to do with what type of regulator either.

It really is important to know how this stuff works you know.

The rest I agree with you on.

Drew

Quote:

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Originally Posted by Limestone Cowboy

It's not splitting hairs. The gas in your tank does not expand, period.

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Well in the spirit of splitting hairs: :twisted:

The air in the tank does expand as it leaves the tank thru the regulator. As a closed system the total volume of the gas certainly expands - or if you consider it as an open system the gas that doesn't leave the tank "expands" to fill the void of the gas leaving the tank and the absolute pressure of the remaining gas is lower.

Not only that the `3.5 cu ft you get (from 104s ascending 100') isn't really 3.5 cuft in the tank. The volume of the gas in the tank is relatively fixed and the 3.5 cuft of gas is it's measure at STP. The tank is not at STP as it is likely still compressed to at least the ambient pressure at depth.

When considering the differential pressure reduction gained from ascent and the relative equivalent volume of gas at STP that becomes available when exiting the regulator to the diver also however consider the the gas released will expand to a larger volume at 33' then at say 66' or at 99'.

104s ascending from 100' to the surface providing ~3.5 cuft is plenty of gas to make the ascent. It is quite a few "breaths" when you consider a mean tidal volume of about 0.05 cuft X ATM but in terms of time only about 2.5 min even at 33' (3.5 cuft / 2 ATM / .7 cuft/min SAC). That is neglecting the acent and the fact you don't have the full 3.5 to work with because you haven't fully ascended to the surface yet.

For that matter spare air generally come in 1.7 3.0 and 6.0 cuft canisters (3.0 is standard). So it is still less then one might get from a spare air.

Enough for a controlled ascent but not much more. Still better to avoid running out of air in the first place. ;)

OK - I'm done :) :twisted:

ONE breath on the way up from 100' to the surface is probably enough IF you don't care about ascent rate.

The problem is that you do..... especially if you just ran out of air, as that is likely accompanied by a fairly significant inert gas load. Very rapid removal of the pressure on your body is going to lead to you having a very bad day.....

Adding to this is the paradox that high-performance regs actually make detecting an imminent OOA situation very hard. They breathe REALLY WELL down to 150psi over ambient pressure - unlike the unbalanced regs that start to get tough to suck on at 500psi or so. You can basically suck a tank to near-vacuum before you get any warning at all with most high-performance regulators.....of course if you run out of gas, who's fault is it that you were not looking at the gauge?

The more serious potential event is one that results in NO air being available. The most obvious example is a blown low pressure hose (or turret on regs that have them), which will immediately drop the IP to zero and render any second stage on that post instantly worthless. Even if you can shut off the tank and preserve some of the contents you can't get to it through that first stage any more.....

I have extremely serious "issues" with the various agencies over many aspects of so-called "dive training", which, due to the rules here, I can't be explicit about. However, this is one of the more obvious - is it REALLY that hard to teach people to rig a pony as a stage and dive it? No. Does it put into what I believe is the proper perspective what is the only TRUE emergency underwater (nothing to breathe!)

YES.

Problem is, putting it into that (proper) perspective detracts from the "diving is as dangerous as bowling" mind-set that many in the industry seem hellbent on promoting......