Should I buy a pony bottle?

[boulderjohn]

Hey, I'd like to read that. I presume it's on the DAN website?

Yep.

Yeah, I'm reading a couple of books about real diving fatalities among wreck divers off the northeast coast of the U.S. I'm kind of amazed at the things these guys would do--diving to 250 feet on air without a buddy, for example. Goading each other to dive in severe seas. I would very much like to believe that, if I'm sensible, watch out for my own safety, don't dive when it doesn't feel right, etc, that I'll be okay.

In a thread on a related topic a few months ago I mentioned that reading the fatality reports gives you the sense that a major cause of fatalities is people doing things you wouldn't dream of doing.

Wow! I was wondering about that. I've read that, as you ascend, the air in your lungs as it expands somehow gives you the feeling that you're not as low on air as you are...?

Your body has no real signal that it needs air. The panicky urge to breathe comes from CO2 buildup. As you exhale, some CO2 goes out, so you don't feel the urge as much as you would expect to. If you feel the urge to breathe while still performing a CESA and exhaling, it's no problem. You cannot inhale while exhaling. That sounds obvious, but if your lungs are full enough that expanding air is escaping as you ascend, it is not possible to inhale. That is why you can inhale safely while doing a normal ascent.

Would it make sense to practice a CESA from 100 feet (supervised by an instructor, I mean)?

I know some people who would indeed advise it, but I don't think you need to. Just remember that you can do it and remain calm should the need arise.

Wouldn't you have to keep it under 60 feet per minute (30 feet per minute per current guidelines)--then it would take you almost 2 minutes (or over 3 minutes).

That's suggested but not critical. You can go somewhat faster, and I probably would.

Because my understanding is that no-deco diving assumes you are unlikely to get the bends if you ascend at less than 30 fpm (but not unlikely to get the bends if you ascend faster).

If you are within NDLs, the risk of DCS is miniscule, even at the faster ascent rate. It is certainly a lot less risky than being under water without air. The consequences of a minor DCS hit are also pretty minor in comparison to drowning.

And even staying within the recommended limits some people get the bends, so perhaps this would be a dangerous exercise.

That's why I would not recommend it.

Here's one more thing to know about OOA and the CESA:

Your tank is not empty. It just thinks it is.

If your tank does not have roughly 140 PSI greater than the pressure you are under at depth, the regulator cannot give you air. You will usually feel it harder to breathe as you approach the critical level for that reason. (That does not happen at shallow depths, though.) As you ascend, the pressure you are under decreases. That means that after a partial ascent, if you inhale, you will get air from your tank. The closer you get to the surface, the more this is true. Thus, if you do blow out all your air too quickly, just inhale and get some more.

Oh, and in the absolute worst case scenario of ascending with no air in your lungs and a truly empty tank, your blood has enough O2 in it to keep you conscious until you reach the surface from most recreational depths.

 

[Hawkwood]

Hm, I didn't know that...

Matt, remember when you breathed off of a free-flowing regulator in your pool sessions? Well, your instructor may have told you one reason the regulator can free-flow, sounds like he/she might not have told you other reasons. In cold water the first stage can freeze up, leading to a free-flow - giving you all the air.

Bill

 

[AaronRiot]

A CESA from 100ft actually sounds pretty intimidating... I noticed when we did ours from much shallower I had air still near the end but I never physically noticed that I wasn't running out as fast as I should have been. I wonder what that would be like if attempting it from much much deeper? And if there would be enough expansion to not have to ascend faster than what is suggested as safe as per the guidelines? Edit answered above...i type slow lol

dumpsterDiver "Even though I would probably not trust my "new-found-friend" with the key to my hotel room, I am entirely comfortable trusting him, his equipment and his training with my life. I'm fully confident knowing that "my buddy" will always monitor his air supply and will definitely ALWAYS reserve enough to get us both to the surface in an emergency."

-you make a very solid point here among the others.

Perhaps it warrants a rental and a tryout on one of those open pool nights.

 

[dumpsterDiver]

Yep.

....If your tank does not have roughly 140 PSI greater than the pressure you are under at depth, the regulator cannot give you air. .

Do you have any reference for that piece of information?

 

[Pullmyfinger]

That sounds more like something that would relate to a Poseidon regulator (my wife dives them exclusively, I have one for a single tank reg).
I believe the 140 PSI is required for the 1st stage to function.

Hopefully someone knowledgable about Poseidons will comment.

-Mitch

 

[FPDocMatt]

Oh, and in the absolute worst case scenario of ascending with no air in your lungs and a truly empty tank, your blood has enough O2 in it to keep you conscious until you reach the surface from most recreational depths.

Wow, your last 2 posts have been very very informative, not to mention reassuring. Thanks!

---------- Post added at 09:57 PM ---------- Previous post was at 09:50 PM ----------

Matt, remember when you breathed off of a free-flowing regulator in your pool sessions? Well, your instructor may have told you one reason the regulator can free-flow, sounds like he/she might not have told you other reasons. In cold water the first stage can freeze up, leading to a free-flow - giving you all the air.

Bill

I didn't know that when first-stages malfunction it's with a free-flow (rather than the regulator simply not giving you any air). However, now that I think about it, I have read that regulators are specifically designed to malfunction with the valves open rather than closed. So that does make sense.

And it's quite reassuring, actually. We've got these 2 regulators on which our lives depend, and if one of them malfunctions all it's going to do is give you free-flow air. That's kind of nice.

You know, breathing off the free-flowing regulator was way easy. That would not be a problem for me at all. Hm, well, I guess the main concern there is how long it would be before the air were exhausted altogether. Is this an easy-to-calculate number? I imagine it varies by depth...?

 

[redacted]

I didn't know that when first-stages malfunction it's with a free-flow (rather than the regulator simply not giving you any air). However, now that I think about it, I have read that regulators are specifically designed to malfunction with the valves open rather than closed. So that does make sense.

Do not be so assured that you ignore the possibility of a first stage failure resulting in no breathable gas at your 2nd stages. If some 1st stage connections are severely over torqued, the 1st stage can fall apart and all the bubbles will be behind your head, A piston spring failure may leave the piston firmly sealed against the HP seat and there will be no bubbles anywhere. But such failures are quite unlikely. The most common failure is human error rather than equipment failures. That is, divers breath their tanks empty. The great thing about a reliable redundant gas supply (including a GOOD dive buddy) is the failure mode does not much matter - you are protected against any single failure.

 

[elan]

Wow, 28 posts and no mention:

The plastic snap bolt is not DIR.

 

[tadawson]

That sounds more like something that would relate to a Poseidon regulator (my wife dives them exclusively, I have one for a single tank reg).
I believe the 140 PSI is required for the 1st stage to function.

Hopefully someone knowledgable about Poseidons will comment.

-Mitch

A Jetsream tends to free flow at low pressure. A Cyclon should have no issues whatsoever, and I am not sure about the X-Stream, but suspect it will be similar to a Jetstream.

There are a lot of myths out there about Poseidons, but most are crap . . . they are one of the best regulators out there, and the choice of many Navy and commercial dive teams who aren't in the habit of buying either junk or dangerous gear.

- Tim

 

[TSandM]

Matt -- the most important thing to realize is that the most common reason for being out of gas is being out of gas . . . in other words, not planning your dive, not diving your plan, and not monitoring your gas. If you read Bob Bailey's article on gas management, you will learn that it isn't particularly difficult to ensure, before you get in the water, that you have enough gas for the dive you want to do. In fact, even using as simple a rule of thumb as never diving deeper than the number of cubic feet in your tank will help a lot. Cultivating the habit of diligently checking your gauge as you dive will just about fix the rest of the issues -- as you see you are getting lowish on gas, you thumb the dive!

The malfunctions that leave a careful and diligent diver without air to breathe at depth are rare. Freeflows DO occur in cold water, and I have had two; one was slow and easy to manage, and the other was violent and unnerving, but neither resulted in me being without gas to breathe for even ten seconds. My buddies donated and I received and we aborted the dive; easy-peasy. Dip tubes can clog, especially with poorly maintained aluminum tanks, but I've actually only heard two stories of it happening to anybody, and in both cases, again, buddy donated, dive over, nobody got hurt.

People get hurt when they use up all their gas without being aware that they are doing it. Such people often also don't have a buddy nearby, and aren't on top of things enough to execute simple procedures to cope with the problem. If you think about things, and practice your emergency skills, then when an emergency occurs, you'll shrug and deal with it. Don't you take ACLS, to be ready for the rare occasion when somebody arrests in your office? You do it so you're ready when it happens, and they make you recertify every few years so you'll have some practice that's reasonably current. In diving, the equivalent is to do air-shares on your safety stops, or during your quarry dives, if you stay active by diving locally.

If you want to buy a pony bottle, then I think, as a solo traveler who will primarily dive with instabuddies, that one can make an argument for that being reasonable. But practice using it regularly -- and don't give up the dive planning and monitoring that keeps you from ever needing to deploy it in anger.