Reg setups: a Philosophy Question

[H2Andy]

a completely lucid, unemotional, and reasonable response to this. Something this thread has been sorely lacking.

wow... the whole thread?

the entire thread, all eight pages of it, sorely lacking lucidity, logic, and reason?

just because i disagree with you?

man ...

 

[ShallowDiverDave]

Thank you, Dive-aholic for a completely lucid, unemotional, and reasonable response to this. Something this thread has been sorely lacking.

-Charles

Dude, you must have missed my post on the merits of the Spair Air unit. You better go back and look.

 

[Dive-aholic]

First it was "APEX." Now it's "Air II" ?? People, it's always been AIR 2...

http://www.scubapro.com/prod/erog/erogatori/air2/air2octo.htm

Well, being I don't dive one... Isn't it actually AIR TOO, meaning you can get air from this too?

 

[munitor]

Interesting. I'm currently in the process of doing a fault tree analysis for various configurations to determine if there is any significant difference in risk. Considering mechanical reliability as well as human factors.

Resurrecting the issue of reliability, I've finished doing the FTA. I did it twice, once using NPRD-95 data, which is what's used for mil-spec FTA, and once using data from BSAC reports, scaled to match the overall incident rates reported by BSAC and DAN (which agree well). I’ve excluded human error, such as diving with an empty tank, failing to turn on the air, or failing to monitor air supply.

Of course, I take no responsibility for anyone using the information for any purpose whatsoever.

Bottom line is that for a single tank with primary and octopus, the likelihood of getting a rapid failure of air supply (60 seconds or less to no gas) is 1:500 dives to 1:2,500 dives. These numbers are roughly plus or minus 50%, which seems like a lot but is typical in the quantitative risk assessment business.

For a main and backup pony rig, the likelihood is 1:1,000,000 to 1:10,000,000.

In each case the higher frequencies (edit: lower ratios) are for the BSAC data, which makes sense given their high 1st stage free flow rates (usually due to icing).

As a sanity check, I checked the rates I got doing a component based NPRD analysis against the overall failure rate for oxygen demand regulators in military aircraft service, and they agree pretty well. Unfortunately, the database doesn’t break down the failure modes for the oxygen demand, so had to do the check on overall only.

Just as a information point, if I include the specific ‘failure to monitor gas supply’ (only available from the BSAC information), the likelihood of failure jumps to 1:250 dives.

Since many people consider their buddy to be their backup, I took a look at the data and it appears that the likelihood your buddy will be too far away to help ranges between 0.3% to 4% of the time, depending on whether you use BSAC or DAN incident data. In the end I calculated that the average risk that a diver with a single tank plus octopus rig will be OOA and no buddy available, due to mechanical failures alone, is 1:100,000 dives to 1:50,000 dives. Throw in typical rates for other human error (all those oopsie reasons people end up OOA) and it at least doubles the frequency. With a pony backup, of course, you don't need a buddy for air, so I'm back to the 1:1,000,000 to 1:10,000,000.

 

[JMcD]

So, I guess the main questions are:

1. is a pony bottle a better choice than an octo in the types of diving I'm going to be doing, in your opinion?

2. what setup would you choose for the diving I'm talking about?

Thanks for your thoughts,

KoAT

[edited to fix a few little things]

At the risk of dragging out a thread...

I think the OP suffers from a clash of concepts - no insult intended.

The question of an octo vs a pony seems to me to be missing the point that, in my opinion, the octo is primarily for your buddy to use - if I'm diving with you, I'd rather you have one - while a pony is more suited for personal redundancy - for you to use. Especially if one considers the many ways pony's can be carried, it becomes more confusing for your buddy to determine what air to go to you for and how to get it.

I'd prefer to think of the Octo as my buddy's redundancy - so I want one for my buddy and I want him to have one for me. (As an aside, I do dive with a friend that has a very old set-up with only one second stage... buddy breathing is ok, but just another thing to make a stressful situation more stressful.)

The great folks here can fight your hearts out on 7ft/5ft/short... Whatever, If i'm OOA i'll take whatever is offered and I trust you'd do the same. Here is where configuration clearly needs to align with the diving you're doing.

I don't carry a pony, and most of my dives are lower vis, cold dives, but I make it clear to my buddy that we are sticking together in the water. I stick with them and I expect them to stick with me. If I was at all concerned about a buddy not being around... I'd be looking for personal redundancy. Decide if that looks like a pony, doubles or , if necessary a "spare air (I'm not a fan of the small size).

 

[King_of_All_Tyrants]

Gents-

Thanks for the two recent posts. My comments:

Munitor- thanks for doing the finger-work on the statistics. Though both scenarios are extreme, the inherently lower risk of the pony bottle appears to be significant.

JMcD- no problem dragging out the thread. I'm still reading. And far as a clash of concepts, I did say that the question is more about philosophy differences rather than equipment.

Fundamentally, it's a matter of how should prepare for and react to an OOA, what equipment is most suitable for OOAs in my dive conditions, and how should I set it up?

My thoughts after reading over all these threads:

1. the DIR way makes intuitive sense. As I recall, for open water dviing DIR recommends a 5 foot hose on your primary and a bungied octo.

2. in many of the one-tank dives I might be choosing to do on charters in the Northeastern ocean, a pony is a requirement.

3. as munitor notes, you reduce your chances of an accident substantially by using a pony.

4. at the same time, many tropical dive sites require an octo, pony or not.

5. you also want to help a buddy in need

6. finally, I want to spend as little money on redundant equipment as possible.

The choice I'm leaning to now is sort of a hybrid. I'll have a primary and a pony, with a high-performance regulator on the primary and a rock-solid, reliable regulator on the pony. No matter how it's mounted, I intend to bungie the pony second stage around my neck DIR style, and use a 5' hose on 2nd stage of the primary regulator. When diving in the tropics, I'll use the cheaper second stage as an octo. If a buddy is OOA with my primary/pony setup, I will give out the primary, turn to the pony, and abort the dive, slowly ascending to the surface.

(again, I intend to do no-deco diving and don't want the hassle of doubles for now. I also think that this "doctrine" will work along the full spectrum of diving that I might do. And I'm open to comments or crticisms of this plan, as long as they're based on actual experience or common sense).



Thank you all for your thoughts,

KOAT

 

[JMcD]

KOAT,

One quick last comment on your "Hybrid" - I find it is always helpful to clarify: you say "when diving in the tropics" and go on to mention use of a Pony. I assume you mean that for the tropics you will remove your pony 2nd stage and add it to your "travelling" 1st stage as an octo. Your comments about a pony are for when you are not travelling. right?

I say "assume" because, as was briefly mentioned I think, getting a pony to the tropics will be a problem. As I understand it, the only way you can take a bottle of any type on a plane is with no valve - completely depressurized. Not a state that you really want to put a tank in just to travel. Not to mention the weight requirement for those baggage handling police.

 

[dumpsterDiver]

problem is that if your inflator hose connection fails (or something else goes wrong with it), you've lost both the AIRII and your BC inflation ... and now you only have one working second stage

whereas having a second stage separate from your BC hose will eliminate this problem

that's the thinking. you can accept or discard.

Is that really it? I always wondered why they are so bad (especially when I put one on my wife's and son's BC's. I always thought that there was some terrible danger associated with the more rapid inflation rate or that someone had statisics that said the AIR2 fails more often.???

Is it really that a hose will blow (or a connection will fail) at the same time my buddy needs air? That seems pretty silly to me.

Heck the simple fact that should a free-flow start, the ease (and speed) with which the AIr 2 hose can be disconnected (over a standard inflator) would seem to be a huge net benefit, since we know that inflator sticking problems are much much more frequent than an inflator hose blowing or the connection failing.. Right?

 

[H2Andy]

yeah... the problem is that now you have disconnected your back up regulator, and only have one regulator should the brown stuff hit the fan

remote, yes, but accidents happen in a chain ...

personally, i prefer a dedicated second stage for that reason

will you ever in your diving career encounter the problem? probably not ...

but ... the chance is there

 

[munitor]

KOAT,

Just to clarify, you significantly reduce the likelihood of being OOA due to equipment failure by going to a pony setup. One could say you also significantly reduce the likelihood of being OOA for doing something you shouldn't have - as long as you have the discipline to not use your backup for 'a little extra bottom time'.

Human errors are actually risks easily exceeding the risk of mechanical failures. Since no one has produced an error free human, think about it.

One also has to consider insta-buddy problems. If your pick-up buddy is OOA near the end of a dive and you don't have at least 500 psi, he could easily breathe you both dry in an ascent from 80', even if you skip the safety stop.