Reg setups: a Philosophy Question

[MSilvia]

What if it is a deeper dive and my 19cu pony might be cutting it close, why not beable to both breath off the 100cu i have on my back and work our way safely back to shore/ boat if there is enough air do the saftey stop.

Just playing Devil's advocate, but if you had brought an adequately sized pony, you wouldn't have this problem. Instead of a 19cf, use a 30 or 40 so you won't ever have to worry about "cutting it close". If you know enough to use 100cf of back gas for that dive instead of (for example) a 72cf tank, why bring an undersized backup?

 

[munitor]

I am not entering into the philosophy question about regulator hose length arrangements but I like munitur' fault tree idea--please do that but where will you get non antedotal data?

The objective is to see if there are big differences, not small ones. From a risk engineering perspective, the differences between different brands of piston regulator are insignificant and from experience I can tell you that testing interval has more effect on short term reliability than anything else. Most people know this intuitively. After all, if you just thouroughly checked its operation, how likely is it to fail in the next 60 minutes?

What I will do is try to get some industry failure rates for comparable bits of kit and use some harsh grading to find big differences. That means looking at the worst possible typical combination (which is probably no pony, two 2nds off a single 1st, k valve, 1 SPG, no pre-dive function check) and best combo (which I won't know until I finish digging up the base data, but obviously includes pre-dive function checking, DIN valve, etc), then looking at the differences. I have the incident rates for diving pretty well pegged so I have base risk rates. I can then estimate failure rates, use the error rates for humans under pressure, and take a look at the numbers.

If the differences in rig reliability are lost in the noise, or can be mitigated by pre-dive checking to the point of insignificance, then it tells me all that needs to be known. If the differences are significant, then I can take a swipe at what the "safest" rig is likely to be, including emergency response. And no, I'm not doing doubles. I just want to know what the best setup for the typical one tank diver looks like, including whether better pre-dive checks are called for.

Just as a data point, did you know that crash rates on engine failure for double engined private planes are four times those for single engine? Reason: time critical task overload. Something to think about.

 

[Buoyant1]

What about "H" valve configurations?

Two seperate first stages and second stages. One reg free flows, you can shut it down and breathe off the other on a single tank. If you go with doubles you're already used to that set up, and configured.

 

[King_of_All_Tyrants]

It really doesn't matter which reg you donate, both work quite well. The OOA diver almost never (despite popular belief) grabs for the regulator in your mouth. They almost alway accept the regulator you give them. I've brought up lots of OOA divers. One reached for my octo, one (a cave instructor) reached for the reg in my mouth, all the others have accepted the one I handed to them.

BTW, with option # 1, you can also donate your primary. It's actually quite common.

This all brings up a seperate question, which is really inseperable from the rest of the thread: what is the most common cause of OOAs? And how does your rig and philosophy help you get out of your (or your buddy's) OOAs in your normal diving conditions?

 

[dumpsterDiver]

Another option is to use an AIR2 on the Bc inflator (giving you an octopus), breath off of a short primary hose and keep the pony bottle second stage bungied around your neck. You can go on vacation and ditch the pony and still follow PADI guidlines of a safe second if you choose.

A failure analysis of gear types will probably be of limited use for most recreational diving settings. The primary cause of serious problems with breathing from a scuba unit is usually "operator error" in my opinion. Having a completely redundant system, can help mitigate the "idiot factor" that either you or your buddy may deliver to the dive site on any particular day.

 

[H2Andy]

what is the most common cause of OOAs?

almost always poor gas planning or failure to properly monitor gas supply

rarely it is an equipment failure

 

[munitor]

A study in the UK saw at least a couple of OOA fatalities due to SPGs reading very high, something I thought wouldn't be an issue.

When you get down to the bottom line, people die because they tend to panic under life-threatening stress. Keeping it simple saves lives. I think dumpsterDiver will turn out to be right on the money that the ultimate mitigation for OOA, especially since most are operator error, will be a necklaced 2nd from a redundant system. Things go wrong, put in the backup and go up. It just doesn't get any simpler.

 

[FoSheZZie23]

Just playing Devil's advocate, but if you had brought an adequately sized pony, you wouldn't have this problem. Instead of a 19cf, use a 30 or 40 so you won't ever have to worry about "cutting it close". If you know enough to use 100cf of back gas for that dive instead of (for example) a 72cf tank, why bring an undersized backup?

Because i got the tank with a DIN valve NEW for $40. Even if i didnt get the smokin deal i would never have bought a 30 or 40 for a pony, I rather run twins instead of having that huge pony attached to my main. I wouldnt even attach that to my main. Ive dove with a 40 before as a sling for a off gas bottle. The 19cu feels perfect next to my 100, doesnt put me off weight on one side at all, small enough and light enough not to be a pain in the *** either. Now when i do my lake mead B-52 bomber (is b-52 right? b someting or other) dive I will run twin 100's and a 40 sling with the obious deco bottles on the line. one day i swear ill do it!!!!!

 

[Walter]

Andy is correct. The most common reason for OOA is human error.

 

[Gilldiver]

A bit of background, and this goes back to only air diving with depths up to about 200 feet. The original Pony configuration for wrecks in the 60’s-90’s were:

1) A 30 or 40 foot tank strapped to a single tank, usually a 72 or an 80. This gave you an independent system to get you to the surface from the shallower wrecks.

2) The same pony but strapped between twin independent tanks (72’s or 80’s). Again it gave you a totally independent rig to get to the surface. With the independent tanks the process was to switch off every 500 psi so that both main tanks were drawing down evenly. But some guys wanted the pony as insurance incase they lost a main tank towards the end of the dive.

3) Twins, but with a cheater bar or single post manifold. Again, the pony was for if you lost the main air supply

4) Twins with a 2 post manifold – The pony was just safety gas and used mostly as a hold over from prior practices

Then in the early 90’s we started working with Billy Deans and getting into the Voodoo gasses – NITROX and Mix. Billy also brought up a lot of caver techniques like a slung stage with deco gasses, etc which changed the whole pony system into slung stages, which are much better any way you look at it. I started diving home brew mix in about 93, we had no tables or mix computers then. What we found out was that if you used 21/25 with 100% O2 at 20 and 10 you could use the old Navy air tables and get away with it.

Some other things to consider when understanding how these things came about and have changed:
A) In a wreck you are rarely more then 100’ and 3 minutes from the exit. Caves are completely different due to longer distances and times to get to open water. We just didn’t feel the need for larger safety tanks and the rule of 3rds. Some still don’t.
B) Using a 2 post manifold and a pony strapped to them resulted in 3 - 2nd stages around your neck. More then a few divers jumped in on the pony by mistake and found themselves on the bottom out of air. A few of these panicked and died with full tanks on their backs. To avoid this we would have 3 different 2nd stages so you could tell them all apart by feel -Poseidon Odens and Thors for main tanks and a USD SE2 for the pony was common. The slung stage removed the 3rd second stage from the neck and eliminates this possibility.