No gas -- what do you do?

[liuk3]

Depends upon the scenario for me.

If I am going OOG and know from looking at my SPG that I am about to empty my tanks, I would signal my buddy and share gas.

However, if it occurred out of the blue, I would at least try my backup reg once I found my primary reg breathing hard. Takes less than a second to do in order to help myself and keep myself sufficient on my own gas supply. If I can breathe off of the backup, I then do a flow check to diagnose and potentially fix problem. That's what I did when it happened to me. If I can't breathe off of the backup, I'll share gas with my buddy.

 

[Thalassamania]

NO alt air.
Instructor AND assistant instructor.
Nice example.:shocked2:

As you can see alternate air is rather unnecessary for recreational diving limits, for a decently trained diver. Oh, I guess I forgot to mention that this was in 1971, does that make a difference to you or change reality?

 

[liuk3]

I can think of some possible scenarios where primary reg is unbreatheable but backup reg is working. Of of the top of my head:
1) malfunction in primary 2nd stage
2) kink in hose off right post leading to primary 2nd stage
3) malfunction in primary 1st stage on right post
4) right post valve turned off
5) isolator on manifold accidentally closed and sucked down right tank leaving left tank full and spg showing gas completely full.

EDIT: It just occurred to me that this is for double tank configuration, and I don't know if the question was directed towards a single tank configuration. Sorry if this just confuses the issue.

 

[Rhone Man]

I can think of a couple situations where a primary second stage might stop delivering gas, but an alternate second stage would still function. The most obvious one is the one that happens in just about every episode of Sea Hunt and every second James Bond movie - traumatic disconnection of the second stage from the first stage. Oh just how disappointed would be the baddie be after cutting 007's air hose if James just smoothly switched to his octo (and if it is Sean Connery, is it called an octopush)?

But I suspect that in 99% of cases, if your primary second stage isn't delivering gas, reaching for the secondary is unlikely to bring relief.

 

[Jim Lapenta]

Saw a reg fall apart when a student stuck it in his mouth to test breath it. The instructor quickly picked it up, screwed the faceplate back on and said here it'll be fine. I go for my back up since it's under my chin and also tell students that the octo is as much for them as it is for their buddy. Why not go for it while signaling their buddy? Seems that choice was left off the poll.

 

[noreastDIVER84]

I would signal my buddy first and share air, if I could switch to my secondary at that point I would, then I would end the dive.

If I was solo, I would be either carrying a pony or double sidemount, and then end the dive/

 

[Fish in a Barrel]

I figure in the time it takes to signal my buddy and get his reg I could also reach up and hit the purge on my octo. If there's bubbles, great; if not, then I've already got the ball rolling on the air sharing.

Hopefully this will never be anything more than an academic discussion for me, though.

 

[Dive Bug Bit Me]

To be fair, the comment that sparked this thread off was in the solo section. Suffice to say buddy not an option when solo, but based on redundant air source principals, you would be best going for your alternate which should be attached to a separate first stage on either doubles or a pony.

If you have a buddy, thats what he is there for, signal him!

Tough to think of many situations that will stop a first stage from delivering gas without giving off a massive free flow while leaving the alternate attached to the same first stage working.

 

[Gombessa]

Is anybody else aware of a failure mode in any reg other than an upstream regulator, that will cause a 2nd stage to stop delivering gas?

How about this blast from the (recent) past:

Recall Dry Suit Inflation hose - Removal of Flow Restricton Insert

http://www.sitech.se/files/documents/recall/press release v 3 0 090404.pdf

"Hazard: The hose contains a flow restricting insert, of color black, blue or green. Reports of an indicated malfunction of the flow restricting insert in the hose for the suit have been submitted to SI TECH. The insert may malfunction by dislodgement from the connection valve, potentially causing an obstruction of the air flow."

The danger was that the small flow-restriction insert could fall out of the drysuit inflator hose, into the first stage, and travel up through a regulator hose and obstruct the airflow to that second stage.

I don't think anyone sells hoses with these restrictors anymore, but it's likely that some of these are still out in the wild.

 

[TMHeimer]

Can't vote, varies too much.
On say a 60'+ dive with a buddy I would go to his alternate. Deeper like 100' I may go right to my pony since I would probably have it at that depth, but then go to the buddy (soloing down there just isn't for me). If I'm soloing at my usual 30' or less I'd do a CESA (which I regularly practise), as there would be no buddy or pony.