Doubles?

[Rick Murchison]

... What is not a small deal is the idea that you are going to have your buddy actively attempting to diagnose your problem and shut down your valve(s)...

You don't diagnose a big leak and then shut down valves. You shut down valves and then diagnose the leak. The difference in our approaches is when the diagnosis - beyond "Oh, sh**, got a big leak" - begins. If you've ever had one, you know that it's "exciting." I say shut 'em all down (as a practical matter I start with isolator and left post, then right post - the isolator is usually closed first - but until I have two closed both hands are busy closing valves, and all three are closed pretty quickly), then start the downstream diagnosis; you say "shut down the isolator" and then start the diagnosis.
Let's think about this immediate action difference and where we are in the sequence after the first step... my way, my immediate action has the possibility of two different results; I get an immediate clue as to what the problem is, because if the leak continues I already know I have a leak that can't be stopped with a valve shutdown; if it stops I already know a post shutdown will do the trick. Either way I'm well on the way to a decision, and the "excitement" factor is reduced. Your way guarantees that you'll still have the leak after step one, and that you're no closer to knowing what the problem is after you've completed step one than before it. And, by shutting down both posts immediately and simultaneously, I've a pretty good chance of losing less gas than by shutting down one at the time.

... Personally the way I learned was that each diver only handled his own valves, and the buddy stood by to assist with an air share if needed. Of course the buddy could signal the diver in distress as to where the problem was if he could see it.
You can see how our different techniques could get us into some confusion if you were helping me with my valves and I didn't know what you were doing ...

Let's not overthink a buddy's participation here. The buddy switches to his secondary and offers his primary. The diver with the leak decides to either continue with his own valves or accept the proferred reg. If he accepts the reg he's turning the valves over to the buddy. The idea is to have the buddy's assistance available before anyone gets in "distress." If your buddy is available, he has a much better angle (mechanical advantage) to handle valves quickly, and view to determine what the leak is and how best to situate valves to best handle it.

So each doubles diver should make sure he knows in his own mind (and practices) the shutdown sequence, and communicates in advance with his buddy how this emergency would be handled...

Agree wholeheartedly - team members should be crystal clear on what's to be done in case of a catastrophic leak, who's to do what and under what circumstances. And they should practice! Having a firm plan and following it is even more important than the details of the plan itself.
Rick

 

[WD8CDH]

Since my redundant gas is alway enough to "get me home" (I usually dive triples with one tank independant) I switch to my backup gas, shut off both posts on the main tanks and then diagnose the problem.

 

[Jin]

Thanks for the clarification guys.

 

[Steve_Dives]

I was taught right to left, one valve at a time, and open each valve before closing the next. I didn't like method, so thanks for the question and comments.