Manifold open or closed?

[matt_unique]

Suppose you had EAN36 in both tanks, closed the isolator and went diving. After the dive you get your tanks refilled and a shop that banks EAN30 (typical for the NC coast). They don't realize that the isolator is closed and fill one cylinder only. You analyze the tank and see you have EAN30 which gives you a MOD of 121 ft. You plan your dive to 115ft. No problem...until you switch to the other tank with EAN36 in it (with a MOD of 95ft @ 1.4/ 113ft @1.6).

Jason

This would be bad and the owner would not be paying very good attention if this were to happen. Ha ha ha, it's like "say you are about to enter the water for a deco dive and someone hands you a stage bottle with 80% and you think it's 36%....." Of course if someone were stupid enough to use a tank with unknown/properly analyzed contents they are going to experience duress in short order.

--Matt

 

[Soggy]

The point is very simple. You get in the water with your isolator closed. That's bad enough, but when did it get closed? Was it filled closed, was it analyzed closed? What side did you analyze? If your 'system' of checking for an open manifold has failed all the way up until the point where you are *diving*, you absolutely cannot trust the contents of those tanks. If your dive is planned using 18/45, but the last time you dived them you had 32% in them (i.e., one tank is 18/45, the other is 32%), not only is your deco going to be wildly off, you're also seriously risking an oxtox episode if you open the manifold underwater.

 

[Jason B]

Matt, I realize that it shouldn't happen, and if the isolator is left open as it is intended it couldn't happen.

Jason

 

[Soggy]

Unfortunately, it *does* happen and those that it happens to need to understand that the gas in their tanks is suspect and potentially lethal. The problem is solved back at the dive shop, probably days before getting on the boat, but if it does happen, one should know how to respond to the situation.

 

[Jason B]

Matt, here's what I was addressing...

my experience was the other way around, (and yes I screwed up in not doing pre dive check of it) .
The ace who filled my tanks closed the isolator after he filled them. When I was at the end of my dive on the hang, I looked and "Wow" the spg still read 3000! At first I thought the needle was stuck, but then I reached back and opened the isolator (it only took a second) and as soon as it opened I heard a "woosh" and the gage dropped to abt 1600.

To which Soggy replied...

Ouch...that could've led to a *really* bad situation as you now have a completely unknown FO2....If I discovered my isolator was closed during the dive, I would *leave* it that way and abort abort abort. At least I know that what I analyzed is what I am probably breathing. I might even go 'OOA' and share gas with my buddy who at least now has a known breathing supply.

To which SeanQ asked...

How does the F02 change when this happens?

That is where my post was going to.

Jason

 

[wedivebc]

Unfortunately, it *does* happen and those that it happens to need to understand that the gas in their tanks is suspect and potentially lethal. The problem is solved back at the dive shop, probably days before getting on the boat, but if it does happen, one should know how to respond to the situation.

Who does it happen to? Do you personally know of anyone?
When you begin a dive you ensure that your posts are open and you may even check the isolator position. When I complete a dive I instinctively open the isolator. When I fill my tanks I check my isolator. When I analyze my gas I check my isolator. When I am ready to put my tanks on my back I check both my posts and my isolator (as you probably do too). If I were to find the isolator closed at that point I would suspect the analysis of the gas but it hasn't happened yet.
Since you feel this is a common error that is causing divers to drop dead all the time please let me know about it because I haven't heard of any.
Everything about diving is risk management we just use certain procedure to reduce that risk. I know lots of people who dive this way including many of my students.

 

[novadiver]

I think, at the level of diving wedivebc is talking about , a mistake like this is very unlikely. I know I set my valves before every dive. I don't like them Full open because it's harder to turn them when the tank has high presure. I keep them all at 1/8 turn from the stop. This helps with a smooth valve shutdown drill. If it took me one minute to shut down an offending valve , I would just take the pack off and pull it in front of me , then shut down the valves in record time BUT if you can't reach the valves, then you might need another plan. I think that's what wedivebc was talking about.


I've seen plenty of good divers wearing suicide doubles, they plan their dives knowing what gear goes were, and have no problems.

 

[Soggy]

Who does it happen to? Do you personally know of anyone?

Yes. I know of more than one case where someone did a complete dive and had their isolator closed. Up above a few posts in this thread is someone who confessed to it.

When you begin a dive you ensure that your posts are open and you may even check the isolator position.

As do I...I check my isolator probably a dozen times from the moment I analyze my gas to just before jumping off the boat. I'm really quite paranoid about it.

If I were to find the isolator closed at that point I would suspect the analysis of the gas but it hasn't happened yet.

We agree with each other. It's a dumb error, but it can happen, and if it does happen, the analysis is nullified.

Since you feel this is a common error that is causing divers to drop dead all the time please let me know about it because I haven't heard of any.

I have never said it was a common error, just that it can and does happen. Just because people aren't dropping dead all over the place doesn't mean it can't happen. It also doesn't mean that we shouldn't be aware of the issue.

Everything about diving is risk management we just use certain procedure to reduce that risk. I know lots of people who dive this way including many of my students.

We've already established that the majority here think your way of diving doubles is beyond comprehension, but I'll accept it and we can move on with the discussion.

 

[wedivebc]

I think, at the level of diving wedivebc is talking about , a mistake like this is very unlikely. I know I set my valves before every dive. .

You'd be surprised, I was diving with an inspiration rebreather instructor one day who forgot to turn his handset on before descending. He was seeing stars before he realized the mistake. Richard Pyle said "complacency kills" and if you do something the same way all the time it becomes automatic. I have done this the same way since I started doing tech dives about 6 years ago so it's just habitual.
My wife says she can't drive a standard vehicle because she can't look at the gearshift and the road at the same time. The expression being used these days is muscle memory and that has alot to do with it.

 

[Diver0001]

Unfortunately, it *does* happen and those that it happens to need to understand that the gas in their tanks is suspect and potentially lethal. The problem is solved back at the dive shop, probably days before getting on the boat, but if it does happen, one should know how to respond to the situation.

Going way back to teh beginning of this point, you never did ask the guy if he knew what was in the other tank.....

On another point, suppose both tanks are full but different. If you opened the isolator after the fill, how long do you think it would take for it to mix up?

Personally if I had any doubts about it at all, it's time to empty everything and start over. Wouldn't even think twice about it.

R..