Doubles with isolation open or closed Lesson Learned

[justcallmecam]

This is for informational purposes only, use it or don't.

My right post valve failed during a dive. You can see the o-ring pushed out. I was able to switch to my backup and shut the right post leaving me with all my gas. This would not have been possible in SM or ID configurations.

With correct planning however, its a non issue, even in side mount, even with thirds, even at your turn point.
1/3rd in, with well timed switches leaves 1/3rd of total gas in each tank, catastrophic failure of a valve renders one side totally empty, still leaves a third on the other side for exit.
But of course when talking gas more is always merrier...

 

[Akimbo]

…
But of course when talking gas more is always merrier...

Well, maybe not always

 

[Garth]

wasn't talking about cave

---------- Post added October 24th, 2013 at 12:48 AM ----------

1- My buddy was close by. 2- I dove my first dive with the same tanks and the isolator was open. 3- I never close the isolator and it was closed accidentally before the second dive. 4- I had enough cubic feet to dive the 15- 20 minutes bottom time planned since the first dive. 5-. I ended up with the same pressure or cubic feet in both tanks I would normally on a similar dive dive. 6- I mentioned Cave training due to the instilment of work it out do not panic. 7- I filled both tanks and isolator was full open. Anything is possible but two different gasses in one set of doubles is a stretch. Again anything is possible but it is so unlikely it should not be part of your check list. 8- Yes I made mistakes, I would not end a dive for a faulty transmitter. because I dive with my SPG. 9- I do not do two cave dives on one set of tanks and the isolator stays open.10-Opening the isolator causing a blown burst disc again is possible, but it is another stretch anything can happen but that causing a burst disc to go is unlikely. 11-Also the tank was not empty, it had 110 psi or 3.52 cubic feet of gas. 12- it was a mistake to open the isolator and not close it. It reduced the amount of breathable gas. not by much, but breathable gas is less than if I left it closed. 13- For an instructor to say wtf, to me or anyone else, he doesn’t deserve the title. Go yell at your children and see if they listen. 14- I posted this to share an experience and gather data. I try to always dive safe. Most of you guys are the best. You come up with knowledge advice opinion and experience, teaching me and other people reading this without being VULGAR or Demeaning. You guys are the best. 15- God Bless

The most interesting part about this thread is that a failure occurred due to situational awareness. Then the OP states that because one thing is so unlikely that it should not be included in checklist.

Yikes.

Whether one diver chooses to dive with isolator open at all times (as I did when I dove doubles), with isolator closed entire time, or progressive isolator equalization, the diver must understand what he or she is doing.


I think that a lot of experienced divers on your thread have provided you with valuable information on how they feel you should proceed so I hope you have defined your process and plan to eliminate this from occurring in the future. I will say by the verbiage listed in the quoted post it appears you are either defensive to criticism which is understandable given your intent of the original thread or you are shrugging off threat due to likelihood of the given failure which in my opinion is dangerous.

Thanks,
Garth

 

[flots am]

I reached back and opened my isolator which now I consider a mistake. It equalized both tanks, but it gave me less time than if I would have left the isolator closed for marinating a higher pressure in one tank would give me more breathing time than sharing the gas in both.

Don't beat yourself up too bad over that one. The only time it would have made a difference is if you screwed up badly enough to have breathed almost all your air on both tanks.

Most regs will breath just fine until the tank gets down to the reg's IP. By opening the closed isolator, you only lost however long the extra 140PSI would have gotten you.

flots.

 

[Garth]

When I dive my doubles I always had full tanks. The local shop sold a unlimited air sticker which wasn't cheap with two tanks but I felt it was a bit of a safety measure because I never felt the need to jump in with half filled tanks. No point to that as it wasn't any additional money to fill them.

Even some of my bigger dives I didn't even use half the gas. Steel 120's carry a lot.


Garth

 

[MaxBottomtime]

I have always dived with my isolator open all the way. Other than drills, I've never had to touch it. My LDS filled all of my doubles for years. I got lazy one day and didn't check the isolator. Why would I? The shop never closed it. I never closed it. At 180 feet on a wreck my spg was lower than I expected it to be ten minutes into the dive. I knew I wasn't over-breathing and there were no leaks. I aborted the dive and began my ascent. At twenty feet I thought about the possibilities of what went wrong. I reached back and opened my isolator. Suddenly I had the gas I expected to have. Not enough to go back down, but enough to get mad at myself for not checking the valves before the dive.

The shop had a new employee who was filling my doubles with two whips. I told him he only needed one to fill both tanks. It should have dawned on me that he had closed the isolator.