DaleC
Contributor
His approach isn't flexible, it's adding unnecessary tasks ( reg switches, valve manipulation ) to an already "high risk" dive.
What has the pony got to do with any of this?
When you have a failure what do you go to first; Isolator or Post?
This debate is really about manifolds or Independent tanks. That person, if he is like me, probably prefers to dive ID's. It's a different gas management philosophy based on when certain actions are performed and what risks are being mitigated.
With the manifold closed, yes I do reg swaps but these are all done in non stressed states (and hey, isn't it good to know both those regs work well). I also always have part of my gas supply "isolated" pre-incident so it cannot be lost. My decision is either left or right post. I have access to all gas, post incident, by shutting down offending posts, opening the manifold etc... I exchange true redundancy for reg swaps - that's it. That's important to me because I solo dive and I have no other source of reserve gas.
With the manifold open others have no reg swaps true, but are diving basically one big tank. Preserving gas is based on a reaction under stress, during an incident. Post incident we both have the same access to gas. They are exchanging no reg swaps for the need to isolate.
Having the manifold closed is also one way to prevent breathing through rock bottom reserves. If one keeps that value in both tanks as a minimum. It is a small point I know but one area I see this as relevant is the habit some divers have of using doubles to do two dives. Dive one is ok but dive two can leave very little in the way of reserve gas to isolate and preserve.
I concede that this approach is not for everyone but it is erroneous to assume those who do use it have given no thought to the subject.
The pony question was a subtle way of suggesting that the same piece of equipment can be used in different, but equally serviceable, ways.
---------- Post added March 21st, 2013 at 08:45 PM ----------
He's going to wack himself someday breathing the wrong mix. Judi Bedard was diving Eagle's Nest in 2005 and ended up breathing pure helium because of an isolator which had been closed during filling. She passed out on the dive due to hypoxia, but her buddy rescued her and she managed to survive. I believe she even dives again but I'm not sure about that.
Isolators should remain open except for a functionality check and when there's an actual manifold failure underwater (which are very rare compared to regulator issues).
rjack, I'm not familiar with this persons habits. Was she intentionally diving independent doubles or was it a poorly executed open manifold dive plan coupled with failed fill procedures?
It seems to me that open manifold use is based, partly, on being proficient and diligent in valve drills. Seems an argument against them that a failure to perform just one such a drill could result in such an event.