JT:

Thanks for your comments, however a few of your points were more 
statements than explanations. Could you please further explain some of 
your comments?

You wrote:

>If you can't close the isolator by yourself then you shouldn't be diving.
>Where's your buddy?

In tight situations (restrictions) or with certain equipment 
configurations (thick heavy suits) it may well be impossible to get to 
the isolator in time or even at all.  In those cases you would be 
better off with closed isolators or independent doubles.

Regarding buddy assistance, in those conditions; restrictions, zero or 
near zero visibility, you cannot expect your buddy to solve your 
problem because he quite simply may be unable to do so on time or even 
be unaware of your problem.  And if you were in the way between your 
buddy and the exit, and you would get into trouble, your buddy would 
also be in trouble, basically because you are in the way between him 
and the exit. Remember, we are talking about tight places & zero or 
near zero visibility. In wide open spaces obviously you or your buddy 
may open or close anything, even take all your gear off and put it on 
again!  So it's better to solve the problem before it arises, keep the 
isolator closed.  You may open it later if you need to for some reason.

Unless of course there is any powerful reason to keep it open?  If so 
please let me know what it is.

>Unnecessary task loading for no reason.

Granted that, at first, diving Closed Isolator or Indep. Doubl. 
generates task loading due to regulator switching, but once the 
gestures become automatic  (like driving a car) this task loading 
diminishes to the point where it vanishes.  The reason for this T.L. is 
the added safety of two Indep. Systems.  Regulator switching is a very 
basic skill that is taught at open water level, as part of training for 
buddy breathing, or for BC inflation without a power inflator.

> Independent doubles have huge problems in them selves.
> This system also requires two pressure gauges and
>increases the possibility of screw-ups.

Apart from the mentioned task loading, and the possible expense of a 
second pressure gauge (not a very great expense when compared with the 
full cost of one's gear), and the failure potential of HP hoses, I see 
no big problem.  Please explain the additional problems & screw-ups.


Among the disadvantages of independent doubles you mention:

>Two pressure gauges required.

Ok two pressure gauges mean an additional possibility of gas loss due 
to blown hose, etc.  However, if you have two gauges you can "manage" 
your gas during your exit.  Having the knowledge of your remaining gas 
allows for better exit gas management and planning which can also help 
to reduce stress in what is already a stressful situation.  One doubles 
the probability that one HP hose will burst, but one also reduces the 
probability that all gauge information will be lost, basically because 
there's a back-up gauge and a tank that are unaffected by the other 
tank & regualtor's problems .  That' safer.

>  Possible confusion during high stress moments.

What are you going to confuse? You have two second stages, use them as 
always!  You have two gauges, each indicates to which regulator they 
belong. You have no valves to open, no valves to close. Just manage 
your gas.  Where's the problem?

>No air sharing.

What will prevent you from sharing gas? You have two second stages, 
hand one to the out-of-gas diver and exit together. Even then it's 
pretty difficult to have double system failure, though it has happened 
at least once. The buddy, also on Independent Doubles shared gas with 
the treoubled diver.  Why should gas sharing be different if coming 
from manifolded doubles, isolator manifolded doubles, independent 
doubles or a single tank with an "H" valve?  I've shared gas in 
different circumstances, and found no difference.  To me, sharing gas 
is sharing gas.  Please explain me the differences.

> Unclean dive configuration requiring additional gear to make up for 
deficiencies.

Ok,  perhaps one gauge means marginally less "clutter", but I'd rather 
have two and always know *for sure* my remaining pressure.  On the 
other hand,  what's unclean about two pressure gauges that are neatly 
routed, marked and placed close to your body where they won't catch on 
to anything (line, etc.).  If we were talking about dangling or badly 
placed gear, I'd agree with you, but in this case...  please explain 
"unclean"....

>Exley screwed up twice.  First he dove with the stoke.  Then he allowed the
>idiot to run off and leave him at max penetration.  You have to ask your
>self what this dip shit was thinking about when he heard air leaking, saw
>no buddy in sight, but still didn't check his own air.  I'm sorry but if I
>had that much air leaking from my tanks I'd know it.

You are absolutely right in pointing that  Exley's partner made a  
wrong evaluation of the situation.  According to Exley's book, they 
were 4521 feet (1378 mts) into the cave and at a depth of 175 feet 
(53.34 mts), and apparently using air, so I wonder if N2 narcosis 
coupled with fatigue could have distorted Fulghum's judgement.

Also, in this particular case, wouldn't Fulghum have been better off 
with Independent Doubles?

>Independents are out.  They clearly identify a diver who has no regard for
>his buddy's safety or his own.

Please explain why Indep. Doubl. are out & why they necessarily 
identify a diver with no regard to his buddy's safety nor his own.

>Sumps and sidemount require special cases.  Sumps do require special
>portage of tanks.  This is by far not the norm in most cave sites.
>Sidemount requires the negotiation of passage where buddy assistance may be
>difficult.  Both are compromise configuration based on special needs.
>DON'T COMPROMISE IF YOU DON'T HAVE TOO.

I'm afraid it's more like "low ceilings require sidemounts" ;-) , and 
in those tight spots buddy assistance may not only be difficult, but 
often impossible.  In such environments, I can see no safer gear 
config. than I.D. , not a compromise, simply the best for that 
particular environment.  And low ceilings are not only fornd in sumps. 
However I'm not necessarily referring to sidemounted I.D.s, but I.D. in 
general (ie. back mounted).

When you use the word "compromise" it rings like "second best" or "less 
good option but unavoidable under the circumstances".   I don't see 
I.D.s the same way, rather the opposite, for me Isolated manifolded 
doubles are "second best" while I.D. are best.

Just a couple of questions for you:

1- How do you carry your stage tanks, one on each side or held together 
by a manifold with isolator?

2-  Does the fact that your stage tanks are *in fact*  independent 
doubles make them any more dangerous than the isolated manifolded 
doubles on your back?

3-  If so, why?

>Have fun and God help those that dive with you.

God help us all enjoy our dives!  Granted that God's help is always 
handy, however in the rare occasions when those that dive with me have 
had problems, they have always received the necessary assistance, and 
the precise gear configuration I had didn't prevent them from getting it.

You may eventually convince me that isolated manifolds are better than 
Indep. Doubles for all situations, but I'd like to know the reasons why 
this may be so. Until then, I'll continue using I.D.'s and believing in 
their superiority.   And take note I'm not trying to convince anyone...

On a side, ever tried to share gas with only one twin-hose regulator?  
Tricky the first time... though (just for the record) I no longer use 
them... ;-)

Regards & safe dives


Conrad

>----------
>De: Tomsits
>Para:
>Asunto: RE: seeking opinions on isolator valves
>Fecha: Jueves 26 de Marzo de 1998 5:09
>
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>Date: Wed, 25 Mar 1998 22:59:01 -0500
>To: cavers@ww*.ge*.co*
>From: Tomsits <odyssey@at*.mi*.co*>
>Subject: RE: seeking opinions on isolator valves
>In-Reply-To: <199803251547_MC2-37EE-2CC5@co*.co*>
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>
>Conrad,
>
>You have got to be kidding?  This must be a troll.
>
>At 03:42 PM 3/25/98 -0500, you wrote:
>>a)-	Should the isolator valve be open or closed during a dive, if so why?
>>
>>	If it's open you can breathe from one regulator out of the two tanks,
>>but depending on how quickly you can close the isolator, if at all, you
>>may lose half your gas or all of it, in case of trouble.
>>
>
>If you can't close the isolator by yourself then you shouldn't be diving.
>Where's your buddy?
>
>>	If it's closed you'll never lose more than half your remaining gas,
>>provided you breathed from both regulators evenly, that is making
>>switches every 10 bar/20 bar or so.  This is similar to using
>>independent doubles.
>>
>
>Unnecessary task loading for no reason.  Independent doubles have huge
>problems in them selves.  This system also requires two pressure gauges and
>increases the possibility of screw-ups.
>
>>b)-	What could happen if it were open & trouble happens?
>>
>>	It happened to Exley's partner in a dive in the Atlantida lava hole in
>>the Canary Islands.  The diver in question didn't realize the noise
>>came from his own gear, thinking Exley had a problem, by the time the
>>mistake had been cleared, almost all the gas in both tanks had been
>>lost.   Only their great experience & training allowed them to get to
>>the stage cylinders and eventually survive the dive.
>>
>
>Exley screwed up twice.  First he dove with the stoke.  Then he allowed the
>idiot to run off and leave him at max penetration.  You have to ask your
>self what this dip shit was thinking about when he heard air leaking, saw
>no buddy in sight, but still didn't check his own air.  I'm sorry but if I
>had that much air leaking from my tanks I'd know it.
>
>>c)-	What could happen if it were closed & trouble happens?
>>
>>	In the previous example, exit from the cave would have been
>>considerably less stressing, as Exley's partner would have had a full
>>third in one of his tanks.
>>
>
>But still no brain between his ears.
>
>>d)-	With a regular manifold, how redundant is your gear?
>>
>>	Only as quick as you are in closing the valves... if they can be
>>closed, and if the problem is not a tank neck O-ring.  I don't like the
>>idea of using a regular manifold (without isolator) in an overhead
>>environment or in a decompression dive.  For me it's either with
>>isolator, or else independent doubles.
>>
>
>Independents are out.  They clearly identify a diver who has no regard for
>his buddy's safety or his own.
>
>>e)-	Are there any advantages/disadvantages to independent doubles?
>>
>>	Advantage: It's very improbable that you will be left without gas
>>provided you balance tank consumption.  It would require a double
>>system failure something very improbable (has happened though! Partner
>>provided gas to exit cave).  If a low cave ceiling forces you to
>>side-mount your tanks, then you have no choice but to have independent
>>tanks.  Also you KNOW for sure that both regs are in perfect working
>>order, as you're switching from one to the other regularly. The nature
>>of many caves/sumps  make the porterage of single tanks easier than
>>manifolded ones through complicated extensive dry cave sections.
>>
>
>Sumps and sidemount require special cases.  Sumps do require special
>portage of tanks.  This is by far not the norm in most cave sites.
>Sidemount requires the negotiation of passage where buddy assistance may be
>difficult.  Both are compromise configuration based on special needs.
>DON'T COMPROMISE IF YOU DON'T HAVE TOO.
>
>>	Disadvantage: More task loading (frequent regulator changes), requires
>>a diver that switches regulators instinctively, therefore training is
>>longer. If you don't change regulators properly, then you'll not have a
>>balanced redundancy in case of failure.  Some divers may have a hard
>>time adjusting to perpetual exchange...  some argue that this produces
>>excessive task load, but most tech divers and cave divers in Europe
>>dive this way.
>
>Two pressure gauges required.  Possible confusion during high stress
>moments.  No air sharing.  Unclean dive configuration requiring additional
>gear to make up for deficiencies.
>
>
>>No system is pefect nor foolproof, just pick the one you think best
>>suits you diving needs and use caution and common sense.
>>
>>
>>Conrad Daubanton
>
>
>Have fun and God help those that dive with you. - JT

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