From: adb@geek.ca.geac.com (Anthony DeBoer)
Subject: Re: Nitrox Diving
Date: Tue, 15 Dec 1992 22:55:43 GMT
Organization: Geac Computer Corporation

In article <1gl8g8INN83u@transfer.stratus.com> gd@gehenna.sw.stratus.com (Greg Dawe) writes:
>In article <1992Dec15.135928.11277@newssun.med.miami.edu> dbrown@newssun.med.miami.edu (Daniel Brown) writes:
>>In article <1992Dec14.151657.4167@cattnts.canada.ncr.com> craig@cattnts.canada.ncr.com (Craig Campbell) writes:
>>
>>>	    he unexpectedly experienced a complete air failure.  (suck..no
>>>	    air forthcoming)  He thought he was finished.  He reached back
>>>	    and turned his (dual tank) isolation valve.  Thwump!! 2000 PSI
>>>	    now available.  Someone on the boat had closed his valve (by 
>>
>>While this is a commendable reaction to a stressful, my first reaction was
>>to ask myself, "shouldn't this guy have checked his air before he did his
>>giant stride?"  The last thing I do before I go underwater before EVERY 
>>dive is check my air while watching my SPG -- to make sure the air hasn't been
>>accidentally turned off!
>
>All of my double tank rigs have dual valve isolation manifolds.  One of the
>things I've learned the hard way is that "Nobody is allowed to touch the
>valves."  When I bring these tanks to a shop for air, I personally open all the
>valves to ensure that both tanks get filled.  When I'm gearing up I check the
>valves myself and then tell the DM or mate NOT to touch them.  I've had
>instances where they've spun the valves on me just prior to getting into the
>water, and I've backed-up, taken the set off, checked the valves, and then
>regeared.  I have no problem getting to the valves underwater, but they can
>be confusing to use (try it while reaching back over your shoulders) and a
>well-meaning DM not intimately familiar with their operation can easily turn
>them OFF - particularly the valve on the diver's LEFT shoulder which opens in
>the opposite direction from what one might expect.

As a Divemaster myself, I do regard checking valve settings as being
important, especially with newer divers.  Normally, I'll just turn it
ahead to the full on stop and back a quarter to half turn, where the
diver had it.  Anytime it isn't where I think it should be, I will
discuss the setting with the diver, in case they either want it the way
it was (in the case of one diver I know who keeps his pony bottle turned
off until such time as he might need it), or so that they'll be less
likely to leave their main tank turned off or only cracked partway open
next time (when there might not be a divemaster around to catch it).  I
went into the water with my air off once when I was a new diver, and it
wasn't a tremendously happy experience.

If a diver did say he didn't want his valves touched, I'd respect that,
but would want him to be certain about the settings himself.

>Unfortunately, because of all the gear many technical divers wear, particularly
>in cold water it's very easy for the diver NOT to feel a well-meaning DM step 
>up behind him and gently spin a valve.  In the case of a closed isolation valve
>the only clue you have is a higher-than-expected air consumption rate, since
>you're only breathing off of one tank.

Or you could have no air consumption rate at all.  Some divers of my
acquaintance with similar rigs have the gauge on the opposite first stage
from their primaries.  That way they won't have to give up their favorite
second stage if they ever have an HP hose burst.
-- 
Anthony DeBoer       <adb@geac.com | uunet!geac!adb>
 At but not speaking for Geac Canada Ltd. (Toronto)
 NAUI #D5482, Z8800 but not speaking for them, either.