Rodney,
While the incident you described did not occur during rebreather training,
instructors could learn an important lesson from it.  As reported by you,
the problem was not picked up during predive checks and could have easily
been fatal.  Now imagine that it was the instructor having the problem on
the first rebreather dive with a student.  Furthermore, the instructor
focusing all attention on his student fails to notice the signs of
hypercapnia as he is playing Mr Murphy with his students and unplugging
things while keeping a sharp eye on the them to see if they notice and solve
their instructor induced problems.  The instructor then sees the student did
not solve his problem and starts to give the stressed student the long hose,
while he himself passes out.  The student panics and drowns as does the
instructor, what about the other students? Your experience should serve as
support for the theory that Rebreather instructors should not dive
rebreathers with their students, at least during the initials phases.  Maybe
even at all.  Yesterday, a recent graduate of mine and I went scootering.
He on his rebreather and me on my doubles.  We did 100 minutes with no
problems, nor was my being on doubles a problem (except missing some warmth
of the breather even though I dove dry).  Max depth 105 feet, no deco or
safety stops were performed, rather we ended our 100 minutes by scootering
all the way in to the reef in 20 feet.
Errol Kalayci
www.technicaldiving.com
-----Original Message-----
From: Rodney Nairne <topgun@On*.co*.au*>
To: rebreather@nw*.co* <rebreather@nw*.co*>
Date: Tuesday, April 21, 1998 5:03 AM
Subject: Re: Hypercapnic incident at 78msw


>Just wanted to add the most surprising thing about this incident was that
>the 20 minutes pre-dive Suzie spent on the breather did not show up the
>problem.  I also breathed off the unit post dive and had no positive
>indication (despite being hyper aware there WAS a problem).
>
>I guess this is a function of workload, CO2 output, RMV and the increased
>gas density at depth contributing to increased blow-by of the hung up
>inhalation valve, and hence the dead air space at depth compared to the
>surface.
>
>RN
>
>----------
>> From: Rodney Nairne <topgun@on*.co*.au*>
>> To: rebreather@nw*.co*
>> Subject: Hypercapnic incident at 78msw
>> Date: Sunday, April 19, 1998 12:39 PM
>>
>> Hypercapnia incident report
>>
>> Wednesday. April 15, 1998.
>> A wreck called the Koputai. A paddle wheeler off Bondi Beach, Sydney,
>> Australia. In 78 msw (257 ft)
>>
>> Calm sea with no current. 3 fully closed rebreathers divers, Scott
>> Leimroth, Rodney Nairne and myself. Took 6 minutes to decent keeping set
>> point at 1.0 with Heliox. When I reached bottom I Ok’ed both buddys and
>we
>> started the dive. Within a minute of reaching the bottom my head was
>> realing and work of breathing was immense. Seemed impossible to reach
>> Rodney only 5 ft away to give him a thumbs up. On the line I switched off
>> my mouth piece and was handed off an open circuit reg by Rodney. With a
>20
>> minute ascent Rodney controlled my buoyancy and vented my breather while
>I
>> was in a semi-conscious state. Half way up the ascent (about 10 minutes
>> later and at 90 feet) I was shaken awake and was able to control my
>> bouyancy, breath off my own bail out and get out of the water on my own.
>>
>> Cause of problem was inhalation one way check valve stuck part way open.
>It
>> was unseated during over zealous rinsing of the loop, the high water flow
>> against the valve forcing it through part of its retaining cage.
>>
>> Unfortunately pre-dive checks failed to show up the problem. A noise test
>> of breathing in and out to hear both check valves slap passed because one
>> half of the check valve still slapped. (This is a known problem, alluded
>to
>> in the last issue of the AARG Journal) In addition we crimp both hoses
>and
>> vacuum and pressure test the valves; this test was unsuccessful for
>> revealing the problem due to my particular hoses being impossible to
>crimp
>> effectively. Lastly, 20 mins of pre-breathing the unit failed to give any
>> warning or indication as I assume I was not working hard enough.
>> Subsequently I recommend a visual check which I will be doing from now
>on.
>>
>> I can only assume that I was building up CO2 for the entire 6 min.
>descent
>> while not feeling it because my diluent add is upstream of the mouth
>piece
>> and I was receiving fresh gas about every second breath. When I reached
>the
>> bottom I *didn’t* have a gradual build up (such as in canister break
>> through) which is the only reason I was unable to determine the problem.
>> Normally any CO2 buildup in the loop is handled with a flush-thru and if
>> necessary a switch to open circuit.
>>
>> It is interesting to note that even upon switching to open circuit I felt
>> no better and it took a further 10 minutes for me to regain control. I
>> required assistance from my buddy during this time. I recommend a good
>> buddy who knows your rig, sticks close and knows how to help with
>potential
>> problems on a fully closed rebreather.
>>
>> A succesful dive with no problems to 64 msw (215 ft) the following day
>with
>> the same  mix, and canister fill confirmed the cause of the incident.
>>
>>
>> Suzie Dudas
>

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