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Hi Dave,

Thanks for getting back to me with Jack's response.  Here's my reply.

> Please note that the statement in #3 was SOME manufacturers. Nevertheless,
> I am only aware of one electronically  controlled unit that used a single
> sensor and non-polling circuitry, the Westinghouse CCM.

[...]

> If you are aware of others, I would very much appreciate any information
> you could provide on them.

I'm sorry if my comment sounded like an attack - I promise it wasn't.  The
Cis-Lunar Mk4 & Mk5 primary computers display both a pooled average, and
the individual sensor readings before the values are pooled.  In addition,
a separate set of leads directly to the sensors supply the three readings
to three independent passive displays - there is no combined circuitry on
the passive display whatsoever, and the primary display is wired in such a
way that a total failure of the computer system will not affect the
outpout of the sensors to the passive display. Three simultaneous 
failures are required to lose all O2 sensor readings. 

> I could also use some enlightenment as to what
> electronic closed circuit rebreathers don't rely on some type of  circuitry
> or electrical device to function.

Almost none of them do. To me, the word "rely" implies that without the 
electronics, the diver has no way of knowing that the loop mix is 
breathable.  On the contrary, with a known O2 fraction in the diluent 
supply, two known loop volumes (counterlungs empty and counterlungs 
full), and with sufficient practice and training, a diver can create four 
different gas mixtures in the loop and use them in such a way that there 
is high confidence in the breathability of the loop gas -- even without a 
spec of electricity.

> RBC doesn't recommend bailout procedures other than to state that all
> bailouts should be to a separate open circuit source that includes whatever
> redundancies are considered desirable for the depth or environment in open
> circuit technical or "extended range" diving. There are so many variables
> to be considered that I am leery of the liability associated with
> misconstruing more detailed procedures. 

I COMPLETELY agree!  I just wanted to know if you had certain 
recommendations for various general conditions, or if you leave it 
totally up to the end-user.

> I'm often asked how long a cave or
> pipe penetration can be made with our units, and my stock answer is that
> you should not get into ANY situation with a rebreather that you can't
> recover from with a separate open circuit bailout ON YOUR PERSON.

Then why bother with a rebreather at all?  If you replace the rebreather 
components with bottom-gas supply, and your decompression gas supply is 
the same for both dives (as it would be to ensure you had enough gas on 
your person to get out on open circuit), it would be a similarly-sized 
package without the added complexity of a dynamic FO2 and a potential 
scrubber failure.


> You
> shouldn't count on being able to reach another diver or the last staged
> tank(s) should you have a total system failure on the rebreather, such as a
> breathing loop breach.

That's why OC bailout is such a tricky part of decompression rebreather 
diving.  If you can't carry enough gas on your person to do a complete 
OC bailout, then you need to carry enough to ensure you can get back to 
stage bottles.  If, as you recommend, enough OC supply be carried that 
you can complete all decompression, then rebreathers do not offer much 
advantage over OC mixed gas diving.
 
> You are 100% correct in stating that divers will die using rebreathers and
> most of them will die because of user error. In over 30 years of rebreather
> use, including several hundred hours on electronic sensor polling units, I
> have had three associates die on rebreathers. In one case, there was
> absolutely nothing wrong with the closed circuit mixed gas electronic unit
> involved. The diver simply ignored the alarms when the oxygen supply was
> depleted, probably because of task overload. In the other two cases, the
> units failed and the divers were apparently not able to rectify the
> situation, even though they had been trained to do so. It has been
> suggested that too much time had elapsed since training without adequate
> emergency action drill reinforcement. I know at least three people that
> would agree with that assessment as a more widespread problem: Dr. Morgan
> Wells, Tom Mount and Hal Watts. I do not know Dr. Egstrom personally, but I
> know that he has long been an advocate of periodic knowledge and skill
> reinforcement. This is an important issue for rebreather divers that has
> yet to be addressed by any manufacurers or training agencies that I am
> aware of.

I totally agree. Rebreathers, particularly fully closed circuit units, 
require constant use and constant practice to keep the skills up. 

> I have had seven personal close calls with rebreathers. Six were on various
> electronic units, two as result of simple electronic failures and four as a
> result of electronic failures due to water intrusion. The seventh was on a
> Drager FGG III and was caused by a temporary bout with that most deaded of
> diver diseases, terminal dumbass. Common sense no ka oi.

I know the feeling.  All three of my close calls have been due to "T.D." 
disease. My philosophy is that all rebreathers should be designed to 
function, and all rebreather divers should be trained to operate the rig, 
when all electronics are dead.  That way, the electronics just make the 
rig more useful and easier to operate.  The problem is, the more reliable 
the rebreather is, the more dangerous it becomes (in a twisted sort of 
logic) because the diver is more apt to become complacent and simply 
TRUST the electronics.  As I'm sure you already know, complacency kills.

Thanks for taking the time to respond.

Aloha,
Rich

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