>   Richie, I love you but you are unrealistic: we are so intensely
concentrated 
> on what we do we would never know the machine failed. We are also in such 
> increidble physical condidion that hypoxia is a joke to us - we get no
warning.

These are excellent reasons why you probably should not consider 
rebreathers for the dives you do.  You probably forgot, but about a year 
ago I told you the same thing - they do require more concentration.  As 
long as you blended the gas correctly, if you can breathe from an OC 
regulator, you're probably OK (unless, of course you breathe the wrong 
mix). With a rebreather, the fact that you're breathing does not 
necessarily mean that you are OK - your PO2 could be slipping away, and 
like you say, people of your physical condition might have a very narrow 
margin of warning for hypoxia.

On the other hand, you should not discount them entirely, either.  You 
should at least take opportunities to play with some of the different 
models when you get a chance.  You might find, as I have found, that the 
benefits outweigh the costs.  Then again, you might not.

>   What happend to Bill is that the sensors loaded up with condensation and
all 
> stuck at the last reading, telling the machine that the PPO2 was ok. This 
> happens once in a while. He has gotten some longer times out of it, but the 
> problem is that it will happen eventually no matter what. You do a real long 
> time in the right conditions, it will happen to you.

George, I've known about this problem for more than two years.  Stone has
known about it for several years - I think since before Gavin even blacked
out.  That's why he designed a very simple solution. I'm not sure if the
specifics of that solution are covered by the papers I have signed, so I
will not describe it here.  If you want to know what it is, ask Stone or
Nordstrom about it. 

The problem of condensate sealing off the sensors is very real - and to 
be honest with you, it blows me away that more people aren't talking 
about it. For those who don't understand the problem, it is very simple: 
most O2 sensors have a screen in front of their sensing surface. If you 
put a drop of water on this screen (say, water from condensation), then 
the water plugs the holes of the screen due to surface tension.  This 
isolates a small pocket of gas against the sensing surface.  If this 
happens to all three sensors, and the small pockets of gas have a PO2 
lower than setpoint, then the solenoid will continue to fire, raising the 
PO2 in the breathing loop indefinitely.  If the small pockets of gas are 
higher than setpoint, the solenoid will not fire at all, and the diver 
will brun off the O2 in the loop until he/she blacks out from hypoxia.

I rarely see all three sensors do this simultaneously - but it has 
happened.  I have seen the problem show up as early as an hour into the 
dive. The thing about this problem that is so dangerous is that it is 
directly affecting the sensors - which means both your computer and your 
passive display are telling you one thing, but you are breathing 
something altogether different.  In other words, the rebreather cannot 
warn you of this problem - you have to be well-trained to be able to 
recognize the problem yourself.  One tool a rebreather can provide you 
that will help you spot this problem is the ability to monitor all three 
sensor simultaneously.  That way, if only one or two sensors are affected 
by it, it will be obvious by the discrepency between the sensors.  
Another tool is to make the precision of the PO2 readings high enough 
that you can see microfluctuations in the PO2 as you breathe.  This lets 
you know that the sensor readings are dynamic.  If the readings are 
static at relatively high precision, then you can be pretty sure that 
condensate has sealed them off from the loop.

Incidently, before I get a bunch of messages telling me that O2 sensors 
consume O2, and therefore the PO2 inside the small pockets of gass would 
drop, let me say that this drop happens over a much longer time than what 
it takes for the PO2 in the loop (the PO2 that you are breathing) to go 
all to hell.

> You have forgotten that 
> these things are not intended for huge long times, but for the convenience of 
> tiny gas supplies. 

The rebreather I am using is designed for long-duration dives. I have 
already told you, I can flood the entire loop with water (including the 
chamber with the O2 sensors), recover, and continue to dive for hours and 
hours exactly as if the flood never happened.  What you have forgotten is 
that I am not as big a bonehead as you like to think that I am.

> You also forget that with the exposures you do, if the 
> machine fails in the other direction - too much oxygen - you are likely to
get 
> away with it on your dives, and it may in fact help your deco. For us, this
is 
> not possible, as we are now down to 1.0 or less ppo2s and less than 1.4 at
deco 
> just to not tox. 

I don't understand - why is there a difference?  I sometimes bring the 
PO2 down to 1.2 or less if I know the dive time will be more than 4 hours.

>     The main thing that you are not acknowleding here, which is rule number
two 
> in rebreather diving, is that task loading is what kills - that means
anything 
> that calls your attentiion away from the machine. 

Well, I dunno about that.  Fish collecting is pretty darn task-loading - 
so is maintaining vertical position and neutral buoyancy on a vertical 
drop off.  So is managing strong currents. So is keeping an eye on 
Carcharhinus albimarginatus - the Silvertip reef shark, which is 
amazingly abundant below 200 feet and grows amazingly large for a reef 
shark. So is managing your ability to get back to stage bottles on an 
open reef in the event of an OC bailout.  So is taking pictures with a 
bulky camera housing.  I quite often am doing all of the above 
simultaneously, and I son't have any trouble.  If the rebreather is 
designed well, the concentration required to keep you alive is not all 
that huge.  No, I don't think task loading kills on a rebreather - ask 
Farb about how task-loaded he is on an average dive.  Ask Howard Hall 
and Bob Cranston how task-loaded they are when making underwater films 
with a 3-D IMAX camera. What REALLY kills in rebreather diving is 
complacency.  In other words, a lack of discipline.  This is what I have 
been trying to say all along, but it seems that most people refure to 
take the cotton out of their ears.
 
>    Richie, for what we do, the diving apparatus must require no attention,
for 
> what you do, it its most of the fun. Please be careful what you suggest to
these 
> storkes on here - they know they can not copy me, it is too much work, but
they 
> think they can copy you since you try to make it sound so easy. 

Whoa! Man! It took me a long time to stop laughing when I read that!  
Don't you see th hypocricy?  Or were you just trying to be "feces-ish"? 
Georgie-Boy, people are one HELL of a lot more likely to die emulating 
you than they are emulating me.  Jesus! Get serious. Besides, I have 
NEVER encouraged ANY storkes to use rebreathers.  In fact, I don't think 
any rebreather manufacturers have built a mouthpiece that a stork could 
hold in its beak, let alone a rebreather that would fit on a stork's back.

Rich

P.S. How full of shit am I now?

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