> I think my main point here is that I am fishing for symptoms of hypercapnia
> and trying to better understand the dynamics of the scrubber. It sounds
> like there are substantial warning signs that precede the black out and
> they are being noticed by working cameramen. That in itself is a relief.

The USN guys at the forum were insisting that hypercapnia symptoms are NOT
reliable precurors to blackout, whereas we civilian divers tended to think
it was a reliable indicator.  I am convinced that the USN guys are not
stupid (and marginally convinced that we civilian rebreather divers are
not especially stupid either).  So, the only way I can rectify this
discrepency is that some people (I suspect people who are classified as
"CO2 retainers") do not get adequate warning, whereas the rest of us
usually do.  The only question left to be answered, then, is whether or
not "CO2 detectors" are consistently so, or whether the range of variation
WITHIN an individual is relatively large.  To find out for myself, I
usually try to push every canister I use as far as I can take it (always
in very shallow water), so that each canister charge gives me another
datapoint on my own persoanl ability to detect hypercapnia symptoms prior
to CO2 buildup becoming a serious problem.  So far, I have found that the 
range of variation for me is small (i.e., I consistently see subtle signs 
about an hour of moderate exertion time before less subtle signs, which 
themselves preceed serious hypercapnia symptoms by about 2 more hours).  
But that's me.  John has narrower windows of time, because his body burns 
O2 (and produces CO2) at a higher rate than mine does at a given workload.

> How does pressure affect the scrubber?  The question seems obvious, but
> someone has to say, "like this...." or it remains a hypothesis in my mind
> which isn't comforting.

I'd like to know more about this also.

> Confidence in my understanding of the gear is my target before I start
> going deep.

EXCELLENT philosophy!

Rich

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