Rich, the Navy took into consideration depth and temperature as variables
in the report of less scrubber life on a deep dive. Essentially, at the
same temperature, the depper you go the less scrubber time you got. Maybe
an intelligent hyperbaric physician will comment on the compression
theory. It does happen on dives, especially at your extremities. What I
want to verify from someone is whether increased lactate production has
been seen say, in chamber tests. My problem with hyperbaric physicians is
that most are non-divers- diving in water is different than in chambers
and consequently they know a lot of irrelevant stuff, but even a blind
squirrel can find a nut every now and then so maybe someone has stumbled
onto the lactate issue. 

On the issue of the scrubber depletion on a one shot pot vs several
shorter exposures, I think several shorter exposures are more efficient
than one long exposure because the scrubber would be used more efficiently
at short exposure intervals than the long one. But, I never did the
experiment. If you assume that more moisture would accumulate throughout
the cannister (vapor, liquid, etc) during a longer exposure- it is colder
on the outside of the scrubber for longer- and if moisture is what makes
the world go round in scrubbing circles- then you would expect the
scrubber bed to get "thinner"  (as far as unused scrubber goes) faster
than short exposures (we're talking axial flow here) and finally, all
things being equal, the diver down for a long exposure- I would bet- is
outputting more CO2 over the long exposure time than the diver making
multiple short excursions whose cumulative time is equal to the long
exposure time- more exertion during long exposure means more CO2, you are
more rested during short dives thus less exertion; more rested means fewer
breaths, etc., etc. And, finally, ambient water temp. being equal for long
and short exposures, if it is colder outside the scrubber housing for
longer during long exposures, then there is more time for the "cool" to
quench the scrubbing action, i.e., wick away the exothermic heat so
essential for efficient scrubbing, so you gets less scrubber life on the
long exposure, i.e, scrubber is used more efficiently in short bursts
because the heat isn't wicked away to the same extent as in long 
exposure. What do you think? No proof but it seems right. Rod 


On Mon, 4 Nov 1996, Richard Pyle wrote:

> 
> > Regarding the question, why the Navy reports that scrubber life is less at
> > depth. How's this: The deeper you dive, the more compressed your body
> > becomes, the tissue bed becomes less saturated with blood leading to an
> > acidotic condition with an increased lactic acid production. Cardiac
> > output increases to compensate for less blood in the tissues, metabolic
> > rate goes up, the increased lactate is metabolized in the liver to CO2,
> > the excess CO2 results in scrubber being depleted sooner than it would be
> > at shallow depth. 
> 
> That MUST be it!!!
> 
> > Here's a question: Is a cannister of scrubber that is
> > dived one time for eight hours depleted to the same extent as the
> > cannister that is dived eight times for one hour? Rod
> 
> A serious question, I assume.  Here's my understanding:
> 
> 
> The CO2-absorbent bond is for practical purposes a one-way reaction. 
> Absorbent does not, according to my sources (many & varied) reconstitute
> itself significantly over time of non-use.  However, it does seem that you
> will "peg-out" a canister of absorbent sooner on a single long-shot dive
> than you would on a series of shorter dives (i.e., you could get a single
> 8-hour dive out ot the same canister that you would get 6 2-hour dives out
> over over a period of days).  I'm not sure I've noticed this myself yet
> (not enough datapoints), but the rationale, as it was explained to me, is
> that during surface intervals, the CO2 molecues somehow "redistribute"
> more homogeonously within the absorbent particles.  If more molecules
> migrate towards the center of the particle, that opens up more binding 
> sites on the surface.
> 
> I don't know if any of this is true (makes sense, but I'd like some
> corroboration from a chemist), but if it is, then we can draw a couple of
> conclusions.  1) a single dive will max out a canister in fewer dive-hours
> (at a given CO2 production rate) than several shorter dives with decent
> surface intervals will. 2) The reason for this would be that on the single
> long dive, the surface of the particles would become saturated, even if
> there is "room"  within the particles to accomodate more CO2, simply
> because there is insufficient time to allow the CO2 to homogeneously
> distribute within the particles. 3) The effect of this would be larger 
> for absorbents with larger particle sizes (because of the lower surface 
> area:volume ratio). 4) color indicator could be bright purple immediately 
> after a dive, but be white again several hours after a dive.
> 
> Any chemists care to comment?
> 
> Rich
> 
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