I thought you were kidding about the lactate stuff.  Do you really think 
it could be a significant contributor?  I would think (and have been 
taught) that the excess CO2 from increased work of breathing would have a 
much greater effect that physical compression of periferal tissues.

I like most of your arguments about the better efficiency on the shorter
dives (I think they make more sense than mine did), but I'm not so sure I
buy the thermal effect.  If the canister warms up relatively quickly due
to the exothermic reaction (which it does), then I don't see any
difference between a long single exposure and a bunch of short exposures. 
If the issue was a gradual loss of heat that the absorbent started with, I
might buy it.  But given that the exothermic reaction warms it up more
than the starting temp, then I'm inclined to believe the heat loss is a
function of absolute hours in the water, with no difference between
whether it is one long dive or many short dives. 

Rich

On Tue, 5 Nov 1996, rfarb wrote:

> 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
> > 
> > --
> > Send mail for the `techdiver' mailing list to `techdiver@terra.net'.
> > Send subscription/archive requests to `techdiver-request@terra.net'.
> > 
> 

Richard Pyle
deepreef@bi*.bi*.ha*.or*
*******************************************************************
"WHATEVER happens to you when you willingly go underwater is
COMPLETELY and ENTIRELY your own responsibility! If you cannot
accept this responsibility, stay out of the water!"
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