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> 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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