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Date: Wed, 29 May 1996 18:07:01 -0700 (PDT)
From: "Peter N.R. Heseltine" <heseltin@hs*.us*.ed*>
To: Richard Pyle <deepreef@bi*.bi*.Ha*.Or*>
cc: Jim Bembanaste <lungs@ic*.ne*>, Mike Cochran <mcochran@ne*.co*>,
gasmixers@ao*.co*, techdiver@terra.net
Subject: Re: Physiologic safety parameters for SC rebreathers

Rich,

In reply to:

On Wed, 29 May 1996, Richard Pyle wrote:
>
> If it's designed right it should.
>
By far the greatest limitation to CO2 extraction by any canister system is
getting the CO2 (expired) gas to actually make contact with active
absorbent pellets. You can calculate that theoretic amount of CO2 that
will be absorbed by the weight and chemical composition of the absorbent,
but channeling (which may be realted to how the canister is filled) and
canister design greatly affect the "life" of the absorbent.

Drager has a rubber gasket that is placed in the middle of the canister
half way through the fill process to limit the channeling that may occur
at the absorbent/canister interface. This doesn't prevent channeling in
the material itself. Dragersorb is different in consistancy from Sodasorb
etc., with less dust and different sized pellets. I think these factors
have a far greater effect on the life of a canister than variance between
divers in CO2 production given that you abide by the manufacturer's
usually very conservative 'sorb use tables. Dragersorb is about 2.7 L per
fill and is rated for (I think) four hours.

slainte

-ph

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