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Date: Wed, 29 May 1996 11:42:36 -0700 (PDT)
From: "Peter N.R. Heseltine" <heseltin@hs*.us*.ed*>
To: Carl Heinzl <cgh@ma*.ai*.mi*.ed*>
cc: deepreef@bi*.bi*.Ha*.Or*, 72650.220@co*.co*,
     chris@ab*.co*, darwin@co*.sp*.tr*.co*, huggins@mi*.us*.ed*,
     lungs@ic*.ne*, mcochran@ne*.co*, ramsdenr@cs*.or*.za*,
     scuba@ma*.ne*, smwixson@in*.co*, dlv@ga*.ne*, gasmixers@ao*.co*,
     techdiver@terra.net
Subject: Re: Physiologic safety parameters for SC rebreathers

On Wed, 29 May 1996, Carl Heinzl wrote:

>
> >But isn't the CO2 being pulled out of the loop by the absorbent canister?

The scrubber works, but the volume of gas you breath has to be enough for
you to exhale the CO2 you generate. e.g., somewhere about 750 to 800 cc
per breath. Similar to shallow or skip-breathing on OC, you get CO2
retention.

> That brings up an interesting point - can the scrubber pretty much
> absorb ALL the CO2 being exhaled, leaving none to return in the input
> or does *some* fraction return in the breathing loop?  If so, what
> fraction returns, and, is this a function of scrubber lifetime (i.e.
> how far along you are in the usable life of the scrubber) AND, what is
> the function of time to predict CO2 retention in the loop?

If the scrubber is maintained properly and refilled according to the
manufacturer's parameters, they work quite efficiently. But yes some will
be returned to you, hopefully not more than you will get on OC. You are
right, the manufacturer needs to specify that the pPCO2 on the inlet side
is below say (?) OSHA standards.

-ph

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