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Date: Thu, 30 May 1996 15:08:38 -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 Thu, 30 May 1996, Richard Pyle wrote:

> When you say "amount of CO2" above, do you mean the total number of CO2
> molecules, or do you mean a RATE of absorbtion (i.e., number of molecules
> per given unit of time)?

I meant total no. of CO2 molecules, but your point is well taken. What's
important in a system pushed at or close to its limits is the rate of
absorbtion.

> I agree that the size/shape/packing of the pellets or granules of
> absorbent, and the size/shape/design of the canister have a huge
> influence on absorbtion efficiency, but I was saying that if you hold
> those things constant, you can still get a two to tenfold difference in
> actual canister duration depending on workload and diver metabolizm.

Surely the manufacturer just makes a canister that will do the job for the
biggest user - i.e., someone who will take the VO2 to the max (see below)?

> How
> can a manufacturer give a rating for a canister life in terms of hours
> of diving when there can be such a huge variation in consumption?
>
> My suggestion is to key canister life to O2 consumed (when possible),
> rather than hours diving.

For a fixed flow (constant mass) SCR that is essentially the same. You say
change the canister for every x hours dived which is bar/2 mins for the
Atlantis I using the 7.5 L @ EAN50. It's assumed that you've been using
the O2 at a constant rate, which will probably underestimate your actual
use.

-ph

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