[PSUBS-MAILIST] was- pressure hull sizing/now adding O2

[William Alford <walford@dbtech.net>]

At 11:09 AM 5/4/2002 -0600, Coalbunny wrote:
>Nothing stupid about it Adam.  I've wondered that myself.  I imagine the
>pressure would increase, and you're really not doing anything about the
>CO2, just adding O2.  I would bet that would soon lead to a very toxic
environment.

The beginning of the thread did say that CO2 scrubbers would be used.
Divers who use "rebreather" gear and scrub the CO2 do this all the time.
The trick is that the O2 is added at the same rate of metabolism of the
subject (changes with divers with exertion, etc) and his respiration
consumes the O2 from the environment and since the CO2 is removed and bound
to the scrubber chemical, so ideally the pressure would not change (for a
static environment, exertion, no. of people, etc). Realistically, the
atmosphere should be sampled with an O2 meter (can buy a cheap but
excellent kit WITH O2 sensor for about $100 from www.oxycheq.com/ ) and the
rate of O2 varied to maintain a healthy atmosphere. Since the CO2 is
removed by the scrubber, ideally that should be monitored as well. It can
be very dangerous to scrub all CO2 from the atmosphere and NOT monitor O2
since the human external respiration is driven by CO2 levels in the blood
and *not* O2. If all CO2 were removed and then your O2 depleated, you would
die without even knowing you had a breathing problem. In fact this is the
basis for one so-called "assisted suicide" machine. A nice primer about
O2/CO2 and breathing is at
http://web.archive.org/web/20010802183457/http://www.tekniskdykking.org/tekn
iskdykking/artikler/breathing.htmRebreather. divers are smart enough to
know that any failure of their system can end in death and so they
typically have THREE independent O2  monitors in their loop since any O2
sensor can fail suddenly or begin giving erroneous output. If you had only
two . . . which one would you believe? With three, you can infer that the
two which agree are likely right, but for safety the dive should be
aborted. Some rebreathers have computer driven solonoids which add the O2
according to their settings and depth, and these units could likely be
easily adapted to subs. some interesting ideas about O2/CO2 relationship
for scrubber at http://www.trimixdivers.com/aarg/scrublife.html

CO2 buildup would eventually become toxic over time if not scrubbed. 
William Alford
walford@dbtech.net

Tout comprendre c'est tout pardonner