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

["Sean T. Stevenson"<sts@telus.net>]

Oxygen addition in the context of a 1 ATM submersible is best accomplished through
direct compensation for the internal pressure, as opposed to requiring oxygen
addition based on oxygen sensors - less electronics, lower failure potential.
 As the carbon dioxide within the vehicle is removed, oxygen is added by a
regulator to bring the vehicle pressure back to normal.  In this case, your
check is the cabin pressure, although a passive reporting sensor may not be
a bad idea.  In the alternative, you are relying on the sensors themselves,
the electronics (if using averaging, etc), and the solenoid/valve operation
for your life support.

-Sean

>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
>
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