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[PSUBS-MAILIST] re: 1atm life support
NOTE: This is the 4th time I've sent this....it just hasn't shown up
yet....if all copies eventually show up, I apologize in advance for the
redundancy.
What kind of safety are you going to add by keeping the O2 at 25%? The
sub atmosphere will sustain life with an O2 level down to 17%. A person
at rest will only consume between .5 and .75 liters of O2 per minute.
Using a manual flow control is the most simple method while monitoring
the FO2 with an oxygen meter and the cabin pressure with a barometer.
It's not rocket science and I believe Kitteredge didn't even use O2 or a
scrubber in his early subs and I think he was good for 1hr submersion
time. Obviously if you want to get more complex and high tech you could
have a closed loop system like a rebreather where the system injects O2
through a solenoid controlled valve based on FO2. I do agree with Vance
regarding the need of a purge valve for over pressure or for use at the
surface with a negative pressure. Trying to open the hatch with a
slight negative pressure in the sub might be somewhat difficult.
AFA a diving rebreather, if you are talking about a fully closed circuit
rebreather, the only time the loop purges is on ascent due to gas
expansion. All other times it is fully closed. A semiclosed rebreather
does purge the loop every so often based on the flow rate of the
constant mass flow orfice (in the case of the Drager Atlantis I) which I
trained on.
Al
Paul Suds wrote:
>
> Wouldn't you want to keep the O2 a little bit higher (25%) for safety
> purposes? Also, i would think that some type of digital and redundant O2
> monitor controlling the O2 inleakage would be better than guessing. I've
> trained people on using rebreather (biomarine) for emergency response, but
> never taken a rebreathing diver class. Don't you occasionally purge
> rebreathers underwater on ascent. i guess this wouldn't apply to a 1 atm
> unit though. Hmmmm..just thinking out loud. I did a balanced equation on
> this a while back and with an excess of O2, I came up with 7psi buildup over
> 5 hrs. Actually, it was a differenial equation. Maybe I figured in the
> pressure from heat as well. O2 + CO2 - CO2 - O2 + ht I can't remember why,
> but I think there was pressure increase, however so light. Any rebreather
> experts out there?? Suds
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--
Al Secor ARS: WA3PWX Scuba Instructor SSI DCSI 5528
http://people2.clarityconnect.com/webpages6/wrkdiver