[PSUBS-MAILIST] Life Support

Hello every one, since i´m almost done with the construction of my k-350, i´m starting to think about life support for it, and me and my friend ronny came out with this:

the cabin of the k-350 holds air enough for two people for about 1 hour, then as captain kittredge says i should surface and ventilate the cabin air, for this i don´t need any equipment, just the air trapped inside the cabin before closing the hatch. i wasn´t so sure about that so i followed the link to the extended air site and visited their store, at the end of the page there is a program that calculates the o2 and co2 levels in a confinated space, the cabin area of my k-350 is about 60 FT3, in order to use their software i tiped 1 in the "L" space, 1 in the "W" space and then 60 in the "H" space, i did this becouse their program is built for square spaces and my sub is cilindrical, so i calculated my sub volume in the same unit of the program (FT3) and then multiplicate it for 1 and for 1 again. the aswer was what we all expected, i don´t need to use their kit for the first hour, and then i will have to use their kit for the following six hours, and if i plan to stay longer i will have to use a replacement every six hours, of course i dont intend to be sumerged for days, but i was hoping to have a 72 hours life support system in case of emergency. the kit cost 350$ and each replacment cost 250$. so if i intend to have this this system installed in my sub i will have to spend 350$ for the kit and 250$ x 11 = 2750, that´s a total of $3100.

so here comes the idea, if i don´t want to spend this money i will have to surface every hour and ventilate the cabin air but if there is an emergency and i can´t surface i need to be able to ventilate the cabin underwater, for this i have a very simple system in mind:

imagine a scubba tank filled with air (not O2), like scuba divers use, and this tank is constatly bleading air into the cabin in small portions, (i haven´t calculate the air flow yet...), then i will have a pressure sensor that will activate a small 12 volts compressor to suck the cabin air and expel it to the ocean, i know the description of this system is very poor and is not technical but i think it will work for the following reasons:

1) the cabin air is being ventilated constantly, so the air inside the cabin is always breathtable

2) the pressure sensor will acitvate at 5 PSI, and will shut it down at 1 PSI, at this pressure humans don´t have any nytrogen absortion problems

3) the O2 level should remain within acceptable levels because we are bleading air into the cabin not O2

4) the CO2 level should remain within acceptable levels because the cabin air is bein constantly changed, by this i mean that the compressor sucks the breathed air and the thanks bleeds new fresh air into the cabin

5) the contamination of the air by oil (added by the compressor) is not a problem because this breathed and oil contaminated air is being expelded out of the cabin, the reason for using a compressor is to defeat the outern pressure and be able to change the cabin air.

i know there is a lot of people in this forum that are experienced in this matter so please let me know what you think.