Nitrox Fills

[padiscubapro]

pufferfish once bubbled...


Where does the CO/CO2 come from?

co/co2 can com from the compressor itself.. if there is co which is worse than co2 you can use hocolite to convert it to co2 which isn't as bad..

we will assume there is no CO or CO2 being generated by the compressor.. since the membrane system is feeding the output back on it self, the co2 from the atomsphere keeps getting concentrated.. The higher the required FO2 the higher the co2 content will be..

"normal" air is usually in the range of 200-400 PPM (.02-.04)%, indoor air is typically 500-2500 ppm, normal grade "E" air has been 500ppm limit but that standard has been downgraded by many..

even a little CO2 at depth can be a problem, with nitrox its worse since co2 is a catalyst for otox.

for simplicity sake (Its a good enough analogy) say it takes the equivalent of two passes through the membrane to achieve 36% then if the compressor is fed with outside air it can be as high as 800ppm co2, if the compressor inlet is inside(many dive stores don't have a snorkel to the outside) its much worse up to 5000ppm .. 10 times the cga limit.

Don't take the numbers to be exact, however they are pretty realistic

you can see how easily the co2 can climb through the ceiling.. Have you ever got a headache during or immediately after a dive... co2 is a good bet..

 

[plsdiver4377]

Actually I wouldn't mind seeing a more detailed description of how the membrane system works as well. Thanks

 

[padiscubapro]

plsdiver4377 once bubbled...
Actually I wouldn't mind seeing a more detailed description of how the membrane system works as well. Thanks

ok here is simplied description but should be adequate

a membrane system requires a LP air source to feed the membrane.. many dive stores use their air banks after passing it through a pressure regulator and filter.. its better to use a high volume lp compressor and filter..

this gas is then fed into a membrane, its waht they call semi premeable, there are openings for the nitrogen to pass through that the oxygen (and other gasses do not due to size) 1 output is waste which is basically 100% nitrogen the other output is oxygen, trace gasses and some nitrogen.. as a membrane gets older it requires higher and higher feed pressures to obtain the same oxygen concentration..

the "good" gas is no fed to an intake of a compressor and this gets bumped up..

the reason trace gasees are in much higher concentrations than in normal is is the trace gases make up a higher percentage of the volume that has passed through the membrane.. the ammount of molecules is the same but since nitrogen was removed all the other gases are in higher proportion..
now after the hgas passes through the membrane it has to be filtered again for oil and other contaminates..

as you can see there is plenty of opportunity for co/co2 to get increased

 

[plsdiver4377]

Thanks, I appreciate the info.