Quote: (Originally Posted by
bhackett)
Uh, 10 liters of O2 would be 20%, not .2 PO2.
.2 PO2 / 5ata = .04 FO2. .04 FO2 * 50 liters = 2 liters O2.
Brian
You're right, that's FO2 and not PO2.
Let's think this one through.... and then its going to be time to get out the timer and dump the data from my handset to see why I'm not getting what I expect
Ok, we want a constant PO2.
Let's say its 0.5 for the sake of argument.
At 1 ATA that's 50% of loop volume, or 5 liters in a 10 liter total.
We decend to 5 ATA (132fsw.) The PO2 if we have the same PERCENTAGE would be 2.5 (!)
So to get a PO2 of 0.5, we would need 1 liter of O2 in 9 liters of inert gas (.10 FO2 * 5 ATA = .50 PO2)
This is the same 5 liters at STP, which would mean that it
should bleed off at the same rate at 5 ATA that it does at 1 ATA if we shut off the injection, since our metabolic demand is in
moles (or liters at STP, which is the same thing using different units.) It also means that in terms of MOLES of O2 in the loop they are the same for a given PO2 irrespective of depth - and both IANTD (and lots of other people, including how I've been looking at it) are wrong.
But - experimentally - it doesn't work that way.
This raises the question "why not?"
Time to go looking for the answer to that one.
(This also means that the injection interval should not be compensated for depth - just error from the desired PO2!)
I'm going to throw some instrumentation at this over the next week or two.