3dent:Hi all,
Please help this rb wannabe in his continuing education...
If Im understanding all this right, the hyperoxia concerns stem from the fact that adding diluent with a higher FO2 (relative to air) will cause a larger positive swing in the loop PO2. Please correct me if Im worng.
Your above statement implies (by its converse) that there is some benefit to using NITROX 32 for manually-controlled RBs. The only benefit I can see would be not having to manually inject O2 as often. Are there other benefits?
I guess, in the middle of a dive, if you hit your low PO2 limit just before an anticipated decent (where diluent will be added) you could refrain from adding O2. In contrast, an eCCR would add O2 solely based on the current state of the loop, not being able to anticipate.
Also, by constant manual CCR, you are talking about a constant mass flow, manual add (KISS-style) O2 feed, correct?
With a constant flow of O2 it seems to me that the positive PO2 swing (relative to setpoint) would have a longer duration due to the fact that its being constantly fed O2. Wouldnt this increased time above the setpoint additionally increase your risk of hyperoxia? Is there some way to easily increase the duration of your loops low PO2 state to counterbalance the high PO2 state? Or is this slight deviation trivial when talking about the OxTox timeframe?
Thanks, again.
Don't want to insult your intelligence but I need to lay a little ground work for those following this thread.
-if you inspire .21 po2 at the surface and exhale .17 po2 you have used up .04 po2
-if you go to 100 fsw or 4ata you will inhale 4*.21 or .84 po2 but you will only use up[ the same amount of O2 as you did on the surface so you will exhale .83 po2 and use up .01 (or 1%) of the available O2.
-this example assumes air diluent and no O2 injection so far.
-let's say we want our setpoint to be 1.3 we need to add O2 to get it from .83 to 1.3
-if we have a constant mass flow system, the orifice will replace the 1l/min or so we use up at rest and we will manually replace O2 used due to higher workloads and when the diluent is added.
-if we have a higher o2 in the diluent we will have to add less O2 during a descent but after a few minutes it will make little difference because at constant depth only the O2 needs to be replaced and the diluent will stay constant except for any amount absorbed by our tissue which is minimal (but not zero).
-we will be limited by the MOD of the diluent due to PO2 spikes when flushing or changing depths
-so what all this is saying is for my money air diluent is better because it allows me more depth (up to 150fsw) with little benefit from an O2 point of view.
I hope I have explained that clearly (at least it makes sense to me )