ahhhh now i see why they changed back to that system. makes sense. thx.
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I believe the reason for the split, and the selection of EAN32 as the point of the split, is that for the "rec depth limit" of 130ft you are still below a PPO2 of 1.6ata. At higher O2 concentrations you exceed 1.6ata at less than the "max" depth.
WOW fed regs as I know do not agree with that. CFR's i believe says 23.5 as pressures above something like 50 or 150 psi when it comes to O2 cleaning requirements. Im not saying I agree what that but only that that is what is calls for. Its terrible that teh O2 clean stuff was originally at red lined at 60% by NASA but called 40% because of the introduction of RECREATIONAL USE OF NITROX which was limited to 40%.I took the course. The card lets you buy NITROX for most banked mixes up to 40%. The 40% limitation is kinda, sorta imposed by the seller of the gases where 40% and below does not absolutely, positively have an O2 clean tank or regulator since it is banked. The physics of the dive with enriched air is still calculated (MOD, TAD and EAD) for PPO2 for the percentage. Don't sweat it... You will see the what I mean when you do the math.