Not quite the answer to the question but sitting in the pool tuesday night at 0.7bar on the YBOD I turned off the oxygen. 9 minutes later the pressure in the hoses and regs was exhausted and the SPG read zero so the solenoid could no longer supply O2 so the ppO2 started to drop. About another nine minutes later it hit 0.4 bar and started beeping and flashing lights at me which is what I wanted to see so I turned the O2 back on.
Since the effective volume of my lungs and the counterlungs is constant the ppO2 represents a specific quantity of O2 regardless of depth so the graph will always slope off at this rate for the same activity level (not doing much).
Nine minutes to drop 0.3bar so I would say quite a bit longer to drop from 1.3 to 0.16 but then I'd be finning about a bit. 20 minutes maybe?
Here's the dump. Time across the bottom and ppO2 up the side.
You are getting three traces each from the two computers.
The other trace at the bottom is depth so you are seeing my hand move up and down looking at the handset on my wrist.
(edit)Actually the plot is distorted by the ADV kicking in and adding 18/40 to the loop as I use up the O2 and decrease the loop volume to the point that it can no longer supply a full breath. Naturally this effect is much much larger at 3m in the pool than 30m in the sea so the steepening of the curves is an artifact of shallow where the 18% O2 dil dilutes the >30% (0.4ppO2/1.3abs) loop gas.(/edit)
