increasing PO2 on deco

gallathan

Ok, just trying to get a feel for this. I normally dive at 1.3 setpoint, but want to up my setpoint to 1.4 on deco. I know how to do this, but trying to get a rule of thumb/ feel for when to do this. I know if done to early, because I'm breathing out lots of inerts, it will be difficult to do this. I know the loop will 'stabilise' but I want to balance shorter deco vs loop stability.

JS1scuba

It's trivial. The time savings is not that big a deal.

For example a 70m dive on 10/50 for 45 min at 1.3 atm yields a total runtime of 153 min with a cns of 77% whereas upping the setpoint to 1.4 atm on ascent brings the runtime to 146 min but runs the CNS% up to 84%. the 7min savings is not a big deal.

Now if you were running 1.2 atm set point and then ran your PO2 up to 1.4 you may save about 10% of your total time.

The small difference between 1.3 and 1.4 really is that... small.

Cheers

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Mdemon

On the other hand, by decoing as if still on 1.3, you have a little extra conservatism.

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It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

Juz

I think it all depends on the dive. I run the loop at 1.3 until I have 25 mins of stops left. I then flush the loop and manually fly it at 1.4-1.45, doing a full flush every 5-7 mins.

At the beginning of the stop you'll see the loop 'crash' quite quickly, but towards the end of the stop the loop PPO2 stays up with no intervention from me - I consider this to mean that I am relatively clean.

I still run o the VR3 times though and just use the increased PPO2 and flushes to give extra conservatism.

I have found that this gets me out of the water feeling much better than previously.

Juz

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dan@scuba-training.net

I remember when I had this very epiphany.

At the begining of the deco stage you are exhaling nitrogen and helium into the loop, dropping the PO2.

At the end of the deco, the PO2 drop should be at your metabolic rate.

That is how you know that almost all of the excess nitrogen and helium are gone.