Variable END when diving air dil at low setpoint.

J

jwd

New Member
Hi everyone,

Hoping someone can help me out with the basic math for a hypothetical (really!) question.

1. CCR diving with air dil at 50m.
2. I leave the setpoint at 0.7
3. I dive to 50m (6ATM)
4. Arriving at 50m (assume I just did a dil flush)
* My PP02 would be (0.21 x 6 = 1.26ATM)
* My PPN2 would be (0.79 x 6 = 4.74ATM)

Can someone advise if I am correct on the following statements:

5. Because my setpoint is at 0.7, no new O2 is going to get injected (ie I would just breathe down the O2 in the loop)
6. Given the nitrogen is not being metabolised as fast, the relative PPN2 would increase as it becomes a larger and larger percentage of the loop volume
7. I would therefore be way more narked on air dil at 50m with a 0.7 setpoint than I would be breathing air on OC at 50m

8. Using the example above, how could I calculate the equivalent narcosis depth of the O2 depleted air I was breathing.

I'm sure there is a simple formula for this.

Thanks
 
Partial pressure of N2 is 4.74bar with OC and 5.3bar with CC 0.7 setpoint.
The EAD depends on how nartotic the O2 is defined.
 
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Yes, you are correct... but....

First, using air dil at 50 meters is not advisable... Most training agencies state that the PO2 of your dil shouldn’t be higher than 1.1 bar at maximum depth. That way, one can actually flush done the loop if the gas inside it becomes suspect.

Additionally, the density of air at 6 bar pressure, at 23 degrees C, is over 7 g/L. The NEDU, IIRC, has found that the risks from CO2 retention go way up when the breathing gas density gets higher than 6 g/L... Hypercapnia also lowers the threshold for taking a CNS O2 hit, so that becomes a double whammy... And, I’ve yet to discuss the effect of narcosis on trying to manually maintain your set-point...

With the above said, there are lots of CCR divers who’ve dived air dil to 50 meters and more, myself included... However, my personal experience with doing so was not fun... To me, the loop gas felt like I was trying to breathe soup... Now, whenever I go below 40 meters, I keep the gas density below 6 g/L and that also keeps the max PO2 of the dil below 1.1 bar and the equivalent narcotic depth somewhere above 30 meters. That, IMHO, makes for happy diving!

HTH...
 
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