Need an excel formula that will calculate CNS%

[samnickls]

Hi Did you get this to work? any chance of sharing thanks

 

[scubadada]

Hi Did you get this to work? any chance of sharing thanks

14 years ago

Edit: sorry, saw it was your first post

 

[inquis]

Since it's been resurrected, see attached for a vlookup approach. Example on row 20. Divide your time at that depth by the max time for %cns.

 

[samnickls]

Thanks

 

[John C. Ratliff]

Okay, I haven’t looked at this closely, but you may want to specify that this is for nitrox, and the various percentages of the nitrogen/oxygen ratio that is being breathed. Also, I see no reference to tissue type that this is made for. This may be because of my ignorance of what you’re doing, but it seems that these approximations are based upon assumptions that have not been explained.

SeaRat

 

[inquis]

NOAA goes by partial O2 pressure (depth pressure * Fraction O2). They also [EDIT: Other agencies including PADI (but NOT NOAA)] assume a 90 minute half-life for repetitive diving:
CNS2_start = CNS1_end * 0.5^(Surf Hrs/1.5)

 

[scubadada]

NOAA goes by partial O2 pressure (depth pressure * Fraction O2). They also assume a 90 minute half-life for repetitive diving:
CNS2_start = CNS1_end * 0.5^(Surf Hrs/1.5)

Last time I looked at NOAA O2 exposure, they still had cliff vesting at 24 hours, that has changed? Sorry if I am out of date. Many computer algorithms use the 90 min half life, but not all.

 

[inquis]

@scubadada, good catch. NOAA does NOT use an explicit half-life concept. Thank you for that. Instead, they track OTUs with another table of multi-day limits.

I do know that PADI uses 90 min half-life, although their tables are incredibly quantized. PADI also teaches the OTU approach. Less certain: I believe BASC uses 120 minutes. I seem to recall that TDI does use a CNS half life; I would guess 90 minutes, but I don't know that for sure.

 

[scubadada]

@scubadada, good catch. NOAA does NOT use an explicit half-life concept. Thank you for that.

I do know that PADI uses 90 min half-life, although their tables are incredibly quantized. Less certain: I believe BASC uses 120 minutes. I seem to recall that TDI does use a CNS half life; I would guess 90 minutes, but I don't know that for sure.

Shearwater uses a 90 min half life. Pelagic Pressure Systems, at least Oceanic, still uses 24 hour cliff vesting. I am able to exceed the PPS O2 limit when I do 4 dives per day, using 36% in SE FL. This gives 5 dives in the 24 h window.

 

[inquis]

FWIW, the OTU calculation is:
OTU/min = (2 * PPO2 - 1)^(5/6).