CNS Equation

lizardland · 26th May 2006, 15:04

Quote: (Originally Posted by Andyg)

Hi All
My question is not about CNS equation but is about CNS%.
I would like to know from those that are doing or planning
long deep dives (150M+) what CNS% you are finishing the dive with

As I remember when it was introduced, %CNS (aka the CNS clock) was a mathematical fudge created by IANTD to assist in teaching Adv EAN and above. I could be wrong but I don't think there was ever any testing of the idea that trading O2 exposures over a range of values was accurate. There's a lot of anecdotal evidence that where exposures come in the profile, what gases used (2bar on air is a lot more tolerable than 2bar on O2) and probably a range of other factors have a bigger effect than a simple bit of number buggering can predict.

***caveseeker7*** · 26th May 2006, 17:47

ANDI has the CNS O2%/min conviniently listed in a table in their CCR manuals,
for example 1.0 ata pO2 = 0.33%, 1.1 ata pO2 = 0.42% etc.
All you need to do is multiply by your dive time.

Drmike · 26th May 2006, 19:28

Quote: (Originally Posted by lizardland)

As I remember when it was introduced, %CNS (aka the CNS clock) was a mathematical fudge created by IANTD to assist in teaching Adv EAN and above. I could be wrong but I don't think there was ever any testing of the idea that trading O2 exposures over a range of values was accurate. There's a lot of anecdotal evidence that where exposures come in the profile, what gases used (2bar on air is a lot more tolerable than 2bar on O2) and probably a range of other factors have a bigger effect than a simple bit of number buggering can predict.

yeh I think its all bollocks too

GKAM · 26th May 2006, 22:52

I think the widely accepted formula is:

%CNS=100*(TD/TT)

Where:
TD= time spent at depth (min)
TT=Allowable time at depth using the NOAA single dive time limit

Isn't that what most people are using?

devilgas · 27th May 2006, 19:20

Did not know IANTD created the CNS formula. Could have sworn that NOAA set up those limits. But now I'm a believer because I read it on the internet

lizardland · 29th May 2006, 22:40

Quote: (Originally Posted by devilgas)

Did not know IANTD created the CNS formula. Could have sworn that NOAA set up those limits. But now I'm a believer because I read it on the internet

NOAA set the specific limits i.e. x at 1.6bar, y at 1.4bar, etc. The idea that you could use 75% of your 1.4bar time then follow it with 25% of your 1.6bar time or any other O2 exposure horse trading (i.e. the oxygen clock/%CNS concept) I'm pretty sure was "invented" afterwards by someone else.

26th May 2006, 15:04	#11 (permalink)
lizardland Yak Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Classic Kiss Home Build Join Date: Mar 2005 Location: North... Posts: 1,237	Re: CNS Equation Quote: (Originally Posted by Andyg) Hi All My question is not about CNS equation but is about CNS%. I would like to know from those that are doing or planning long deep dives (150M+) what CNS% you are finishing the dive with As I remember when it was introduced, %CNS (aka the CNS clock) was a mathematical fudge created by IANTD to assist in teaching Adv EAN and above. I could be wrong but I don't think there was ever any testing of the idea that trading O2 exposures over a range of values was accurate. There's a lot of anecdotal evidence that where exposures come in the profile, what gases used (2bar on air is a lot more tolerable than 2bar on O2) and probably a range of other factors have a bigger effect than a simple bit of number buggering can predict. __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
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26th May 2006, 17:47	#12 (permalink)
*caveseeker7* Who loves ya, baby Current Rebreather/s: Sport Kiss Other Rebreather/s: Prism Topaz Join Date: Jan 2005 Location: Too far from Neverland Posts: 5,416	Re: CNS Equation ANDI has the CNS O2%/min conviniently listed in a table in their CCR manuals, for example 1.0 ata pO2 = 0.33%, 1.1 ata pO2 = 0.42% etc. All you need to do is multiply by your dive time. __________________ Cheers Stefan "Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.'!"
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26th May 2006, 19:28	#13 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,128	Re: CNS Equation Quote: (Originally Posted by lizardland) As I remember when it was introduced, %CNS (aka the CNS clock) was a mathematical fudge created by IANTD to assist in teaching Adv EAN and above. I could be wrong but I don't think there was ever any testing of the idea that trading O2 exposures over a range of values was accurate. There's a lot of anecdotal evidence that where exposures come in the profile, what gases used (2bar on air is a lot more tolerable than 2bar on O2) and probably a range of other factors have a bigger effect than a simple bit of number buggering can predict. yeh I think its all bollocks too __________________ Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you
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26th May 2006, 22:52	#14 (permalink)
GKAM digital nomad Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: May 2005 Location: Greece Posts: 250	Re: CNS Equation I think the widely accepted formula is: %CNS=100*(TD/TT) Where: TD= time spent at depth (min) TT=Allowable time at depth using the NOAA single dive time limit Isn't that what most people are using? __________________ Stay #
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27th May 2006, 19:20	#15 (permalink)
devilgas CCR Instructor Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Inspiration Vision Evolution Join Date: Apr 2005 Location: FL, USA Posts: 191	Re: CNS Equation Did not know IANTD created the CNS formula. Could have sworn that NOAA set up those limits. But now I'm a believer because I read it on the internet __________________ www.deeptek.net Inspiration / Evolution, O2ptima Instructor
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29th May 2006, 22:40	#16 (permalink)
lizardland Yak Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Classic Kiss Home Build Join Date: Mar 2005 Location: North... Posts: 1,237	Re: CNS Equation Quote: (Originally Posted by devilgas) Did not know IANTD created the CNS formula. Could have sworn that NOAA set up those limits. But now I'm a believer because I read it on the internet NOAA set the specific limits i.e. x at 1.6bar, y at 1.4bar, etc. The idea that you could use 75% of your 1.4bar time then follow it with 25% of your 1.6bar time or any other O2 exposure horse trading (i.e. the oxygen clock/%CNS concept) I'm pretty sure was "invented" afterwards by someone else. __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
(Offline)

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