CNS Equation

VTR · 12th February 2006, 14:22

Does anyone know the equation for calculating CNS for a given PO2?

Cheers

Giles.

Nad · 12th February 2006, 14:54

Quote: (Originally Posted by VTR)

Does anyone know the equation for calculating CNS for a given PO2?

Cheers

Giles.

Sorry?
Do you mean dividing the actual exp. time at a given PO2 by the allowed time for that exposure?

Nad

VTR · 12th February 2006, 16:08

If you look up on a CNS chart for a given PO2 you'll get a % of toxicity for the amount of mins, for example;- for 1 min exposure at 0.65 PPO2 = 0.16% CNS. I would like to know the equation that is used to arrive at the % figure.
The OTU equation is 1OTU = t(2PO2-1)^0.833, but I can't seem to find the CNS equation, or I've missed it

Giles

Benthic · 12th February 2006, 16:31

Actually, you've pretty much got it. For example, the limit for a p02 of 1.0ata is 300 min. Therefore 1 min = 1/300=0.00333=0.333%. If you want to double check yourself, 150 min (at p02=1.0ata) should be 50% of your allowed exposure, right? So 150min * 0.333%/min = 49.95%.

Hope that's helpful.

Brian

edster · 12th February 2006, 16:46

Quote: (Originally Posted by VTR)

If you look up on a CNS chart for a given PO2 you'll get a % of toxicity for the amount of mins, for example;- for 1 min exposure at 0.65 PPO2 = 0.16% CNS. I would like to know the equation that is used to arrive at the % figure.
The OTU equation is 1OTU = t(2PO2-1)^0.833, but I can't seem to find the CNS equation, or I've missed it

Giles

The percentage allowed per minute comes form the tables which are AFAIK derived empirically from when people start doing the chicken dance, rahter than a direct mathematical correlation between ppO2 and time. But if you have some hardcore maths in your background, perhaps you can derive a correlation?

Good luck !!

cheers

Ed

dantheman · 12th February 2006, 16:46

For a fuller description in his inimitable style, see Erik Baker's paper at:

ftp://ftp.decompression.org/pub/Bake...lculations.pdf

--dan

ROB DAVIE · 12th February 2006, 17:00

Quote: (Originally Posted by edster)

The percentage allowed per minute comes from the tables which are AFAIK derived empirically from when people start doing the chicken dance......

Cheers!

Ed

Ed,

I always find it best, as you do, to use the correct technical term "chicken dance" or, alternatively, "Doing the Chicken!" to describe things accurately, even though students may find such academic terminology puzzling!

Rob

**nigelh** · 12th February 2006, 17:20

Quote: (Originally Posted by VTR)

Does anyone know the equation for calculating CNS for a given PO2?

I ran a curvefit program on the usual CNS table and couldn't get a reasonable fit so I just flat line modeled it.

Andyg · 26th May 2006, 13:27

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.
I use VPM-B 0n a +2 setting for all my deco diving. I've been playing around with VPM-B for a deep dive and the CNS% what's coming up is over 200% which is well above the VPM-B limit. I use a set point of 1.1 bottom and up it to 1.3/4 during the shallow stops, which works for me.

I would be interested to hear views on what people think is an exceptable CNS% to run.

Andyg

demo0034 · 26th May 2006, 14:10

Quote: (Originally Posted by ROB DAVIE)

Ed,

I always find it best, as you do, to use the correct technical term "chicken dance" or, alternatively, "Doing the Chicken!" to describe things accurately, even though students may find such academic terminology puzzling!

Rob

I was always told it was the "crappie flop"

12th February 2006, 14:22	#1 (permalink)
VTR New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Nov 2005 Location: Devon Posts: 39	CNS Equation Does anyone know the equation for calculating CNS for a given PO2? Cheers Giles.
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12th February 2006, 14:54	#2 (permalink)
Nad Rebel to the Bone Current Rebreather/s: Ouroboros Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Mar 2005 Location: Europe Posts: 960	Re: CNS Equation Quote: (Originally Posted by VTR) Does anyone know the equation for calculating CNS for a given PO2? Cheers Giles. Sorry? Do you mean dividing the actual exp. time at a given PO2 by the allowed time for that exposure? Nad __________________ The Impossible is often the Untried
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12th February 2006, 16:08	#3 (permalink)
VTR New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Nov 2005 Location: Devon Posts: 39	Re: CNS Equation If you look up on a CNS chart for a given PO2 you'll get a % of toxicity for the amount of mins, for example;- for 1 min exposure at 0.65 PPO2 = 0.16% CNS. I would like to know the equation that is used to arrive at the % figure. The OTU equation is 1OTU = t(2PO2-1)^0.833, but I can't seem to find the CNS equation, or I've missed it Giles
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12th February 2006, 16:31	#4 (permalink)
Benthic MEGalomaniac Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2006 Location: Pensacola, FL USA Posts: 222	Re: CNS Equation Actually, you've pretty much got it. For example, the limit for a p02 of 1.0ata is 300 min. Therefore 1 min = 1/300=0.00333=0.333%. If you want to double check yourself, 150 min (at p02=1.0ata) should be 50% of your allowed exposure, right? So 150min * 0.333%/min = 49.95%. Hope that's helpful. Brian __________________ Well lit rooms will not repel determined beer ninjas.
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12th February 2006, 16:46	#5 (permalink)
edster Mr Cheesebox Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Apr 2005 Location: Avening UK Posts: 149	Re: CNS Equation Quote: (Originally Posted by VTR) If you look up on a CNS chart for a given PO2 you'll get a % of toxicity for the amount of mins, for example;- for 1 min exposure at 0.65 PPO2 = 0.16% CNS. I would like to know the equation that is used to arrive at the % figure. The OTU equation is 1OTU = t(2PO2-1)^0.833, but I can't seem to find the CNS equation, or I've missed it Giles The percentage allowed per minute comes form the tables which are AFAIK derived empirically from when people start doing the chicken dance, rahter than a direct mathematical correlation between ppO2 and time. But if you have some hardcore maths in your background, perhaps you can derive a correlation? Good luck !! cheers Ed __________________
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12th February 2006, 16:46	#6 (permalink)
dantheman Emoticonoclast Current Rebreather/s: Sport Kiss rEvo Other Rebreather/s: Classic Kiss rEvo Join Date: May 2005 Location: NorthEast USA Posts: 393	Re: CNS Equation For a fuller description in his inimitable style, see Erik Baker's paper at: ftp://ftp.decompression.org/pub/Bake...lculations.pdf --dan
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12th February 2006, 17:00	#7 (permalink)
ROB DAVIE Administrator Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: HOUSTON, REPUBLIC OF TEJAS Posts: 1,120	Re: CNS Equation Quote: (Originally Posted by edster) The percentage allowed per minute comes from the tables which are AFAIK derived empirically from when people start doing the chicken dance...... Cheers! Ed Ed, I always find it best, as you do, to use the correct technical term "chicken dance" or, alternatively, "Doing the Chicken!" to describe things accurately, even though students may find such academic terminology puzzling! Rob __________________ [SIZE=2]"CC Rebreathers will become a viable part of tech diving [U]WHEN PIGS FLY[/U]!!"--GI3[/SIZE]
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12th February 2006, 17:20	#8 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 824	Re: CNS Equation Quote: (Originally Posted by VTR) Does anyone know the equation for calculating CNS for a given PO2? I ran a curvefit program on the usual CNS table and couldn't get a reasonable fit so I just flat line modeled it. __________________ nigelh
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26th May 2006, 13:27	#9 (permalink)
Andyg New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Mar 2005 Location: Sheffield Posts: 25	Re: CNS Equation 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. I use VPM-B 0n a +2 setting for all my deco diving. I've been playing around with VPM-B for a deep dive and the CNS% what's coming up is over 200% which is well above the VPM-B limit. I use a set point of 1.1 bottom and up it to 1.3/4 during the shallow stops, which works for me. I would be interested to hear views on what people think is an exceptable CNS% to run. Andyg
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26th May 2006, 14:10	#10 (permalink)
demo0034 New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: May 2006 Location: Great Lakes Posts: 11	Re: CNS Equation Quote: (Originally Posted by ROB DAVIE) Ed, I always find it best, as you do, to use the correct technical term "chicken dance" or, alternatively, "Doing the Chicken!" to describe things accurately, even though students may find such academic terminology puzzling! Rob I was always told it was the "crappie flop"
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