Air strategy for 4-5 tank dive days?

[BRT]

I'm concerned by the trend of some in this thread to downplay the risks of oxygen toxicity and advocating to 'wing it' with rough guesses instead of using the tools they have the way they were trained to.

I would need research showing the risk is insignificant when diving 36% like it is 21%. I don't like blind luck and my own guesses determining what's 'safe enough' oxygen exposure when all the while I'm carrying a device programmed to quantify this risk according to the best current understanding of the risk. Why not program the gas you're actually breathing and add conservatism to your dive profile by consciously staying further away from the NDL?

One rhetorical question and one incredulous question:

Why do recreational computers track oxygen exposure? Why do some feel this feature is unnecessary and can be ignored (by falsifying % input data)?

(Sidebar: dove gladly at ppo2 1.6 today)

Cameron

I will never worry about the CNS clock. I read the Oxyhacker book. Took a look at how much diving I'd have to do at deep depths and high PO2's and realized the CNS clock was not something I was capable of exceeding. I never dive 7 days straight.

 

[BRT]

More like 20.

Most divers never violate the CNS clock. It requires fairly aggressive diving including lots of deco. It's there for the very few who do. I don't know that I've heard of any diver falsifying % to get around that.
I do know many divers who violate depth limits. Most do fine, but there are always a few who don't. That's the beauty in a rebreather: always the best mix and there's no need to violate those PPO2 limits.

But by maintaining average PPO2 at a higher level you probably don't want to take the peaks as high during the active part of the dive.

 

[The Chairman]

But by maintaining average PPO2 at a higher level you probably don't want to take the peaks as high during the active part of the dive.

1.3 for most dives and longer ones get 1.2.

realized the CNS clock was not something I was capable of exceeding.

Until you dive a rebreather. Then it becomes more probable. I like a day between long dives, although sometimes I'll dive two in a row with a mandatory day off. There's nothing down there worth injuring yourself over.

 

[nodakdive]

I will never worry about the CNS clock. I read the Oxyhacker book. Took a look at how much diving I'd have to do at deep depths and high PO2's and realized the CNS clock was not something I was capable of exceeding. I never dive 7 days straight.

No CNS clock problems doing two 90 minute dives to 95 feet on EAN36 in one day?

How about four 1 hour dives, same mix, 75 foot max depths?

 

[northernone]

No CNS clock problems doing two 90 minute dives to 95 feet on EAN36 in one day?

How about four 1 hour dives, same mix, 75 foot max depths?

Ran it quickly. Looks like ~40% really roughly staying in NDL with 1hr surface interval.

 

[BRT]

1.3 for most dives and longer ones get 1.2.

Until you dive a rebreather. Then it becomes more probable. I like a day between long dives, although sometimes I'll dive two in a row with a mandatory day off. There's nothing down there worth injuring yourself over.

I understand. But recreational open circuit divers like myself really have not way to exceed the CNS clock.

 

[northernone]

I understand. But recreational open circuit divers like myself really have not way to exceed the CNS clock.

Pretty hard to do I think with common rec diving. What CNS clock % is your threshold?

I wonder what mix of gas would push you over. EAN32, EAN36, EAN40 or even EAN80? How many dives at what depths over how many days?

Seems there's a fizzy line somewhere, I just wonder where it is. Even the ballpark for dives staying within NDL.

 

[nodakdive]

Ran it quickly. Looks like ~40% really roughly staying in NDL with 1hr surface interval.

I must be misunderstanding/misusing the NOAA Oxygen Exposure table. Or misunderstanding the term "CNS clock". Or something else.

What I'm seeing is that the limit for 1.2 ppo2 diving is 210 minutes and that the limit for 1.4 ppo2 diving is 150 minutes.

So, in the first example I used, after the first dive to 95 feet(approx 1.4 ppo2), I'd have used 60% of my exposure. (60 minutes would be 40%, another 30 minutes adds 20%, subtracted from 100% I'd have 40% remaining exposure time for the 2nd dive.) On that second dive I'd use the remaining 40% after 60 minutes. If I did the entire 90 minutes, my exposure would be 120%?

http://www.anaspides.net/documents/scuba_diving_documents/NOAA CNS Percentage Table.pdf

I didn't consider 90 minute half-time during the SI.

 

[BRT]

Pretty hard to do I think with common rec diving. What CNS clock % is your threshold?

I wonder what mix of gas would push you over. EAN32, EAN36, EAN40 or even EAN80? How many dives at what depths over how many days?

Seems there's a fizzy line somewhere, I just wonder where it is. Even the ballpark for dives staying within NDL.

For me it is just not possible.

 

[BRT]

I must be misunderstanding/misusing the NOAA Oxygen Exposure table. Or misunderstanding the term "CNS clock". Or something else.

What I'm seeing is that the limit for 1.2 ppo2 diving is 210 minutes and that the limit for 1.4 ppo2 diving is 150 minutes.

So, in the first example I used, after the first dive to 95 feet(approx 1.4 ppo2), I'd have used 60% of my exposure. (60 minutes would be 40%, another 30 minutes adds 20%, subtracted from 100% I'd have 40% remaining exposure time for the 2nd dive.) On that second dive I'd use the remaining 40% after 60 minutes. If I did the entire 90 minutes, my exposure would be 120%?

http://www.anaspides.net/documents/scuba_diving_documents/NOAA CNS Percentage Table.pdf

I didn't consider 90 minute half-time during the SI.

Or the fact that you didn't have enough air to stay at 95' for 60 minutes and if you did you would need a bunch more air for the deco.