Monitor oxygen as nitrogen

[tursiops]

I think I understand.

Nitrogen and Oxygen act differently.

You have a hard limit of 1.4 (or whatever you want) because O2 goes toxic at some point. One starts to see some deaths, and an increasing number with PO2s over 1.6 and a few at 1.6 with activity.

With Nitrogen there is not a hard limit other than the higher the PO2 the quicker you will have to do deco on the way up. More nitrogren may narc you more but it does not put you into convulsions which result in drowning.

In addition, we actually DO set a limit on PPN2, it is about 3-4ATA. This is the limit many people use to avoid narcosis (for air that is about 100 or 130 ft). The analogy to O2 toxicity limits of PPO2=1.4 is pretty good; in both cases it is the partial pressure causing the problem, not the depth or the time.

 

[Polari]

We SET a PP of 1.4 O2 to avoid the risk of CNS and toxing out on O2 at depth. 1.6pp O2 is considered the max safe threshold, so most go conservative with 1.4pp.

Oxygen toxicity is a time duration phenomenon: that is, both time and partial pressure play a role.So if is 1.4 or 1.6 or 1.8 does not matter.Is the relation with time that matters.
1.4 is more dangerous than 1.6 or even 2.0 if time is not calculated for toxicity level not to be exceeded.


So seems reasonable to calculate the ppo than to have the limit 1.4
Iam not saying i will do that just something that stack to my mind and needed to talk about it.

 

[Steve_C]

So seems reasonable to calculate the ppo than to have the limit 1.4

Assuming of course you know your dive profile ahead of time and can anticipate anything that might alter it.

The lmit is chosen so that you will hopefully not get in O2 toxicity during the expected dive.

I would much rather find myself in NDL violation with some minor deco than to be at 1.8 and find the dive taking longer than I had planned for whatever reason. An O2 hit is serious trouble.

 

[g1138]

Oxygen toxicity is a time duration phenomenon: that is, both time and partial pressure play a role.So if is 1.4 or 1.6 or 1.8 does not matter.Is the relation with time that matters.
1.4 is more dangerous than 1.6 or even 2.0 if time is not calculated for toxicity level not to be exceeded.


So seems reasonable to calculate the ppo than to have the limit 1.4
Iam not saying i will do that just something that stack to my mind and needed to talk about it.

Fair point.

 

[Polari]

I would much rather find myself in NDL violation with some minor deco than to be at 1.8 and find the dive taking longer than I had planned for whatever reason. An O2 hit is serious trouble.

[-]Let me give an example.[/-]
Wrong example

 

[pdhenry]

In addition to monitoring for Oxygen toxicity, we accumulate a daily oxygen exposure count (allowing for surface intervals in some models) to avoid reaching the 100% daily central nervous system maximum. I thought this is what the OP was alluding to/searching for. It seems somewhat similar to counting down Nitrogen No Deco time on a deep dive. Just as you have a maximum nitrogen exposure (depth/time related) to avoid DCI you have a maximum Oxygen exposure (depth/time related) to avoid CNS impacts.

 

[NAM001]

Polai

I get your point and it is a good question. I think hte flaw in this concept is that the higher the concentration the more evil the gas is. unless you are diving less than 20% o2 you will not get increased effect of N2 in your system. Dive nitrox > 21% will only increase the O2 issue and relieve the N2 issues. If you did somehow know when narcing gets to you,,,, you could do it as well with a depth gage value corrected for the gas you are using.

 

[Polari]

I would much rather find myself in NDL violation with some minor deco than to be at 1.8 and find the dive taking longer than I had planned for whatever reason. An O2 hit is serious trouble.

If you pass the exposure limit time of 1.4 you have the same trouble or chance of CNS as if you pass the exposure limit of 1.6.

If a diver, probably new diver who does not have a certificate or the knowledge using nitrox then for him to pick up a nitrox tank and dive is really dangerous.
The same goes for here.If you dive with 1.6pp without knowing anything about pp then you really are in trouble.
Is just that as the partial pressure gets higher,the recommended exposure time gets shorter.

----------------------------------------------------------

The maximum single exposure limits recommended in the NOAA Diving Manual are 45 minutes at 1.6 bar, 120 minutes at 1.5 bar, 150 minutes at 1.4 bar, 180 minutes at 1.3 bar and 210 minutes at 1.2 bar.

 

[Damselfish]

Oxygen toxicity is a time duration phenomenon: that is, both time and partial pressure play a role.So if is 1.4 or 1.6 or 1.8 does not matter.Is the relation with time that matters.
1.4 is more dangerous than 1.6 or even 2.0 if time is not calculated for toxicity level not to be exceeded.

So seems reasonable to calculate the ppo than to have the limit 1.4

There are 2 types of O2 toxicity. Pulmonary O2 toxicity is a time duration event. CNS O2 toxicity is not, but dependent only on the PP.

 

[PfcAJ]

There are 2 types of O2 toxicity. Pulmonary O2 toxicity is a time duration event. CNS O2 toxicity is not, but dependent only on the PP.

That is not accurate.

Cns bs toxicity is certainly time related. It's related to both partial pressure and time just like
pulmonary toxicity.