Likelihood of getting oxygen toxicity at 1.4 PPO

[boulderjohn]

The following quote may be helpful. In response to a question about long term oxygen exposure, Karl Shreeves of PADI explained the research done by DSAT in creating its table for long term exposure. Here is an excerpt from his description of that history:

When we developed the DSAT versions, we examined no stop and deco diving and found that we could simplify further by staying with the single exposure limits for everything. NOAA allows deco diving so that didn’t meet their needs, but if you stay in no stop limits and 1.4 and under, you can dive all day within the single exposure table. You can get off the table by diving your brains out using higher oxygen content than you would need to (e.g., 6 two hour dives to 20 feet using EANx36, or 5 one hour dives to 50 feet using EANx40 ), but this would even apply to the 24 hour limit table which is the same at the single table at 1.0 and above.​

 

[Storker]

I like it. But then, I'm an avid fan of the KISS principle.

 

[Storker]

I once had to take a chamber ride for some slight numbness in my hand. It was 60 feet on 100% O2

The risk of toxing at high pPO2 is a lot lower if you're topside than if you're underwater. And if you tox topside, you don't drown. Besides, you're already bent, and ameliorating the bends is a pretty good reason for accepting a higher probability for a non-life-threatening case of oxtox.

So, a much higher pPO2 than 1.4 bar is acceptable in a chamber. Even if it's not unheard of that people tox during a Table 6.

 

[boulderjohn]

So, a much higher pPO2 than 1.4 bar is acceptable in a chamber. Even if it's not unheard of that people tox during a Table 6.

....and for some reason, it generally takes a much higher PPO2 to tox in a chamber than under water.

 

[2airishuman]

The drag with CNS toxicity is that response is likely to vary a lot person to person. Are you prone to it or not? Who knows! (Leaving aside the exercise/CO2/drug interaction issues that raise the probability.)

The best available evidence suggests that there is more situational variation than individual variation.

 

[Searcaigh]

It's covered during a FFM class, if you take one. You've got options, the option that's common to all models is to take off the mask and stick your buddy's octo into your mouth. If are risk averse, you will have a backup mask in your pocket to throw on. Most masks also support a second hose for connecting an alternate air source. Could be another tank, could be a pony, etc. You could also or instead use a quick disconnect.

What FFM did you train on @kelemvor

 

[Magnus Lundstedt]

I have a dim memory that I read somewhere that in "the good old days" they had a recommended limit of 2 or 2.1. Later on when understanding get better and risk awarnes rise, the limit was altered to 1.6 and now 1.4

I would not do a dive on 2 or even 1.6, but i see no problem planning a dive to 30 meters on 32%, and a MOD on 32m, PPO2 1.4. But it is then important to keep control on my depth so I don't go down to deep.

There are always a probability of oxtox when PPO2 rises, but I think that if I keep under 1.4 the probability is so small that it is close to zero. There are some safety marginal already in the recommendations.

 

[AfterDark]

The Cousteau team used PPO 2.0 diving the Britannica that's a 400FSW dive if my memory is right. I'd guess 1.4 is ok.

 

[NAM001]

ystrout

i would say very unlikely. I did a spread sheet long ago ad included not only the dive tables but otu and cns calculatons. If i can find it i will include it.
When yo run the cns calculation the answer gives you a % of your limit you accumulate per minute. the graph of those amounts is pretty linear untill you get to a PPO@ of about 1.65 to 1.7 at that point rates increase at a exponential rate. here is a table and some stuff on it

Look what happens starting at 1.6 PPO2. and then what you have at 1.8 PPO2

Diving at 1.6 is where the % rate starts to become nonlinear with depth. 1.6 is still very managable with littel threat. 1.8 is a different matter all together. 1.4 is well with in the linear rate.

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

Based on a % per minute according to the PPo2 you are at. The higher the PPo2 the more per minute the rate is set. TDI manuals and others have the rates.

This is an example from the web - do not use as I can't check it against a manual from here...

PPO2 1.4 = 0.65% CNS per minute
PPO2 1.5 = 0.83% CNS per minute
PPO2 1.6 = 2.22% CNS per minute
PPO2 1.7 = 10.0% CNS per minute
PPO2 1.8 = 50.0% CNS per minute
PPO2 1.82 = 100.0% CNS per minute

Most tables will then have a maximum exposure per single dive, and a maximum exposure per 24 hours.

cns calculations focus on noaa 1.6 PPO@ gets 2.22% % of your limit per minute look above for 1.7 and above. Standard safety says you dont go beyond 1.6. You can do it (recommended for short intervals, like picking up a dropped tool. You plan to not exceed 1.4 for normal diving. You do you gas mixing as yo see fit. Normally the protocol is to use 1.4 for determining best mix. It does not hurt to do a mix depending on location for say 20 ft deeper than you plan for and keeping the limit of 1.4. others will say 1.3 at desired depth to allow more room to go deeper if needed.

PO2 NOAA CALC
0.55 0.12 0.12
0.60 0.14 0.14
0.65 0.16 0.16
0.70 0.18 0.18
0.75 0.20 0.20
0.80 0.22 0.22
0.85 0.25 0.25
0.90 0.28 0.27
0.95 0.30 0.31
1.00 0.33 0.34
1.05 0.37 0.37
1.10 0.42 0.41
1.15 0.44 0.44
1.20 0.48 0.48
1.25 0.51 0.52
1.30 0.56 0.55
1.35 0.61 0.59
1.40 0.67 0.65
1.45 0.72 0.72
1.50 0.83 0.86
1.55 1.11 1.14
1.60 2.22 2.08

 

[NAM001]

I have a dim memory that I read somewhere that in "the good old days" they had a recommended limit of 2 or 2.1. Later on when understanding get better and risk awarnes rise, the limit was altered to 1.6 and now 1.4

I would not do a dive on 2 or even 1.6, but i see no problem planning a dive to 30 meters on 32%, and a MOD on 32m, PPO2 1.4. But it is then important to keep control on my depth so I don't go down to deep.

There are always a probability of oxtox when PPO2 rises, but I think that if I keep under 1.4 the probability is so small that it is close to zero. There are some safety marginal already in the recommendations.

When I went through n the 60's we were told that at ppo2 of 2.0 most all will start having symptoms of ox tox. by 3.0 you are physically a veg and 4.0 dead. 297 ft was an important depth in there. probably the 10 ATA's that gave you PPO2 of 2.0 on air. Max depth on air.