Nitrox when others are on air

[BlueTrin]

Oxygen Toxicity

Oxygen toxicity happens with partial pressures overwhelm the body. Severe cases of oxygen toxicity could cause cell damage or other symptoms.

dan.org

 

[BlueTrin]

This one speaks about the levels where you had convulsions during experiments

Oxygen Exposure Management

Today, community practices limit oxygen exposures to a PO2 of 1.2-1.4 bar for the working phase of the dive and 1.4-1.6 bar for decompression depending on circumstances, training agency recommendations, and platform. Things were not always this way. In the early days of tech diving, there were...

gue.com

 

[BlueTrin]

In the last page, an example of why there may be no contradiction of the relationship is not linear

 

[OctopusLover]

That only contradicts it if you only know linear functions …

PADI Nitrox material mentions seizures

Tidbits here:

Oxygen Seizures at PO2 ≤ 1.6 Bar: How Rare?

Learn about the signs and symptoms of central nervous system (CNS) oxygen toxicity and the likelihood of oxygen seizures.

www.shearwater.com

When I said the training material didn't cover this level of detail, I meant the fact that there's actually two distinct mechanisms by which oxygen toxicity is dangerous that have different onset characteristics, not that I didn't know about seizures!

I just read the article you linked. It says the only known cases of CNS toxicity under 1.6 are due to inadequate scrubbing in rebreathers causing hypercapnia, which in turn increases blood flow to the brain such that the amount of oxygen in the brain is as if PPO2 > 1.6, and the examples they gave were for very long rebreathers dives.That all makes sense and seems to reaffirm my assessment that descending to 36 meters on 32% on open circuit for one minute has a negligible risk.

 

[OctopusLover]

One last interesting quote on Wikipedia:

"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."

You tell me how 1 minute at 1.5 is in any way dangerous

 

[BlueTrin]

When I said the training material didn't cover this level of detail, I meant the fact that there's actually two distinct mechanisms by which oxygen toxicity is dangerous that have different onset characteristics, not that I didn't know about seizures!

I just read the article you linked. It says the only known cases of CNS toxicity under 1.6 are due to inadequate scrubbing in rebreathers causing hypercapnia, which in turn increases blood flow to the brain such that the amount of oxygen in the brain is as if PPO2 > 1.6, and the examples they gave were for very long rebreathers dives.That all makes sense and seems to reaffirm my assessment that descending to 36 meters on 32% on open circuit for one minute has a negligible risk.

And I insist that during the basic PADI Nitrox class, I believe that they mentioned short term risk is seizures and for longer repeated exposures you can have airways inflammation for example.

So that’s two different mechanisms and taught at rec level in the entry level Nitrox class. It’s possible I remember incorrectly though.

Yes, I never said it’s not a negligible risk: it’s probably relatively low. I only clarified your point on tec dives.

For the rest, I encouraged you to make your own opinion, hence why I mostly posted third party links.

 

[BlueTrin]

You tell me how 1 minute at 1.5 is in any way dangerous

Nobody said that.

 

[OctopusLover]

Nobody said that.

I was reacting to

"@OctopusLover , I feel like your are a little too complacent about the high PO2 risk from short term exposure. The Seizure risk is not a "how fast your clock is running" type risk."

In any case, thanks for all the links. I did learn a lot, maybe the Nitrox class did explain this and I just don't remember.

What seems clear to me at this point is that the reason 1.4 was chosen is because it leaves a safety margin both for depth and duration. Give a depth excursion is impossible with the seabed at 36 meters and I consciously only stayed there for a very short time, I'm happy the risk was acceptable.

 

[L13]

That all makes sense and seems to reaffirm my assessment that descending to 36 meters on 32% on open circuit for one minute has a negligible risk.

Low, not negligible. Also, Wiki is good, but incomplete and sometimes dated.

You tell me how 1 minute at 1.5 is in any way dangerous

Slightly risky, depending on all the other factors.

I was reacting to

"@OctopusLover , I feel like your are a little too complacent about the high PO2 risk from short term exposure.

It is the terminology that you are using, not the action. ie:

• negligible vs. relatively low risk
• not in any way dangerous vs. relatively low risk

There is risk. You should be aware of and acknowledge it. But it is not high.

Choosing to cruise at 150km/h is very different from choosing to accelerate to 150km/h to evade and accident or pass an irritatingly slow driver.

 

[BlueTrin]

Apologies, I think we all agree I think that it’s very unlikely something will happen if you go to 1.5 quickly on OC.

Personally I am a “by the rules” type of guy, I’d avoid knowingly violate one of my rules if I can avoid it, but I can see what you are saying too and like you said, it’s a matter or judging what’s acceptable as a risk.