Maximum Operating Depth (M.O.D.) S.C.U.B.A. Diving On Air.

[tbone1004]

15m? Wow...

work of breathing on a CCR is no joke, trimix below 15m is not uncommon on a CCR, especially since it's cheap. I agree with that recommendation.

 

[tursiops]

Hello, Everyone. I was curious what the MOD is for air (20.95%) using a PPO2 of 1.4
I'm certain the answers will vary. Is 1.4 a safer single exposure limit than 1.6 or is the difference negligible?
Can you control the effects of elevated partial pressures,
or are there any warning signs to a possible CNS-02 hit?
Is your exposure expressed as a percentage, or is it a count down in minutes?
Also, what is your "Maximum." depth on air, and what physiological effects did you experience?
Cheers.

It is hard to believe that a Nitrox instructor would be asking these questions, unless they are "testing" the readers.
Are these real questions?

 

[Degenerate]

It is hard to believe that a Nitrox instructor would be asking these questions, unless they are "testing" the readers.
Are these real questions?

The first question is pretty alarming, as the answers can't vary at all.
MOD for air with a max PPO2 of 1.4 is literally set in stone.
How on earth would the answers for that question vary?
Not an instructor I would want to take a course for...

 

[Akimbo]

I was curious what the MOD is for air (20.95%) using a PPO2 of 1.4
I'm certain the answers will vary. Is 1.4 a safer single exposure limit than 1.6 or is the difference negligible?

It varies quite a bit. All the factors impacting OxTox apply. This thread talks about it quite a bit:
Oxygen Toxicity Limits & Symptoms

Maximum Operating Depth (M.O.D.) S.C.U.B.A. Diving On Air?
The options and guidelines change over time, data available, and value judgements relating to risk mitigation. For example, the max PPO2 was 2.0 when I was in the US First Class Diving School. That is why certification on air was limited to 285'/87M.

That limit was down from a PPO2 of 3.0 before tests at the Admiralty EDU (Experimental Diving Unit) during WWII.

 

[Dominik_E]

work of breathing on a CCR is no joke, trimix below 15m is not uncommon on a CCR, especially since it's cheap. I agree with that recommendation.

Well, I am not an active CCR diver. I have some try dives, also a bit deeper than 15m. WOB was quite trivial. Deeper depths, this may be different, I can not and will not comment. I do however have to say I am quite critical about advocating trimix for ever shallower depths. CCR to be honest I do not really care, as the loss is small. But OC, we are using a finite resource.

 

[Boston Breakwater]

It varies quite a bit. All the factors impacting OxTox apply. This thread talks about it quite a bit:
Oxygen Toxicity Limits & Symptoms

Maximum Operating Depth (M.O.D.) S.C.U.B.A. Diving On Air?
The options and guidelines change over time, data available, and value judgements relating to risk mitigation. For example, the max PPO2 was 2.0 when I was in the US First Class Diving School. That is why certification on air was limited to 285'/87M.

View attachment 596605​

That limit was down from a PPO2 of 3.0 before tests at the Admiralty EDU (Experimental Diving Unit) during WWII.

Hello. That's a cool piece of history. (I love the wording.) Also, thanks for the link that leads to more links.......Very informative.
Cheers.

 

[dmaziuk]

http://www.tecvault.t101.ro/REPEX0.PDF

-- CNS toxicity "is avoided by staying below 1.5 bars PO2 except for short excursions" and "may develop within a few to many minutes ... above 1.8 bars".

At 1.8 it's ~76 m or 250 feet.

 

[tursiops]

http://www.tecvault.t101.ro/REPEX0.PDF

-- CNS toxicity "is avoided by staying below 1.5 bars PO2 except for short excursions" and "may develop within a few to many minutes ... above 1.8 bars".

At 1.8 it's ~76 m or 250 feet.

That reference is over 30 years old. Do you suppose we've learned anything since then?

 

[scubadada]

That reference is over 30 years old. Do you suppose we've learned anything since then?

Have we? In my 1970 LA County Course, the pO2 limit was 1.6. In my PADI course in 1997, the pO2 limit was 1.4. What is the data supporting the the current limit? Were there an unacceptable number of ox-tox episodes at the higher limit? Is this an evidence-based recommendation or what?

 

[dmaziuk]

Have we? In my 1970 LA County Course, the pO2 limit was 1.6. In my PADI course in 1997, the pO2 limit was 1.4. What is the data supporting the the current limit? Were there an unacceptable number of ox-tox episodes at the higher limit? Is this an evidence-based recommendation or what?

Well 30 years ago they reckoned long-term exposure above 1.4 could lead to pulmonary toxicity, but as far as divers were concerned, the damage appeared to be fully reversible "with time". "Unlike in the hospital setting."

Maybe "we" no longer think that.