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

[Boston Breakwater]

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,
and, 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.

 

[pauldw]

Hello, Everyone. I was curious what the MOD is for air (20.95%) using a PPO2 of 1.4.

187 feet.

 

[Ukmc]

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.

187.87 fsw
192.9 ffw

 

[Graeme Fraser]

Technically it's 56m. Although I used to go there on air in the old days, there's no excuse to go close to those limits now, especially with overwhelming evidence against these practices.

Regarding CNS, at a PPO2 of 1.4 working phase and 1.6 deco phase, a hit wouldn't be my main concern as this is within the limit, subject to exposure.

My primary concern at that depth on air would not necessarily be elevated O2, but unacceptable gas density levels.

Regarding narcosis, although I've not knowingly experienced issues, I know it's there and I'd be a fool to think I could fully function at a PPN2 of 5.2. I've certainly seen people completely off their faces at much shallower depths than that.

 

[Celt]

If you stay above 56meters you won’t go over a 1.4 ppo2 but the time spent at the depth and what your doing is a critical factor. Also no one can predict the affect of partial pressure of gasses on an individual. Narcosis can be controlled by some but oxygen intolerance can be a problem for others. Personally I’ve never had a problem with either , as for gas density I’ve never taken a blind bit of notice of it.

 

[grantctobin]

For a suit gas bottle, pretty deep. Otherwise your END should be a hard limit well before your PO2.

 

[PfcAJ]

Oxygen is only part of figuring out your MOD.

Narcosis is just as important.

Deeper than about 100’, and I want some helium in my gas.

 

[Angelo Farina]

These are the US Navy tables i did use for 40 years, util I bought my first computer one year ago:

As you see the maximum depth is 64m. I always followed them scrupulously (also the part on the ascent speed: 10 m/min up to 15m, and then 5m/min up to the surface):
I was never bent, nor had any symptom of oxygen intoxication. This also depends on the exposure time, which at depth is very short (at 64m the maximum time is 15 minutes):
Regarding narcosis, well, ehm, erh, I had some quite good cases below 60m... So that's the limiting factor for me...

 

[halocline]

Oxygen is only part of figuring out your MOD.

Narcosis is just as important.

Deeper than about 100’, and I want some helium in my gas.

That's a little too conservative for my tastes. There is plenty of evidence that air is absolutely fine for recreational depths, generally accepted to be around 130 ft. 32% is absolutely fine, again with many years and thousands of dives as evidence, down to 110 ft, and it wasn't long ago that the generally accepted PPO was 1.6, or 132 ft for 32%. Maybe I'm mistaken, but I certainly don't recall a rash of oxtox hits in recreational divers pushing 32% to 130 ft.

A somewhat more mainstream plan would be air (or an appropriate nitrox blend) for recreational depths and trimix for anything deeper. That's still very conservative, and expensive!

 

[Boston Breakwater]

That's a little too conservative for my tastes. There is plenty of evidence that air is absolutely fine for recreational depths, generally accepted to be around 130 ft. 32% is absolutely fine, again with many years and thousands of dives as evidence, down to 110 ft, and it wasn't long ago that the generally accepted PPO was 1.6, or 132 ft for 32%. Maybe I'm mistaken, but I certainly don't recall a rash of oxtox hits in recreational divers pushing 32% to 130 ft.

A somewhat more mainstream plan would be air (or an appropriate nitrox blend) for recreational depths and trimix for anything deeper. That's still very conservative, and expensive!

This is where.....I get flack for saying someone is off topic....The post specifically says "Air."
Considering, I became an Enriched Air Instructor 19 years ago......I'll take your information under advisement.