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

[ginti]

I was just using the standards set by the major recreational training agencies like PADI. So, 130ft max depth, clear path to the surface, no mandatory decompression. It's hardly an airtight definition, and I'm not defending it as such. It's just for discussions like this one, you need some sort of frame of reference, and following guidelines that literally millions of divers have been trained by (for better or worse) is a logical place to start. This is especially true in this thread because the OP made no mention of technical diving; actually his question was a little vague and arbitrary, and I probably should have just stayed out of it.

There are certainly lots of 'gray area' dives where one person might think "this is a technical dive, I should only do it with the right tech diving training, equipment, and gasses" while another person would gladly do the dive with only recreational gear and training, on air. Who is right? That's where the opinions start!

I totally agree with you, and I bet almost everyone is. But I believe this point is fundamental to discuss maximum depth, especially our personal limits.

The reason why I believe so is that, as far as I understand, stress can be a significant factor for oxygen toxicity, narcosis and so on. Even if at 130ft oxygen toxicity doesn't play a big role, other effects can (1) become important and (2) be emphasized by environmental conditions. Frankly speaking, considering recreational dives the ones that require nothing more than basic equipment (BCD, tank, regulators, wetsuit, fins, mask, weights and computer), then I can without any problems agree that diving air to 130ft is ok. I do not like it, but I am not going to say it is deadly dangerous, because it is not.

But anything more than basic equipment, even just a light, and the situation changes. In this case, the recreational limit becomes personal. If you are used to perform wreck penetrations at 80mt/260ft depth in the arctic water, sure that any non-overhead diving at 130ft is recreational. But if you are used to dive just to see a bunch of fishes underwater in the tropical sea, like most divers... well the situation is completely different, and even the needs of a light can add significant problems.

In my perspective, basically the maximum depth depends on the diver and on the dive - not on PPO2. However, conservative limits take everything into account and do not ruin too much diving, which is the reason why I like to be conservative.

Going back to the topic, my limit for air diving is 40m in open water with acceptable visibility, shallower (max 30) if visibility is very poor. Actually, I try to follow GUE standards as much as I can (nitrox, 30m max), since I agree with them... unfortunately, it is hard to avoid air where I live, and to find people who want to stay shallow...

 

[seeker242]

Technical diving, that's a different story. Those are longer and/or deeper dives or in some other way much more challenging, and in those cases it makes sense to adhere completely with whatever practices the technical training recommends.

It's not just technical training from those agencies that has those limits. All the recreational training, and only recreational training, also has those limits.

 

[Rose Robinson]

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.

Hello Boston Breaker,

The responses to this point are reaching the needle red line to controversial, so I don't want to go there.

The MOD for 21% at 1.4 ATA is 186.9.

I think the technical divers call this deep air...

I also think that a lot of folks would get goofy head diving with 21% long before 187 feet is reached.

This is a subject suited to the technical diving experts, of which I am not one.

I can only hope you receive a response meeting your satisfaction.

Rose

 

[boulderjohn]

The variety of answers here comes from people applying a lot of different factors to the definition of MOD. If the only factor is what was in the opening sentence of the thread (PPO2 = 1.4), there is only one answer, provided we are talking about diving in the ocean. (Answers below are rounded off.)

1. Start with the equation to find the ambient pressure in atmospheres for that PPO2 on air: 1.4/0.21 = 6.67.
2. Next, convert 6.67 to depth in feet by subtracting the atmospheric pressure (1) and multiplying by the depth of water equaling an atmosphere (33): (6.67-1) X 33 = 187 feet.

That works for diving in the ocean. If you are diving in a mountain lake at 6,000 feet elevation, it is different. The 6.67 will be the same, but the depth to reach that limit will be different. The atmospheric pressure is only 0.8, and the depth of freshwater equaling an atmosphere is 34 feet. (6.67-0.8) X 34 = 200 feet.

The altitude answer will be a surprise to many people who were mistakenly using theoretical depth tables to determine MOD and thinking it would be shallower, not deeper.

 

[tursiops]

Hello Boston Breaker,

The responses to this point are reaching the needle red line to controversial, so I don't want to go there.

The MOD for 21% at 1.4 ATA is 186.9.

I think the technical divers call this deep air...

I also think that a lot of folks would get goofy head diving with 21% long before 187 feet is reached.

This is a subject suited to the technical diving experts, of which I am not one.

I can only hope you receive a response meeting your satisfaction.

Rose

The problem is, the OP asked for the MOD of air for 1.4 ATA. As one of the responses said, and was made fun of by the OP, there is no ambiguity on what this means. It is a simple calculation, as you have done. But apparently the OP -- and most of the responses -- did NOT mean MOD (as defined), nor did they mean air, nor did they mean 1.4 ATA. They used how deep THEY were willing to go on air, they used Nitrox and Trimix, and they used whatever PPO2 appealed to them.

So the question as asked was very simple. But apparently that was in error or perhaps not intended. The OP actually asked six questions:
#1

I was curious what the MOD is for air (20.95%) using a PPO2 of 1.4
I'm certain the answers will vary.

I have no idea why the OP thinks the answers might vary, unless he does not mean MOD, or air, or 1.4.
#2

Is 1.4 a safer single exposure limit than 1.6 or is the difference negligible?

Good question, but how can the answer -- based on the literature and training agencies and manuals like NOAA and Navy -- be anything other than Yes?
#3

Can you control the effects of elevated partial pressures,

No, no evidence of this, other than pure testosterone and/or imagination, or maybe endless training (c.f. @Akimbo).
#4

are there any warning signs to a possible CNS-02 hit?

No...there are possible signs, but they do not always present.
#5

Is your exposure expressed as a percentage, or is it a count down in minutes?

Confusing two different things here.
#6

Also, what is your "Maximum." depth on air, and what physiological effects did you experience?

Good question, most responses just addressed this.
My personal deepest on air was 185 fsw; I was seriously narced, have almost no memory of the dive, if anything had gone wrong I would likely not have been able to address it. and that was in warm, clear, tropical water. Never again.

 

[Rose Robinson]

The problem is, the OP asked for the MOD of air for 1.4 ATA. As one of the responses said, and was made fun of by the OP, there is no ambiguity on what this means. It is a simple calculation, as you have done. But apparently the OP -- and most of the responses -- did NOT mean MOD (as defined), nor did they mean air, nor did they mean 1.4 ATA. They used how deep THEY were willing to go on air, they used Nitrox and Trimix, and they used whatever PPO2 appealed to them.

So the question as asked was very simple. But apparently that was in error or perhaps not intended. The OP actually asked six questions:
#1

I have no idea why the OP thinks the answers might vary, unless he does not mean MOD, or air, or 1.4.
#2

Good question, but how can the answer -- based on the literature and training agencies and manuals like NOAA and Navy -- be anything other than Yes?
#3

No, no evidence of this, other than pure testosterone and/or imagination, or maybe endless training (c.f. @Akimbo).
#4

No...there are possible signs, but they do not always present.
#5

Confusing two different things here.
#6

Good question, most responses just addressed this.
My personal deepest on air was 185 fsw; I was seriously narced, have almost no memory of the dive, if anything had gone wrong I would likely not have been able to address it. and that was in warm, clear, tropical water. Never again.

Thank you Tursiops,

You're last three line paragraph was my primary concern, lose control of your ability to think clearly, lose everything.

Rose

 

[tursiops]

Thank you Tursiops,

You're last three line paragraph was my primary concern, lose control of your ability to think clearly, lose everything.

Rose

Luckily, one of the not-much-mentioned benefits of 32% Nitrox is its 1.4 ATA MOD helps mitigate really serious narcosis.

 

[Rose Robinson]

Luckily, one of the not-much-mentioned benefits of 32% Nitrox is its 1.4 ATA MOD helps mitigate really serious narcosis.

Yes,

This mix also seems to be one of the most common banked blends and with your extensive knowledge, for good reason.

Thank you for sharing.

Rose

 

[dmaziuk]

Is 1.4 a safer single exposure limit than 1.6 or is the difference negligible?

Good question, but how can the answer -- based on the literature and training agencies and manuals like NOAA and Navy -- be anything other than Yes?

Yes, it's one or the other.

 

[MaxBottomtime]

Luckily, one of the not-much-mentioned benefits of 32% Nitrox is its 1.4 ATA MOD helps mitigate really serious narcosis.

Enriched Air Misconceptions