Deep Diving on Air

[Reef_Haven]

Unfortunately Charlie failed to post any additional details of his dive, leading me to believe it was not planned well. There was no indication in his first post that it wasn't planned well.
For all we knew, he could have been diving doubles with two deco stage bottles and two safety divers.

 

[boulderjohn]

Forget Narcosis... Doesn't "air" become toxic below 220 ft? 21%o2 @ 220 = 1.61 PPo2. How are people diving 400 feet on air and not getting a tox hit?

Remember that the 1.6 limit is considered to be safe. It is not as if you will die if you hit 1.61 for a minute or two. As you go past 1.6 and as the time you are at that level increases, the odds that you will have a toxic reaction increase. It is by no means easily predictable when it will occur.

so there are a million Deep Air Divers at least, and there are only a few dozen here on SB that are against it, the rest do not post so not have to justify there dives.

I am not positive, but this could easily be the most absurd post I have ever read on ScubaBoard or possibly anywhere. Millions of divers routinely violate limits, and only a few down are opposed to it. Wow. Amazing that no agency supports it.

 

[boulderjohn]

As for agencies that do teach deep air...

I have certifications from one such agency: TDI. Their Extended Range class does teach deep air, although not to the level that PSAI does. I did not take the class, but since the manual for it is included in the manual for the trimix class I did take, I do have the manual and I did read it.

The deep air certifications from these agencies are nothing like what is being described in this thread. The only way they are different from the trimix classes is that they don't use trimix. They still teach having adequate gas supplies to deal with emergencies. They teach following a carefully planned decompression schedule using different nitrox mixes in additional tanks. Divers train intensely to deal with emergencies and solve problems. The road to that certification is a long one and includes rigorous training. They are not in any way teaching the bounce diving advocated here.

 

[knotical]

I have dived air to depths significantly beyond recreational limits. Not to see something special, not to set a personal record, but to gauge how deep I might go to assist another diver.

I did these dives solo, with only a recreational rig because that is the likely circumstance if a need arose. After several such dives I have a rough calibration in my head of how deep I would go to help someone. The depth varies depending on the diver needing aid. Is it a stranger? an insta-buddy? a regular buddy? my student? or my spouse?

No other justification for deep dives on air works for me.

 

[Moonglow]

No other justification for deep dives on air works for me.

Deep air dives are "justified" simply because they can be done-- like anything else in life.

 

[VooDooGasMan]

Charlie glad you pointed that out, its the same as when the new diver wants to go to over 100' and get narced the anxiety is now a bit controlled. Now this is where it is to the divers that make it there and then they learn how to have more time and get there sac down. Glad you have given more info on your dive, and have many safe dives for learning on each dive.

 

[Rick Murchison]

Couple of points...

OxTox -
Air reaches a PO₂ of 1.6 ATA at about 220', so if you plan to spend more than 45 minutes on the bottom (!) at 220 then OxTox might be a problem... but I reckon the 6+ hours of deco might be a bit more of a concern, eh? In the only real high PO₂ experiment I know of, all the test subjects endured a PO₂ of 3.1 ATA (about 450 FSW on air) for at least five minutes before any signs of OxTox (test subjects were put on 100% oxygen at 70FSW in a chamber every day for 30 days running; each day until OxTox symptoms were observed). And as alluded to earlier, it appears that high PN₂ takes the edge off OxTox as well, so of the big three (OxTox, Narcosis and decompression obligation), it appears that for most "Deep Air" dives OxTox is rarely a significant factor.
Narcosis -
Often underestimated. Why? Because you are your own worst judge of narcosis. I hear people say "I don't get narced at all at xxx feet." It just ain't so... There was a fellow over in England not long ago that ran a little narcosis class at 100FSW. Nearly *all* his students were *absolutely sure* they didn't have any narcosis at 100 FSW. But he was able to demonstrate that every single one of them was in fact narced at 100' simply by getting them to do something stupid that they'd agreed not to do under any circumstances before the dive! I can nearly hear the "not me"s out there as you read this, but his results are conclusive. I know, for example, that when I pass 100' going down, that when I look at my gauges I have to think about what they're telling me and consciously register the information, otherwise I'll look at 'em and stow 'em and then realize that though I read them I didn't register the info. Perhaps my favorite narcosis story comes from my brother-in-law John. He relates how after tracking a grouper for a few minutes at 130', "pretty soon I was a fish... right up 'til I ran out of air." Scuba history is replete with divers who "just kept going" on deep air until it was too late to make a safe ascent... who either perished at depth or ended up hurt really bad or dead from DCS. (Two very recent cases attest to this)
Narcosis is the one of the big three that usually gets divers to violate the limits of the other two. If a diver insists on diving deep on air, he must make all critical dive decisions - depth, time, minimum ascent gas, abort criteria - before getting in the water, and stick to the plan period. I don't care how confident you are of your decision-making at depth, it is impaired. Make the decisions topside.
Decompression obligation -
In my deep air days I must admit I often carried far too little gas for contingencies. It was only by being totally anal about the dive plan that I didn't slip into that "just another minute" at depth that runs the deco obligation beyond the gas supply. Many divers today still dive deep air with too little gas onboard. It literally takes "just one more minute" or "just a few more feet" to get that big fish and to put the diver at extreme risk for DCS due to not enough gas.

Bottom line... there are ways to do (moderately) deep air with a margin of safety that's acceptable to me, but my envelope has shrunk considerably with age, and especially with the wider availability of helium.
Rick

 

[dumpsterDiver]

Couple of points...
OxTox - Air reaches a PO₂ of 1.6 ATA at about 220', so if you plan to spend more than 45 minutes on the bottom (!) at 220 then OxTox might be a problem... but I reckon the 6+ hours of deco might be a bit more of a concern, eh? In the only real high PO₂ experiment I know of, all the test subjects endured a PO₂ of 3.1 ATA (about 450 FSW on air) for at least five minutes before any signs of OxTox (test subjects were put on 100% oxygen at 70FSW in a chamber every day for 30 days running; each day until OxTox symptoms were observed). And as alluded to earlier, it appears that high PN₂ takes the edge off OxTox as well, so of the big three (OxTox, Narcosis and decompression obligation), it appears that for most "Deep Air" dives OxTox is rarely a significant factor.
Narcosis -
Often underestimated. Why? Because you are your own worst judge of narcosis. I hear people say "I don't get narced at all at xxx feet." It just ain't so... There was a fellow over in England not long ago that ran a little narcosis class at 100FSW. Nearly *all* his students were *absolutely sure* they didn't have any narcosis at 100 FSW. But he was able to demonstrate that every single one of them was in fact narced at 100' simply by getting them to do something stupid that they'd agreed not to do under any circumstances before the dive! I can nearly hear the "not me"s out there as you read this, but his results are conclusive. I know, for example, that when I pass 100' going down, that when I look at my gauges I have to think about what they're telling me and consciously register the information, otherwise I'll look at 'em and stow 'em and then realize that though I read them I didn't register the info. Perhaps my favorite narcosis story comes from my brother-in-law John. He relates how after tracking a grouper for a few minutes at 130', "pretty soon I was a fish... right up 'til I ran out of air." Scuba history is replete with divers who "just kept going" on deep air until it was too late to make a safe ascent... who either perished at depth or ended up hurt really bad or dead from DCS. (Two very recent cases attest to this)
Narcosis is the one of the big three that usually gets divers to violate the limits of the other two. If a diver insists on diving deep on air, he must make all critical dive decisions - depth, time, minimum ascent gas, abort criteria - before getting in the water, and stick to the plan period. I don't care how confident you are of your decision-making at depth, it is impaired. Make the decisions topside.
Decompression obligation -
In my deep air days I must admit I often carried far too little gas for contingencies. It was only by being totally anal about the dive plan that I didn't slip into that "just another minute" at depth that runs the deco obligation beyond the gas supply. Many divers today still dive deep air with too little gas onboard. It literally takes "just one more minute" or "just a few more feet" to get that big fish and to put the diver at extreme risk for DCS due to not enough gas.

Bottom line... there are ways to do (moderately) deep air with a margin of safety that's acceptable to me, but my envelope has shrunk considerably with age, and especially with the wider availability of helium.
Rick

Very good post! Narcosis is the issue and it gets to be exponentially more important as you go deeper.

 

[Rick Murchison]

Marci and I are a team in every sense if the word, but we are real clear that if things go south, one if us needs to get out of the cave to raise the pre-schooler.

It's a conversation every diving couple needs to have.

The Lovely Young Kat just doesn't go in the caves with me.

Rick

 

[Rick Murchison]

As for agencies that do teach deep air...

Don't know if they still issue these, but here's what one looks like

Rick