Deep Air Dives In Tech Classes

[CWK]

40m on air equates to a PPO2 of 1.05. I believe the purpose of deep air dives is to let divers experience nitrogen narcosis whist diving under supervision on air up to a PPO2 of 1.4. The PPO2 for deco gas is 1.6, so I presume diving on air up to 66m is safe.

I've heard of people doing dives to 100m on air, which equates to a PPO2 of 2.3. I'm not sure when oxygen toxicity will get you.

 

[Kevrumbo]

Over heard some discussion among some tech students about some of their deeper dives being on air and being narc'ed. Is there are purpose to doing such dives? Do most tech classes have this as a component? I know a few agency's do not but was just wondering why add a possible issue to a tech class. Not really asking if you agree or disagree just looking for some explanation if there is any.

Thanks,

When I took PADI's Tec50 class, I had the choice to do the last two experience dives on Trimix or a "best mix" EANx mix. I figured since I would be certified to do theses dives on deep air, better to do them in class with an instructor, rather than on my own.

I was very narc'ed in the low vis, cold (40's F) lake water, and going forward, pretty much decided to follow some other agencies' recommendations regarding Helium for dives deeper than 100'.

Back when I was doing those dives there was no alternative. Now, as @JohnnyC relates, helium may be unavailable or cost prohibitive. In these cases it is better to have an understanding and experience with narcosis so, if nothing else, you can remove yourself from the situation before it gets out of hand.


Bob

I guess it depends on your definition of deep air. Most likely these folks are talking about their experience with the TDI ext range course (180’ max?). 180 is very manageable from a narcosis standpoint in blue water that’s nice and warm...I have never seen it taught in cold dark water...where it is much less tolerable.

I don’t blink at a 170’ air dive off Hatteras or KL. That’s not “deep air” to me. Now off NJ...I don’t want to dive air at that depth. I think it’s a personal limitation that takes some sort of real world experience to appreciate...thus I think that particular course is beneficial in that it shows you (or at least has the ability to) how narcosis can truely be a ****** experience.
I find it would be even more helpful to do 2 dives in that range..one on air and one on mix...in the same conditions to give the student a reality check of how clear headed they are on mix vice air.

Figured that would be one reasoning to get the feeling so you know when its about to happen, not trying to go a different direction but wonder if doing more deep dives on air and getting narc builds a tolerance or just the ability to handle it if need be.....Thanks for the response.

I can't speak for any agency but narcosis management is best learned under direct supervision.

Since it's a common risk which I've suspected I've encountered as shallow as 40ft I'm glad in different conditions I've been exposed to how to respond with an experienced mentor. I don't believe adding helium is the inoculation as there are other significant factors involved which might result in a diver narced. When that situation comes, I'd be glad my instructor taught me a few things practical about it.

Defining "deep" rather nebulous as well. Just drying out from a dive to 250' which might be deep to some or the first deco stop for others.

Dive and let dive,
Cameron

It happens on a sliding scale depending on conditions in the water and yourself, it's happening as you go deeper and it becomes your number one job to know how you are impaired. As far as have determined I do not build up a tolerance, but can manage narcosis better if I work up to deep dives slowly.


Bob

40m on air equates to a PPO2 of 1.05. I believe the purpose of deep air dives is to let divers experience nitrogen narcosis whist diving under supervision on air up to a PPO2 of 1.4. The PPO2 for deco gas is 1.6, so I presume diving on air up to 66m is safe.

I've heard of people doing dives to 100m on air, which equates to a PPO2 of 2.3. I'm not sure when oxygen toxicity will get you.

There is no way to "adapt" or gain tolerance for the extreme narcosis with progressively deeper dives following the PSAI Deep Air Course Levels 1 thru 6 (30m; 40m; 46m; 55m; 61m and 73m). Any work or exertion at these depths -66m and deeper- resulting in a heavy labored increased breathing rate (tachypnea and/or dyspnea) will immediately initiate the spiraling vicious cycle of CO2 retention/poisoning into Hypercapnic stupor and unconsciousness, along with the increased risk of Oxygen Toxicity Syndrome & Convulsions.

One additional compounding factor to consider as well is the water temperature:
Cold Shock Response lasts for only about a minute after entering the water and refers to the effect that cold water has on your breathing. Initially, there is an automatic gasp reflex in response to rapid skin cooling. . . [Usually not a severe issue jumping in cold water in a drysuit with appropriate insulating undergarments]

A second component of the Cold Shock Response involves hyperventilation. Like the gasp reflex, this is a natural reaction to the cold. Although this physiological response will subside, panic can cause a psychological continuance of hyperventilation. Prolonged hyperventilation can lead to CO2 retention, Hypercapnia and additive effects of Nitrogen Narcosis at deep depths, so the key thing is to concentrate on controlling your breathing. . .

However even with a Scooter/DPV providing mobility to reach 90msw and then only floating relaxed horizontally in neutral buoyancy, just the increased work-of-breathing (WOB) due to the high gas density is potentially enough by itself to elicit CO2 retention along with compounding the anesthetic effects of extreme Nitrogen Narcosis.

27 Aug 2017.
Oil Rig Eureka Bounce Dive, Solo;
1min Bottom Time @ 90msw depth (10ATA);
The ppO2 atm of Nitrox 21% (Air) @ 10ATA: 2.1 bar;
Gas Density @ 10ATA: 12g/L (approx 10x more dense WOB than Air at surface);

Descent Rate (via DPV/Scooter): 30m/min;
SPG reading at Start of descent (10m depth): 180bar;
Depth Consumption Rate (Open Circuit) @ 10ATA: 20bar/min;
Amount of Gas consumed & used to inflate Wing & Drysuit on 3min descent to 10ATA: 40bar;
SPG reading at elapsed dive time 4min (3min descent plus 1min BT @ 10ATA): 120bar. In other words, 60bar total was used in 4min;

Ascent Rate: 10m/min from 90msw to 15msw;
Deco Time Required (on Air): 1min @9msw; 3min @6msw and 7min @3msw;
Total Time of Dive: 30min;
SPG at End/Surface, remaining Air: 40 bar;

Single Tank Aluminium 13L with 210 bar initial fill;
Apeks XTX100 Regulator;
Dive Xtras X-Scooter Sierra, 150m depth rating;
Water temperature at depth: 14°C.

The scary part other than the black abyss outside my primary light source, was the temptation to just drift off with the anesthesia of the extreme N2 Narcosis -and that was within one minute at 90msw with no physical activity, but with increasing work-of-breathing trying to expel metabolic CO2 even in a non-exertion, "resting" state floating neutrally buoyant. In other words, even though completely relaxed with deliberately slow and deep inhalation & exhalation respiratory cycles, I couldn't get rid of Carbon Dioxide fast enough because of the higher Air density at 10ATA Pressure -it just became too hard to breathe efficiently anymore without going into prompt Hypercapnia.

Good reference article on Gas Density, and an implied explanation on why the Recreational Depth Limit on Air just happens to be around 40msw:
Advanced Knowledge Series: The Gas Density Conundrum | Dive Magazine

 

[PfcAJ]

Deep air is absolutely stupid. The only reason to dive deep air is because you don’t have enough money to do the dive in the first place.

 

[Bob DBF]

I'm on a rather limited budget, and have been since the early 60's.


Bob

 

[Schwob]

Deep air is absolutely stupid. The only reason to dive deep air is because you don’t have enough money to do the dive in the first place.

OK, do you need to rub it in?
I don't dive that deep at all, but I do drive a rattle box on my way to diving... and I like it (the diving), even if when I purely listened to my alternate budget minded ego I should'nt do it...
Why not let anyone dive at their own recognition and risk to the budget they care to afford?

 

[Germie]

What is too deep? I teach the advanced nitrox course, 42 m on air.
But I don't teach the technical diver, but I am allowed to teach it. Why not? I am responsible when teaching. I find this too deep to teach on air. But on the normoxic trimix course, when there is time I try to do a 40-42m dive on air and then a couple of hours later the same dive on trimix. And yes, most feel the difference, some not. From there I tell them to be a thinking diver. And tell my own story:
I was never narced, have done lots of deep dives till 60m depth on air. I thought I was not narced, till I started diving with helium. Now I recognise being narced. That is a good lesson. And I hope the divers I take to 40-42m on air recognise after this 2 dives the feeling of being narced also.
You are allowed to decide yourself at what depth you want to take a trimix and what the END is (course standards say 36m-40m). For most people somewhere between 40 and 45m it means they will take a trimix. I tell the bestmix vs standardgases also and their advantages and disadvantages.
But I don't like people who tell me I have to take trimix when diving to 30.2 m depth. I decide myself. And yes, on some holidays I do deep air (50m). No problems with that, it is my own decision. It is not a secret, most important is that you have overviewed the options and then decide. Warm water, no current, or strong current, dark waters, maybe overhead? For me these are important issues to decide what gas. Of course I tell people about CO2 issues that can be there at depth on oc (and CO2 is more narcotic than N2). 60m on air is too deep. But what is too deep? For me 40m-45m is no problem, even sometimes the 50m. Overhead I take helium earlier. But others will say 40m is already too deep, or maybe shallower. Respect the choices a person makes if he can give you arguments why. I do that too.

Doing deeper dives on air does not mean no money, there can be different reasons, sometimes no helium available also. But remember, there is no cheap technical diving.

I always use an nice example when people discuss standardgases as better than best mix. On 55m the DIR-gas is 18/45, with ean50 and 100%. Ok, END will be around 20m then. Yes <30m. Decoplan is made. Safe dive. Now you can spent 15 euro less on a fill. Take an 18/35. Bad gas? Why? END =28m WOW, still within the <30m limit for END. Other decoplan? not needed. So the same dive, all within the same safety margins but 15 euro cheaper.

 

[BoltSnap]

Here in Libya due to several reasons, economics and availability of expertise, MANY local divers dive to 50 - 60 meters on air and do spearfishing. I know some that do it at night. They decompress on 100% O2 and survive to talk about it. They do it frequently. He is incredibly expensive and out of reach for most divers and/or unavailable.

The 50 - 60 meter diving is done on a recreational rig withOUT redundancy

 

[TrimixToo]

I was at 180' on air a while back (because I thought it was shallower there) for about 3 minutes to tie in a marker buoy. It was tied in nicely and neatly. I thought. The following week I went back to start the dive there on 18/35. It's a miracle the buoy stayed put, and I spent several minutes untangling and retying before continuing the planned dive. I knew I'd been narced on the prior dive, but what surprised me was how poorly I'd tied in the marker.

If this ever happens again I'll just call the dive. There is no good reason for me to go any deeper than 145' on air, and even at 145' I'd rather be on a light mix to knock the END back. I can sit it out, if necessary. The bottom will wait for me to come back with what I need.

This is within the limits of Extended Range certification, I'll note. But that doesn't make it a good idea. To quote RFC 1925:

"(3) With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead."

(Full text of RFC 1925 here: RFC 1925 - The Twelve Networking Truths)

 

[Patoux01]

MANY local divers dive to 50 - 60 meters on air and do spearfishing. I know some that do it at night. They decompress on 100% O2 and survive to talk about it

I haven't seen anyone say they were going to die. I do have many examples of people that died on or following a dive to 50-ish m on air however. I still won't say that it's
going to kill you, what I do say is that deep air seems to help getting yourself in trouble.

Current data shows that the gas density issue appears around 40m. Gas density guidelines

Not gonna go into the "I'm not narced" thing.

 

[Germie]

Gas density can be a problem on deep ccr dives also. The EADD will be over 40m too. Calculate it for an 6/72 diluent with setpoint 1.3 at 135m depth.