Diving air to 60m

[Khrissi]

This thread isn't about air mixes or rebreathers. It's abt a rather sad death. I have 8 dives under my belt and would not have done that dive like that with her. If my buddy weren't happy or looked panicked, it would be stop fr a bit then probably ascend. It's OK to look at this from yr armchair. She could be alive now. K

 

[beester]

Put forward your argument that I’m safer on a rebreather or trimix than I am on air and stop telling me what other people do.

I'm sorry but you are turning the question around. I don't need to proof to you that it's safer for you to a 60m dive on trimix than on air, you need to proof this to yourself. I don't give a flying ass what you do underwater, in the end it's about you and your own risk assessment.

Me, I'm not diving trimix because it's a religious experience, I'm not a trimix crusader, the gas is too bloody expensive for that. But I've done over 300 deep(er) dives (deeper than 45m), about half of them on air and half on trimix, I've had incidents underwater, I've experienced hypercapnia and narcosis, and have seen it in other buddies, I've had to safe other divers (including helping a diver on a 90m dive with 2,5 hours of deco), I've dived the same wreck on air and on trimix, and I've come to the conclusion that for me there are too many risks associated with deep air diving.

My question to you is, how do you assess, that it's safer for you to do a 30' bottom time dive at 60-70m on air, than using trimix? Because it's cheaper? Because nothing has happened so far? Because you are very good and experienced diver, and you are in control? How come you are convinced the advantages of He are a myth? Do you even have trimix experience, can you compare? I'm truly interested in knowing your rational behind your decision. Not to break it down, but to try to understand it.

The reason I'm asking is, because all divers I know that have dived deep air, and have a trimix ticket, understand the difference and advantages (yes there are also some disadvantages to diving a high He mix, but let's not pollute the topic) of diving trimix in the context of deeper longer (no bounce dive) dives. They might opt in some cases to still dive air, because of lots of reasons already mentioned, but they are aware that the risk is greater and that it's a compromise.

You are it seems unique in that you are totally convinced (against scientific fact, and anecdotal evidence) that doing deep dives on air is as safe or safer than diving a mix with helium. In the 90s a lot of people would share your opinion (and me too), in 2019... not many, if any.

In any case I wish you many safe dives.

 

[mafi]

@beester, I really start to think that @mac64 is just a troll. He asks for some arguments, but after I gave him data from DAN and people like Dr. Pollock on gas density, CO2 retention, his reply was:

The increase in WOB at 60 meters is hardly noticeable and a load of hype. Maybe you should do a bit of chest thumping it might improve your lung function.

We got to a point where @mac64 holds a cube in his hand but is still convinced he can roll it like a ball.

 

[Celt]

I'm sorry but you are turning the question around. I don't need to proof to you that it's safer for you to a 60m dive on trimix than on air, you need to proof this to yourself. I don't give a flying ass what you do underwater, in the end it's about you and your own risk assessment.

Me, I'm not diving trimix because it's a religious experience, I'm not a trimix crusader, the gas is too bloody expensive for that. But I've done over 300 deep(er) dives (deeper than 45m), about half of them on air and half on trimix, I've had incidents underwater, I've experienced hypercapnia and narcosis, and have seen it in other buddies, I've had to safe other divers (including helping a diver on a 90m dive with 2,5 hours of deco), I've dived the same wreck on air and on trimix, and I've come to the conclusion that for me there are too many risks associated with deep air diving.

My question to you is, how do you assess, that it's safer for you to do a 30' bottom time dive at 60-70m on air, than using trimix? Because it's cheaper? Because nothing has happened so far? Because you are very good and experienced diver, and you are in control? How come you are convinced the advantages of He are a myth? Do you even have trimix experience, can you compare? I'm truly interested in knowing your rational behind your decision. Not to break it down, but to try to understand it.

The reason I'm asking is, because all divers I know that have dived deep air, and have a trimix ticket, understand the difference and advantages (yes there are also some disadvantages to diving a high He mix, but let's not pollute the topic) of diving trimix in the context of deeper longer (no bounce dive) dives. They might opt in some cases to still dive air, because of lots of reasons already mentioned, but they are aware that the risk is greater and that it's a compromise.

You are it seems unique in that you are totally convinced (against scientific fact, and anecdotal evidence) that doing deep dives on air is as safe or safer than diving a mix with helium. In the 90s a lot of people would share your opinion (and me too), in 2019... not many, if any.

In any case I wish you many safe dives.

I dive alone, my only concern is my safety. I can pump air and I can carry all my gas in a 12ltr twin set. I can maintain all my gear myself. It’s not possible for it to be safer for me to start pumping, blending and using multiple gases and deco gases. I know my limitations at 60meters and what I can and can’t do. I also know as I get older I will have to do less. But air suits me. Furthermore air is the best option for some and should be taught by training agencies

 

[Celt]

@beester, I really start to think that @mac64 is just a troll. He asks for some arguments, but after I gave him data from DAN and people like Dr. Pollock on gas density, CO2 retention, his reply was:



We got to a point where @mac64 holds a cube in his hand but is still convinced he can roll it like a ball.

If I don’t have a problem with gas density at 60 meters then that’s what it is for me, if you have a problem with it then deal with it what ever way you see fit. No 2 people are the same. I’m not telling you how you should do it.

 

[TrimixToo]

Now that someone has gone to the trouble of moving all this stuff I’m going to make my position clear. The notion that you are more safer at 60 meters on a rebreather or trimix than you are on air is a myth. It’s not about the method it’s about the person using it.

Sigh.

Nobody here likely cares what *you* choose to do. I certainly do not.

However, many of us worry that people will choose to disregard the risks inherent in narcosis and high gas density after reading what you post. We have more than adequate data to show that 60m on air is less safe than 60m on trimix from the standpoints of mental impairment and gas density. That you choose to do it does not magically make it as safe as the alternatives.

I'll go further. In my opinion, TDI should discontinue their Extended Range certification class with its 180' depth limit on air, which has a gas density of 7.7g/l at that depth. Given what we knew when the class was created it seemed quite reasonable, and as it happens I have this certification. Given what we know now, I have difficulty understanding why any agency would want the liability associated with teaching the use of deep air. Were I a TDI instructor (I am not), I would refuse to teach this class.

Trimix is expensive and inconvenient. Safety equipment in cars is likewise expensive and inconvenient. You want to dive deep on air? Go ahead! You're (presumably) an adult and it's your choice. Want to drive 100mph in an early 60's Ford Mustang with no seat belts, no air bags, and so on if you can find a road where that's legal? Go for it! Nobody will stop you from doing that, either. But asserting that these activities are somehow just as safe as the alternatives is irresponsible. They are not.

Nothing and nobody seems capable of convincing you of this, so I will stop trying. I hold some hope that anyone that reads this far has already decided to make their own decisions based on fact and their personal level of risk tolerance.

 

[beester]

I dive alone, my only concern is my safety. I can pump air and I can carry all my gas in a 12ltr twin set. I can maintain all my gear myself. It’s not possible for it to be safer for me to start pumping, blending and using multiple gases and deco gases. I know my limitations at 60meters and what I can and can’t do. I also know as I get older I will have to do less. But air suits me. Furthermore air is the best option for some and should be taught by training agencies

If I don’t have a problem with gas density at 60 meters then that’s what it is for me, if you have a problem with it then deal with it what ever way you see fit. No 2 people are the same. I’m not telling you how you should do it.

So let me get things straight here:
- You have never dived trimix? But you keep stating that the advantages of trimix is a myth.
- You never use a decompression gas on deeper dives?
- You have done 30' bottom time at 60m (this you stated before), without a deco gas?
- You think gas density and narcosis doesn't exist.
- Agencies should go back to teaching deep air.

Yes I'm done! you are a troll, or you can't count. I guess your "60m" dive is just a quick bounce to 60 and then the rest averaging 40m, because there is no way in hell that you can decompress on backgas (air) with a bottom time of half an hour at 60m.

Also I hope it's perfectly clear to any bystander or beginning tech diver reading this (much too) long post, that you have no idea what you are talking about, and that they should progress into deeper diving, using techniques and knowledge of the 21 century... there is nothing heroic about diving deep air, you are not more competent if you dive deep air, and real divers doing real dives, have already a long time ago decided that air is a dead end.

 

[Germie]

First, deep air is still teached. PSAI for example has a 73m deep air cert. CMAS 2* and 3* have a limit of 57 (current standards), a PO2 of 1.4 or national regulation (we don't have a law, so our cmas certs are 57m, even if we aren't allowed to go deeper than 30m in a course. My old 3* is a 60m cert.

Second, Deep air is still done a lot in France and you don't see more accidents or incidents.
I also have done deep air, oc and ccr (ccr till 63m, oc till 74m). Yes, I have learned a lot on these deep dives. The 70+m dives on air I have done the calculations like you do on the 'deep diver' specialty and I was NOT slower than on surface. I still could change diopters on my camera. A buddy on rimix took a video, because I was curious about signs of narcoses. I also had some 20/25 with me so I could change to trimix. Sadly I had no single sign of narcoses on that depths. The reason I wanted to know is that I see it in students. Sometimes already around 40-42m, the limit of adv. nitrox. I can say for myself I feel narcoses as tunnelvision always around 44-46m. Sometimes I feel it around 38m, but than wait a minutes and it is ok. On dives deeper than 50m I can have a headache, this means co2. But only if I did long bottomtimes. 20-25 minutes. My deepest dive on air with bottomtimes was 58m. The deeper dives where only bounces with sometimes a few minutes at depth to do the calculations or change diopters.

Does this mean I promote air? No. There are a lot of risks. The signs and feelings of narcoses can be soooo different. Even the depth it happens. On 1 dive in 4 degrees water I was in love with some stupid stones at 43m on air. I liked the dive, I realised it was narcoses, so I wanted to have the same feeling again and 2 hours later I went to 55m on air and nothing happened. I don't teach the technical diver, that is 50+m on air. I only teach normoxic trimix. I am responsible then. But I can tell people about my experiences.
I am not a diver who says at 30.2m you need to take trimix, but make the end a personal one. Course standards say most times max 40m. But after a course you are free to choose. But an end of 50 is high, even if you think you will never get any problems with narcoses.

Third: CO2 can be a real problem. OC less than ccr, but it still can be possible. Gasdensity, you really feel it on oc and ccr when you dive over 50m depth. People who say we don't feel it I don't believe.

Fourth: The PO2 of max 1.4 is exceeded on deep air dives. Remember that CCR the PO2 is 1.3 or less. Yes, this has a reason for cns, but also that the risk of a problem on 1.3 is already smaller as the 'allways' considered safe 1.4 The problem with 100+m dives is that the lower the PO2 at bottomphase, the longer the deco will be, so there can be a reason to dive on 1.4. But if you decide to dive over 1.4 in the bottomphase on deep dives, there risks are really rising. Especially if you are sensitive for oxtox (and you normally will never know), or it seems for example the widely used pseudoefedrine for divers can make you more sensitive. At 70m your PO2 is already 1.68 So if you are not sensitive for narcoses YOU ARE EXCEEDING another safety limit and that is the adviced PO2.
And if you know that CO2 is also rising at such depths because of the WOB of the used gas, CO2 can be contributing to oxtox as it can be contributing to narcoses.
A nice and easy read: Oxygen Seizures at PO2 ≤ 1.6 Bar: How Rare? - Shearwater Research

Fifth: The CNS-clock (if you believe in it)
Also remember the maximum cns time at 1.5 is 120 minutes, at 1.6 it is only 45 minutes. So at 1.7 you will have ONLY 7 minutes left if you look at this table:
Shearwater and the CNS Oxygen Clock - Shearwater Research
Even if you use other calculations it will be a max of 15 minutes. This means that at 70m depth you cannot dive normal bottomtimes on air and stay within CNS limits (and the decompression phase is not included).

Maybe you don't believe in cns, but the fact is that the pulmonary part and especially oxygen induced myopia is NOT a lie. I know from several ccr divers that they had it. Yes it is harmless, it takes 2 weeks to get your normal vision back, if you dive on oc deep air you still get the risk on this. Not on a single dive, but if you do this a couple of days, yes for sure.

The question of 18/45 or 18/35 at 60m: The END of 18/35 is 31m so on the limits of DIR diving. Some hold completely 30m, others say 31 is also ok. Go to 58m on 18/35 and you are in the 30m END limit (O2 not narcotic). 18/45 has at 60m an end of 22m, so is absolutely within the limits. If you look at the 36-40m standards of most agencies, both gases are absolutely usable. For a 60m dive I would use the 18/35 if I can choose between these 2 gases. No single issue with END, all within limits, if you want you can still use the ratio deco 1:2, you can use the same decogases, and you will save around 15 euro on a fill. If your buddies or teammates want to dive 18/45, they can do and you can use the same decoschema.
And 20/25 is also a common used gas for a 60m dive. You lower the PO2 and the END. The END is <40 then (O2 not narcotic). So within most agency limits, the helium lowers the risk of narcoses, also lowers the CO2 risk, the PO2 is better than on air because of oxtox. So cheaper than 18/35 and also within (most) limits.

Remember: THERE IS NO CHEAP TECHNICAL DIVING.

 

[mafi]

The increase in WOB at 60 meters is hardly noticeable and a load of hype. Maybe you should do a bit of chest thumping it might improve your lung function.

No, it's not.

Hypercapnia, a favorite buzz word among divers and a non issue on open circuit, not only did I work hard on air but used crow bars, water lances, cutting gear. lifting bags and laid explosives without suffering as much as a minor headache. Anyone with any symptoms of carbon dioxide toxicity using open circuit diving gear needs to consult a professional it is not normal.

Wrong again.

Now that someone has gone to the trouble of moving all this stuff I’m going to make my position clear. The notion that you are more safer at 60 meters on a rebreather or trimix than you are on air is a myth. It’s not about the method it’s about the person using it.

Another NOPE.

Put forward your argument that I’m safer on a rebreather or trimix than I am on air and stop telling me what other people do.

Again try this: Alert Diver | Performance Under Pressure (primary sources from industry experts in the footnote)

Putting forward an argument from the article, as requested:
Helium appears to be the immediate solution for divers who are concerned about WOB and correlated medical issues (immersion pulmonary edema, CO2 retention, etc.) and for technical divers who are doing even normal dives to moderate depths.

@mac64: Please do at least a single dive with helium before engaging in gas density, WOB and narcosis in air vs. trimix discussion for which you have no frame of reference at this point.

 

[Celt]

I can carry 25 min at 60meters. You can twist my words all you like but that doesn’t mean I said I done 30 minutes bottom time on a 12ltr twin set. ( a dive which could be done if I pumped to 300 bar )I also said the notion that trimix is safer than air is a myth, its not possible for it to be safer to use multiple gases than a single gas.