An age-old question: ways to 60m.

[leadduck]

I want to derail your conversation by going on topic again.
Recap:
0-50 meters is Nitrox
70-120 meters is Trimix on OC or CCR
CCR makes sense if you dive alot.
120 and beyond is CCR

50-70 meters is the weird range for OC because of the cost of Helium. If Helium was cheap and easily available, this depth would be Trimix. Since Helium is not cheap or easy to get, some OC divers go for it with Air and accept the added risks. Others, find this risk unacceptable and choose not to dive recreationaly without Helium beyond 50 meters.

Is this a correct summary of the argument?
Comment for yes and for no

In OC this can be a continuum, depending on how you pick your mix vs depth.
If you stick to standard gases only, then a rule like "EAN32 until 30m, 21/35 for 30-45m" makes a 35m dive very expensive. There's a big price step from air or EAN32 to 21/35, and no surprise that people want to avoid that extra cost by stretching the envelope.
Whereas if you dive best mix., for example 27/15 at 45m or so, then the cost of the gas fill grows smoothly with depth and you don't have to think in hard steps, easier.

 

[NothingClever]

If you stick to standard gases only, then a rule like "EAN32 until 30m, 21/35 for 30-45m" makes a 35m dive very expensive.

You’re correct, it’s an expensive dive especially if we’re approaching the dive casually. In contrast, I think the cost of that dive is offset when we have a well-defined set of objectives for the dive.

A buddy of mine races for BMW (cars). What his team spends on tires for one morning practice session is my entire budget of practice AND race tires for an entire weekend in MotoAmerica (motorcycle) racing. However, in either motorsport event, to the average car or motorcycle enthusiast the budget is jaw-dropping and we try to never lose perspective of that. So you can be darn sure when we go out on track, we have very specific objectives for those laps so that we’re not casually eating up our allocation of expensive race compound tires. Of course we’re focused on the race line but also braking markers, gear selection for each corner, passing zones, etc. If we didn’t have specific objectives, we’d both be fired by the factory race department and our sponsors.

I have a twinset of 21/35 and another of 18/45 ready to go. You can bet when I mash the down button I’m going to be on a mission-focused dive. Otherwise, I should fire myself as a technical diver for being casually wasteful.

 

[LFMarm]

In OC this can be a continuum, depending on how you pick your mix vs depth.
If you stick to standard gases only, then a rule like "EAN32 until 30m, 21/35 for 30-45m" makes a 35m dive very expensive. There's a big price step from air or EAN32 to 21/35, and no surprise that people want to avoid that extra cost by stretching the envelope.
Whereas if you dive best mix., for example 27/15 at 45m or so, then the cost of the gas fill grows smoothly with depth and you don't have to think in hard steps, easier.

Exactly for this reason it is better to start by defining your own personal limits on gas density, END, pO2 so that you know beforehand what you need for what depth to be safe and comfortable. The cost and availability for me is a second step where you decide if going to that depth is possible and worth it or if you should be planning for a shallower dive.

 

[wetb4igetinthewater]

Presentation on the Uluburun shipwreck on Youtube. Dr Cemal Pulak briefly explains the diving procedure at beginning of presentation.

The Ships that Changed History Lecture 2 Cemal Pulak …

So I genuinely appreciate the link, as on my flight over the atlantic I did watch it (as well as the next one, will watch the others later). Doesn't really get into details there as probably no one in the audience really cared. That's not what that event was about. He did mention being narked out of his mind when attempting to attach a DSMB to a large rock at just 45 meters which turned out to be a pythoi (large storake jar). Not sure if you got that far.

 

[CG43]

Minute 50 in the video.
The archaeologist successfully completed his planned task of placing the buoy at the right spot.
It's funny that he did not realize what he had tied his rope to.
What part narced played in that and what part selective perception remains speculation.

When Cousteau tried to tie a rope to an anchor chain at a depth of about 70 meters under difficult conditions, he succeeded only on his second attempt.
To be found in "The Living Sea" chapter "Port Calypso".
It is very likely that the planned task failed on the first attempt because JYC was too narced.

 

[old frogman]

I want to derail your conversation by going on topic again.
Recap:
0-50 meters is Nitrox
70-120 meters is Trimix on OC or CCR
CCR makes sense if you dive alot.
120 and beyond is CCR

50-70 meters is the weird range for OC because of the cost of Helium. If Helium was cheap and easily available, this depth would be Trimix. Since Helium is not cheap or easy to get, some OC divers go for it with Air and accept the added risks. Others, find this risk unacceptable and choose not to dive recreationaly without Helium beyond 50 meters.

Is this a correct summary of the argument?
Comment for yes and for no

Yes, a good summary which leads to the next step in a bit more detail. Risk management. Regardless of which gas you eventually chose, it should be underpinned by first establishing the context of the dive, followed by a situational analysis, then identifying the risks and rewards and then, assessing them. Then identifying any mitigating controls that may be applied to reduce the risk to a level that is tolerable. Finally decide if the dive is to go ahead or cancel.

Ultimately it will be up to the individual or team, based on their perception of risk and ability to function with exposure to mild to moderate narcosis.

Perception of risk and ability to function are the controlling factors in the overall discussion.

The risk management process is referenced in literature by IANTD, TDI and the US Navy.

 

[SelfDiver]

Yes, a good summary which leads to the next step in a bit more detail. Risk management. Regardless of which gas you eventually chose, it should be underpinned by first establishing the context of the dive, followed by a situational analysis, then identifying the risks and rewards and then, assessing them. Then identifying any mitigating controls that may be applied to reduce the risk to a level that is tolerable. Finally decide if the dive is to go ahead or cancel.

Ultimately it will be up to the individual or team, based on their perception of risk and ability to function with exposure to mild to moderate narcosis.

Perception of risk and ability to function are the controlling factors in the overall discussion.

The risk management process is referenced in literature by IANTD, TDI and the US Navy.

Hey,
Don't bring your logic and pragmatism in here. This is ScubaBoard.
My thesis is that 50-70 meters is a "twilight zone" for OC divers.
Some of us have done air "bounce" dives to 80 meters. And in excellent conditions 65 meter dives. It can be done, but does anyone recommend it as a regular thing? -from the hive mind of 100 monkeys with typewriters- NO.

I made another circlejerk comment in this thread about the "normalization of deviance" in deep air diving.
Initially, use of Nitrox and Helium was the deviation.
The successes were so resounding that Nitrox and Helium became the norm and deep air is the deviance.
They are both right.
Helium and Nitrox are not an absolute requirement to 50 meters.
Helium and Nitrox are an absolute requirement beyond 70 meters

 

[J-Vo]

I want to derail your conversation by going on topic again.
Recap:
0-50 meters is Nitrox
70-120 meters is Trimix on OC or CCR
CCR makes sense if you dive alot.
120 and beyond is CCR

50-70 meters is the weird range for OC because of the cost of Helium. If Helium was cheap and easily available, this depth would be Trimix. Since Helium is not cheap or easy to get, some OC divers go for it with Air and accept the added risks. Others, find this risk unacceptable and choose not to dive recreationaly without Helium beyond 50 meters.

Is this a correct summary of the argument?
Comment for yes and for no

Not bad except most CCR divers I know tend to do nearly all dives on the CCR. This is partly because being on CC is simple a blissful way to dive, and because you don't just strap on a CCR and do a 60/70 meter dive without lots of recent practice.

 

[WreckWriter]

Well, interesting thread. I'll share my thoughts.

I started diving way back in the early 70s when there was no option besides air. Through the 1990s I dove air, including hundreds of deep dives. I've been sub 200 FSW on air many times and once to 300. Do I recommend it? Nope.

Somewhere in the early 2000s I got trimix certified. We dived heavy 100CF steel doubles with Nitrox and O2 tanks slung under our arms for deco. Rebreathers were not yet mainstream. Getting on a boat in rough seas with this type of rig is what ended my deep diving career.

If I had it all to do over again I would go CCR without question. Yes, higher initial expense. Yes, maintenance required beyond what open circuit requires. Advantages? Increased bottom time, easier custom mixes, less expensive than open circuit trimix.

On the other hand, going deep just to go deep is a bad idea. The ocean floor is littered with people who did that....

Just the thoughts of a guy that's been there.

 

[wetb4igetinthewater]

What part narced played in that and what part selective perception remains speculation.

The issue isn't performing a task where narcosis makes it harder.

The issue is handling an emergency (like equipment failure) when one is impaired by narcosis.

That's the crux of the issue from my POV. You (and others) may think completely differently due to the fact that equipment failures are rare. My understanding from Dr. Simon Mitchell's research is that sufficiently high gas density (with some correlation to narcosis) with an equipment failure is at a higher probability for having a really bad day.

This being scubaboard, I do not expect a science based counterargument.