Next step for longer bottom times on deep dives?

[Celt]

There’s no short cut from where you are to spending 45 minutes at 40 metres.

 

[MichaelMc]

Whilst it would be a pity to "waste" a rich helium mix in a 10m/30' puddle dive, it wouldn't really matter as I'd use very little anyway - mostly for the wing. So rocking up at a boat dive on a rebreather doesn't matter as the costs are negligible.

I'm still not asking this right.

On a rebreather, how shallow is it a waste of helium to use 15% helium diluent:
always, 180', 160', 140', 120', 100', 80', 60', 40', 20'.
For narcosis and disregarding the negligible cost on a rebreather.

Said differently, when would you switch to air or nitrox, as the helium would be silly. Assuming you have bottles with 45, 30, 15, and 0% helium sitting ready and free. (and ignoring NDL for helium shallow)

 

[Gareth J]

I'm still not asking this right.

On a rebreather, how shallow is it a waste of helium to use 15% helium diluent:
always, 180', 160', 140', 120', 100', 80', 60', 40', 20'.
For narcosis and disregarding the negligible cost on a rebreather.

Said differently, when would you switch to air or nitrox, as the helium would be silly. Assuming you have bottles with 45, 30, 15, and 0% helium sitting ready and free. (and ignoring NDL for helium shallow)

Personally, beyond 40m (132') I would prefer to use Helium. Shallower, there is less point. Shallower than 30m, I wouldn't bother using Helium. That said, if you are topping off a partially used Trimix DIL, cylinder I would probably just add air and have a very light Trimix DIL, rather than dumping the remaining gas and replacing it with air.

One of the big factors is conditions. Low visibility, high workload dives, make using Trimix shallower a much better option. Narcosis is caused by a combination of factors, stress and depth being two of them.

I much prefer the benefits of Helium, on deeper dives. The reduction in Narcosis, and improved clarity, give you, not only a better and safer dive, but you remember more of the dive.

I haven't read through the whole thread. To answer the original question.
If you want longer no-stop bottom times, you have the option to dive shallower, and/or (dependent on PO2), reduce the Nitrogen by increasing the Oxygen (i.e. use Nitrox).
If you are using optimum Nitrox, and have insufficient bottom time. Then the only remaining option is a decompression stop dive.

The fundamental problem, is in North America, dives involving compulsory decompression are treated as if they have some special mystic. The transition from No-stop dives, to dives involving staged decompression, is less onerous, than the initial task of learning to dive. It is a modified application of existing skills and knowledge, rather than the requirement to learn new skills and knowledge.
A large number of the European agencies teach staged decompression as a progression within their core diver training programs.

Your next logical course is something like ADP and / or a twinset course. Initially, you don't need to do accelerated decompression. A straightforward dive, with limited decompression stops can easily be done on the back gas. (Assuming you have properly planned it, and have sufficient gas/redundancy).
The highest proportion of the diving in my club involves, compulsory decompression stops, without accelerated decompression!
Progressing to accelerated decompression can be done, (if required,) after practicing and becoming confident and comfortable doing 'light' deco dives.

One of the big advantages of decompression diving is the reduced compulsion to rush the ascent that comes with a focus on no-Stop diving. As long as you have the gas (and redundancy), you can focus on safe ascents, rather than a rush to the surface to ensure you don't break the no-stop restriction. If needed, you can pad out the stop with no concern.

You may, or may not progress to CCR. That is a decision for down the road. CCR becomes more attractive as you progress into Trimix. As others have said, Helium is expensive, but then a CCR is not exactly a cheap investment.
I have a CCR, and I 'like' diving it. Most of my twinsets are on loan to friends, I so seldom dive OC. It should be remembered, that you still need your OC skills on CCR in the event you have to bailout.

 

[jlcnuke]

If we asked Dr. Simon Mitchell if it is his professional recommendation that all recreational training agencies limit all recreational diving to 100' or below due to the gas density and/or narcosis safety concerns/risk in the current 101-130' recreational range until divers are trained on and using trimix to make the dive safe? I'd be very, very surprised to hear him say that should be done as a blanket "rule" for diving. I know he doesn't endorse "deep air diving", but I don't know that he 'opposes" diving on air/nitrox at 101' for instance. It seems to be that some people are saying that's his position however, so I'd love to get clarification on his professional thoughts for that scenario.

I could be wrong, and I'd love to hear his answer, so maybe @Dr Simon Mitchell will answer that question.

 

[100days-a-year]

For those of you who haven't blocked me✌ Thanks for playing
Since we're all sciencey.
Regarding the use of rebreathers, what is the risk of death or injury vs. OC?
Not how much money I can save.
Not how smart rebreather divers are at mitigating the risks.
Not how much safer they are now.
What is the verifiable rate of death/injury per number of RB divers vs rate of death/injury of OC divers.
And if its significant, why are people so quick to recommend them?
Just trying to understand this concern for other people's safety.

Not even going to bring up dive travel, boating safety, foreign travel or myriad other concerns that go MIA errytime HE gets brought up in recreational depths.

 

[MichaelMc]

Not even going to bring up dive travel, boating safety, foreign travel or myriad other concerns that go MIA errytime HE gets brought up in recreational depths.

What does recreational HE have to do with boating safety?

What are the myriad other concerns for travel beyond is it available and at what price?

 

[100days-a-year]

Risk aversion or mitigation.
The reason that has been given for using HE in recreational depths.

 

[MichaelMc]

Risk aversion or mitigation.
The reason that has been given for using HE in recreational depths

I don't understand. The issue with recreational HE for boating safety is that those divers will be risk adverse and act to mitigate risks?

 

[ginti]

Regarding the use of rebreathers, what is the risk of death or injury vs. OC?

You can have a look at these reports, but they're a bit old:
http://media.dan.org/RF3_web.pdf
http://www.swiss-cave-diving.ch/PDF-dateien/2008TechDiverReport.pdf

Wikipedia has a lot of references here:
Rebreather - Wikipedia
Scuba diving fatalities - Wikipedia

There was a report about diving safety citing three categories of divers at high risk:
(1) newbies (<100 dives of experience)
(2) people who dive often (>300 dives per year)
(3) rebreather divers
Unfortunately, I do not manage to find this report anymore... so take my information with caution

All these reports are relatively old, so things may have changed now; the idea I got is that 10 to 20 years ago they were less safe because they were less known. Now I believe things are changing - but it's just an impression, nothing more.

 

[100days-a-year]

I don't understand. The issue with recreational HE for boating safety is that those divers will be risk adverse and act to mitigate risks?

Bravo, truly one of the more clever responses I've seen in a while.