Next step for longer bottom times on deep dives?

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This reminds me of my first photography trip to the Colorado in late September of 1997. Now the previous month, 12 people died in Lower Antelope Canyon, one of the last slot canyons before Lake Powell that is fed by a huge area of smaller slot canyons, washes, etc.. That year, monsoon season dragged on a little longer than normal. I stopped at a store to ask about going into that slot canyon where people had died. A Navaho told me "I woulnd't recommend it." That was good enough for me. There wasn't a RULE against going into it (just pay an access fee), but there was a RECOMMENDATION against it. As the person I asked definitely had greater expertise on weather, drainage, risk, than me, I headed his RECOMMENDATION. :rofl3:
 
Have we had a poll of:
On a rebreather, how shallow does helium seem silly?
always, 180', 160', 140', 120', 100', 80', 60', 40'.
- For narcosis (as safety risk or enjoyment limiter)
- For work of breathing (which is worse on a rebreather)

Seems like that would put most of this side debate to bed. Then it is a matter of cost/benefit. Which has different tradeoffs for seeing pretty fish or hunting lots of them all week long to sell at a profit.

"Most people on cattle boats X Y Z", means very little. Given the many suboptimal things they do, and their level of training and education.
Put it this way; if planning a dive to 60m/200' and you turn up a the boat to be told that dive's off but we'll do a sheltered one at 30m/100'....

On OC you'd probably throw some toys around and take your kit home rather than face throwing away £100/€120/$140 of gas.

On CCR you'd say "lets go diving!"
 
Put it this way; if planning a dive to 60m/200' and you turn up a the boat to be told that dive's off but we'll do a sheltered one at 30m/100'....

On OC you'd probably throw some toys around and take your kit home rather than face throwing away £100/€120/$140 of gas.

On CCR you'd say "lets go diving!"
But that is still an economic argument vs a missed dive day.

Say you have diluent bottles with 45, 30, 15, and 0% helium sitting ready. In increments of 15%, to avoid bickering about 5% helium. For a shallower dive, likely you pick a lower percentage of helium. At what depth do you dive the 0% as using helium diluent is just silly?
always, 180', 160', 140', 120', 100', 80', 60', 40'
 
I can’t speak for Dr. Mitchell as I don’t know the man personally but I have a number of friends who are scientists in different fields. Prior to publishing their work or results of studies, they consult other scientists to examine the data And conduct a mini peer review prior to publishing. Now as I said I don’t know if Dr. Mitchell does the same. But I’d be willing to bet money that he doesn’t operate in a vacuum.

When you say community do you mean us divers? Because if you do I would take the knowledge and recommendation of a single individual that studies decompression science over thousands of non-scientists.

Now people can accuse me of name dropping, but it isn’t that. It is citing a credible source. An expert source that overrides one’s hubris of knowing better than anyone else based upon whatever.

No, when I say community I mean the scientific community. I give you a parallel with medicine. Listen to a single doctor can be misleading: the doctor can make mistakes or, even worst, is a fraudster; if you have no competence in medicine, you cannot distinguish the good suggestions of this doctor from the bad ones. However, if you listen to the entire medical community (that is, the union of all the doctors, as, for instance, the WHO), you are less likely to make mistakes.

In research, it is slightly different. All good scientific papers are peer-reviewed, but these papers deal with really advanced stuff and can be controversial (and sometimes they should be!), so read with caution. But if a suggestion is not on a published paper, the same argument that I made for the doctors holds, and it is better to listen to what the scientific community has already accepted (which, in diving, it's a bit more complicated...). Although I have the feeling that nobody is a fraudster here, better be cautious, everyone is a human and can make mistakes (plus, there can be misunderstandings)
 
Put it this way; if planning a dive to 60m/200' and you turn up a the boat to be told that dive's off but we'll do a sheltered one at 30m/100'....

On OC you'd probably throw some toys around and take your kit home rather than face throwing away £100/€120/$140 of gas.

On CCR you'd say "lets go diving!"

This is exactly what used to happen on New England dive charters. I mean it probably still does but it's not as common as it used to be with rebreathers being more popular.
For a ~60m dive (200ft) I would often bring 2 sets of doubles with me. If I was told we couldn't get out to the deep wreck due to weather in the parking lot well I guess I'm diving my other doubles. It some cases it meant bringing both sets out on the boat provided there was space.

Of course the economic argument can obviously be made but I simply don't care about wasting a 15/55 diluent fill on a 100' (30m) wreck. That's like a $5-10 worth of gas for me.
Most people on rebreathers don't care about wasting trimix on shallow dives.

Let's be honest, somebody that has already spent $7-10k on a rebreather plus associated training should really not be crying about wasting a $150 dollar trimix fill but it happens. Given the option if I had a lesser trimix fill or nitrox with me; I'd simply dive that.

I don't consider it cheaping out or being frugal. I've "wasted" trimix fills on 100-130' dives when the wreck got changed. I didn't cry about it. It was either that or I sat on the boat pouting and didn't go diving that day.

I've done the same thing with rebreather bottles but it typically bothers me less. I've brought multiple sets of diluent bottles with me. Example: We were supposed to dive a wreck in 190' but weather prevented it but we knew we could get to a wreck in 100' that was sheltered. It was either that or don't go diving. Luckily I had a bottle of 18/20 (it was an air top off from another trimix fillI). I swapped out to my other diluent bottle and was good to go.
 
But that is still an economic argument vs a missed dive day.

Say you have diluent bottles with 45, 30, 15, and 0% helium sitting ready. In increments of 15%, to avoid bickering about 5% helium. For a shallower dive, likely you pick a lower percentage of helium. At what depth do you dive the 0% as using helium diluent is just silly?
always, 180', 160', 140', 120', 100', 80', 60', 40'

Have a couple of diluent cylinders; one's kept with a 45% helium mix, the other with about 15% (topped off, but also topped off with mix). 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.

Spinning back to OC; I would choose not to go rather than waste £80/€100/$130 on backgas. If I had no choice, as in the relocated boat dive and on OC, I'd probably choose to do the dive if it's a "nice" but shallow dive.
 
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)
 
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.
 
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.
 
https://www.shearwater.com/products/teric/
http://cavediveflorida.com/Rum_House.htm

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