Light back gas deco

[Gareth J]

We get the speel this is a non deco dive boat, if you go into deco you won't be doing the second dive
If you treat us like children you get children

!!

Interestingly I've seen divers on tech boats all clumped on the line together
so no communication on the boat to stagger them, and ascending far too slowly
all looking at each other to see who's going to move up to the next stop first, and stopping far too long

Staggering dive teams is not practical if the slack window is small. As you hit the longer (shallower) stops, you inevitably will overlap, if you are all on a shot.
Three cheers for the Jon Line .
A trapeze reduces the issue.
With what we are discussing here, just floating free under a DSMB would normally suffice, the stops will be short, so the divers shouldn't be strung out to far for the boat to keep track of.

 

[Blackcrusader]

Hi folks, Do you recreational divers ever do light back gas deco?

Yeah we had this thread as well.

Overshooting NDL and mandatory deco stops

 

[J-Vo]

...The third point is about the "model" employed for computing the length of deco stops. This model (Bulhmann) considers a number of fully-independent compartments (tissues), each trapping a certain amount of nitrogen, and releasing it based on the difference between the pressure of the trapped nitrogen and the partial pressure of nitrogen in the mixture in your lungs.
This is an over-simplistic model, not taking into account the transfer of nitrogen from one tissue to another.
Furthermore, the speed of release of nitrogen does not only depends on the pressure difference between the nitrogen in the tissue and the nitrogen in the lungs, it also depends on the ambient pressure (which does not change breathing pure oxygen).
In conclusion, I think that the Bulhmann model, albeit having proven reliable and reasonably safe for decompression in air, has not been tested enough for these accelerated deco profiles in pure oxygen...

Why are tissues independent? – The Theoretical Diver

Plopping this link here in attempt to make sure we keep up with modern thinking on decompression theory (not that I'm an expert).

If I read correctly I believe mathematically parallel and interchanging compartments are not different as long as the full spectrum is covered.

Bulhmann does take into account both ambient pressure and PPN2/PPHe.

I believe myself and many others on Scuba Board would probably be dead if accelerated deco did not work with the Bulhmann model.

Bulhmann isn't even close to perfect, but way more can go wrong with equipment and environment without accelerated deco, then I see caused by the practice. That said, for the short durations being discussed by the OP, it is probably not worth it.

 

[Diving Dubai]

If you are diving a single 12, you are unlikely to have sufficient gas to require stops in a single days diving

You've clearly never dived with my wife, I swear she exhales the gas back into her cylinder...

But in all seriousness, as I posted up thread, my wife had/has no interest in deco diving, nor deep particularly, but if there is something of interest, and in our local that'll mean a whale shark or a Mola, which are neither rare nor common, she no longer has the "fear" of NDL=0 since I pushed her through her Tech 40 (with a good instructor) She knows she has the tools and the ability to make an educated decision if she wants to hang out a bit longer enjoying the moment and then is able to make a chilled out worry free ascent (generally clearing deco en route leaving us with little more than a few mins extra at the SS)

I would much rather people have knowledge so that they can be equipped with the right tools rather than living in "fear" of NDL=) and the unknown, or worse still riding their computer on a wing and a pray hoping that it'll be okay

 

[tursiops]

they where told they where going to die if they dived beyond the NDL

This is a common refrain on SB. But it is hyperbole, and I doubt it has actually been said much, if ever.
Maybe it would be better not to repeat it as if it were a fact.

 

[Gareth J]

You've clearly never dived with my wife, I swear she exhales the gas back into her cylinder...

But in all seriousness, as I posted up thread, my wife had/has no interest in deco diving, nor deep particularly, but if there is something of interest, and in our local that'll mean a whale shark or a Mola, which are neither rare nor common, she no longer has the "fear" of NDL=0 since I pushed her through her Tech 40 (with a good instructor) She knows she has the tools and the ability to make an educated decision if she wants to hang out a bit longer enjoying the moment and then is able to make a chilled out worry free ascent (generally clearing deco en route leaving us with little more than a few mins extra at the SS)

I would much rather people have knowledge so that they can be equipped with the right tools rather than living in "fear" of NDL=) and the unknown, or worse still riding their computer on a wing and a pray hoping that it'll be okay

My late partner had no desire to have to wait prolonged periods doing staged decompression on dives. She was a keen underwater photographer.
However, we did do some dives where she completed mid ocean staged decompression, her limit was around the 20-30 minute mark. This was done when she 'really' wanted the opportunity to dive a particular site, or see a particular 'critter'.

She regularly completed dives with staged decompression though, but these would be on sites (like walls), where we could continue to look at stuff and take pictures during the decompression stops.

We had planned an expensive trip to the USA, when she found that all diving had to be no-stop she said there was no way she would pay for a trip with that kind of restriction.

I remember a guide asking me how come we where always the first in and last out on all the reef and wall dives. It was because Sarah would happily sit in 6-2m of water at the end of the dive breathing her gas down to the reserve waiting for something to poke its head out of a hole, so she could get the shot she wanted. It's amazing how long that last 20 bar will last when you're chilled out in a few meters of water just waiting. To look at the print out of the dive, it would often look like we had done a 30 minute (or longer) stop, when all we where doing was taking pictures and using the last of our gas.
(They had said no time limit, but you must exit with your reserve.)

 

[Gareth J]

This is a common refrain on SB. But it is hyperbole, and I doubt it has actually been said much, if ever.
Maybe it would be better not to repeat it as if it were a fact.

You are absolutely right, I was exaggerating a little.

But ridicules statements by people who should know better often leave new divers racing the NDL 0 back to the surface. More fearful of breaking the 'NDL Rule' , than ensuring they ascend safely.

 

[tursiops]

But ridicules statements by people who should know better often leave new divers racing the NDL 0 back to the surface. More fearful of breaking the 'NDL Rule' , than ensuring they ascend safely.

Agreed.

 

[Angelo Farina]

Angelo,

Your historical perspective is often wonderful, but when your data is 20 years old and you respond in a non-historical context, you may be confusing other divers instead of helping them.

Sorry for causing confusion. My point is that here we are talking about RECREATIONAL diving. I consider accelerated deco with pure oxygen as advanced tech diving, requiring specific training (not the standard basic course we were taught when we were students) and additional hardware tools (an extra tank, plus an advanced tech computer).
As said, all this is entirely overkilling for shortening the deco time by just 4 or 5 minutes...
Accelerated deco, instead, makes more sense for deep dives in trimix, where gas switching is already practiced at depth, and where the diving profile requires perhaps one hour or more of deco.
But I do not think that anyone can call these dives "recreational", here we are well beyond the limit between rec and tech, however you want to define it...
Furthermore, we should keep an eye of what is written on our certifications. They allow for deco, but only breathing air. We would need some other advanced certifications for being trained to accelerated deco in pure oxygen or high-Nitrox...
Please note that I am NOT a tech diver, nor a tech instructor. I am a plain basic rec diver and my 3-stars CMAS instructor certificate still has the same limits as my 3-stars scuba diver certification: 50m max, in air, with deco and with a buddy.
I have nothing against tech divers and their advanced setups. Simply I cannot afford it, too demanding, both physically and economically.
So I dive my standard 15-liters steel single tank, filled with air, and whenever needed, I go happily beyond NDL, knowing that my tank is plenty enough for doing some minutes of "light" deco in air before surfacing.
I always plan a dive assuming that some minutes of deco will be needed, as I think that is better to be prepared to deco than being sorry when discovering that you are beyond NDL and you are not equipped for doing the required deco stops.