Is a super computer needed for gas switching?

[TSandM]

Originally Posted by beaverdivers
I like the Scubapro Galileo Sol because it is air integrated you know that you are breathing the correct gas due to the pressure change.

This is actually hogwash. The only way you know if you are on the right gas is to trace the regulator to the tank, and verify the pressure drop on that tank when you purge that regulator. AND you have your team confirm it. People die from oxygen toxicity from switching to the wrong gas . . . as recently as last year it happened. In that case, the diver switched to the tank he wanted to use and confirmed it was that tank -- but it wasn't HIS tank, it was his buddy's, and it wasn't the gas he thought he was breathing.

Most staged decompression dives are planned using some kind of desktop software, like VPM or DecoPlanner or Gap. Those of us who use Ratio Deco use a different approach, and RD is covered in Mr. Powell's book. But ALL staged decompression dives are preplanned and the gas is thoroughly figured out beforehand.

 

[rongoodman]

So they don't all use the same algorithm, eh?

By the time you get through "Deco for Divers" you will have been introduced to most of them. The nice thing about choosing one the the widely used "generics", such as VPM or Buhlmann-GF, is that they're available on so many platforms, from desktop computers, through smart phones, down to the dive computer itself. The source code is freely available. The proprietary algorithms, such as VGM or Suunto's version of RGBM, might keep you from getting bent, but they can be pretty opaque as to how they're doing it.

 

[FPDocMatt]

. . . as recently as last year it happened. In that case, the diver switched to the tank he wanted to use and confirmed it was that tank -- but it wasn't HIS tank, it was his buddy's, and it wasn't the gas he thought he was breathing.

Is there an article somewhere you can refer us to to read about this incident?

In Deco For Divers (my Bible, as Jay Leno says) is discussed the fact that hypoxia gives you no warning whatsoever. So you could be breathing a mixture with too low a partial pressure of oxygen, and have no idea that there's anything wrong until you suddenly lose consciousness. Scary!

But ALL staged decompression dives are preplanned and the gas is thoroughly figured out beforehand.

The weird thing about all this gas stuff (you can tell I'm a newby here) is that you're down there watching the fish, no problems, everything's fine, and now you have to switch gases, or ascend, or decompress. But no symptoms! And the reason you're doing it is so that you won't die (a horrible death, at that). It's all intellectual, it's all in your mind--until you do something wrong and disaster strikes.

 

[IanBrit]

Is there an article somewhere you can refer us to to read about this incident?

In Deco For Divers (my Bible, as Jay Leno says) is discussed the fact that hypoxia gives you no warning whatsoever. So you could be breathing a mixture with too low a partial pressure of oxygen, and have no idea that there's anything wrong until you suddenly lose consciousness. Scary!



The weird thing about all this gas stuff (you can tell I'm a newby here) is that you're down there watching the fish, no problems, everything's fine, and now you have to switch gases, or ascend, or decompress. But no symptoms! And the reason you're doing it is so that you won't die (a horrible death, at that). It's all intellectual, it's all in your mind--until you do something wrong and disaster strikes.

It's only intellectual in as much as decompression theory is just that... a theory. Well tested, but still with large gray areas.

There is always a risk to diving mixed gases but that's why it's all planned, trained and prepped for ahead of time. The gas switches normally occur on the way to or from the main dive attraction and therefore you're generally focused on the transit part of the dive at that point, not looking around at fishes etc. At all stages in the dive, the diver MUST be aware of the mix they're on. If you look at photos of decompression divers in action, you'll generally see the tanks marked with big bold numbers indicating either the MOD or the mix.

Forming a consistent behavior is also critical. For example, the mantra "Lean is left, Rich is right" works for differing gases, plus I use a mouth piece plug in my high octane mixes to provide another reminder that this particular regulator is connected to the richest of the mixes. At this level of diving, the computer is providing timing and depth information and while it may be providing decompression status, that has ALWAYS been precalculated ahead of the dive using something like V-Planner and written down, together with bail out and FUBAR escape plans.

A lengthy way of saying "Yes, you could switch to the wrong mix".. but if you plan your dive and dive your plan and take rigorous precautions, the risk of the wrong switch is minimized. Oh, and never trust the mix label on a tank unless you personally have analyzed it.

 

[rongoodman]

Is there an article somewhere you can refer us to to read about this incident?

http://www.scubaboard.com/forums/accidents-incidents/385666-fatality-wkp.html

This was a case of hyperoxia, with a ppO2 of about 3.5. The amazing thing was how long he was breathing a mixture that rich before he finally seized.

 

[Sat Diver]

Am I the only one who doesn't use a computer for deco diving?

No ....

 

[Sat Diver]

This is actually hogwash. The only way you know if you are on the right gas is to trace the regulator to the tank, and verify the pressure drop on that tank when you purge that regulator. AND you have your team confirm it. People die from oxygen toxicity from switching to the wrong gas . . . as recently as last year it happened. In that case, the diver switched to the tank he wanted to use and confirmed it was that tank -- but it wasn't HIS tank, it was his buddy's, and it wasn't the gas he thought he was breathing.

Most staged decompression dives are planned using some kind of desktop software, like VPM or DecoPlanner or Gap. Those of us who use Ratio Deco use a different approach, and RD is covered in Mr. Powell's book. But ALL staged decompression dives are preplanned and the gas is thoroughly figured out beforehand.

This is absolutely true.

Be very very careful about information you get on the internet.

This area you are getting into is a place where you can find yourself in trouble very quick.

Find a mentor and learn the right way.

 

[Sat Diver]

I like the Scubapro Galileo Sol because it is air integrated you know that you are breathing

the correct gas due to the pressure change. .

I understand that everyone needs to sell computers, but that is just plain dangerous misinformation.

 

[Bombay High]

 I like the Scubapro Galileo Sol because it is air integrated you know that you are breathing

the correct gas due to the pressure change.

Sorry to flog a dead horse, as this has already been covered by TS&M and Sat Diver, but I can think of instances where you could wind up in trouble that way. (for eg a backgas post leak)

 

[PfcAJ]

It's tough to get into a really hypoxic situation on open circuit scuba. It can be done, but fatalities from that are exceedingly rare.

I think the last one I heard of involved a diver switching from a travel gas to a bottle of helium at depth. Iirc, she didn't check her valves or analyze, which lead to her not discovering that the isolator was closed during filling. I'm pretty sure she lived through it, however.