HowManyCubicFeet

[GregO]

Question: What assumptions do people use related to deco time impact on emergency exit? Playing with a couple of longer profiles I could see this requiring 10?s of feet of gas. Basically a slower exit.

Greg


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[bent]

It wasn't explained well to me the first time either,
and I hate doing math.
Fortunately, if you are diving consistent tank sizes, then you just kind of memorize stuff, but the math work is good to stretch the 'ol gray matter from time to time.

I had a gas matching calculation for a while, I didn't think to add one for 1/2+200 math. I've added one for 1 or 2 stages, shows you how many cubic feet you need to subtract from available cubic feet on backgas and your resulting new turn pressure.

It's at the very bottom, happy scrolling!

http://divebhb.com/gas-planning/

You should try metric for this... it's so much easier.
I'm self-taught stage diving though but here is my calculation:
A set of 12 liter (about same size as LP85s) tanks and one stage is 8000 Liters. I dive quaters most of the time.
Half a stage is 1000 Liters so I can take another 1000 Liters from the SM tanks before I have to turn which is 40 bars. It easy math you can do in your head.

[bent]

But people I know who took a stage class from other agencies are hit or miss on that point. And those that are ?self-taught? to dive a stage pretty ubiquitously dont subtract from backgas

If they didn't learn to calculate with the total amout of gas, what did they learn in that class? Other than gas planning, what's to learn in a stage class anyways?
I really wonder what I would learn a class like that and whether it'd be worth taking it.

[mrki]

1/2+200 on stages and thirds of backgas is the absolute minimum gas needed.

That's assuming your stage tanks and regs will always work flawlessly. It will be a bit difficult to share the remaining stage, although you'd likely be able to feather the valve on the malfunctioning one.

P.S. It really is easy in metric - with 2x12l back tanks and 11.1L stages (S80) you can just divide stage pressure by 2 to get back tank pressure, with only 8% calculation error (which adds to conservativism anyway).

[rddvet]

If they didn't learn to calculate with the total amout of gas, what did they learn in that class? Other than gas planning, what's to learn in a stage class anyways?
I really wonder what I would learn a class like that and whether it'd be worth taking it.

They learned gas management and stage handling. But their gas management strategy didnt include removing gas from backgas. And apparently thats very common.

I personally never took one, but I was lucky enough to have good mentors. And naui cave 2 includes stages


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[kensuf]

Question: What assumptions do people use related to deco time impact on emergency exit? Playing with a couple of longer profiles I could see this requiring 10?s of feet of gas. Basically a slower exit.

Greg


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Hahaha! You're funny. Dive planning??? Most just follow what their computer says and hope they've got enough gas.

[OFG-1]

Hahaha! You're funny. Dive planning??? Most just follow what their computer says and hope they've got enough gas.

Well, if you don't have a plan, then nothing can go wrong. Right?

[kensuf]

Well, if you don't have a plan, then nothing can go wrong. Right?

Please run for congress.

[MORGAN]

Well, if you don't have a plan, then nothing can go wrong. Right?

Indecision is the key to flexibility.

[OFG-1]

Please run for congress.

"Pro and con are opposites,
that fact is clearly seen.
If progress means to move forward,
then what does congress mean?"

Nipsey Russell