Mixes >40% O2?

[Blackwood]

I'm not familiar with DecoPlanner (only ever used it in classes), so I don't recall an "optimum deco gas" computation.

How does that work? Does it run through a bunch of gases and pick the shortest runtime?

 

[ianr33]

I'm not familiar with DecoPlanner (only ever used it in classes), so I don't recall an "optimum deco gas" computation.

How does that work? Does it run through a bunch of gases and pick the shortest runtime?

Guessing you see where your first stop is, then mix a gas that has a pO2 of 1.6 at that depth.

 

[rjack321]

I'm not familiar with DecoPlanner (only ever used it in classes), so I don't recall an "optimum deco gas" computation.

How does that work? Does it run through a bunch of gases and pick the shortest runtime?

I got the impression Rhone Man's "optimum" aka "best mix" included cf of oxygen required in the mix so there was some sort of $$ vs. "benefit" going on.

 

[Rhone Man]

I'm not familiar with DecoPlanner (only ever used it in classes), so I don't recall an "optimum deco gas" computation.

How does that work? Does it run through a bunch of gases and pick the shortest runtime?

Basically yes, except it doesn't do it automatically - you have to keep running numbers until you come up with the smallest amount of O2 required - the various trade offs (richer mix means less deco time; leaner mix means longer deco time, and higher SAC rate due to greater depth).

I got the impression Rhone Man's "optimum" aka "best mix" included cf of oxygen required in the mix so there was some sort of $$ vs. "benefit" going on.

Yes. You actually get an S-curve - the absolutely cheapest way to do it is just to deco on backgas (obviously), but if you accept the use of one deco gas, you can work out the way to get yourself out of the water reasonably quickly in the most cost effective way. If you have time to keep plugging numbers through.

Just for the record, I don't actually use Deco Planner (TM). I use HLPlanner, because it is free and I am that cheap.

 

[Rhone Man]

You convince your buddy to dive the same mix and switch at 50ft? How much 64% did you bring? What was your profile and bottom mix? How much deco did you have?

No buddy on that dive; 30 cu ft; 22 minutes at 180 feet (planned) on 24%; 34 minutes (planned).

It didn't form part of my deco profile or my gas planning, but I also carried 30 cu ft of 30% as my 'oh &$^#!' gas (because up to 30% was free on the boat).

If we want to turn it into a critique, a good place to start would be planning a bottom mix with 1.55 ATA.

 

[rjack321]

No buddy on that dive; 30 cu ft; 22 minutes at 180 feet (planned) on 24%; 34 minutes (planned).

It didn't form part of my deco profile or my gas planning, but I also carried 30 cu ft of 30% as my 'oh &$^#!' gas (because up to 30% was free on the boat).

If we want to turn it into a critique, a good place to start would be planning a bottom mix with 1.55 ATA.

Thanks just wondering what you were doing.
Weird that up to 30% was free but more than that was $2cf for O2.

 

[Rhone Man]

Thanks just wondering what you were doing.
Weird that up to 30% was free but more than that was $2cf for O2.

I believe that they had a membrane system which could produce up to 30%, but blending anything richer meant partial pressure blending, and importing the O2 was hideously expensive (this was in Micronesia).

 

[rjack321]

I believe that they had a membrane system which could produce up to 30%, but blending anything richer meant partial pressure blending, and importing the O2 was hideously expensive (this was in Micronesia).

Odd that their membrane wasn't capable of at least 32% Most can produce 36% even.

 

[Rhone Man]

Odd that their membrane wasn't capable of at least 32% Most can produce 36% even.

I think it could, but the way it was explained to me was that it was such a hump to do so, that they kept it set at 30%.

 

[kierentec]

I'm often tempted to use 50% when I'm teaching an OW class since I tend to have to go up/down so often!

IMHO this is a terrible idea. In a situation where you would have to share air with an out of air diver, and somebody was injured, explaining why you allowed a student to breath a gas they were not certified to dive might be tricky... Just my 2 cents....