Choice of breathing gases

gathan

I though I would initiate this thread after having read Johan's article here: http://www.rebreatherworld.com/gener...-deep-50m.html

There are always more than one way to skin that cat as the saying goes, and given our individuality as divers, we're bound to have different views regarding what we think is safer and/or more efficient when it comes to selecting our dil and bailout gases.

For myself, after going through some experimentations of my own, I have settled with basically 3 mixes. My decision was primarily based on what I perceived to be; simplicity, flexibility, and acceptable deco efficiency.

Dill is 10/50 for all depths (not too many areas exceed 100m near where I live). I like the idea of easily being able to mentally compute what my PO2 readings should be following a dill flush if required at depth and I don't fancy the idea of carrying more than one type of dil, if I can get away with it.

Bailout gases consist of 10/50, 30/25, and 50/25. I like to think that He is my friend not only for warding off narcosis at depth but also for it's off-gasing properties. Minimizing a N2 spike if having to go to a bailout gas seems like a good thing in my mind also. I have these mixes in 40s and 80s and will mix and match depending on depth and BT duration.

Any thoughts?

Andre

pchanning

Hi Gathan,

I see you dive a KISS. So youre BOV is plugged into either inboard or offboard bottom mix and both are hypoxic. Is this really sensible?

The designs I ended up with can be found below. They are of course my own personal take on it and should be treated as such. Food for thought though.

http://www.rebreatherworld.com/techn...ccr+gas+tables

Thre are plenty of instructors on this forum who are far better placed to advise you though. (Disclaimer ).

HTH
Paul

__________________
Cheers
Paul

The key to enlightenment... is survival.

gathan

Hi Paul,

Point taken, however, unless I'm dumb enough to bail out to the OC/DSV and breathe from the dil, for more than a short time, in less than 6M of water, I don't see this as being a big issue. At the same time, I never engage in a dive where I am not carrying at least one bailout cylinder that I can use throughout the planned water column.

Andre

Curt Bowen

Lets see

Bottom diluent I prefer is 10/50 but normally will take what ever is available at the location to get the dive done. Air even works

Bail out I prefer is what ever trimix is available, 50% and 100% or if nothing is available AIR will work just fine for all. Decompression might suck!

Of course I calculate my dive according to what ever gases I have at the time and location.

And NO, helium is not available every place on the planet. And most of the remote places you could possibly get it, it would cost more than you can afford to get it there.

Please dont use what I prefer as a standard. Most of the time I have a job to do and photos to take so I use what ever I can get.

If all else fails for CCR, strip off your rebreather and go sidemount 80's with air :-)

Curt Bowen

Peter Steinhoff

I always thought helium was available everywhere they are welding (or making balloons for the kids) which I figured would cover most countries.

Peter

Curt Bowen

Yes, you could probably have some helium shipped in to the remote location your diving. If you found a supplier in the country and IF you arranged someone to drive it out to the place your diving a hundred plus miles away. Probably would only cost around $1000.00 + for each bank cylinder, IF it showed up on time.

Helium is not available for every dive location, so if your going to plan to dive deep in extreme locations, plan far in advance, have very deep pockets $, and a rabbits foot around your neck if you want helium.

Curt Bowen

I just returned from CCR trip to Truk Lagoon with Ron Benson of Going Under Dive.

I asked him how he was able to get helium and oxygen to Truk

He said you start about 6 months in advance

1st You have to get ahold of a supplier on Guam
2nd Arrange for the cylinders to be placed on a ship that goes to Truk. The key is, this ship only goes to Truk, Once-A-Month and your shipment might not be on it.

The cost of a single oxygen bank cylinder to Truk was $275.00 each
The cost of a single helium bank cylinder to Truk was $600.00 each

Anyone who has ever traveled to remote islands or locations knows first hand that NOTHING ever runs smooth or on-time.

Dont forget, you also have to ship in your scrubber material also.

Travel enough to remote locations and one day you will find yourself with an aluminum 80 on your back or on your sides with only air, getting ready to dive. Been there, got the T-shirts

This is the main reason why my CCR harness is really a Sidemount harness first.

Peter Steinhoff

Thanks Curt,
It's a major PITA and expensive too in other words...the only upside being if you get the helium and the oxygen there you are not using too much of it

Cheers,
Peter

Scuttle

I would have to agree with all the comments so far. Another problem to ponder is returning the empty G's & ongoing rental fees that stack up. Sometimes cylinders get lost in transit & in some cases you end up purchasing the lost Tank's to end the costly process.

Too easy going to a destination that has it already there.

Curt Bowen

This is true

I had to buy a bank cylinder in Mexico because it got "MISPLACED".

Funny on how all but one made it back. But whats another $190.00, hell I own a dive magazine right. :-)

If I wanted to get rich by owning a magazine, it would have been a porn mag and not a diving mag.