Equivalent Air Density Depth (EADD)

Steve

In this thread http://www.rebreatherworld.com/technical-rebreather-forum/2289-new-v-planner-3-70-a.html I asked Ross if he could include and EADD calculation into V-Planner. Ross has PMed me and thinks the idea has some merit.

OK here is the bit about my bright idea I just don’t know much about. How deep an EADD is too deep? I think it’s important to at least be aware of this as breathing too dense a mix at depth can easily predispose one to CO2 accumulation. Gas selection is not just about ppO2 and narcosis. A figure indicating the equivalent resistance of breathing air when diving very deep dives would be handy to know.

What is a meaningful number?

To save you reading the other thread here is a bit of a cut and paste to summarise what I’m on about.

I’m after a feature that provides an Equivalent Air Density Depth (EADD) ie breathing 5/80 @ 150m is like breathing air @ 'x' m

This would be of particular use for very deep dives when factoring in gas breathability V's EAD V's CNS V's Deco considerations

As far as I know (please don't hold me to this) its a straight forward case of gas % x gas density at STP x pressure at depth = density at depth
Density of individual gases in kgs/m3 at STP is
O2 1.429
N2 1.250
He 0.179
CO2 1.977

eg density of air at 40m (O2 + N2)
(1.429 x 21% x 5ata) + (1.250 x 79% x 5ata) = 6.438 kgs/m3

eg 2 density of trimix 5/80 at 200m (O2 + He + N2)
(1.429 x 5% x 21ata) + ( 0.179 x 80% x 21ata) + ( 1.250 x 15% x 21ata) =8.4375 kgs/m3

Which gives an EADD of 58m

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jradomski

Yes your example is valid.. This concept is Taught in ANDI level 3 and level5 programs.. since most calcs are done in liters the better unit to use is g/l which is 1g/l= 1 kg/m3!!

This is the numbers we use

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

Steve

Thanks for the clarifications Joe. What are ANDI's recommendations?

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jdz

OK, so a natural extension of this is what happens in a scubber at depth (especially +100m).

I have been thinking of the mass (read density) of gas travelling through a scrubber bed at depth and can only imagine the velocity of such a gas travelling around the loop.

Either the mass moves very slowly causing possible co2 buildup and increased WOB or the gas travels so fast that the dwelltime is reduced causing inefficient scrubbing...

Is there any merit in this discussion...??

Cheers, JDZ

jradomski

Unfortunately there is no agreed upon standard.. We use the concept to show how ther gas density effects WOB, and how ratings for RBS like the Inspiration are derrived..

We also use this to show how contamination by argon (oxygen made by a PSA system) will effect loop breathing characteristics as time goes on..

one of the intersting things you see when you run lots of calculations, if you keep the narcotic depth ( using oxygen is NOT narcotic) of the loop below 40m, on RBS like the inspiration, the gas density is generally below that of the the tested WOB limits (obviously this isnt the case when you get to extreme depths, since people generally dont count He as narcotic (COMEX studies show He starts becomming narcotic with a PHe of arount 6 atas) )... (you need to run breathing resistance calculations as well)

On the test gas used in the inspiration, using air at 50m results in almost the same gas density as their test trimix for 100m so the relative WOB should be about the same..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

silent running

Hi Steve and Joe, never thought about gas density at depth as it relates to WOB. I'm just starting to read my course material for my Trimix training in Feb. I will be on the look out to make sure this is delt with then. Thanks for bringing it up. WOB usually comes up as a comfort issue, but it does relate very certainly to CO2 production. It's a big a deal, because it seems that a significant # of CCR fatalities may be due to CO2 hits. And until we get some simple, reliable CO2 monitors, it makes sense to pay attention to anything which could increase WOB on a deep dive.-Andy

Crazyduck

I talked to Peter about this when I was in Tennessee and that was one of the reasons for certain design characteristics of the PRISM. They did heavy mathematical processing on the flow patterns, dwell time, and how gas moves around the loop. A very interesting conversation.

Andrew

silent running

Well then Andrew, do tell us what Killer Pete had to say. Can you give the highlights? Or do I have to rattle his cage myself? Thanks-Andy

koputai

Seems like a good time to rehash this:
http://www.deepdiving.net/rants/norcotic.html

Just use norcotic trimix Steve.

Jason.

caveseeker7

Very intresting idea, Jason.
Have you tried dived it? Does it work for you?

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Cheers
Stefan



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