Just Started Diving Again and Found out I'm an Idiot ?????? Need advice.....

[DevonDiver]

One of things taught on ANDI technical courses is the efficiency ratios of decompression gasses. This is a good tool for selection, that I've not seen in other agencies as standard.

A.N.D.I. Theoretical Gas Efficiency For Decompression:

[TABLE="class: grid, width: 500, align: center"]
[TR]
[TD="align: center"]Deco Gas [/TD]
[TD="align: center"]Efficiency Ratio[/TD]
[/TR]
[TR]
[TD="align: center"]Air[/TD]
[TD="align: center"]1:1[/TD]
[/TR]
[TR]
[TD="align: center"]32%[/TD]
[TD="align: center"]1:1.16 (16%)[/TD]
[/TR]
[TR]
[TD="align: center"]36%[/TD]
[TD="align: center"]1:1.21 (21%)[/TD]
[/TR]
[TR]
[TD="align: center"]40%[/TD]
[TD="align: center"]1:1.26 (26%)[/TD]
[/TR]
[TR]
[TD="align: center"]50%[/TD]
[TD="align: center"]1:1.32 (32%)[/TD]
[/TR]
[TR]
[TD="align: center"]80%[/TD]
[TD="align: center"]1:1.37 (37%)[/TD]
[/TR]
[TR]
[TD="align: center"]100%[/TD]
[TD="align: center"]1:1.41 (41%)[/TD]
[/TR]
[/TABLE]

 

[dumpsterDiver]

what the heck is efficiency ratio? A measure of the reduction in deco time relative to air?

 

[DevonDiver]

The relative decompression efficiency, relative to air.

(Air having a 1:1 ratio was a clue )

 

[dumpsterDiver]

The relative decompression efficiency, relative to air.

(Air having a 1:1 ratio was a clue )

Really, so what does that mean in practical terms? equivalent to reduction in time?

 

[DevonDiver]

It's theoretical efficiency - so it relates to off-gassing. Time, however, is also dictated by your decompression software/calculations and the various parameters they use.

 

[Wookie]

Really, so what does that mean in practical terms? equivalent to reduction in time?

It means Ed was standing around without enough other stuff on his mind, so he came up with a chart for relative efficiencies of different deco gasses. In the real world it means little. But it made Ed happy. And it makes Andy happy.

 

[DevonDiver]

LOL I think it's useful from an instructional perspective. Some people have over-expectations when it comes to a tendency towards richer deco gases.

 

[dumpsterDiver]

LOL I think it's useful from an instructional perspective. Some people have over-expectations when it comes to a tendency towards richer deco gases.

It would have more instructional value if the chart consisted of % versus reduction in deco time. Efficiency is a nebulous metric.

 

[waterpirate]

To the OP. I would dive the gas that you are comfortable with and let it go. At the end of the day you are the one " the line " for the deco that you execute. I have what other people consider odd choices for mixes, but they make me happy.

The only thing missing from this disscussion is a window that has o2 in it and someone useing the word stroke.

Eric

 

[bap]

I would dive what is safe (relative to MOD, CNS) and what you feel comfortable with.

From their attitude of saying "only idiots dive ..." it sounds like they firmly subscribe to the "trust me" model. Don't let anybody dictate your actions, you are ultimately responsible for your choices.

Just running this through a planner and the difference is really small for a single dive to 130 FSW for 30mins BT on 28/0 with last stop at 20ft using 30/70 GF:

with 100%: 23 mins of deco
with 80%: 22 mins of deco (first switch at 30 FSW)