How much deco does 80% remove?

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crispos

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I am planning on diving 150 ffw, on 28% EANx (MOD 155 @ 1.6 pO2).

If I use my Canadian DCIEM tables, and dive this as if it was an air dive, my expected 20 minute dive will require 6 minutes at 30 ft, 8 minutes at 20 ft and 11 minutes at 10 ft.

I am going to use 80% O2 for decompression (MOD 34 ffw), starting at 30 ft. How much of my deco would be removed. My IANTD tables give accelerated deco for 50% but I have nothing to handle the 80% mix.

Thanks, any and all help appreciated, even sending custom tables or an Internet source. Otherwise, I will do my whole deco as if I was breathing 28% EANx. I am using an Aladin Pro Nitrox computer.
 
My quick and dirty calculations using V-planner don't show a huge difference for this as a 20 minute dive. I get six minutes less deco using 80%.
 
On the tables I use, the run times are:
Air - 62
Air/80 - 43
EAN 28 - 44
EAN 28/80 - 36
Rick
 
Hello,

What's interesting about this dive is the difference in 80/20 and 100% is almost non-existent.

Ed
 
What is more interesting is the REASON people have for using 80/20 instead of 100 O2.
 
blacknet once bubbled...
What's interesting about this dive is the difference in 80/20 and 100% is almost non-existent.

Ed
Any difference on percentage of CNS clock used with 80/20 vs 100%?

CRISPOS: go to www.gap-software.com and download a decompression planning program. Another, less tested program using a new algorithm is at http://www.v-planner.com
 
Charlie99 once bubbled...
Any difference on percentage of CNS clock used with 80/20 vs 100%?

CRISPOS: go to www.gap-software.com and download a decompression planning program. Another, less tested program using a new algorithm is at http://www.v-planner.com

Hello,

80% = 32.3%, total time = 15 mins.
100% = 36.6%, total time = 16 mins.

With this profile you shave a whopping 1 min of deco time by using 80/20. Question is, is it worth blending 80/20 for 1 min?

Ed
 
sheck33 once bubbled...
What is more interesting is the REASON people have for using 80/20 instead of 100 O2.
With the equipment I have available, I can decant 2000 - 2200 psi O2 into an empty bottle, depending on its size. If I top that bottle with EAN 32 premix, which my LDS banks, I'll get a full bottle of 80/20, which will cover deco for about 20% more bottom time than the oxygen alone. So, my reason for choosing 80/20 is that for any given set of bottles, I can have up to 20% more bottom time available than with pure oxygen. When I can get my hands on an oxygen haskel & get full bottles of O2 then I'll switch to pure O2.
What's your reason for using (or not using) 80/20?
Rick
 
Rick Murchison once bubbled...

With the equipment I have available, I can decant 2000 - 2200 psi O2 into an empty bottle, depending on its size. If I top that bottle with EAN 32 premix, which my LDS banks, I'll get a full bottle of 80/20, which will cover deco for about 20% more bottom time than the oxygen alone. So, my reason for choosing 80/20 is that for any given set of bottles, I can have up to 20% more bottom time available than with pure oxygen. When I can get my hands on an oxygen haskel & get full bottles of O2 then I'll switch to pure O2.
What's your reason for using (or not using) 80/20?
Rick

The number one reason given by divers i have seen use 80/20 was 'it gives you a larger margin of error in bouyancy control' They are obviously 'afraid' of 100% O2. It gives them more room to play with (read: screw up) at the 20ft stop
They use 80/20 to compensate for bad bouyancy control.

this is not my conclusion btw, they TOLD me this :D

and why use a deco gas on the 20ft stop with any nitrogen at all? its the N2 you want to get rid off in the first place.
 
Thank you all for this information. Unfortunately my dive was cancelled due to weather. Yes, I was asking myself, why am I making 80% when I could have kept it 100% (although the topoff takes a matter of a few seconds)? So many texts (including the TDI Advanced Nitrox I was reading) cite 80% deco mix. So far I have been trained in 50%, and yes, I kind of like the fact if the **** hits the fan, I can get up to 70 feet and use it. No buoyancy control is not a problem, I agree why breathe any N2 when you want to get rid of it. Also, could be used for a backup O2 unit in an emergency?

Perhaps I have a lingering fear that a smoker might walk over to my car or my tank and it might be leaking....I guess I figure the 80% is abit less combustible (probably not). and lo and behold, I was woken up last night at 4am, my (late night owl) roommate said my car was hissing, and it turns out somehow my big tank valve got slightly cracked open. I will analyse all this and improve my dive decision making. Thanks, again.
 
https://www.shearwater.com/products/swift/

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