How much deco does 80% remove?

[crispos]

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.

 

[Drew Sailbum]

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%.

 

[Rick Murchison]

On the tables I use, the run times are:
Air - 62
Air/80 - 43
EAN 28 - 44
EAN 28/80 - 36
Rick

 

[blacknet]

Hello,

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

Ed

 

[sheck33]

What is more interesting is the REASON people have for using 80/20 instead of 100 O2.

 

[Charlie99]

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

 

[blacknet]

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

 

[Rick Murchison]

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

 

[sheck33]

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

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.

 

[crispos]

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.