f02 formula for given ATA

[lermontov]

is there an easy (ish) formula to work out deco time for a given depth at various F02

e.g

if 21% @ 6m = 40 min
then 50% @ 6m = y min
or 100%@ 6m= z min

 

[The Chairman]

I use the rule of 120 for air and 140 for 32... but that's for rough guessing. My PDC has the final word.

 

[guruboy]

Your thread title is rather unclear.

 

[lermontov]

Im curious to see the correlation ( I'm sure there is) between fo2% and time at a given depth - for deco only- for the same dive profile

 

[gfaith]

@lermontov

I ran a dive plan in Subsurface to 150' and got the following deco at 20'.
Buhlmann GF 35/80
21% @ 20' 32min 67 total run
50% @ 20' 16min 51
100%@20' 8min 43

Now if the 50% is switched at 70' the total run time is 8 min less.
Not sure this is what you are looking for...

 

[Kevrumbo]

Im curious to see the correlation ( I'm sure there is) between fo2% and time at a given depth - for deco only- for the same dive profile

Cascading Deco:

Your 6m O2 stop and 21m Eanx50 total stop times are both equal to "n" x Bottom Time for the particular depth listed below:

45m = >1/2 * Bottom Time;
60m => 1 * Bottom Time:
75m = >1.2 * Bottom Time;
90m => 1.5 * Bottom Time;
105m => 2.2 * Bottom Time;
120m => 3 * Bottom Time.

So for 40min Bottom Time at 45m depth, your 6m O2 and 21m Eanx50 deco total stop times are 1/2 x 40min = 20min.

There are five Eanx50 deco stop depths: 21m, 18m, 15m, 12m and 9m, so further divide the 20min by five -hence each depth has a deco stop of 4min.

The 6m O2 deco stop can be for the entire 20min, or do 14min at 6m followed by a slow 1m/min ascent to the surface.

For 40min at 60m, the O2 and Eanx50 times are each 1 x 40min = 40min;
For 40min at 75m, the O2 and Eanx50 times are 1.2 x 40 = 48min;
For 40min at 90m, O2 & Eanx50 are 1.5 x 40min = 60min; etc.

 

[KevinNM]

This is what ratio deco does. (The GUE version - which has been renamed to something I forget) It's a useful tool, but doesn't seem like a good place to start if you don't have experience.

 

[lermontov]

Cascading Deco:

Your 6m O2 stop and 21m Eanx50 total stop times are both equal to "n" x Bottom Time for the particular depth listed below:

45m = >1/2 * Bottom Time;
60m => 1 * Bottom Time:
75m = >1.2 * Bottom Time;
90m => 1.5 * Bottom Time;
105m => 2.2 * Bottom Time;
120m => 3 * Bottom Time.

So for 40min Bottom Time at 45m depth, your 6m O2 and 21m Eanx50 deco stop times are 1/2 x 40min = 20min.

There are five Eanx50 deco stop depths: 21m, 18m, 15m, 12m and 9m, so further divide the 20min by five -hence each depth has a deco stop of 4min.

The 6m O2 deco stop can be for the entire 20min, or do 14min at 6m followed by a slow 1m/min ascent to the surface.

For 40min at 60m, the O2 and Eanx50 times are each 1 x 40min = 40min;
For 40min at 75m, the O2 and Eanx50 times are 1.2 x 40 = 48min;
For 40min at 90m, O2 & Eanx50 are 1.5 x 40min = 60min; etc.

thanks- i see that the 6m stops are inextricably linked to the deeper deco stops so my formula either wont work or is too complex to do without a dive planner anyway

I ran 3 options fro deco (21% 50% 100%) trying to force my perdix to stop only at 6m only but what was interesting was the relationship between the times and the f02 ( as a %)

21% = 30 min@36m was 8 minutes at deeper stops and 35 min at 6m
50% was 8 minutes @ deep stops and 17min at 6m
100% was 8min at deeper stops and 11 min at 6m

so 21% = 43min ( nearly 200%o f the f02)
50% =25 min ( nearly 50% of the f02)
100% =19 min (nearly 20% of the f02)
I was hoping it could be a much simpler formula however i cant relate it to other fo2%

it might work on shallower dives but then it becomes less relevant

 

[tbone1004]

remember, especially when walking about decompression. the fO2 doesn't matter. ppO2 matters only for hypoxia and hyperoxia.
ppN2 is what matters. That is what creates the gradient across the tissues that will drive the nitrogen out. Talk about fO2 is not an accurate way to describe decompression.

If you want to force the Perdix to only do 6m stops for that dive profile, then you have to set the GF-lo to 90.
With gf 90/90, this gives 21min of deco on 21%, 14min with 50%, and 10 min on 100%

Ratio deco is designed for a much lower GF-lo and as such is going to be problematic when trying to force it to only do 6m stops and getting the results you want.

As a general rule for NDL, I use the "rule of 130" which is depth in ft + time =140 for NDL diving when on EAN32, and rule of 120 for air diving same as @The Chairman , but those have mandatory 5 minute precautionary/deco stops. If you blow them, you'll be at a GF-hi of about 100, which is not where I really want to be.

For decompression diving, you can do rough ratios as well, but it can get very complicated especially if you dive with GF's that are outside the preprogrammed ones and you have to come up with your own ratios

 

[The Chairman]

rule of 120 for air diving same as @The Chairman , but those have mandatory 5 minute precautionary/deco stops.

Again, I only use them as vague guidelines and sanity checks and not to actually guide my dive. If my PDC is telling me that I can do 90 minutes at 100 ft on 32, then I know something, somewhere is 'off'.