Question deco time 50% and Air

[Shi]

Hi everyone,

I have a question, we all know that 50% gas is twice as fast as air at deco time, but how is it calculated?

Thank you!

 

[tursiops]

The higher efficiency of 50% is because it is only 50% N2, compared to 79% N2 in air. It is not "twice" as efficient but it is more efficient. The calculation is based on the gradient between the N2 concentration in your tissues vs the N2 concentration in the Gas you are deco'ing with.

 

[rhwestfall]

You can follow the calculations on this spreadsheet from @EFX

Dive Calculation Spreadsheet

While playing around with the spreadsheet I noticed on the VER sheet I did not add the version information for v34.2. I added the information and updated the website. Here is the link if you want to download it: https://ecfehlau.wixsite.com/my-site If you are a little familiar with Excel you...

scubaboard.com

 

[Shi]

The higher efficiency of 50% is because it is only 50% N2, compared to 79% N2 in air. It is not "twice" as efficient but it is more efficient. The calculation is based on the gradient between the N2 concentration in your tissues vs the N2 concentration in the Gas you are deco'ing with.

Yes, I calculated Pn2 for the two gases before this, 0.5:0.79. They are not a two-fold relationship, I used deco software to do a few simulated dives and reference the data, but I got a 2-fold relationship. Maybe I think I don't have to struggle with this. Because it may return that physiology cannot be digitized and can only follow a widely accepted "correct answer".

 

[tursiops]

Yes, I calculated Pn2 for the two gases before this, 0.5:0.79. They are not a two-fold relationship, I used deco software to do a few simulated dives and reference the data, but I got a 2-fold relationship. Maybe I think I don't have to struggle with this. Because it may return that physiology cannot be digitized and can only follow a widely accepted "correct answer".

I cannot duplicate your "two-fold" result. What depth, BT, deco profile are you using?

 

[Shi]

I cannot duplicate your "two-fold" result. What depth, BT, deco profile are you using?

I am using translation software, "two-fold" means 2 times

 

[broncobowsher]

It is not a simple calculation, that is why there is software and computers. And even those are all wrong. They work, most of the time, but not all the time.

 

[tursiops]

I am using translation software, "two-fold" means 2 times

I understand two-fold.
I don't understand how you got that result.
What dive profile did you use to get that result?

 

[kensuf]

Hi everyone,

I have a question, we all know that 50% gas is twice as fast as air at deco time

It isn't really. Please don't think you can cut a 30 minute decompression obligation to 15 minutes by breathing 50%.

The deco schedule is calculated based on the fraction of inert gas that is inspired versus a theoretical limit on how much internal pressure your tissues can handle (this is called an m-value). These combine to control the rate of off-gassing from the tissues in your body due to the principles outlined in Henry's law.

In the most simplistic terms, gases like to achieve equilibrium, which means when you are ascending they go from a higher concentration (your tissues) to a lower concentration (the gas you just inhaled into your lungs) until they are close to equilibrium. The rate of this exchange is dependent upon many factors (blood flow, tissue permeability, etc), but one of the important ones is how much inert gas is in the lower concentration (gas in your lungs).

 

[larsdennert]

I guess it's in that ballpark if you dive air as your bottom gas.